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Equipment Discussions >> Refractors

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aa6ww
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Using refractors for Deep Space Observing
      #5190175 - 04/25/12 04:10 PM

Do many out here use refractors for deep space observing? Over the years, I've started to move away from my largest scopes in favor or smaller more portable (somewhat) scopes for deep space hunting. These scopes almost always end up being refractors because I love the pin point stars they offer and wide field views. Of course there are still times when the skies are very dark and I take a journey to my dark site location, then I have to set up my biggest SCT, but generally, I find myself moving more toward using my refractors even for deep space observing. My 150mm and 180mm refractors are very fun to use, and still have plenty of aperture for deep space hunting. Maybe unlike most, I find myself more challenged looking for dim objects in my smaller scopes than finding the urge to want larger and larger scopes to dig out distant galaxies.
That seems to be my latest approach to this hobby.
One of my friends calls it "The less is more" mentality. Though my 180mm Refractor is quiet a beast, its still a feather weight compared to my 11 and 14" SCT's. Do others seem to enjoy this approach to astronomy also?

...Ralph in Sacramento


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desertlens
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Re: Using refractors for Deep Space Observing new [Re: aa6ww]
      #5190223 - 04/25/12 04:45 PM

Call be crazy (or masochistic) but I enjoy DSOs with an 80mm Triplet. Less aperture presents an interesting challenge and wide field context. Charles Messier certainly did a lot with small refractors.

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JIMZ7
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Re: Using refractors for Deep Space Observing new [Re: desertlens]
      #5190250 - 04/25/12 04:57 PM

Nothing wrong with DSO using refractors. 100% clear aperture & sharp images at lower power. I had a Orion 100mm f/6 & Antares 105mm f/6.3 RFT's & they were fun because of the portability each of them provided. When using 2" eyepieces with 3 or 4 degree fov viewing-it's "jaw dropping" to say the least.

Jim


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Refractor6
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Re: Using refractors for Deep Space Observing new [Re: desertlens]
      #5190263 - 04/25/12 05:02 PM

One of my favorites ways to observe when far away from light pollution is with bigger achros. In the past i've suprised myself on more than one occasion on what i've managed to pull in at the ep of my 152 f/6.5 achromatic refractor...this sometimes observing with bigger scopes of other designs right near by that had more difficulty nailing down the same objects such as some challenging galaxies and such.

Karl {Galaxyman} and Mr. Bill and many other members use larger achromats at dark sites for deep sky object observing and targets. The sharp pinpoint stars and very good image contrast afforded by an achro refractor with good collimated optics especially when you get to a 6" class of instrument can't be beat per aperature for the task at hand in my view.


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simpleisbetter
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Re: Using refractors for Deep Space Observing new [Re: Refractor6]
      #5190286 - 04/25/12 05:12 PM

I absolutely enjoy refractors on DSO's and find they make very good scopes for it. I moved from a 12" f/5 GSO dob to a 4" f/7 APO which I happily used for 3.5yrs until just recently moving to a 6" f/8 achro. I much prefer a refractor to a reflector, the views just seem more pure for lack of a better way to qualify what I see and "feel". Refractors also cool down much quicker so you get in more quality observing time. And you really can see plenty with them; whether anyone chooses to believe me or not, I've observed Stephen's Quintet with my 4" on two occasions, both very transparent dark nights. I also find refractors to be lower maintenance and easier to clean when needed. All these plusses are what make up for the lower aperture for me. Now if I had a big 16" dob fixed in an observatory at a dark site like Carol...

Edited by simpleisbetter (04/25/12 05:15 PM)


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hfjacinto
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Re: Using refractors for Deep Space Observing new [Re: simpleisbetter]
      #5190315 - 04/25/12 05:30 PM

While I like the view through my 120 Apo, aperture rules for DSO's. And here is the killer I use my refractor more, it's just easier to use.

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jrbarnett
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Re: Using refractors for Deep Space Observing new [Re: aa6ww]
      #5190323 - 04/25/12 05:35 PM

"Do many out here use refractors for deep space observing?"

Yup.

I have a lot of telescopes, refractors included, at my disposal, including, for example, a 16" Dob and 11" SCT. Nonetheless, 4" and 5.5" refractors get more use for DSO observing than the larger aperture scopes.

If aperture is king (debatable) then contrast must be queen and optical quality, prince. No other design comes close to the efficiency per inch of aperture as a quality refractor. Under all but the most perfect of conditions, larger scopes of other designs introduce some amount of "mush factor" into the image. Sure, Jupiter in the 20" Dob at 300x may show additional belts and bands compared to the TC 140 at 200x, but the planet in the TEC is razor sharp, the limb is crisp and the object has three-dimensional shading. The edges aren't crisp in the bigger scope and the inter-belt transitions are a little hairy, even though there are more of them.

It is the ability to deliver 99% of its capability, 90% of the time that makes me come back time and again to refractors as DSO observing tools. Of course, it just makes me want a bigger refractor.

This year OFLI, my club, will do a week long dark sky trip, and I'll be taking the TEC 140 rather than the Teeter-Lockwood (though the Dob will go on the late summer observing trip to Pinnacles National Monument again this year).

Good post.

- Jim


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hfjacinto
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Re: Using refractors for Deep Space Observing new [Re: desertlens]
      #5190335 - 04/25/12 05:42 PM

Quote:

Call be crazy (or masochistic) but I enjoy DSOs with an 80mm Triplet. Less aperture presents an interesting challenge and wide field context. Charles Messier certainly did a lot with small refractors.



I don't know if Charles Messier is a good example everything is his catalog is supposed to be comet like, I guess he needed a larger scope to see that none of his objects look like comets.


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Jan Owen
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Re: Using refractors for Deep Space Observing new [Re: jrbarnett]
      #5190355 - 04/25/12 05:58 PM

Agreed. That pretty much mirrors my thoughts & experience.

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GeneT
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Re: Using refractors for Deep Space Observing new [Re: aa6ww]
      #5190377 - 04/25/12 06:07 PM

You are just a refractor guy. If I had the room, I would add a good 4 inch refractor to use with my 12.5 inch Portaball.

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desertlens
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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5190399 - 04/25/12 06:23 PM

Quote:

I don't know if Charles Messier is a good example everything is his catalog is supposed to be comet like, I guess he needed a larger scope to see that none of his objects look like comets.




Nah... He just needed to see they weren't moving.


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ken hubal
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Re: Using refractors for Deep Space Observing new [Re: desertlens]
      #5190420 - 04/25/12 06:36 PM

I will always take the clear aperture of a refractor to that of an obstructed reflector!

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rwiederrich
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Re: Using refractors for Deep Space Observing new [Re: aa6ww]
      #5190429 - 04/25/12 06:39 PM

Refractors are all I use. Since I use a 6"f/15 and a 10"f/15 permenantly mounted in an OB...why would I need to switch? The 10"f/15 is awesome on DSO's. Not to mention the 6"f/15 with its Devany Objective.

Rob


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Sean Cunneen
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Re: Using refractors for Deep Space Observing new [Re: rwiederrich]
      #5190461 - 04/25/12 06:55 PM

Most of the real "WOW" moments I've experienced with DSO's in this hobby were with my refractor. Using it isn't easy but when it pays off, it pays off big! I can still close my eyes and see the detail in the Whirlpool from my view at the Bootleggers star party 2010. I was on my back in the grass with a too-friendly ant crawling on me...

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dscarpa
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Re: Using refractors for Deep Space Observing new [Re: aa6ww]
      #5190486 - 04/25/12 07:09 PM

I've got a very good C9.25 and IM715 but find myself enjoying the WO ZS110 for DSOs just as much. A friend of mine has a Meade 10 and he keeps bringing up the DSO viewing he's done with the ZS. There's just something about the star colors he says. David

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John59
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Re: Using refractors for Deep Space Observing new [Re: aa6ww]
      #5190615 - 04/25/12 08:32 PM

I have had many scopes over the years and I have made the full circle back to refractors. Currently I have a really nice 12" Goto Dob but it rarely gets used. I seem to always chose the 152MM refractor. As stated below cools faster than anything else and the views are very pleasant.

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Friendly Giant
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Re: Using refractors for Deep Space Observing new [Re: aa6ww]
      #5190636 - 04/25/12 08:43 PM

As you can see from my signature, I currently have only a small (72mm F6) refractor and a 10" dob. I went out with some club members to our favorite dark site a week ago (with both scopes). Obviously a 10" dob has more resolving power and light reach, and yet, I found myself enjoying looking at the brighter galaxies more in the 72mm refractor. I looked at M81/M82 in the dob, then in the refractor (same magnification framing the two galaxies together). I just found the view in the refractor more pleasing (crisper, contrastier). I don't think I'll ever get rid of the dob because there are times you just need that resolving power or light reach, but when I look back on that evening my fondest memories are of the views through the refractor.

I'm actually thinking now of getting a refractor at the midpoint between the two... a 5" scope. Although a 130mm Tak would be nice, it would be very expensive and take a while to cool down. I'm therefore also considering a D&G 5" F15 scope. From what I hear, the D&G would give views comparable in quality at least to a top 4" apo, but would have more magnification reach (and also a little more resolving power owing to the higher aperture). The only thing that gives me pause to go for the long D&G is the mounting requirement and being able to work with that long scope as the eyepiece position moves up and down.


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mikey cee
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Re: Using refractors for Deep Space Observing new [Re: John59]
      #5190653 - 04/25/12 08:51 PM Attachment (104 downloads)

I've just started with my setup. True I don't see any detail but then again I'm under a milky suburban light bubble too. A few of the DSO I've seen of late. Messier objects M65-66-95-96-51 and NGC's 205 and 2309. Thank God my refractor darkens the sky enough I can see them heck if I had a reflector no way Jose' they would be lost in the milky white field! Mike

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Vondragonnoggin
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Re: Using refractors for Deep Space Observing new [Re: Friendly Giant]
      #5190655 - 04/25/12 08:51 PM

Very much enjoy my 5" refractor for DSO's. It just makes things look so good. Well for larger DSO's anyway. I think a 6" is in the plans eventually, but for now the 5" is very lightweight and great for DSO's plus more. Was economical too.

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watcher
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Re: Using refractors for Deep Space Observing new [Re: Vondragonnoggin]
      #5190677 - 04/25/12 09:05 PM

The only mirrored scope I own,(IM715) I only use for planets. Well OK globs too, but that will change when my 6" F/5 ISTAR arrives. Planning on a 9" F/7.7 refractor that will be for DSO only duty also.

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galaxyman
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Re: Using refractors for Deep Space Observing new [Re: aa6ww]
      #5190960 - 04/26/12 12:50 AM

Quote:

Do many out here use refractors for deep space observing? Over the years, I've started to move away from my largest scopes in favor or smaller more portable (somewhat) scopes for deep space hunting. These scopes almost always end up being refractors because I love the pin point stars they offer and wide field views. Of course there are still times when the skies are very dark and I take a journey to my dark site location, then I have to set up my biggest SCT, but generally, I find myself moving more toward using my refractors even for deep space observing. My 150mm and 180mm refractors are very fun to use, and still have plenty of aperture for deep space hunting. Maybe unlike most, I find myself more challenged looking for dim objects in my smaller scopes than finding the urge to want larger and larger scopes to dig out distant galaxies.
That seems to be my latest approach to this hobby.
One of my friends calls it "The less is more" mentality. Though my 180mm Refractor is quiet a beast, its still a feather weight compared to my 11 and 14" SCT's. Do others seem to enjoy this approach to astronomy also?

...Ralph in Sacramento




Hi Ralph

As Stan (Refractor6) mentioned, I only use my refractors for DSO's, and do get great results.

Jim also points out a bit why refractors do so well.

Over the past couple years I've done some hardcore galaxy observing with the 8", and in particular the ARP's.

I also notice you have an APM 7.1" f/6. Is that the APO or achro? A clubmate does have the 7.1" f/6 achro, and he gets great DSO results with that scope.

You also might want to check http://tech.groups.yahoo.com/group/deepspacewithrefractors if interested.



Karl
E.O.H.

Chesmont Astronomical Society - www.chesmontastro.org
Deep Space with Refractors - http://tech.groups.yahoo.com/group/deepspacewithrefractors
Telekit (Swayze optics) 22" F/4.5 Dob
Homemade (Parks Optics) 12.5" F/4.8 Dob
TMB/APM 8" f/9 Refractor”The Beast”. One great DEEP SKY achro
ES 6" f/6.5 achro. Good one
Celestron Omni XLT 102 refractor.
Celestron 10x60mm Binos


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Alan French
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Re: Using refractors for Deep Space Observing new [Re: galaxyman]
      #5191130 - 04/26/12 07:13 AM

An odd topic. Why would anyone NOT use a refractor for deep sky observing?

Even a small refractor can show a lot under reasonably dark skies. And one with a short focal length will provide wide true fields not attainable in most other types of instruments.

Clear skies, Alan


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Jim Curry
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Re: Using refractors for Deep Space Observing new [Re: simpleisbetter]
      #5191217 - 04/26/12 08:33 AM

Quote:

And you really can see plenty with them; whether anyone chooses to believe me or not, I've observed Stephen's Quintet with my 4" on two occasions, both very transparent dark nights.




No surprise there, I've bagged them with my 140. It took the club's 16" to split the close members but smallish refractors can handle their workload. When you think of the equipment upgrade to go from a 13 mag. limit to 16 mag. the small refractors in a dark sky environment will provide endless satisfaction.

Jim


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curiosidad
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Re: Using refractors for Deep Space Observing new [Re: Jim Curry]
      #5191408 - 04/26/12 10:36 AM

Alan, I have a LP 66ED / 400mm focal lenght, for this, a Truly wide angle vistas..!! Also I have others telescopes much more Big, but for this observations the small refractor I think it´s THE KING!!

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aa6ww
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Re: Using refractors for Deep Space Observing new [Re: Alan French]
      #5191443 - 04/26/12 10:56 AM

Quote:

An odd topic. Why would anyone NOT use a refractor for deep sky observing?

Even a small refractor can show a lot under reasonably dark skies. And one with a short focal length will provide wide true fields not attainable in most other types of instruments.

Clear skies, Alan





Over the last few years, I find myself doing more and more astronomy either by myself or with one other astronomer whos never lost the passion for astronomy. Everyone else has fallen out of this hobby because its too much hastle for them to put it the effort to get anything out of this hobby. Since now most of my astronomy is close to home, Ive found myself digging my 6" F/5 Celestron Omni with the XLT coating on the front lens. It gives me 6 clear inches of aperture and excellent field of views. The optics are so sharp for excellent star patterns and deep space also, and its such a lightweight fun scope. Im working on my the Herschel 400 with this scope now, it may takes a few years but its a fun game plan and with Ethos, ES and Nagler eyepieces along with my upgrades William optics 10:1 focuser, my larger scopes and mounts ( I use a GP-DX with this scope) will be spending more and more time at home now. Its gonna be another fun year of astronomy, definately!

...Ralph in Sac


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Scott99
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Re: Using refractors for Deep Space Observing new [Re: aa6ww]
      #5191668 - 04/26/12 01:08 PM

Refractors are ALL I use for deep-space viewing! the bigger the better, however sometimes I'm amazed at what a 5 or 6 inch refractor can do compared to larger scopes.

A lot of people with truss dobs don't use a shroud, which is hard for me to understand. My smallish refractor will often give better views than big dobs because the view is totally washed out by the open tube. Many people seem to enjoy just having a huge scope and not really optimizing the views they're getting.

With a good refractor your view is 100% optimized every time


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Jim Romanski
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Re: Using refractors for Deep Space Observing new [Re: Jan Owen]
      #5191682 - 04/26/12 01:16 PM

Quote:

Agreed. That pretty much mirrors my thoughts & experience.



Hmmm...were you trying to make a clever pun? I've been reflecting on your comment now for a while.


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Alan French
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Re: Using refractors for Deep Space Observing new [Re: Jim Romanski]
      #5191722 - 04/26/12 01:32 PM

But if you really want to cruise the Veil, or get fantastic views of deep sky objects, it's impossible to beat a 28"+ telescope with any commercially available refractor.

Clear skies, Alan


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Jan Owen
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Re: Using refractors for Deep Space Observing new [Re: Jim Romanski]
      #5191750 - 04/26/12 01:47 PM

Not at all... No pun; just a coincidence of word placement.

I am a strictly visual amateur astronomer (I got astrophotography out of my system back in the 1980's, in the film days), and have been in amateur astronomy now for... closer to 50 years than I want to contemplate. I use several types of instruments, and have owned and used others. I've been primarily a DSO guy for most of that time. I use all my scopes for DSO's, but the magnificence of the full field in a quality refractor can be stunning.

When I work at improving my reflectors, the aim is always to help facilitate a more *refractor-like* image. I've seen some stunning images in all types and sizes of instruments, but I'm always amazed at the level of quality in the images of a refractor, compared to many reflectors of different types in actual service (as many of them suffer because their owner hasn't worked to achieve the best images the scope is capable of delivering)...

To me, there is nothing I can dream up that's more visually stunning than, for instance, the double cluster, as framed in my EON 120, viewed through a 16 mm Nagler eyepiece.

No pun necessary...


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Jim Romanski
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Re: Using refractors for Deep Space Observing new [Re: Jan Owen]
      #5191817 - 04/26/12 02:21 PM

I guess I just can't resist a good pun.

But kidding aside I understand where you're coming from. I'd owned reflectors for the first 30 years in the hobby. I had access to some observatory refractors (an 8" Grubb and a 10" Clark) so I knew how nice they were. But for DSO I'd always stuck to my reflectors. Then in March of 2008 Televue had a big sale and I bought the NP101...WOW what a great scope. But it's only a 4" scope so a year or so ago I got a good deal on an NP127. I must confess that I've been using it a lot for DSO in my backyard. It's especially nice for star clusters using the 31mm Nagler.

It won't replace my big reflectors but lately I've been using it most of the time just like hfjacinto.


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coopman
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Re: Using refractors for Deep Space Observing new [Re: Jim Romanski]
      #5191897 - 04/26/12 03:20 PM

Yes, the pin-point sharp stars and great contrast make them very good for DSOs. However, eventually a light bucket Dob becomes desirable as aperture fever sets in.

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simpleisbetter
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Re: Using refractors for Deep Space Observing new [Re: coopman]
      #5191917 - 04/26/12 03:33 PM

You're perhaps right Clay, but for me the POV would be that it depends on how one wants to challenge oneself. A large dob is great for galaxies, but I get more enjoyment out of seeing how far I can push my "smaller" refractors, and my eyes. I treat galaxies just like double stars, pushing my equipment and eyes to their visual limits and beyond. There's still plenty to see and never run out in a lifetime of observing.

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Sean Puett
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Re: Using refractors for Deep Space Observing new [Re: simpleisbetter]
      #5192027 - 04/26/12 04:34 PM

I like using them both at the same time. Well not exactly the same time, like cockeyed binoculars but, in the same session. I think it is fun to find an object in one scope, observe it until you have found the best image possible, then try it in the bigger reflector. One target that is great and plays to both of their strengths is pleaides. In a refractor you easily fit them all in the fov and get the tightest possible stars. Then point the 12" reflector (paracorr of coarse) at them and not quite get them all in but, you can see the nebulosity around them and you are treated to the best possible views. I love refractor but until they make a 12" f5 refractor with flat field and perfect color correction on a mount for less than $2000, I'll own reflectors.

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Jon Isaacs
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Re: Using refractors for Deep Space Observing new [Re: Alan French]
      #5192067 - 04/26/12 05:02 PM

Quote:

But if you really want to cruise the Veil, or get fantastic views of deep sky objects, it's impossible to beat a 28"+ telescope with any commercially available refractor.

Clear skies, Alan




Alan:

If it's clear this weekend I will be rolling out the 25 inch and giving it some work. By early morning, before astronomical twilight, the Veil should be well placed and we'll give it a look, it is pretty impressive. But the Veil in the NP-101 and the 31mm Nagler is also impressive, just in a different way.

But that said, those faint galaxies just do kind of pop-up all over the place with a larger scope.

Jon


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Alan French
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Re: Using refractors for Deep Space Observing new [Re: Jon Isaacs]
      #5192109 - 04/26/12 05:29 PM

Quote:

Quote:

But if you really want to cruise the Veil, or get fantastic views of deep sky objects, it's impossible to beat a 28"+ telescope with any commercially available refractor.

Clear skies, Alan




Alan:

If it's clear this weekend I will be rolling out the 25 inch and giving it some work. By early morning, before astronomical twilight, the Veil should be well placed and we'll give it a look, it is pretty impressive. But the Veil in the NP-101 and the 31mm Nagler is also impressive, just in a different way.

But that said, those faint galaxies just do kind of pop-up all over the place with a larger scope.

Jon




Jon,

I certainly agree. It's a lot of fun seeing the entire Veil in one view. But I had about 20 minutes to explore the Veil in a 30" Dobsonian one night at a dark sky site, and the amount of detail was just incredible.

Clear skies, Alan


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Mark Costello
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Re: Using refractors for Deep Space Observing new [Re: Jon Isaacs]
      #5192116 - 04/26/12 05:33 PM

Well, Jon, I waaaaaaas wondering when you'd step into this thread.

I use my 5" refractor for DSO observing and nothing else. That's easy for me to say since my achro is my only telescope at this time. In all seriousness, I like the refractor especially for open clusters. A couple of weeks ago, it was delivering images of M47 and M48 that had me gasping. Ditto last summer with M24.

That being said, I've have on a few times banged up against its 5" limits. And as great as larger refractors would perform, I know that I'm going to set up and so get more out of a larger mirror based telescope as opposed to a larger lens based telescope.

Cheers ....


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ken hubal
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Re: Using refractors for Deep Space Observing new [Re: Mark Costello]
      #5192219 - 04/26/12 06:23 PM

A 5" refractor is ALOT more portable than a 30" Dobsonian!

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rwiederrich
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Re: Using refractors for Deep Space Observing new [Re: Sean Cunneen]
      #5192226 - 04/26/12 06:27 PM

Quote:

Most of the real "WOW" moments I've experienced with DSO's in this hobby were with my refractor. Using it isn't easy but when it pays off, it pays off big! I can still close my eyes and see the detail in the Whirlpool from my view at the Bootleggers star party 2010. I was on my back in the grass with a too-friendly ant crawling on me...





Sean..you need to tern some of that engenuity you have into making a hydraulic pier or some other kind of elevating pier...so you can get out of the dirt and grass...and away from the crawling critters.....

Rob


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Alan French
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Re: Using refractors for Deep Space Observing new [Re: ken hubal]
      #5192348 - 04/26/12 07:31 PM

Quote:

A 5" refractor is ALOT more portable than a 30" Dobsonian!




It depends. If you can just wheel the 30" out of the garage, it could easily beat the set up time of a 5" refractor.

But, in general, you're right. It depends on how much you want the views provided by a large Dob. We don't have any really large Dobs in our club, but we have several folks with pretty large scopes (two with refractors mounted piggyback) that take some time to set up. They find it worthwhile.

Clear skies, Alan


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rwiederrich
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Re: Using refractors for Deep Space Observing new [Re: mikey cee]
      #5192383 - 04/26/12 07:48 PM

Quote:

I've just started with my setup. True I don't see any detail but then again I'm under a milky suburban light bubble too. A few of the DSO I've seen of late. Messier objects M65-66-95-96-51 and NGC's 205 and 2309. Thank God my refractor darkens the sky enough I can see them heck if I had a reflector no way Jose' they would be lost in the milky white field! Mike





The only thing I have to say Mike..is wish you had that scope under darker skies. Being what it is though you can grab the DSO's and bring them in.......Sweet.

Rob


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Re: Using refractors for Deep Space Observing new [Re: rwiederrich]
      #5192613 - 04/26/12 10:52 PM

I use two different scopes for deepsky; a homebuilt 16.5" f/6.7 Newtonian and a 6" f/8 achro. As much as I luv my big Newt, it's the achro that I use most of the time. It's just a joy to use. I gotta be in the right mood to set up the big scope.

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gnowellsct
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Re: Using refractors for Deep Space Observing new [Re: jgraham]
      #5192664 - 04/26/12 11:25 PM

Globs ain't so good, but there are compensations. My best fractor night was with the FS128 watching a comet in the milky way. Greg N

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Jon Isaacs
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Re: Using refractors for Deep Space Observing new [Re: Alan French]
      #5192907 - 04/27/12 06:01 AM Attachment (46 downloads)

Quote:

Quote:

A 5" refractor is ALOT more portable than a 30" Dobsonian!




It depends. If you can just wheel the 30" out of the garage, it could easily beat the set up time of a 5" refractor.

But, in general, you're right. It depends on how much you want the views provided by a large Dob. We don't have any really large Dobs in our club, but we have several folks with pretty large scopes (two with refractors mounted piggyback) that take some time to set up. They find it worthwhile.

Clear skies, Alan




It's true... I haul my refractors back and forth, my larger Dobs live in a garage where the skies are quite dark. Setup time is not an issue for the Dobsonians, they stay assembled.

I often use the larger scopes to locate faint targets and then use the view in the Telrad to guide me with the refractor.

Jon


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Jon_Doh
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Re: Using refractors for Deep Space Observing new [Re: Jon Isaacs]
      #5193257 - 04/27/12 11:53 AM

Jon, you're lucky you have dark skies at home. For me a 30" dob would be useless. I can roll it out, but it's going to be to fairly polluted skies. Transporting it to a dark site where it could shine then obviates the purpose in having one. One day (maybe when I retire) I hope to move to a dark site and build an observatory with a huge lens telescope. Til then I'll have to get buy on smaller SCT's and refractors.

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Scott99
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Re: Using refractors for Deep Space Observing new [Re: ken hubal]
      #5193261 - 04/27/12 11:54 AM

Quote:

A 5" refractor is ALOT more portable than a 30" Dobsonian!




yes, honestly "a friend's" 30-inch dob is my favorite deep-sky scope also!


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TonyF
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Re: Using refractors for Deep Space Observing new [Re: aa6ww]
      #5193340 - 04/27/12 12:40 PM

I use my 100mm refractor for deep-sky "whining" ... Then I go to the 16" reflector as my "finder" then back to the refractor and go "Oh, there it is....." LoL!!

Like another poster mentioned, the 16" dob on wheels is more grab-n-go out the door than any of my refractors.. I need a permanently mounted pier/GEM/observatory setup in the backyard to make it easier... Now if I only had an 8" refractor... Hummmm

CS,

TonyF


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Mark Costello
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Re: Using refractors for Deep Space Observing new [Re: ken hubal]
      #5193425 - 04/27/12 01:26 PM

Quote:

A 5" refractor is ALOT more portable than a 30" Dobsonian!




Weeeeelllll, I'm thinking that a reflector as a second scope would be more along the lines of 7"-11". When I think I can spend the money on one, it'll be my job to find a scope in that size range that would complement my 5" refractor and not so compete with it. As to larger refractors, I might be able to handle a 6" refractor but only if it was a short-tube one and at any rate it'd be a bit of a gamble. And as well as my 5" refractor is doing, I'm not all that motivated to find out. So if I get a scope bigger than 5", it'll focus light mostly or completely with mirrors.


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Pinbout
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Re: Using refractors for Deep Space Observing new [Re: TonyF]
      #5193465 - 04/27/12 01:58 PM

Quote:

... Now if I only had an 8" refractor... Hummmm





@ f3.75


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Jon Isaacs
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Re: Using refractors for Deep Space Observing new [Re: Mark Costello]
      #5193940 - 04/27/12 07:37 PM

Quote:

Quote:

A 5" refractor is ALOT more portable than a 30" Dobsonian!




Weeeeelllll, I'm thinking that a reflector as a second scope would be more along the lines of 7"-11". When I think I can spend the money on one, it'll be my job to find a scope in that size range that would complement my 5" refractor and not so compete with it. As to larger refractors, I might be able to handle a 6" refractor but only if it was a short-tube one and at any rate it'd be a bit of a gamble. And as well as my 5" refractor is doing, I'm not all that motivated to find out. So if I get a scope bigger than 5", it'll focus light mostly or completely with mirrors.




Mark:

I think you are right on target. A 10 inch would make a nice companion for your 5 inch Achromat. It is nice to have some big scopes but something between 10 and 12.5 inches is a nice size and there is plenty to see.

Jon


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coutleef
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Re: Using refractors for Deep Space Observing new [Re: Mark Costello]
      #5193984 - 04/27/12 08:15 PM

Quote:

Quote:

A 5" refractor is ALOT more portable than a 30" Dobsonian!




Weeeeelllll, I'm thinking that a reflector as a second scope would be more along the lines of 7"-11". When I think I can spend the money on one, it'll be my job to find a scope in that size range that would complement my 5" refractor and not so compete with it. As to larger refractors, I might be able to handle a 6" refractor but only if it was a short-tube one and at any rate it'd be a bit of a gamble. And as well as my 5" refractor is doing, I'm not all that motivated to find out. So if I get a scope bigger than 5", it'll focus light mostly or completely with mirrors.




you are rigth on target with that plan Mark.

A big reflector will do things your refractor cannot do and the refractor gives wide views the bigger scope cannot give.

i had ruled out big dobs initially but realized they could be carried easily with hand carts.

you have a nice scope, so take your time.

good luck in your choice


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jrbarnett
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Re: Using refractors for Deep Space Observing new [Re: Jon Isaacs]
      #5194198 - 04/27/12 11:37 PM

The refractor dilemma: dim but perfect versus bright but flawed.

Both scenarios have merit, of course, but there's something beyond compare about having a large (>5") premium refractor out under a truly dark (NELM at zenith of 7+) sky. I actually appreciate my aperture here in the 'burbs more than I do in the boons.

- Jim


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Jon Isaacs
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Re: Using refractors for Deep Space Observing new [Re: jrbarnett]
      #5194409 - 04/28/12 06:27 AM

Quote:

The refractor dilemma: dim but perfect versus bright but flawed.

Both scenarios have merit, of course, but there's something beyond compare about having a large (>5") premium refractor out under a truly dark (NELM at zenith of 7+) sky. I actually appreciate my aperture here in the 'burbs more than I do in the boons.

- Jim




Brightness of an extended object is not dependent upon aperture, it's a function of exit pupil... Telescopes are like camera lenses, choose the right one for the particular job at hand. A 4 inch F/5.4 is just about right for the California Nebula, not so good for 14th magnitude galaxies or globular clusters. The reverse is true of large reflectors.

Jon Isaacs


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aa6ww
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Re: Using refractors for Deep Space Observing new [Re: galaxyman]
      #5194453 - 04/28/12 07:29 AM Attachment (36 downloads)

Quote:

Quote:

Do many out here use refractors for deep space observing? Over the years, I've started to move away from my largest scopes in favor or smaller more portable (somewhat) scopes for deep space hunting. These scopes almost always end up being refractors because I love the pin point stars they offer and wide field views. Of course there are still times when the skies are very dark and I take a journey to my dark site location, then I have to set up my biggest SCT, but generally, I find myself moving more toward using my refractors even for deep space observing. My 150mm and 180mm refractors are very fun to use, and still have plenty of aperture for deep space hunting. Maybe unlike most, I find myself more challenged looking for dim objects in my smaller scopes than finding the urge to want larger and larger scopes to dig out distant galaxies.
That seems to be my latest approach to this hobby.
One of my friends calls it "The less is more" mentality. Though my 180mm Refractor is quiet a beast, its still a feather weight compared to my 11 and 14" SCT's. Do others seem to enjoy this approach to astronomy also?

...Ralph in Sacramento




Hi Ralph

As Stan (Refractor6) mentioned, I only use my refractors for DSO's, and do get great results.

Jim also points out a bit why refractors do so well.

Over the past couple years I've done some hardcore galaxy observing with the 8", and in particular the ARP's.

I also notice you have an APM 7.1" f/6. Is that the APO or achro? A clubmate does have the 7.1" f/6 achro, and he gets great DSO results with that scope.

You also might want to check http://tech.groups.yahoo.com/group/deepspacewithrefractors if interested.



Karl
E.O.H.

Chesmont Astronomical Society - www.chesmontastro.org
Deep Space with Refractors - http://tech.groups.yahoo.com/group/deepspacewithrefractors
Telekit (Swayze optics) 22" F/4.5 Dob
Homemade (Parks Optics) 12.5" F/4.8 Dob
TMB/APM 8" f/9 Refractor”The Beast”. One great DEEP SKY achro
ES 6" f/6.5 achro. Good one
Celestron Omni XLT 102 refractor.
Celestron 10x60mm Binos




My 180mm TMB designed APM is an F/6 Achromat. Its all the refractor I think I could handle, unless and 8" F/6 ever showed up. They are so uncreadibly sharp refractors, I've been offered twice what I paid for it, but there's no way Id get rid of it. Id sell my TOA-130 but this ones a keeper, just as my TSA-102 is also.


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hottr6
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Re: Using refractors for Deep Space Observing new [Re: aa6ww]
      #5194732 - 04/28/12 11:21 AM

For my eyes, and my environment, I will take my reflector everytime for DSOs over my refractors.

Consider the Pleiades. The nebulosity is very obvious in my reflector. Even beginners can see it without being told what to look for. In my refractors, seeing the nebulosity is a stretch. Globular clusters in the big reflector are mind-blowing, then switching to my refractors there is profound disappointment.

For DSOs, I'll take every photon I can capture.


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Refractor6
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Re: Using refractors for Deep Space Observing new [Re: hottr6]
      #5194774 - 04/28/12 11:50 AM

Quote:

For my eyes, and my environment, I will take my reflector everytime for DSOs over my refractors.

Consider the Pleiades. The nebulosity is very obvious in my reflector. Even beginners can see it without being told what to look for. In my refractors, seeing the nebulosity is a stretch. Globular clusters in the big reflector are mind-blowing, then switching to my refractors there is profound disappointment.

For DSOs, I'll take every photon I can capture.




I hear what you are saying BUT I remember one encounter I had in the high alpine about 10 years ago at a dark site of the Pleiades with my 6" refractor at low power with a widefield view the showed the amazing rich color of the reflection nebula in vivid detail that left even the other hardcore observers with bigger scopes around me gasping in awe at the ep.

Under the right conditions {aperture size/scope optics/ep choice/sky conditions etc..} the smaller refractors can truly rock on certain objects....globs it's no contest though in favour of the bigger well collimated reflector from my experience with views in large dobs and such. Certain fainter galaxies showed up better at higher powers in the 6" refractor though at the same location due to contrast related issues I suspect which was interesting.


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Sean Puett
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Re: Using refractors for Deep Space Observing new [Re: hottr6]
      #5194787 - 04/28/12 11:57 AM

I don't know about "flawed" views from reflectors other than spikes on the brightest stars. There is a slight loss of contrast from the CO but even then, the resolution makes up for it. A well cooled and properly collimated newt with a paracorr puts up some amazing planetary views. And deepsky is really no contest. I believe that you need both a large reflector and a 4"+ refractor to get the most of your session. If i had to choose one scope, it would be a 12" reflector. The only thing it can't do is widefield viewing.
Reflectors get a bad rap because they are either not well collimated, well cooled, or there is a problem with the optics. The first 2 options being the most common. A reflector owner needs to be willing to re collimate his scope after dark if it is off and not say "it is close enough" when his stars look like comets.
All that being said i spent twice as much money getting my refractor, mount, and everything needed to use it, than i did for both reflectors and my paracorr. I did this because i like the views a good refractor puts up. They can be the best scope for a given size when all the potential aberrations are controlled.


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CityAstronomer
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Re: Using refractors for Deep Space Observing new [Re: aa6ww]
      #5199329 - 04/30/12 11:34 PM

Quote:

Do many out here use refractors for deep space observing?




That is all I use here in the burbs of Los Angeles and Deep Sky Observing is my main interest. My 4 inch refractor has taken me into the NGC list as well as most of the Messier list in a white zone enviroment. I have had an 8 inch SCT and 6 in intes Mak, but sold them both for the smaller refractor. The refractor gives me the best quality view of what I can see in my backyard with the least hassle.

Sam


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northernontario
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Re: Using refractors for Deep Space Observing new [Re: CityAstronomer]
      #5201058 - 05/01/12 11:24 PM

On the brighter galaxies (M51,81,82,85 for example), my 6" f/5.9 does very well. I've had good success in Virgo.

The Veil is also very nice. Open clusters are crazy good, but Globulars are a bit tough.

M42 is also very nice with a refractor. I love looking at doubles but I guess they don't count as DSOs.

But in the end...I am addicted to my Dob.

jake


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curiosidad
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Re: Using refractors for Deep Space Observing new [Re: northernontario]
      #5201500 - 05/02/12 10:01 AM

And a refractor 4 "F / 5, can be a good low-medium deep sky telescope magnification?
Best


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Sasa
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Re: Using refractors for Deep Space Observing new [Re: curiosidad]
      #5202318 - 05/02/12 05:09 PM

I found myself observing with my refractors (ED100 and AS80) much more than with my 250mm Dobson, even DSO from my background. I like them for their contrast. Newton has quite visible issues with handling straight lights from nearby street lamps. While my refractors don't have this. More over, my Dobson is quite long (f=1600mm) and I have to stay when observing. When I observe at 300+ power (which is quite often, I like planetary nebulas), in no way I can push the telescope and simultaneously guard my eyes against street lamps. With refractors, both on alt-az (with slow control movements) or even better on my Losmandy G8, I can sit and bury the eye into the eyepiece and cover my head with hood. This helps a lot. I could detect even from my backyard, for example, very low surface brightness globular NGC5053 (near M53). I was never successful with my 250mm Dobson.

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Re: Using refractors for Deep Space Observing new [Re: Sasa]
      #5203544 - 05/03/12 11:07 AM

Jake, does your 8" Meade pick up anything that you can't see with the 6" refractor?

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stevetaylor199
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Re: Using refractors for Deep Space Observing new [Re: Jon Isaacs]
      #5203715 - 05/03/12 12:40 PM

Quote:

Quote:

The refractor dilemma: dim but perfect versus bright but flawed.

Both scenarios have merit, of course, but there's something beyond compare about having a large (>5") premium refractor out under a truly dark (NELM at zenith of 7+) sky. I actually appreciate my aperture here in the 'burbs more than I do in the boons.

- Jim




Brightness of an extended object is not dependent upon aperture, it's a function of exit pupil... Telescopes are like camera lenses, choose the right one for the particular job at hand. A 4 inch F/5.4 is just about right for the California Nebula, not so good for 14th magnitude galaxies or globular clusters. The reverse is true of large reflectors.

Jon Isaacs




Interesting. Isn't it also true, though, that exit pupil is controlled by the EP focal length? Can you explain a little more about how aperture and focal length have a role in exit pupil, and what size pupil you'd recommend for extended objects?


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Eddgie
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Re: Using refractors for Deep Space Observing new [Re: stevetaylor199]
      #5203814 - 05/03/12 01:34 PM

First, I keep reading that refractors have better contrast.

This is simply untrue in most cases. If a reflector has more clear aperture (primary diameter minus secondary diameter) it will have as good or better contrast than a smaller unobstructed scope with less clear aperture.

As for exit pupil, what Jon says is 100% true, but the story is more complex.

Let's say for example that you use two telescopes... One is a 10" reflector, and one is a 5" refractor.

If you use a 2mm exit pupil in the 10", you will need an eyepeice that gives 127x.

If want the same 2mm exit pupil in the 5", the magnification will have to be about 63.5x.

What this means is that to get the same size exit pupil in these scopes, the image scale will be twice as large in the scope with twice the aperture!

Or, put another way, I could use the bigger scope at 63.5x and get the same exact image scale, but the exit pupil would be twice as large, so the object would appear much brighter in the larger aperture at the same image scale.

As for contrast, people say that objects stand out against the background better. This is not at all how contrast transfer works. The ratio between an extended object and the average background sky will be more or less the same in an obstructed scope as it will in an unobstructed scope.

The difference is how the light from an extended object is focused within the boundry of the extended object. In other words, it is about how the delicate and faint structure in a galaxy or nebula will be presented. The scope with more clear aperture will do a better job of presenting the details of the structure of the object. This is what contrast transfer is about... How the details within the boundry of an extended target are formed. The telescope with the most clear aperture will do a better job of concentrating the light from the fine details within the structure into the right place so that more and more of these structures become visible.

In the example above, if you pointed both telescopes at the Ring Nebula, and you se a 2mm Exit pupil, the 10" scope sould show the Ring Nebula at twice the scale, making the structure easier to resolve visuaally (and one of the primary functions of a telescope is to increase image scale) and assuming that the 10" scope had more clear aperture than the 5" telescope, not only would the detail be presented much larger for the same exit pupil, it would also be presented with better contrast. You would see more structure within the ring.

And this is why larger apertures are generally better for deep space observing thatn smaller ones.

I personally gave up on small scopes for deep spece. Having owned maybe 6 or 7 4" refractors, as beautiful as the presentation of stars were in the field of view, I just could not get much detail out of them except on stellar targets (clusters, doubles).

Even my 6" APO fails to come close to rendering the detail and structure in extended targets that my 14" reflector does.

In general terms, any deep sky object that will fit into the field of my 14" scope shows far more datial than it does in my 6" refractor.

I love my 6" refractor. It is the best wide field scope I have ever ever ever used. And during the summer or winter, cruising the Mikly Way with it is an absolute delight.

But for deep sky, it simply cannot perform up to the level that I personally require. If I want to study objects in detail, I want a large aperture. Small scopes seem to just not have the light gatbering, image scale, contrast, and resolution that is required for anyting but "Showcase" objects.

But this is just me, and this is the "Refractors are manna from heaven" forum, so I expect that of the posters here, I will be in a tiny minority.

And honestly, if someone is happy with the amount of detail they can see in a 66mm refractor, then who is to say they are wrong to prefer it? Not me!

But seeing much structure in the ring nebula with a 66mm, 100mm, or even 150mm refractor is not quite as easy as with a 10" to 15" reflector.

Everyone should use what they like, but make no mistake... Aperture, and lots of it, is the key to seeing more DSOs, and more structure in DSOs.


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aa6ww
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Re: Using refractors for Deep Space Observing new [Re: northernontario]
      #5204061 - 05/03/12 03:33 PM

Quote:

On the brighter galaxies (M51,81,82,85 for example), my 6" f/5.9 does very well. I've had good success in Virgo.

The Veil is also very nice. Open clusters are crazy good, but Globulars are a bit tough.

M42 is also very nice with a refractor. I love looking at doubles but I guess they don't count as DSOs.

But in the end...I am addicted to my Dob.

jake




Don't forget Markarians chain for how a big fast refactor can capture the entire chain in one field of view. I was with a group of people last year and brought out my 180mm F/6 APM refractor and they questioned why I'd want such a big refractor when their SCT's and Newts give them more aperture. Once they saw Markarians chain under those dark skies, and I compared it to the photos I had on my red screen laptop at the time, they were just mesmerized. Seeing the entire chain in one field of view and making out the "Eye's" in the chain, and counting the entire string, had them inviting me to do more observing with them with my big APM cannon. It's all about matching your scope and eyepieces to the object your observing, to get the most out of this hobby.

...Ralph


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russell23
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Re: Using refractors for Deep Space Observing new [Re: aa6ww]
      #5204788 - 05/03/12 11:31 PM

Quote:

Do many out here use refractors for deep space observing?




Yep - That is primarily what I do with my Vixen 5.5" refractor. For me - in addition to the great views I like the no-fuss aspect of refractors. Easy to set-up, quick cool down times, comfortable to sit at the end of the OTA, wide field views, pinpoint stars, inky black sky background.

I find I spend more time at the eyepiece with a refractor. When I had a large dob I spent more time trying to locate fainter objects that in the end appeared pretty much the same in the dob as brighter objects that were easier to find in the smaller refractor. After I realized that I stopped spending so much time with my nose in the charts and have spent more time just enjoying the view in the eyepiece.

Dave


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galaxyman
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Re: Using refractors for Deep Space Observing new [Re: Eddgie]
      #5204847 - 05/04/12 12:35 AM

Quote:

First, I keep reading that refractors have better contrast.

This is simply untrue in most cases. If a reflector has more clear aperture (primary diameter minus secondary diameter) it will have as good or better contrast than a smaller unobstructed scope with less clear aperture.

As for exit pupil, what Jon says is 100% true, but the story is more complex.

Let's say for example that you use two telescopes... One is a 10" reflector, and one is a 5" refractor.

If you use a 2mm exit pupil in the 10", you will need an eyepeice that gives 127x.

If want the same 2mm exit pupil in the 5", the magnification will have to be about 63.5x.

What this means is that to get the same size exit pupil in these scopes, the image scale will be twice as large in the scope with twice the aperture!

Or, put another way, I could use the bigger scope at 63.5x and get the same exact image scale, but the exit pupil would be twice as large, so the object would appear much brighter in the larger aperture at the same image scale.

As for contrast, people say that objects stand out against the background better. This is not at all how contrast transfer works. The ratio between an extended object and the average background sky will be more or less the same in an obstructed scope as it will in an unobstructed scope.

The difference is how the light from an extended object is focused within the boundry of the extended object. In other words, it is about how the delicate and faint structure in a galaxy or nebula will be presented. The scope with more clear aperture will do a better job of presenting the details of the structure of the object. This is what contrast transfer is about... How the details within the boundry of an extended target are formed. The telescope with the most clear aperture will do a better job of concentrating the light from the fine details within the structure into the right place so that more and more of these structures become visible.

In the example above, if you pointed both telescopes at the Ring Nebula, and you se a 2mm Exit pupil, the 10" scope sould show the Ring Nebula at twice the scale, making the structure easier to resolve visuaally (and one of the primary functions of a telescope is to increase image scale) and assuming that the 10" scope had more clear aperture than the 5" telescope, not only would the detail be presented much larger for the same exit pupil, it would also be presented with better contrast. You would see more structure within the ring.

And this is why larger apertures are generally better for deep space observing thatn smaller ones.

I personally gave up on small scopes for deep spece. Having owned maybe 6 or 7 4" refractors, as beautiful as the presentation of stars were in the field of view, I just could not get much detail out of them except on stellar targets (clusters, doubles).

Even my 6" APO fails to come close to rendering the detail and structure in extended targets that my 14" reflector does.

In general terms, any deep sky object that will fit into the field of my 14" scope shows far more datial than it does in my 6" refractor.

I love my 6" refractor. It is the best wide field scope I have ever ever ever used. And during the summer or winter, cruising the Mikly Way with it is an absolute delight.

But for deep sky, it simply cannot perform up to the level that I personally require. If I want to study objects in detail, I want a large aperture. Small scopes seem to just not have the light gatbering, image scale, contrast, and resolution that is required for anyting but "Showcase" objects.

But this is just me, and this is the "Refractors are manna from heaven" forum, so I expect that of the posters here, I will be in a tiny minority.

And honestly, if someone is happy with the amount of detail they can see in a 66mm refractor, then who is to say they are wrong to prefer it? Not me!

But seeing much structure in the ring nebula with a 66mm, 100mm, or even 150mm refractor is not quite as easy as with a 10" to 15" reflector.

Everyone should use what they like, but make no mistake... Aperture, and lots of it, is the key to seeing more DSOs, and more structure in DSOs.




Interesting Eddgie, for I agree for the most part, for have seen and compared two large scopes (8" refractor & 22" dob) of their respective type side by side in my write-up (and drawings) here a couple years ago (Clash of the Titans 1 & 2). Beyond that I have observed using the 8" refractor with a number of club mates using large dobs up to 25".

Using quality eyepieces in both scopes and similar magnifications, it was both a fun and interesting night.

The conclusion was of course the 22" showed the brighter more detailed image, but the big refractor the "prettier" view. The overall image quality in crispness and darker sky background (which is pleasing to the eye) was in the refractors favor like I said at similar magnifications.

Seeing galaxies in the 14th to 15th mag. range from a good dark site is a testament of what a good large refractor can do.

So Ralph's post here about using refractors for deep space is nice to see, and has substance.

An example can be M-42, and though I've seen this wonderful object through many different scopes over the past 40 plus years, the best overall view I've seen was two years ago on top of Dolly Sods mountain in West Virginia with the 8" refractor. The detail (from obvious to delicate) and color was wonderful. A Hi-Def view for sure.




Karl
E.O.H.

Chesmont Astronomical Society - www.chesmontastro.org
Deep Space with Refractors - http://tech.groups.yahoo.com/group/deepspacewithrefractors
Telekit (Swayze optics) 22" F/4.5 Dob
Homemade (Parks Optics) 12.5" F/4.8 Dob
TMB/APM 8" f/9 Refractor”The Beast”. One great DEEP SKY achro
ES 6" f/6.5 achro. Good one
Celestron Omni XLT 102 refractor.
Celestron 10x60mm Binos


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Messyone
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Re: Using refractors for Deep Space Observing new [Re: galaxyman]
      #5205317 - 05/04/12 10:26 AM

I love my 6" refractor for DSO's so much so I mounted a 4" f5 on it as a wide field viewer... don't know which one to look through sometimes! Also acts as a brilliant counterweight to the heavy objective end. A 16" Dob would be great too but am still thinking about that one. I am a refractor type will have to admit Matt

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stevetaylor199
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Re: Using refractors for Deep Space Observing new [Re: Eddgie]
      #5205690 - 05/04/12 02:07 PM

Says Eddgie:

Quote:


I love my 6" refractor. It is the best wide field scope I have ever ever ever used. And during the summer or winter, cruising the Milky Way with it is an absolute delight.





Interesting. I have a 6" f8 refractor and an 8" f6 reflector (with about a 25% central obstruction). They both have focal lengths of 1200mm. Will they perform equally in this sweeping application? What subtle differences should I notice? (They're both relatively new scopes and haven't seen dark summer skies yet.)


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Napersky
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Re: Using refractors for Deep Space Observing new [Re: jrbarnett]
      #5260456 - 06/07/12 04:22 PM

Jim,

I echo your opinon. The fact is an almost perfect refractor will outperform a larger "Abberation-Limited" Dob or SCT every-time. The optical flaws of mass produced mirror scopes create the "mushy", cotton balls, and fuzies. Often a superior quality handmade refractor like an AP or Stellarvue will show DS0 detail those larger mirror scopes cannot.

Also it is much harder to test properly especially in the figuring process large uncoated mirrors with interferometry.

Mark


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Eric Gage
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Re: Using refractors for Deep Space Observing new [Re: Napersky]
      #5261049 - 06/07/12 10:56 PM

Quote:

Jim,

I echo your opinon. The fact is an almost perfect refractor will outperform a larger "Abberation-Limited" Dob or SCT every-time. The optical flaws of mass produced mirror scopes create the "mushy", cotton balls, and fuzies. Often a superior quality handmade refractor like an AP or Stellarvue will show DS0 detail those larger mirror scopes cannot.




Piffle. I love a good refractor as much as the next person (my personal favs were the NP127 and the TOA130), but my medium sized dob (15") blows them away on DSO's. You have to catch the photons before you can see them.


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maknewtnut
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Re: Using refractors for Deep Space Observing new [Re: Napersky]
      #5261056 - 06/07/12 11:01 PM

Quote:

Jim,

I echo your opinon. The fact is an almost perfect refractor will outperform a larger "Abberation-Limited" Dob or SCT every-time. The optical flaws of mass produced mirror scopes create the "mushy", cotton balls, and fuzies. Often a superior quality handmade refractor like an AP or Stellarvue will show DS0 detail those larger mirror scopes cannot.

Also it is much harder to test properly especially in the figuring process large uncoated mirrors with interferometry.

Mark




The term you might have been trying to refer to is diffraction limited.

To refer to an A-P as a handmade telescope can be argued as accurate. Stellarvue telescopes (at least most, and certainly most all in recent years) use optics made in China, which are also used by several other makers. They are most definitely not hand crafted in any manner that might be considered akin to A-P and TEC.

Your comment about testing uncoated reflective surfaces might be construed as misleading as many superior quality mirrors are effectively tested both during and after figuring.

Edited by maknewtnut (06/07/12 11:19 PM)


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mikey cee
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Re: Using refractors for Deep Space Observing new [Re: Eric Gage]
      #5261068 - 06/07/12 11:07 PM Attachment (31 downloads)

All you really need is a 10" F/11 R30 with a little wide field help from a 6" F/8. Which deals with the photons in a way dobs can't.....sharp and to the point! Mike

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maknewtnut
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Re: Using refractors for Deep Space Observing new [Re: mikey cee]
      #5261102 - 06/07/12 11:22 PM

Perhaps you've never used a high quality Newtonian, or any reflecting or compound telescope for that matter. A well made design with superb optics can and will deliver pinpoint star images, even with that dreaded central obstruction....and all w/o chromatic aberration.

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JimP
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Re: Using refractors for Deep Space Observing new [Re: maknewtnut]
      #5261434 - 06/08/12 07:17 AM

Well, my answer to the original question, and avoiding the refractor vs larger dobsonian (Why is it always larger and not the same?) discussion, is yes absolutely I do. If you have a 6" scope there is a 10" which can gather more light. If you have a 10" there is a 20" which will gather more light. If you have a 20" there is a 30" which can gather more light... and on and on. Where do you stop? I stop with the refractors I have and love so much. My experience is that a guy with a 6" refractor will be found observing Messier or NGC galaxies while the guy down the road, with his 24"Newtonian, is observing very faint Abel galaxies. The interesting thing to me is that the Abel galaxies in the 24" appear no brighter or more detailed than the galaxies the guy with the 6" is observing!! And, Both observers are very happy!
And, Yes, double stars are indeed Deep Sky objects. In fact, they are my Favorite Deep Sky objects and I love to observe them with my refractors.

best,

JimP


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watcher
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Re: Using refractors for Deep Space Observing new [Re: mikey cee]
      #5261480 - 06/08/12 08:09 AM

All you really need? I'm hoping to get by with a little less than that without going to one of those backwards mirror thingies with the spiked stars.

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galaxyman
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Re: Using refractors for Deep Space Observing new [Re: JimP]
      #5261567 - 06/08/12 09:27 AM

Quote:

Well, my answer to the original question, and avoiding the refractor vs larger dobsonian (Why is it always larger and not the same?) discussion, is yes absolutely I do. If you have a 6" scope there is a 10" which can gather more light. If you have a 10" there is a 20" which will gather more light. If you have a 20" there is a 30" which can gather more light... and on and on. Where do you stop? I stop with the refractors I have and love so much. My experience is that a guy with a 6" refractor will be found observing Messier or NGC galaxies while the guy down the road, with his 24"Newtonian, is observing very faint Abel galaxies. The interesting thing to me is that the Abel galaxies in the 24" appear no brighter or more detailed than the galaxies the guy with the 6" is observing!! And, Both observers are very happy!
And, Yes, double stars are indeed Deep Sky objects. In fact, they are my Favorite Deep Sky objects and I love to observe them with my refractors.

best,

JimP




Bingo Jim

Probably more then most, I've used or pushed my refractors on DSO's, and at the same time own two wonderful larger dobs (12.5" & 22").

I've had the 8" refractor next to the 22" dob, and I enjoyed the DSO views in both of course. The big dob shows the very faint stuff, and great detail on the bright stuff. The 8" refractor can go faint, but the views overall are just shall we say "prettier". M-42 is a great example.

I also like it that once in a while of observing in a comfortable seat instead of going up and down a 6' stepladder.

I've always said.

"It's not what the scope can't see, but what it can see"

In the case of my 3 refractors it's just beautiful images at the eyepiece.


Karl
E.O.H.



Chesmont Astronomical Society - www.chesmontastro.org
Deep Space with Refractors - http://tech.groups.yahoo.com/group/deepspacewithrefractors
Telekit (Swayze optics) 22" F/4.5 Dob
Homemade (Parks Optics) 12.5" F/4.8 Dob
TMB/APM 8" f/9 Refractor”The Beast”. One great DEEP SKY achro
ES 6" f/6.5 achro. Good one
Celestron Omni XLT 102 refractor.
Celestron 10x60mm Binos


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jmiele
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Re: Using refractors for Deep Space Observing new [Re: JimP]
      #5261696 - 06/08/12 10:48 AM

Quote:

Well, my answer to the original question, and avoiding the refractor vs larger dobsonian (Why is it always larger and not the same?) discussion, is yes absolutely I do. If you have a 6" scope there is a 10" which can gather more light. If you have a 10" there is a 20" which will gather more light. If you have a 20" there is a 30" which can gather more light... and on and on. Where do you stop? I stop with the refractors I have and love so much. My experience is that a guy with a 6" refractor will be found observing Messier or NGC galaxies while the guy down the road, with his 24"Newtonian, is observing very faint Abel galaxies. The interesting thing to me is that the Abel galaxies in the 24" appear no brighter or more detailed than the galaxies the guy with the 6" is observing!! And, Both observers are very happy!
And, Yes, double stars are indeed Deep Sky objects. In fact, they are my Favorite Deep Sky objects and I love to observe them with my refractors.

best,

JimP





+1 Jim, Well said...

It comes down to the desire of many to have a "one size fits all" strategy. That's not to say that folks using an instrument best suited for a given task or object list, can't learn to push the limits by improving their observing skills.
Even the environment you observe in greatly affects an instruments peak performance/purpose.

You either have a focus and area of interest and purchase and instrument to best meet your requirements given your observing site, or you have an instrument and learn too love what it can do for you.

Joe


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CounterWeight
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Re: Using refractors for Deep Space Observing new [Re: galaxyman]
      #5261806 - 06/08/12 12:02 PM

Last night before the clouds rolled in I took a quick look at Saturn at at about 160x in my TEC160... still and sharp, the atm was co-operating unlike the night before (also clouded over). Popped in the high power and at 320x it was perfect. Sharp / Crisp, 3-D and all the other colorful terms. Sure, getting into tiny exit pupil but I've no big issue with floaters yet for my age. Racing the clouds I popped in a lower wf eye piece and set for M13. Stepped up to about 160x and was nice (though I remeber far better in my big mirrors), lastly swung over to M82 and went back to about 160x again, the fuzzy band again sharp and clear (don't mean for that to sound the contradiction it might sound like). I've been doing this each night there are no clouds to get a perspective on the 3 and comparing largely to only my differing sky conditions. (I've sent my CCD to SBIG for a '~yearly one PM' so imaging not an option until it returns) This before jumping off to anything else if sky conditions allow.

Hard to forget the stunningly beautiful and impressive internal lit chandalier of diamonds (M13) easily seen in my old (well cooled and collimated) C-11 and the disturbed look of M82. I still see these objects in my refractor, and at times I'm still amazed at what I can only call the 'quality' of the view. It's no where near as bright and seems (by comparison to much larger A) only there is not as much to see, but what I see is memorable in it's own way. But 6.5" is still only that, and I guess if you are comfortable with the limitations of any apeture this small or smaller a refractor can and does allow for a lot of enjoyment at the eye piece.

Without reservation though, after a few years with the 160, I can in all honesty admit it's limitations compared to larger apeture scopes as far as what is possible and where. For DSO, I'd say there is a boundry at about 8" no matter the scope type or f/l (though I've never owned an 8" refractor) where the catalog of what is enjoyed and how changes significantly.

Here's the rub when I read these threads. For any object or group of them, it's possible to make statements one way or the other as to if or how might be shown to best advantage. All the optical quality things matter, and there are many to talk about. Over the years I've developed my 'standard candles' of different type objects that I compare in any scope. I think it's an important journey to make, and that you don't need to go up to 30" to get an idea, maybe just 12" would do? No need to be theoretic of abstract or pit one object against another as there will be truth all over the sky, each one it's own. And no surprise that a ~6" refractor can do things a 12" mirror cannot - and things a 12" mirror can do a 6" refractor cannot hope to accomplish (no matter how dark the skies or how much you pay)

IMHO it's not what each type scope can do and what it might be optimal for, it's more what as Eddgie put out about what the apeture can do with the very non abstract or theoretic human eyeball. My own take away is more along the lines of the catalog of potentially enjoyable objects increases with apeture more than the catalog of objects I loose because of FOV. I think the Messier Catalog makes for good standard clandles over time with different apetures as so may are at least detectable in even the smallest scopes. Absolutely under truly dark skies there is much more to talk about with anything, but not many folks I know that are observing day to day have them. Apeture is more a friend on objects outside our solar system, and a great ally in and going outside our galaxy. If it' lensed or reflected they all work, whatever is within your means and ability to use. It's the tradoffs between the objects, views, and apetures that matter - and there's enough to spend a lifetime on at almost any budget.


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Astrojensen
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Re: Using refractors for Deep Space Observing new [Re: CounterWeight]
      #5262104 - 06/08/12 03:24 PM

Sometimes, it's just about using what one has and loves and feels comfortable with and stop dreaming about castles in the air.



It may not be the finest, most expensive, hand-crafted refractor in the world, but it's mine, it has very good optics and is a pleasure to use. If that is not reason enough to use it on any clear night, I don't know what is.


Clear skies!
Thomas, Denmark


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saemark30
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Re: Using refractors for Deep Space Observing new [Re: Sasa]
      #5262157 - 06/08/12 04:03 PM

Inch per inch refractors are king.
But dollars to donuts Newtonians offer more aperture.

A 10" mirror will perform better than an 8" achromat; and there is maybe only 1 vendor of 8" APOS and they are expensive.


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galaxyman
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Re: Using refractors for Deep Space Observing new [Re: saemark30]
      #5262214 - 06/08/12 04:46 PM

Quote:

Inch per inch refractors are king.
But dollars to donuts Newtonians offer more aperture.

A 10" mirror will perform better than an 8" achromat; and there is maybe only 1 vendor of 8" APOS and they are expensive.




Not necessarily true. I've had a number of good 10" newts, and I'll still take my 8" refractor and it's high quality views.

Actually have been able to push the big refractor further using very high power (over 500x), and also seeing galaxies around 15th mag.



Karl
E.O.H.


Chesmont Astronomical Society - www.chesmontastro.org
Deep Space with Refractors - http://tech.groups.yahoo.com/group/deepspacewithrefractors
Telekit (Swayze optics) 22" F/4.5 Dob
Homemade (Parks Optics) 12.5" F/4.8 Dob
TMB/APM 8" f/9 Refractor”The Beast”. One great DEEP SKY achro
ES 6" f/6.5 achro. Good one
Celestron Omni XLT 102 refractor.
Celestron 10x60mm Binos


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saemark30
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Re: Using refractors for Deep Space Observing new [Re: galaxyman]
      #5262231 - 06/08/12 05:03 PM

Karl I think your 8" refractor is superior to the one I looked through, it was not coated and the site was in a red zone. The lack of coatings made it less than a 10" mirror.

No doubt in a dark site I would enjoy looking through a 8" achromat that was fully multicoated and well figured.
I use 15x70 binos and 5" refractors for quick views of Messiers but have a hard time finding them in the city in the red zone. Don't know how someone in L.A. (white zone) can see so much with a 4" refractor.


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Astrojensen
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Re: Using refractors for Deep Space Observing new [Re: saemark30]
      #5262307 - 06/08/12 06:22 PM

Quote:

The lack of coatings made it less than a 10" mirror.




Even the best coatings will still make any 8" refractor have less light grasp than a 10" newtonian with ordinary 88% reflectivity mirrors. That said, the benefits of coatings on a doublet lens are highly exaggerated. The difference between an uncoated objective and even a multicoated one is slight. I am talking from experience.


Clear skies!
Thomas, Denmark


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galaxyman
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Re: Using refractors for Deep Space Observing new [Re: Astrojensen]
      #5262628 - 06/08/12 10:59 PM

Quote:

Quote:

The lack of coatings made it less than a 10" mirror.




Even the best coatings will still make any 8" refractor have less light grasp than a 10" newtonian with ordinary 88% reflectivity mirrors. That said, the benefits of coatings on a doublet lens are highly exaggerated. The difference between an uncoated objective and even a multicoated one is slight. I am talking from experience.


Clear skies!
Thomas, Denmark




Yes Thomas so am I, as In DSO only.

Karl
E.O.H.



Chesmont Astronomical Society - www.chesmontastro.org
Deep Space with Refractors - http://tech.groups.yahoo.com/group/deepspacewithrefractors
Telekit (Swayze optics) 22" F/4.5 Dob
Homemade (Parks Optics) 12.5" F/4.8 Dob
TMB/APM 8" f/9 Refractor”The Beast”. One great DEEP SKY achro
ES 6" f/6.5 achro. Good one
Celestron Omni XLT 102 refractor.
Celestron 10x60mm Binos


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galaxyman
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Re: Using refractors for Deep Space Observing new [Re: saemark30]
      #5262793 - 06/09/12 01:59 AM

Quote:

Karl I think your 8" refractor is superior to the one I looked through, it was not coated and the site was in a red zone. The lack of coatings made it less than a 10" mirror.

No doubt in a dark site I would enjoy looking through a 8" achromat that was fully multicoated and well figured.
I use 15x70 binos and 5" refractors for quick views of Messiers but have a hard time finding them in the city in the red zone. Don't know how someone in L.A. (white zone) can see so much with a 4" refractor.




Yeah, dark skies always makes a huge difference, even in a 4" refractor.

Heck, there are nights from a good dark site, that I'm amazed what my 4" f/10 refractor can see.

The late Walter Scott Houston of Sky & Telescope used a 4" Clark refractor for many of his observations.

Karl
E.O.H.

Chesmont Astronomical Society - www.chesmontastro.org
Deep Space with Refractors - http://tech.groups.yahoo.com/group/deepspacewithrefractors
Telekit (Swayze optics) 22" F/4.5 Dob
Homemade (Parks Optics) 12.5" F/4.8 Dob
TMB/APM 8" f/9 Refractor”The Beast”. One great DEEP SKY achro
ES 6" f/6.5 achro. Good one
Celestron Omni XLT 102 refractor.
Celestron 10x60mm Binos


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Astrojensen
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Re: Using refractors for Deep Space Observing new [Re: galaxyman]
      #5262825 - 06/09/12 02:56 AM

Quote:

Yes Thomas so am I, as In DSO only.




Hi Karl

I am not sure if I made the point clear (I likely didn't! ), but I didn't mean to belittle the refractor in any way. The DSO performance of an 8" refractor must be stunning. Judging from my experience with my own 6" and my excellent C8, an 8" refractor would *overall* outperform a 10" newtonian any day of the week. Only on threshold targets would the light grasp of the 10" make a significant difference. Maybe.

DSO performance is more than just light grasp.


Clear skies!
Thomas, Denmark


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Re: Using refractors for Deep Space Observing new [Re: Astrojensen]
      #5263519 - 06/09/12 02:59 PM

Although I'm only / solely using refractors... the very fact we're discussing this DeepSky topic brings us back to the basic beginners rule:
Moon & planets = use Refractors
Deepsky = use Reflectors


RefractorPhill


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Refractor6
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Re: Using refractors for Deep Space Observing new [Re: PhilCo126]
      #5263528 - 06/09/12 03:10 PM

Well rules are meant to be broken Phil.....

{All refractors here too for BOTH types of observing}


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Re: Using refractors for Deep Space Observing new [Re: Refractor6]
      #5263547 - 06/09/12 03:22 PM

Aperture rules for DSO. PERIOD.

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PhilCo126
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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5263566 - 06/09/12 03:34 PM

Indeed, that's why I wouldn't mind a look through an 180mm TMB designed APM short OTA F/6 Achromat


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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5263617 - 06/09/12 04:07 PM

Quote:

Aperture rules for DSO. PERIOD.




Generally speaking, yes. There are exceptions, such as when wanting very wide fields of view.


Clear skies!
Thomas, Denmark


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Astrojensen
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Re: Using refractors for Deep Space Observing new [Re: PhilCo126]
      #5263623 - 06/09/12 04:11 PM

Quote:

basic beginners rule:
Moon & planets = use Refractors
Deepsky = use Reflectors




Astrojensen's basic rule for beginners: Use whatever the heck you've got to get some experience. Then later get several different types of telescopes for different types and moods of observing.

But by then, you're not a beginner anymore...


Clear skies!
Thomas, Denmark


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Refractor6
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Re: Using refractors for Deep Space Observing new [Re: Astrojensen]
      #5263743 - 06/09/12 05:31 PM

Quote:

Quote:

Aperture rules for DSO. PERIOD.




Generally speaking, yes. There are exceptions, such as when wanting very wide fields of view.


Clear skies!
Thomas, Denmark




+1


And the experienced visual observers know that one all to well when it comes to larger clear aperture refractors {IE:6" class+up} with shorter f ratios on larger scale DSO targets...choose your tools accordingly for the intended job at hand


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Re: Using refractors for Deep Space Observing new [Re: Astrojensen]
      #5263752 - 06/09/12 05:39 PM

In general owners of all refractor sizes have looked thru larger reflectors more often over the years than vice versa. I seriouslly doubt whether most dob or SCT owners have ever looked thru an 8"-10" refractor.....they just don't frequent the party that often. Then they make their assumptions based on hearsay. Over my 50 years of observing I've looked thru countless mirrored large apertures from 10"-30". Not one ever produced a memorable double star pattern or lunar detail like my past and present larger refractors have. I may have a little color on Venus and 1st magnitude stars etc. but I also have true diffraction limited views without mushy and soft images and some with those ever present spikes. Mike

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Re: Using refractors for Deep Space Observing new [Re: mikey cee]
      #5264074 - 06/09/12 10:35 PM Attachment (35 downloads)

I have access to a 10" Refractor any time I want and will take a 14" DOB or SCT over it. Aperture rules for DSO's (OK maybe I can't fit M45 or M31 in a 14"SCT) but the Cat's Eye Nebula sure is nicer in the 14" SCT.

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galaxyman
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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5264250 - 06/10/12 01:54 AM

Quote:

Aperture rules for DSO. PERIOD.




Yes and no.

I don't like the idea that just aperture no matter of quality is great for DSO's. There are some horrible or poorly made large optics out there.

I as a DSO "only" observer will not take less than quality optics. The fallacy about DSO observing and just low power is only needed is just that...a fallacy.

I've had my 4" f/10 refractor (really good optics) next to a massed produced 8" dob. The optics on this dob was certainly not great, and showed "okay" DSO images. Yes, still brighter in the 8" dob over the 4", but the image quality of the refractor gained some ground.

Aperture (4x) still ruled here, but the exquisite views through the refractor was more appealing.

The quality optics and coatings on my 8" refractor has produced surprising results over the years to not only me, but to my observing partners. Seeing 14th mag galaxies is not real hard in dark skies.

It can handle very high power, and even was looking at IC 2149 with a borrowed 2.5mm ortho (715x). This power showed an elongated bar shape, with small nubs on each end. Thank goodness the tracking was working well.

Even when they (observing partners) have their 20" to 25" dobs out and I have my big refractor, I certainly don't stand behind the big dobs all night waiting for a view. The Beast does quite fine.

The "refractor view" is still a pleasure, and is why we love them.


Karl
E.O.H.


Chesmont Astronomical Society - www.chesmontastro.org
Deep Space with Refractors - http://tech.groups.yahoo.com/group/deepspacewithrefractors
Telekit (Swayze optics) 22" F/4.5 Dob
Homemade (Parks Optics) 12.5" F/4.8 Dob
TMB/APM 8" f/9 Refractor”The Beast”. One great DEEP SKY achro
ES 6" f/6.5 achro. Good one
Celestron Omni XLT 102 refractor.
Celestron 10x60mm Binos

Edited by galaxyman (06/10/12 01:57 AM)


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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5264259 - 06/10/12 02:06 AM

Quote:

I have access to a 10" Refractor any time I want and will take a 14" DOB or SCT over it. Aperture rules for DSO's (OK maybe I can't fit M45 or M31 in a 14"SCT) but the Cat's Eye Nebula sure is nicer in the 14" SCT.


That scope doesn't look too spiffy like most public accessable scopes. My scope is collimated and very clean. Plus my observing buds who have a 14" and several 11" scts say repeatedly that their scopes don't measure up to my refractor. They are repeatedly inviting themselves over to my observatory. Go figger. Mike

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hfjacinto
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Re: Using refractors for Deep Space Observing new [Re: mikey cee]
      #5264412 - 06/10/12 08:59 AM

Can we stop with the quality point. Lets gets this out of the way, most mass produced scopes have good quality. I've looked through lots of scopes and seen very few dogs. The premium dobs as a rule have very nice mirrors. The chances of getting a bad telescope is the same no matter the brand ( friend onwed a Tec 140, that came uncolllimated). And I while repeat this again, for DSOs aperture rules.

Mike,

Have you actually looked through the 10" refractor? It was hand made and is over 40 years old. Optically its very good, so my opinion still holds. A 14" SCT or 14" Dob shows more.

Now as this is the refractor forum, I am supposed to state refractors do all perfect, thats simply not true, for deep sky aperture rules and refractors are limited in that regard.


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Re: Using refractors for Deep Space Observing new [Re: mikey cee]
      #5264414 - 06/10/12 09:01 AM

All things being equal in theory Aperture should always win. However all things are not equal, ever.

Take for instance the myth of "Diffraction Limited". There is no such thing. Many good telescopes may approach the diffraction limit as meaured by 99% Strehls but none have hit it. Also take the matter of Gausfehler, which is the German term used by Wolfgang Rohr for spherochromatism. All spherical lenses suffer from these abberations in some form or another throughout their spectrum none are perfect at all wavelengths.

A better quality with less abberations Refractor will outperform a much more abberated larger aperature Reflector.


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Re: Using refractors for Deep Space Observing new [Re: Napersky]
      #5264498 - 06/10/12 10:21 AM

My CPC Deluxe 1100 was sent back to Celestron last month for repairs. So I have to use my Sky-Watcher 120ED for everything now. I've been impressed in how it's been performing on DSO hunts. I took it to a green zone on a night of excellent transparency & seeing and everything I pointed it to stood out clearly. Even objects that are hard to see in my 11" SCT in LP skies were easy to view. Having the ability for super wide views at 2.75° made star hopping fun around the Milky Way region and the Virgo galaxy cluster. I have little star hopping experience almost exclusively using goto but I was able to locate 61 objects that night using only a Voyager alt/az mount and my iPhone SkySafari app. I was able to directly compare views with other large Dobs on site 10" - 18". The finer details were not there of course but it was surprising how well the 120mm APO was doing in comparison to the larger apertures. Others were commenting on how nice the optics were in my APO and the wide star fields were beautiful.

Last night I was viewing in an orange zone and the seeing was excellent again. I was surprised I could see the North American and Veil Nebulae with the OIII in this aperture. Very faint of course and no fine details but just being able to find them and see the shapes in mag 5.5 - 6.0 skies was a thrill.


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Re: Using refractors for Deep Space Observing new [Re: Napersky]
      #5264619 - 06/10/12 11:54 AM

Quote:


A better quality with less abberations Refractor will outperform a much more abberated larger aperature Reflector.




Perhaps, however you can't just assume the larger reflector isn't of high quality. My Mewlon 300 beats the TEC 180 hands down.... Quality refractor, quality reflector. Visualy, if the Mewlon is cooled properly and the seeing permits, you can push the magnification endlessly. That's a 2011 TEC 180FL and a 2012 Mewlon CRS, down stairs next to each other.

This is of course my subjective opinion, however owning both I'm not more vested in one or the other. Similar costs as well. The assessments were made on the same nights with the same EP's on doubles and planetary observations.

All that said however, the TEC will perform at a higher level more often than the Mewlon as the Mewlon is IME, more affected by seeing. I will add that to date - my best planetary views ever were with my 16" Dob.. That includes trumping the Mewlon 300.

Best, Joe

Edited by jmiele (06/10/12 03:49 PM)


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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5264721 - 06/10/12 01:15 PM

Quote:

And I while repeat this again, for DSOs aperture rules.




And I will repeat again: It depends.

Let's take M33, for example. It takes quite a wide field TFOV to frame it nicely in the eyepiece. At the same time, you may want a the magnification to be in the middle range, around 2-3mm exit pupil, to make the sky black and nice, depending on your observing site. At the 2010 MAF star party, I had the opportunity to observe M33 with both a 30" f/5 dob and a TEC 140.

In the 31N5 on the 30", M33 filled the field from edge to edge. The arms were evident, but the view was quite a bit more bland that I would have suspected. The TEC 140 had a 13mm Ethos in the focuser. At 75x, it had a field of view over twice as large as the 30" and framed the galaxy perfectly. The 1.87mm exit pupil made the sky background jet black. The galaxy was fainter, of course, but the image was much more contrasty and the view of the arms has forever been etched into my mind. It was fantastically beautiful. In absolutely no way could I say the view in the 30" was better. Oh, it was bigger, it was brighter, but... It was just lacking something the image in the TEC 140 had in spades. It looked flat and dull, while the TEC had immense depth and "reality" to it, for lack of a better word.

I can hear all of you already: "Ah, but you've got to match exit pupils, use higher power on the big scope, yada yada". Yes, I know. Yes, the 30" showed much detail in the arms at higher powers, but in no way did it ever show M33 as beautiful as the TEC 140. That is the one view I remember perfectly vividly from that night. All I remember of M33 in the 30" is that I was somewhat underwhelmed. It was my first time with such a huge scope and I honestly expected a lot more.

Oh sure, the images are brighter, but brightness is not everything. For a visual observer, aesthetics can be a very important thing. That night, the TEC 140 certainly delivered a very aesthetic image of M33 - and many other, large objects as well. My own 150mm achromat does the same on many nights, where the C8 fails.

Aperture can rule - and often does - but so can a smaller, high-quality telescope. It all depends on what we want. Aperture does not always rule, nor does a small high-end scope.

*Puts soap box back in corner*


Clear skies!
Thomas, Denmark


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Re: Using refractors for Deep Space Observing new [Re: jmiele]
      #5264734 - 06/10/12 01:24 PM

I know this has been touched on but it's worth mentioning again.......

One thing I learned many years ago was the advantage that the refractor has over scopes of other designs on deep sky is the ability to achieve low power WIDE FIELDS of view. This with excellent contrast for the visual observer even under light polluted skies I discovered early on. Combine this with sharp, pinpoint image quality across the whole field of view and you have a winning combo. Take this same winning combo to a truly dark site and you'll truly really "see" more.

This advantage really comes into play if you want to view objects that are best framed with a larger true FOV and brought further out at the ep when combined with the use of a OIII filter and such in the mix. Well the larger scope of another design can see MORE for sure on DSO's but with its longer focal length in most cases in truth it will only see LESS compared to a shorter f/ratio refractor in the 6"+ class of instrument combined with high quality 2" low power eps on the same set of targets. Anyone who has seen whole sections of the Veil in the same FOV, Orion Nebula, M33, M27, North American Nebula, Andromeda Galaxy+companions, both M81+M82, all the goodies in the south in Summer, etc...etc...etc... at the ep knows what I speak with this type of refractor.

Know your tools well and use them accordingly....


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galaxyman
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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5264745 - 06/10/12 01:29 PM

Quote:

Can we stop with the quality point. Lets gets this out of the way, most mass produced scopes have good quality. I've looked through lots of scopes and seen very few dogs. The premium dobs as a rule have very nice mirrors. The chances of getting a bad telescope is the same no matter the brand ( friend onwed a Tec 140, that came uncolllimated). And I while repeat this again, for DSOs aperture rules.

Mike,

Have you actually looked through the 10" refractor? It was hand made and is over 40 years old. Optically its very good, so my opinion still holds. A 14" SCT or 14" Dob shows more.

Now as this is the refractor forum, I am supposed to state refractors do all perfect, thats simply not true, for deep sky aperture rules and refractors are limited in that regard.




Again yes and no

Depends on the type of DSO observing your doing or into. Yes, most massed produced optics are okay, and they'll do okay for general DSO observing. The same can be said for planetary observing.

The high quality optics will benefit pushing DSO observing to the edge (like I have). No different then someone doing the same for planetary.

I've owned 10" newts of fair optical quality, and they could not be pushed like my current 8" refractor. Not saying a very good 10" could not, but even still I'll take the refractor views in this aperture range.


Karl
E.O.H.

Chesmont Astronomical Society - www.chesmontastro.org
Deep Space with Refractors - http://tech.groups.yahoo.com/group/deepspacewithrefractors
Telekit (Swayze optics) 22" F/4.5 Dob
Homemade (Parks Optics) 12.5" F/4.8 Dob
TMB/APM 8" f/9 Refractor”The Beast”. One great DEEP SKY achro
ES 6" f/6.5 achro. Good one
Celestron Omni XLT 102 refractor.
Celestron 10x60mm Binos


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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5264809 - 06/10/12 02:11 PM

I'm not sure if I blindly subscribe or accept the "aperture rules" blanket statement. Here's why. Yes in theory all things being equal "aperture rules". However, nothing is ever equal and this blanket statement that is casually tossed around like a flower girl tosses flowers down the aisle should be re-examined.

Indeed, given the same observer with the physical capacity to lift a 60mm refactor and a 24" reflector the aperture will indeed benefit this individual. Yet, when making this blanket statements we tend to forget that many observers suffer from physical issues that prevent them from moving large and heavy telescopes and equipment. Thus the aperture that would rule for these observers is an aperture that provides mobility, comfort and quality observing time. Having a big heavy telescope of massive aperture and weight is of no advantage if it is beyond the physical, time and comfort limitations of the observer.

Secondly, these blanket statements may make folks with certain physical limitations feel as if they are missing out on some mystical part of amateur astronomy and that is simply unfair and unrealistic. Our hobby is about observing objects that are within the physical limits of our bodies and finances.

There was a time when for me nothing but a 12" or bigger Dob ruled, then somewhere along the line I realized that the amount of work I had to do to get the 12" setup wasn't worth it. Now I observe with either a C6R or a 8" EdgeHD and I'm more comfortable and my observing sessions which are limited to perhaps 40 to 60 minutes per session are more enjoyable and productive.

When tossing around these blanket statements stop and think about those folks that either physically or financially can't afford these big scopes and how these statements may make them feel.

Aperture doesn't rule, looking up and observing does.....

Soap box back in corner. Those that feel like they need to flame me go ahead but someone had to say something.


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Re: Using refractors for Deep Space Observing new [Re: Javier]
      #5264847 - 06/10/12 02:37 PM

Quote:

Aperture doesn't rule, looking up and observing does.....




Bravo!


Clear skies!
Thomas, Denmark


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7331Peg
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Re: Using refractors for Deep Space Observing new [Re: Astrojensen]
      #5264904 - 06/10/12 03:21 PM

A second Bravo!

That statement pretty well puts this whole discussion into the proper perspective.


John


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Re: Using refractors for Deep Space Observing new [Re: Refractor6]
      #5264939 - 06/10/12 03:47 PM

Wayne,

I was addressing a specific statement the previous poster made. That comment was quoted in my response. I was not attempting to dispute or defend the use of refractors for DSO.

Regards, Joe

Edited by jmiele (06/10/12 04:03 PM)


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Re: Using refractors for Deep Space Observing new [Re: JoeR]
      #5264961 - 06/10/12 04:03 PM

It would be an amusing exercise to pull out and compile all the subjective words being used to describe the image of refractors as opposed to other types of scopes. I think if we did that maybe we could get to the truth of this topic: Many people who own high end refractors prefer the views through high end refractors. Put in this way, it's pretty obviously a group sorted for a love of refractors...

Edited by cheapersleeper (06/10/12 04:04 PM)


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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5264979 - 06/10/12 04:16 PM

Quote:



Now as this is the refractor forum, I am supposed to state refractors do all perfect, thats simply not true, for deep sky aperture rules and refractors are limited in that regard.




No, you're not "supposed" to say anything. That's just a cheap shot. IF the 10" refractor you mentioned is collimated and of good optical quality I am shocked that you would prefer a C14 over it for Anything. I can assure you that I would NOT.

JimP


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mikey cee
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Re: Using refractors for Deep Space Observing new [Re: JimP]
      #5265215 - 06/10/12 07:11 PM

Quote:

Quote:



Now as this is the refractor forum, I am supposed to state refractors do all perfect, thats simply not true, for deep sky aperture rules and refractors are limited in that regard.




No, you're not "supposed" to say anything. That's just a cheap shot. IF the 10" refractor you mentioned is collimated and of good optical quality I am shocked that you would prefer a C14 over it for Anything. I can assure you that I would NOT.

JimP


Yeah and that's the name of that tune! OK mods lock'er up! Mike

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Re: Using refractors for Deep Space Observing new [Re: mikey cee]
      #5265247 - 06/10/12 07:45 PM

I don't see much of a reason to lock the thread yet. I'm on my mobile phone but I would like to be able to respond to the original poster's question.

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Re: Using refractors for Deep Space Observing new [Re: aa6ww]
      #5265390 - 06/10/12 10:01 PM

Hi Ralph,

I've also gone the smaller refactor route and let my 12" Dobsonian go to another home. My reasons are many, first yes, I do love the pin-point stars the refractors produce. In the past two years my observing taste has gone from the typical Messier Objects and Open or Globular Clusters to double stars. It's a rare night when I take out my C6R to observe any DSO's. These day's DSO's are objects I may observe if I have time after a double star observing session. This does not have much to do with the light polluted are I live in, rather it has to do with the objects I like to observe.

With that said, when I do observe DSO's such as M3, M13, M31, M42 and open clusters, I find the view through my C6R more aesthetically pleasing than a larger aperture 12" Newt. Also with a refactor, it seems that I notice more subtle structure in many of the DSO's mentioned above. While the DSO(s) many not be as bright as they were in the 12" Dob, I began to notice that while using my refactor I did not use averted vision as much as I did with the Dobsonian.

One other factor that has influenced my choice in gear is time. As the father of a six year old there are many instances where there is not enough time to get home after a school function, trip or whatever and setup a 12" Dob allow it to acclimate (especially during the cold winter). Yet there have been many instances during the winter where we will arrive after say a Parent's Night meeting or an evening school play and I can setup my C6R and within 30-40 minutes I can be observing.

These days I am not finding much of an urge to use a telescope with an aperture larger than 8". In fact I have come to realize that the sweet spot for my taste in gear is either the six or eight inch aperture arena with a preference for my C6R. As a side note, I do own a 8" EdgeHD and while I also find the views through the 8" Edge very pleasing when pressed for acclimation time I also reach for the C6R.


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Re: Using refractors for Deep Space Observing new [Re: Javier]
      #5265426 - 06/10/12 10:28 PM

If you want to view DSO's with a refractor that is great (and many times that is what I do) but for most DSO's a larger aperture scope is better, it shows a brighter image with more details. That is a fact. Whether you want to take out a 6" F8 refractor which is a large scope or a 14" SCT that is up to you. But there is no way a small refractor will show as much as a much larger reflector, no matter what you paid for the premium APO. The endless arguments over how much better refractors over all other scopes are stupid.

Edited by hfjacinto (06/10/12 10:29 PM)


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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5265495 - 06/10/12 11:05 PM

Instead of debating over what scope the observer should be using, why are we not addressing what objects are being observed? Ultimately it's the "object" which determines what kind of telescope the observer should be using. Beginners are not being educated enough on how to observe.

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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5265587 - 06/11/12 12:11 AM

Quote:

If you want to view DSO's with a refractor that is great (and many times that is what I do) but for most DSO's a larger aperture scope is better, it shows a brighter image with more details. That is a fact. Whether you want to take out a 6" F8 refractor which is a large scope or a 14" SCT that is up to you. But there is no way a small refractor will show as much as a much larger reflector, no matter what you paid for the premium APO. The endless arguments over how much better refractors over all other scopes are stupid.




No, I will take out my TMB 10" F/9 apo and you can use your C14! We will Both be happy (At least I know I will be).
And you should consider discussing a topic without resorting to calling people names as it just shows your lack of vocabulary.

JimP


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Re: Using refractors for Deep Space Observing new [Re: Daniel Mounsey]
      #5265715 - 06/11/12 03:07 AM

Quote:

Instead of debating over what scope the observer should be using, why are we not addressing what objects are being observed? Ultimately it's the "object" which determines what kind of telescope the observer should be using. Beginners are not being educated enough on how to observe.




Couldn't agree more and a few of us have taken the time in this thread to cover that very POV. Certain countless deep sky objects can really shine when the target in question is combined with right scope {tool for the job} for the task at hand.

Do you want to see ALL of the North American Neb with room to spare with a OIII in place at the ep with excellent contrast and pinpoint stars across the entire FOV to boot or only a small portion of it with a larger and much longer F/ratio larger aperture scope that can show you only a small fraction of it at a time?

The visual observer who's knows what's required for the job will choose the best scope from experience for that type of large scale deep sky object which is not always the exclusive arena of the bigger scope with a much narrower field of view in many cases for this type of object viewing experience.

Like Daniel said... know the object and know THE SCOPE for best seeing the entire deep sky object you want to observe when it comes to certain beautiful targets in our wonderful night sky. One size {or focal length} does not fit all....


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Re: Using refractors for Deep Space Observing new [Re: Eddgie]
      #5265845 - 06/11/12 08:13 AM

Quote:

First, I keep reading that refractors have better contrast.

This is simply untrue in most cases. If a reflector has more clear aperture (primary diameter minus secondary diameter) it will have as good or better contrast than a smaller unobstructed scope with less clear aperture.

SNIP




Eddgie, there's no doubt that a much larger reflector (Newt, SCT) will collect more light than a smaller refractor, and thus will be more useful for detecting fainter DSOs. However, if a refractor and compound reflector have the same clear aperture, the refractor will exhibit better contrast on extended objects (especially assuming we're comparing a top-notch refractor against a fast food SCT). The SCT's modulation transfer function is compromised because its secondary transfers some of the light energy from the central portion of the Airy disk to the outer rings. The only thing that artifact aids is the separation of double stars of nearly the same magnitude. It cannot enhance the contrast of extended objects or the visual separation of double stars of much different magnitude.


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Re: Using refractors for Deep Space Observing new [Re: maknewtnut]
      #5265851 - 06/11/12 08:18 AM

Quote:

Quote:

Jim,

I echo your opinon. The fact is an almost perfect refractor will outperform a larger "Abberation-Limited" Dob or SCT every-time. The optical flaws of mass produced mirror scopes create the "mushy", cotton balls, and fuzies. Often a superior quality handmade refractor like an AP or Stellarvue will show DS0 detail those larger mirror scopes cannot.

Also it is much harder to test properly especially in the figuring process large uncoated mirrors with interferometry.

Mark




The term you might have been trying to refer to is diffraction limited.

To refer to an A-P as a handmade telescope can be argued as accurate. Stellarvue telescopes (at least most, and certainly most all in recent years) use optics made in China, which are also used by several other makers. They are most definitely not hand crafted in any manner that might be considered akin to A-P and TEC.

Your comment about testing uncoated reflective surfaces might be construed as misleading as many superior quality mirrors are effectively tested both during and after figuring.




He may well have meant aberration limited. While fast food SCTs have their place in an amateur astronomer's arsenal (I'll eventually get a C-14 to "complete" my collection), their optics are compromised compared to those in a high-end apo.


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Re: Using refractors for Deep Space Observing new [Re: Daniel Mounsey]
      #5265852 - 06/11/12 08:20 AM

Quote:

Instead of debating over what scope the observer should be using, why are we not addressing what objects are being observed? Ultimately it's the "object" which determines what kind of telescope the observer should be using. Beginners are not being educated enough on how to observe.




Exactly... And to take that a step further, it depends on what details in an object one is interested in. Viewing the entire Veil in a 4 inch refractor is quite wonderful but if one wants to see details in the various parts a larger scope is more effective.

A simple Target like m7 seems perfect for a smaller scope but comes alive and takes on new dimensions when viewed in a 16 inch... There are aspects of M7 that are just not apparent in a 4 or 6 inch scope.

When the skies are dark and clear, I always setup two scopes. One small and one large... It's really the only way... It's like asking a photographer. "Which is the better lens, a 28mm f/2 or a 400mm f/4?" The answer depends on the object being photographed. There will be one of each in the camera bag.

As far as optical quality and DSOs... It is rare that one is pushing the resolving capabilties of a larger scope when viewing deep sky. It is generally a question of enough light and enough magnification for the eye to see it. A small scope with a camera will show the same detail as a much larger scope used visually. This is not because the smaller scope is of better quality, it would show less if used visually, rather it is because to the resolving power of the eye is the limitation, not the resolving power of the telescope.

The key to seeing more is looking more. Having good quality equipment is important but the message to beginners that it is their equipment that most important is the wrong message. What is important is to get out there with whatever it is you have and spend as much time as possible developing your skills...

Refractors are good for deep space, reflectors are good for deep space. Clear skies, dark skies and time at the eyepiece, that's what its all about...

Jon Isaacs


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Re: Using refractors for Deep Space Observing new [Re: Alan French]
      #5265856 - 06/11/12 08:26 AM

Quote:

An odd topic. Why would anyone NOT use a refractor for deep sky observing?

Even a small refractor can show a lot under reasonably dark skies. And one with a short focal length will provide wide true fields not attainable in most other types of instruments.

Clear skies, Alan




Alan, I don't think your 8" A-P refractor qualifies as a small refractor. ~\8^)


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Re: Using refractors for Deep Space Observing new [Re: cheapersleeper]
      #5265894 - 06/11/12 08:54 AM

Quote:

It would be an amusing exercise to pull out and compile all the subjective words being used to describe the image of refractors as opposed to other types of scopes. I think if we did that maybe we could get to the truth of this topic: Many people who own high end refractors prefer the views through high end refractors. Put in this way, it's pretty obviously a group sorted for a love of refractors...




Your comment is without basis.

I have many different high-end or very good (A-P, Zeiss, Tak, Obsession/premium Galaxy Optics) telescopes of four principal designs (apos, Mak-Cass, Dahl-Kirkham, Newtonian), and will someday get and use a C14. They all have their uses, otherwise I wouldn't have gone through the trouble of assembling the arsenal.

FWIW, I far prefer views of the brighter DSOs through my mid-size refractors (130 mm through 180 mm) and 10" Mak-Cass than through a fast food 11" SCT. Globs and even the top showcase objects (e.g., M42) have much better appearance (better definition of faint details, tighter stars) in relatively large refractors (and my A-P Mak-Cass) and always look mushy through C11s, no matter how long we let the latter cool or twiddle Bob's Knobs. Now, if I want to bag a mag 16 galaxy, I'd of course use a much larger Newtonian.


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Re: Using refractors for Deep Space Observing new [Re: JimP]
      #5265898 - 06/11/12 08:56 AM

Quote:

Quote:

If you want to view DSO's with a refractor that is great (and many times that is what I do) but for most DSO's a larger aperture scope is better, it shows a brighter image with more details. That is a fact. Whether you want to take out a 6" F8 refractor which is a large scope or a 14" SCT that is up to you. But there is no way a small refractor will show as much as a much larger reflector, no matter what you paid for the premium APO. The endless arguments over how much better refractors over all other scopes are stupid.




No, I will take out my TMB 10" F/9 apo and you can use your C14! We will Both be happy (At least I know I will be).
And you should consider discussing a topic without resorting to calling people names as it just shows your lack of vocabulary.

JimP




Jim, your large refractors are located in the wrong place (too far from my home)!


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Re: Using refractors for Deep Space Observing new [Re: JJK]
      #5265942 - 06/11/12 09:24 AM

Removed.


Edited by cheapersleeper (06/11/12 09:32 AM)


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Re: Using refractors for Deep Space Observing new [Re: JJK]
      #5265952 - 06/11/12 09:34 AM

umm.. i know this is may start another debate or lead to some backlash, but reading some of the posts on here lead me to wonder, i mean with the types of scope listed obviously money is not an issue here... why not just get yourselves one of each? I don't have a pool of cash laying around but i did manage to get myself an 8 inch reflector and a just short of 3 inch refractor(intended as a guidescope but found it to be quite a good grab n' go) not much aperture but at least i really enjoy getting out there with both my little guys... and for what it's worth, i actually use my AT72ED very often... only take the "big" guy out on those special nights

I did some scanning around the skies last night with the little 72 and i have to say, it was awesome, didn;t get any DSOs, but the wide view with my 4.7mm EP through it was amazing.


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Re: Using refractors for Deep Space Observing new [Re: JJK]
      #5265960 - 06/11/12 09:38 AM

Quote:

ontrast than a smaller unobstructed scope with less clear aperture.

SNIP

Eddgie, there's no doubt that a much larger reflector (Newt,SCT)will collect more light than a smaller refractor, and thus will bemore useful for detecting fainter DSOs. However, if a refractor and compound reflector have the same clear aperture, the refractor will exhibit better contrast on extended objects (especially assuming we're comparing a top-notch refractor againsta fastfood SCT). The SCT's modulation transfer function is compromised because its secondary transfers some of the light energy from the central portion of the Airy disk to the outer rings. The only thing that artifact aids is the separation of double starsof nearly thesamemagnitude. It cannot enhance the contrast of extended objects or the visual separation of double stars of much different magnitude.




Inch for inch, the refractor does have the advantage for a number of reasons. But in general refractors are small, cats and Newts are large so the fact that the CO moves energy from the central disk to the rings is less important than the fact the smaller aperture increases the size of the disk. So, if one is comparing a 5 inch refractor to a 10 inch SCT, the rings are brighter but the first ring fits inside the disk of the 5 inch.

This is relevant for planets and bright objects, with dsos it is unlikely that the eye resolving details on this fine scale. But if it is, the MTF scaled to include aperture would give the contrast advantage to the 10 inch.

Jon


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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5266028 - 06/11/12 10:18 AM

I wasn't arguing the fact that a larger aperture telescope will show a brighter image. What I find irresponsible is the the all inclusive "Aperture rules for DSO. PERIOD. " statement without consideration for the observer. This type of statement is generalized all too often and can lead folks entering the hobby to purchase equipment that is beyond their physical limits. Sure a larger aperture telescope will indeed show a brighter image. However, if a person new to the hobby lives in a three flight walk up apartment, does a large aperture telescope truly "rule"? No it doesn't, yet many people new to the hobby read or hear these blanket statements and purchase equipment that is too cumbersome for their situation. The equipment then becomes a hassle to setup and transport which leads to non-use which leads to another individual dropping out of the hobby.

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Re: Using refractors for Deep Space Observing new [Re: Javier]
      #5266093 - 06/11/12 11:04 AM

Quote:

I wasn't arguing the fact that a larger aperture telescope will show a brighter image. What I find irresponsible is the the all inclusive "Aperture rules for DSO. PERIOD. " statement without consideration for the observer. This type of statement is generalized all too often and can lead folks entering the hobby to purchase equipment that is beyond their physical limits. Sure a larger aperture telescope will indeed show a brighter image. However, if a person new to the hobby lives in a three flight walk up apartment, does a large aperture telescope truly "rule"? No it doesn't, yet many people new to the hobby read or hear these blanket statements and purchase equipment that is too cumbersome for their situation. The equipment then becomes a hassle to setup and transport which leads to non-use which leads to another individual dropping out of the hobby.


Well said.

The original poster obviously has plenty of funds to invest in the avocation, based on his list of scopes.

I'd guess the percentage of hobbyists owning 8" refractors is quite small!!

The 8" refractor SHOULD surpass 8" compound scopes and equal somewhat larger reflectors.

But I expect 99.9% of hobbyists find even a 6" refractor straining the budget and portablility.

IF I were allowed only one scope then a 5 to 7 inch APO is very appealing.Too big a scope will sit unused because of the hassle factor.


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Re: Using refractors for Deep Space Observing new [Re: BigC]
      #5266149 - 06/11/12 11:40 AM

I have a question for all you refractor folks.. what would be the minimum aperture (for a refractor) to do decent DSO viewing?

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Re: Using refractors for Deep Space Observing new [Re: JoeM101]
      #5266205 - 06/11/12 12:17 PM

Quote:

I have a question for all you refractor folks.. what would be the minimum aperture (for a refractor) to do decent DSO viewing?




I'll ignore the refractor stipulation, since I think it renders the question less answerable.

Larger open clusters: 3" refractor
Bright emission nebulae: 4" refractor, but prefer 8+" reflector or cat
Globular clusters: any size for the biggies, but in general 12+" reflector
Galaxies (other than the brightest): 15-18" reflector

Again, these are minimum apertures and my opinion only. I agree with the above poster who said that the object picks the scope.


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Re: Using refractors for Deep Space Observing new [Re: JoeM101]
      #5266230 - 06/11/12 12:28 PM

Quote:

I have a question for all you refractor folks.. what would be the minimum aperture (for a refractor) to do decent DSO viewing?





Again as with the recent discussion it really depends on the object{s} in question. For my favorite DSO's a shorter F/ratio instrument in the 6" class of refractor is where things really start to get picture framed well and come "alive" from personal years of observing experience at the eyepiece.


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Re: Using refractors for Deep Space Observing new [Re: Eric Gage]
      #5266244 - 06/11/12 12:36 PM

Quote:

Quote:

I have a question for all you refractor folks.. what would be the minimum aperture (for a refractor) to do decent DSO viewing?




I'll ignore the refractor stipulation, since I think it renders the question less answerable.

Larger open clusters: 3" refractor
Bright emission nebulae: 4" refractor, but prefer 8+" reflector or cat
Globular clusters: any size for the biggies, but in general 12+" reflector
Galaxies (other than the brightest): 15-18" reflector

Again, these are minimum apertures and my opinion only. I agree with the above poster who said that the object picks the scope.




thanks, no offense.. i really enjoy using a refractor albeit mine is kind of small, like i said earlier, it was intended as a guidescope. I took it off my AT8 one night and basically grabbed and went to a dark river bank with my kids and wow! now i just really enjoy taking it out and scanning the skies... just so much easier to handle and as for the views, wide with great contrast! This bug has bitten me and now i have refractor aperture fever, though the prices have done the equivalent of 2 extra strength Tylenol... fever broke but still keeping an eye out for a good deal

clear / dark skies!


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Re: Using refractors for Deep Space Observing new [Re: JoeM101]
      #5266325 - 06/11/12 01:22 PM

Joe,

The answer to your question is not as simple as it seems ( at least to me). The minimum aperture would really depend on where you observe and if you need to travel to the observing location. For me I'm very comfortable with my 6" F8 refactor.


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Re: Using refractors for Deep Space Observing new [Re: Javier]
      #5266392 - 06/11/12 02:05 PM

Quote:

Joe,

The answer to your question is not as simple as it seems ( at least to me). The minimum aperture would really depend on where you observe and if you need to travel to the observing location. For me I'm very comfortable with my 6" F8 refactor.




I hear you you loud and clear Javier. I think i will just enjoy what i have for now and accumulate some funds, check out other peoples setup at upcoming star parties and go fro there.

clear skies


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Re: Using refractors for Deep Space Observing new [Re: Javier]
      #5266655 - 06/11/12 04:05 PM

Quote:

I wasn't arguing the fact that a larger aperture telescope will show a brighter image. What I find irresponsible is the the all inclusive "Aperture rules for DSO. PERIOD. " statement without consideration for the observer. This type of statement is generalized all too often and can lead folks entering the hobby to purchase equipment that is beyond their physical limits. Sure a larger aperture telescope will indeed show a brighter image. However, if a person new to the hobby lives in a three flight walk up apartment, does a large aperture telescope truly "rule"? No it doesn't, yet many people new to the hobby read or hear these blanket statements and purchase equipment that is too cumbersome for their situation. The equipment then becomes a hassle to setup and transport which leads to non-use which leads to another individual dropping out of the hobby.




Jav,

If I want to look at Hanny's Voorwerp (approximately 20 to 21 magnitude object) no small refractor will work. I understand that there is a pratical maximun to what is portable and in my opinion the OP's 8" refractor is not portable. My post is that for most DSO's the larger the aperture the better. It will show you more (but as typical in the forum, you get the a smaller quality refractor will show more than a larger anything else, including a fastfood SCT) which isn't true. So yes aperture rules, you just have to figure out what is the maximun aperture you can handle.

Now as to the question of whether you can use a refrator for DSO's the answer you can use anything you want. I use a 120MM Refractor a lot more than my larger scope, but I know that the larger scope will show a more detailed and brigther image. Whether you use a fast food 14" SCT or an 80 MM ZEISS premium triplet, the decision is yours. As to which is better for a small faint object a 14" SCT will show you a more detailed and brighter image. An 18" reflector will show even brigther image and a 48" reflector blows both away (largest I ever looked through). But for M45, using a 120MM F7.5 refractor and a 31MM Nagler is really nice.


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Re: Using refractors for Deep Space Observing new [Re: Javier]
      #5266722 - 06/11/12 04:47 PM

Quote:

I wasn't arguing the fact that a larger aperture telescope will show a brighter image. What I find irresponsible is the the all inclusive "Aperture rules for DSO. PERIOD. " statement without consideration for the observer. This type of statement is generalized all too often and can lead folks entering the hobby to purchase equipment that is beyond their physical limits. Sure a larger aperture telescope will indeed show a brighter image. However, if a person new to the hobby lives in a three flight walk up apartment, does a large aperture telescope truly "rule"? No it doesn't, yet many people new to the hobby read or hear these blanket statements and purchase equipment that is too cumbersome for their situation. The equipment then becomes a hassle to setup and transport which leads to non-use which leads to another individual dropping out of the hobby.




For DSOs, my recent experience with reflector and refractor tells me that

Aperture rules AND aperture does not rule.

Looking at DSOs, especially, requires to see details in faint objects (aperture rules) but also to look at extended targets (for which high magnification just does reveal the true nature) or to place the target into context (aperture does not rule but wide field rules). then you need a refractor.

I am 'relearning' my sky now using a small refractor (3") because seeing the context where the open cluster stands is by itself a very pleasant observation, even if the DSO is a faint fuzzy. I'll use my larger scope to tease the details out of the faint fuzzy, but that is complementary to the wide field viewing.

To satisfy the two opposing rules (aperture does and does not rule), i think you need two (or more) scopes. And the refractor is irreplacable for the wide field views.

If you only want one scope, then you need to make compromises. Those who prefer details will chose aperture and will get a 8" dob or SCT, while those who value the wide field of view and the crisp view of a refractor will get a 5 to 6 inch achro. It will depend on what you want and what annoys you.

I do not think there is a perfect scope now that i use that small apo. I can spend hours looking at well known targets i have seen with large reflectors, just because i rediscover them in context.


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Re: Using refractors for Deep Space Observing new [Re: coutleef]
      #5266742 - 06/11/12 04:55 PM

Over and over I see people acting as if wide fields are an exclusive property of refractors. I have parts that will very soon be a 6" f5 newt in the closet of my bedroom. I assure you it will have wide fields.

The fact is, many of the supposed exclusive virtues of refractors that are being claimed here are merely a function of small aperture.


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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5266760 - 06/11/12 05:06 PM

"Aperature rules, you just have to figure out what is the maximum aperture you can handle." Bingo.....

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Re: Using refractors for Deep Space Observing new [Re: JimP]
      #5266765 - 06/11/12 05:11 PM

JimP... in Helder's defense I don't think he was calling me stupid. I believe he was referring to the other blanket statement that many people make that refractors are simply better for any and all objects (which I don't agree with either). I've known Helder for about three plus years and other than while poking fun at each other I've never heard him insult anyone or me.

Jav


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Re: Using refractors for Deep Space Observing new [Re: Javier]
      #5266817 - 06/11/12 05:41 PM

Here my 2 cents worth, as a picture is worth a thousand words...



piggyback solution, refractor on reflector action!


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Re: Using refractors for Deep Space Observing new [Re: Javier]
      #5266955 - 06/11/12 07:19 PM

Quote:

JimP... in Helder's defense I don't think he was calling me stupid. I believe he was referring to the other blanket statement that many people make that refractors are simply better for any and all objects (which I don't agree with either). I've known Helder for about three plus years and other than while poking fun at each other I've never heard him insult anyone or me.

Jav




Jav nailed it, I never called anyone stupid, what is stupid is the argument that refractors are the best scope. All scopes do things well, don't demean other scopes because they are not refractors.


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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5267041 - 06/11/12 08:39 PM

Don't you think it's stupid to refer to SCTs as "Fast Food" instruments. Really, that's just ridiculous.

/Ira


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Re: Using refractors for Deep Space Observing new [Re: Ira]
      #5267167 - 06/11/12 09:55 PM

Quote:

Don't you think it's stupid to refer to SCTs as "Fast Food" instruments. Really, that's just ridiculous.

/Ira




I think SCTs are excellent scopes. Just repeating what some one else posted. http://www.cloudynights.com/ubbthreads/showthreaded.php/Cat/0/Number/5265894/page/0/view/collapsed/sb/5/o/all/vc/1

I agree the comment was ridiculous, that's why I reposted it. I can't believe no one else caught it.


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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5267199 - 06/11/12 10:15 PM

I saw it and typed out a response but removed it because I felt it would escalate the nastiness.

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Re: Using refractors for Deep Space Observing new [Re: Jon Isaacs]
      #5267265 - 06/11/12 10:44 PM

Quote:

Quote:

ontrast than a smaller unobstructed scope with less clear aperture.

SNIP

Eddgie, there's no doubt that a much larger reflector (Newt,SCT) will collect more light than a smaller refractor, and thus will bemore useful for detecting fainter DSOs. However, if a refractor and compound reflector have the same clear aperture, the refractor will exhibit better contrast on extended objects (especially assuming we're comparing a top-notch refractor against a fastfood SCT). The SCT's modulation transfer function is compromised because its secondary transfers some of the light energy from the central portion of the Airy disk to the outer rings. The only thing that artifact aids is the separation of double stars of nearly thesamemagnitude. It cannot enhance the contrast of extended objects or the visual separation of double stars of much different magnitude.




Inch for inch, the refractor does have the advantage for a number of reasons. But in general refractors are small, cats and Newts are large so the fact that the CO moves energy from the central disk to the rings is less important than the fact the smaller aperture increases the size of the disk. So, if one is comparing a 5 inch refractor to a 10 inch SCT, the rings are brighter but the first ring fits inside the disk of the 5 inch.

This is relevant for planets and bright objects, with dsos it is unlikely that the eye resolving details on this fine scale. But if it is, the MTF scaled to include aperture would give the contrast advantage to the 10 inch.

Jon




Jon, in my Quote reply, I mentioned OTAs of the same clear aperture, not a comparison of a 5" refractor and a 10" SCT.

However, theoretical considerations aside, based on my experience, I would prefer to use my 130 mm Zeiss APQ than a C11 to view the Moon or planets. In the former, the views are etched (e.g., Lunar shadows are jet black) and the contrast is simply stunning.

I'm not anti-compound telescopes. I own and use several, and I look forward to the day when I can also use a cherry picked C14.


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JJK
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Re: Using refractors for Deep Space Observing new [Re: Ira]
      #5267281 - 06/11/12 10:52 PM

Quote:

Don't you think it's stupid to refer to SCTs as "Fast Food" instruments. Really, that's just ridiculous.

/Ira




Ira, I used the term "fast food" SCTs. It wasn't meant to be ridiculous. I meant it to reflect how common (i.e., readily available) some scope types are. I'm sorry if you found the term offensive. As I mentioned here and elsewhere, I look forward to the day I can add a C14 to the arsenal.


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JJK
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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5267330 - 06/11/12 11:35 PM

Quote:

Quote:

Don't you think it's stupid to refer to SCTs as "Fast Food" instruments. Really, that's just ridiculous.

/Ira




I think SCTs are excellent scopes. Just repeating what some one else posted. http://www.cloudynights.com/ubbthreads/showthreaded.php/Cat/0/Number/5265894/page/0/view/collapsed/sb/5/o/all/vc/1

I agree the comment was ridiculous, that's why I reposted it. I can't believe no one else caught it.




You misinterpreted my comment. IIRC, the term "fast food" OTAs may have originated with Roland Christen in a discussion about how his Mak- Cass performed (thermally?) compared to COMMONLY AVAILABLE SCTs. That was the spirit in which I used it in this thread. It was not intended to suggest that SCTs (or any other scopes) are not worthy of consideration. I have several Mak-Cass OTAs (Meade-Wegat 125mm & A-P's 10"), and hope to get a C14.

Should I misinterpret your comment that "SCTs are excellent telescopes" as a suggestion that refractors aren't? Of course not.

If you have an issue with something I or anyone else makes, why not simply ask for clarification? With this relatively casual medium, it's easy to be less than perfectly clear or to misinterpret someone's intention.


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galaxyman
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Re: Using refractors for Deep Space Observing new [Re: JoeM101]
      #5267395 - 06/12/12 01:03 AM

Quote:

I have a question for all you refractor folks.. what would be the minimum aperture (for a refractor) to do decent DSO viewing?




Joe

That's an interesting question.

Last dark window we (some CAS members) were observing at a good dark site. We had 18", 22", and 25" dobs, and I had my 8" refractor. A non-member who we see occasionally had his new 3.5" APO.

Though the much bigger scopes were providing terrific views, this fellow and his smaller refractor had a number of great DSO views, that many would find very appealing.

I also own a 4" f/10 refractor, which I've grown quite fond of, though it's by far my smallest scope.

One night some months back I was out at a local dark site with the 4". The views here again were quite appealing. In fact I kind of made a mistake the following evening to the wife when I said "You know, I could be quite happy with the 4" refractor for my observing (DSO only) if that's all I could either afford or manage".

Thankfully she's a smart gal, and knew what I meant. I hope

So, this could be a very subjective question, but I think from good dark skies a good 4" refractor is a quality instrument for DSO observing. As I mentioned before that the late Walter Scott Houston of S&T (Deep Sky Wonders column) wrote a lot about using his 4" refractor on a number of objects.


Karl
E.O.H.


Chesmont Astronomical Society - www.chesmontastro.org
Deep Space with Refractors - http://tech.groups.yahoo.com/group/deepspacewithrefractors
Telekit (Swayze optics) 22" F/4.5 Dob
Homemade (Parks Optics) 12.5" F/4.8 Dob
TMB/APM 8" f/9 Refractor”The Beast”. One great DEEP SKY achro
ES 6" f/6.5 achro. Good one
Celestron Omni XLT 102 refractor.
Celestron 10x60mm Binos


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Astrojensen
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Re: Using refractors for Deep Space Observing new [Re: JoeM101]
      #5267466 - 06/12/12 02:49 AM

Quote:

piggyback solution, refractor on reflector action!




Naughty! What if they crossbreed? What will that turn into? Mak-newton? Mak-cass? SCT?




Clear skies!
Thomas, Denmark


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Astrojensen
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Re: Using refractors for Deep Space Observing new [Re: JJK]
      #5267467 - 06/12/12 02:53 AM

Quote:

I used the term "fast food" SCTs. It wasn't meant to be ridiculous.




Don't we all like to get a burger with fries once in a while?

Got a very nice C8 myself.


Clear skies!
Thomas, Denmark


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JJK
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Re: Using refractors for Deep Space Observing new [Re: Astrojensen]
      #5267600 - 06/12/12 07:47 AM

Quote:

Quote:

I used the term "fast food" SCTs. It wasn't meant to be ridiculous.




Don't we all like to get a burger with fries once in a while?

Got a very nice C8 myself.


Clear skies!
Thomas, Denmark




Only if the burger is from Mak-Cass Donald's? ~\8^)


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Jim Curry
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Re: Using refractors for Deep Space Observing new [Re: Astrojensen]
      #5267714 - 06/12/12 09:20 AM

>Ultimately it's the "object" which determines what kind of telescope the observer should be using. Beginners...<

While it appears that most folks on these forums are using multiple scopes for their various astro endevours I'd wager a chocolate chip cookie that: 1. A beginner will be thrilled exploring any/all objects in the night sky with anything from 4" on up, the only limitation being portability in and out of the house or apartment; and 2. Moving away from this forum I'll bet most folks only own one scope which obviously is satisfactory for use on any object.

Now, once experience is gained and there's a few nickels in the pocket...the sky's the limit, so to speak.

Jim


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Jon Isaacs
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Re: Using refractors for Deep Space Observing new [Re: JJK]
      #5267802 - 06/12/12 10:14 AM

Quote:

Jon, in my Quote reply, I mentioned OTAs of the same clear aperture, not a comparison of a 5" refractor and a 10" SCT.




I was aware of your stipulation and pointed out that I was in agreement that inch for inch a refractor will provide better contrast.

But many seem to assume that refractors have better contrast regardless of aperture and that is a mistaken assumption, the effect of a central obstruction is small in comparison to the effect of the outer obstruction. (aperture)

From where I sit, I look at Newtonians as providing the optimal larger aperture high performance views. One can buy near perfect optics and build scopes that are actively cooled and free from thermal issues and yet remain manageable and portable.

Jon


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PhilCo126
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Re: Using refractors for Deep Space Observing new [Re: Jon Isaacs]
      #5267949 - 06/12/12 11:53 AM

Loose from the basic beginners' rule (deepsky = reflector), one needs at least a 152 mm refractor to get a good look at DSO.
Therefor I wonder why it's so hard to find a COTS larger diameter achromatic refractor ( e.g. short tube 175 mm )
Scopes larger than 180 mm are "Special order" so out of most of us' league


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Jon Isaacs
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Re: Using refractors for Deep Space Observing new [Re: PhilCo126]
      #5267970 - 06/12/12 12:02 PM

Quote:


Loose from the basic beginners' rule (deepsky = reflector), one needs at least a 152 mm refractor to get a good look at DSO.




I am one those folks who just enjoys the particular scope I happen to be using... I don't "need" anything.. My 60mm F/7 or mJoe's 72mm refractor is sufficient aperture for many objects, my 25 inch is not sufficient for many objects..

Jon


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JoeM101
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Re: Using refractors for Deep Space Observing new [Re: Jon Isaacs]
      #5267979 - 06/12/12 12:12 PM

Quote:

Quote:


Loose from the basic beginners' rule (deepsky = reflector), one needs at least a 152 mm refractor to get a good look at DSO.




I am one those folks who just enjoys the particular scope I happen to be using... I don't "need" anything.. My 60mm F/7 or mJoe's 72mm refractor is sufficient aperture for many objects, my 25 inch is not sufficient for many objects..

Jon




I agree with Jon, my 72 is awesome for most viewing! though i would love to be able to pick up a 130mm TMB someday.. maybe i play the lottery


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saemark30
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Re: Using refractors for Deep Space Observing new [Re: JoeM101]
      #5268126 - 06/12/12 01:44 PM

It depends on the sky brightness.
A 5" refractor at a Bortle 1 location would show more than a 16" in mag 5 skies, I would think.
But for GC its all about aperture. You can use high mags to darken the sky but the stars are just points and stays bright.
An 80mm refractor can never outresolve a 10" Newtonian on GC like M13, M5, etc.


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PhilCo126
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Re: Using refractors for Deep Space Observing new [Re: saemark30]
      #5268173 - 06/12/12 02:20 PM

(Apo-)Refractors smaller than 150 mm are very suitable for DSO astrophotography but I don't know how M31 would look like in a 70 mm refractor for visual observing

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JoeM101
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Re: Using refractors for Deep Space Observing new [Re: PhilCo126]
      #5268204 - 06/12/12 02:42 PM

Quote:

(Apo-)Refractors smaller than 150 mm are very suitable for DSO astrophotography but I don't know how M31 would look like in a 70 mm refractor for visual observing




not very good if anything


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Alan French
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Re: Using refractors for Deep Space Observing new [Re: JoeM101]
      #5268246 - 06/12/12 03:06 PM

Quote:

Quote:

(Apo-)Refractors smaller than 150 mm are very suitable for DSO astrophotography but I don't know how M31 would look like in a 70 mm refractor for visual observing




not very good if anything




Under dark skies, M31 spans 3 degrees. What do you need to see a field large enough the show it all, surrounded by dark sky? The answer is definitely not a lot of aperture and the resulting long focal length.

Clear skies, Alan


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saemark30
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Re: Using refractors for Deep Space Observing new [Re: Alan French]
      #5268257 - 06/12/12 03:11 PM

M31 looks awesome in 15x70 binoculars under a dark sky.
Look at how many 70mm Prontos Al sold.


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ckwastro
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Re: Using refractors for Deep Space Observing new [Re: JoeM101]
      #5268263 - 06/12/12 03:15 PM

Quote:

Quote:

(Apo-)Refractors smaller than 150 mm are very suitable for DSO astrophotography but I don't know how M31 would look like in a 70 mm refractor for visual observing




not very good if anything






Well, that's a matter of perspective. Let's assume the visual observing is under dark skies, of course. If you are looking to see the dust lanes, study structure, and hunt for extra-galactic GC's, then no, a 70mm instrument is not the correct tool for the job. However, if you are looking to frame M31, 32, and 110 with a nice background then a 70mm - 90mm instrument can deliver a very nice view. It all depends what you are looking to accomplish with your observing.

Edited by ckwastro (06/12/12 03:16 PM)


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JimP
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Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5268380 - 06/12/12 04:33 PM


Jav nailed it, I never called anyone stupid, what is stupid is the argument that refractors are the best scope. All scopes do things well, don't demean other scopes because they are not refractors.




OK, no problem. But, #1)I don't think you should say that we or I "should" say anything in particular because this is a refractors forum.
And, #2 I have been observing since 1965. I have owned all types of scopes including a 20" Obsession and an 18" Zambuto Starmaster. Both are gone. They were both in a roll-off roof observatory with my 10" TMB F/9 apo, first the 20" then later the 18", and almost never got used. I DO believe a Refractor is the best scope there is. And I am not demeaning any other scope or what anyone else believes. Just speaking for myself.

best,

JimP


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saemark30
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Re: Using refractors for Deep Space Observing new [Re: JimP]
      #5268411 - 06/12/12 05:08 PM

I like to see a comparison with a 12.5" Zambuto Starmaster. Some if not most of these bigger mirrors have zones and turn downed edges.

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mikey cee
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Re: Using refractors for Deep Space Observing new [Re: JimP]
      #5268414 - 06/12/12 05:12 PM

Right on Jimbo! I agree that all scopes are good for certain things. It's just that larger refractors are more "gooder" at doing more things. I still say that because we have looked thru more large mirrored scopes than reflector or SCT owners have looked thru large refractors we have "banked" the more knowhow to judge. That shouldn't be construed to somehow put down that aperture rules or that achromats don't show some minimal amount of CA etc. Mike

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JoeM101
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Re: Using refractors for Deep Space Observing new [Re: saemark30]
      #5268422 - 06/12/12 05:19 PM

sorry, should have mentioned the light pollution is moderate in my viewing area... under dark skies or not, i still love using my 72. Don't get me wrong, it has become my handy grab n' go and my preferred scope also. When the neighbors bother to put out their flood lights, viewing with this scope is an utter joy, else i usually head down to the river bank where it gets pretty darn dark... comfort is key here, A1 as i just sit in my chair and look down into the diagonal and wonder at the amazing wide field views i get out this little bugger

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JimP
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Re: Using refractors for Deep Space Observing new [Re: mikey cee]
      #5268446 - 06/12/12 05:36 PM

P.S. Why do I think refractors are the best scopes (for me)? Because I consider myself, in spite of imaging in recent years, a visual observer with a primary interest in the Moon, Planets and, Double Stars (Deep Sky). I also concluded, based on personal observations, that a refractor, inch for inch, was the best scope to use for my interests. And, I concluded that 7-8" of aperture was enough to see the kind of detail I was interested in observing. Do I use my refractors for other Deep Sky objects (besides doubles)? Of course! Are there some things I cannot see because my biggest aperture refractor is a 10"? Well, of course! But that does not bother me in the least. I am told that globular clusters are fantastic in the big aperture scopes. I am certain they are. When I want to see more stars in a globular cluster or detect fainter globular clusters, using my small aperture refractors, I just use my Collins I3 eyepiece... :^)

best,

JimP


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ckwastro
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Re: Using refractors for Deep Space Observing new [Re: saemark30]
      #5268484 - 06/12/12 05:55 PM

Quote:

I like to see a comparison with a 12.5" Zambuto Starmaster. Some if not most of these bigger mirrors have zones and turn downed edges.




Just curious why you think this? I might be misinterpreting here, but it appears you are saying most of Carl's mirrors have these issues. If that's the case then I must completely disagree. If not, then I apologize for misunderstanding.

I owned one of Carl's mirrors for almost 7 years, and used another half-dozen on a regular basis and not one had any zone, TDE, rough surface, or astigmatism, that could be detected in a star test. I can also say the same thing about Royce & Spooner mirrors. Unfortunately I've never used a Lockwood or Kennedy mirror so can't speak to those.

I think most of the "premium" mirror makers don't have these issues, and if they do, don't release the product from their shop. They rigorously test for these beforehand.


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saemark30
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Re: Using refractors for Deep Space Observing new [Re: ckwastro]
      #5268562 - 06/12/12 06:46 PM

Not saying any Z mirrors have issues.
But curious as to why you cannot detect any aberrations in the star test in any large mirror?
If you have read Suiter's Star Testing book, it will reveal methods of testing for the various aberrations. And collimation would have to be perfect in a sub f/4 system.

I'm not sure there is a way to denote a mirror is perfect without use of an autocollimation setup and interferometry.
Some refractor manufacturers are using that, but I can't speak for the makers you listed.
Making a large 40" mirror would require at least a 40" optical flat.


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ckwastro
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Re: Using refractors for Deep Space Observing new [Re: saemark30]
      #5268603 - 06/12/12 07:10 PM

Quote:

But curious as to why you cannot detect any aberrations in the star test in any large mirror?





Not saying that. I was merely saying the large mirrors I have used from the makers I listed did not have any zones or TDE that you mentioned. I also didn't notice rough surface (dog biscuit) or astigmatism in any of the star tests, or at least detectable by me. None of the mirrors were sub f/4. I have noticed slight under-correction on some. No mirror is perfect but these guys come ridiculously close.

Edited by ckwastro (06/12/12 07:11 PM)


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buddyjesus
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Re: Using refractors for Deep Space Observing new [Re: ckwastro]
      #5268714 - 06/12/12 08:45 PM

Peanut butter jelly. peanut butter jelly time!





I look forward to the next blow up and the lock. At least I am not too late for this one.

I happen to think the scope you would use the most would be the best for whatever you look at.


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ckwastro
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Re: Using refractors for Deep Space Observing new [Re: buddyjesus]
      #5268904 - 06/13/12 12:45 AM

Quote:

Peanut butter jelly. peanut butter jelly time!


I look forward to the next blow up and the lock.





Wow, I guess people are just itching for flame wars these days. I took absolutely no offense to saemark30's posts, and hope he didn't with mine. From my perspective, we were both just looking for some clarification on our comments, and I even apologized in advance if I had misinterpreted his post. I'd hardly call that a blowup, let alone worthy of a thread lock. Sheesh.


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Jon Isaacs
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Re: Using refractors for Deep Space Observing new [Re: JimP]
      #5269112 - 06/13/12 07:27 AM

Quote:

I DO believe a Refractor is the best scope there is.




I find that there is no one best scope...

A 10 inch f/9 likely ok tor some objects in some situations but the 90 inch focal length makes for a narrow maximum field of view as well as a scope and mount that is difficult to transport and setup. Now if one is lucky enough to live in a black zone with excellent seeing, the manageability is not so important but for those of us who do transport our scopes to darker or more stable skies, there are scopes that are more practical.

As refractors grow in size they inherently become longer because color correction scales with focal ratio/aperture so that while a 10 inch f/5 Newtonian is a reasonable scope to build, a 10 inch f/5 refractor is not...

The best scope, the one I happen to be looking through at the moment.

Jon


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JJK
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Re: Using refractors for Deep Space Observing new [Re: JimP]
      #5269204 - 06/13/12 09:06 AM

Quote:

OK, no problem. But, #1)I don't think you should say that we or I "should" say anything in particular because this is a refractors forum.
And, #2 I have been observing since 1965. I have owned all types of scopes including a 20" Obsession and an 18" Zambuto Starmaster. Both are gone. They were both in a roll-off roof observatory with my 10" TMB F/9 apo, first the 20" then later the 18", and almost never got used. I DO believe a Refractor is the best scope there is. And I am not demeaning any other scope or what anyone else believes. Just speaking for myself.

best,

JimP




Hi Jim,

What was it about the Obsession 20" that you didn't like, compare to the 10" f/9 refractor? My largest aperture refractor is an A-P 180 f/9 EDT (great scope, but I can see the virtue in getting an even larger apo), and my A-P 10" Mak-Cass is as close to a refractor as I could imagine, but I used to have a 20" Obsession (Galaxy Optics premium primary) and it provided stunning views of many DSOs.

I recall vividly studying the NA nebula for over 45 minutes one night (it appeared to have puffy cumulus clouds across it), M20 had pastel colors in it (beyond the standard blue and green), M42 was more detailed and had more color than I see with my A-P Mak-Cass (and the number of jewel-like stars in the heart of the nebula below the Trapezium more numerous) globs were tight and bright, etc.

I replaced the 20" with an Obsession 25" f/4.5, but that scope really deserves to be at a much darker sky site.


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ckwastro
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Re: Using refractors for Deep Space Observing new [Re: Jon Isaacs]
      #5269318 - 06/13/12 10:39 AM

Quote:

I find that there is no one best scope...




Jon, you nailed it here.

I enjoy whichever one I'm using a the time, which all depends on what I want to accomplish on that particular observing session. If I'm hunting Hickson Groups and Abell PNs, I want a big dob. I would always choose a large mirrored scope over any other design for the serious deep-sky work I like to do. Lunar / planetary is usually my Mewlon or my refractor, although the 92mm is a bit small for any serious work in that category. Wide-field vistas under dark skies is where the 92 really shines.

I understand the "je ne sais quoi" with refractors. Whenever I use the AP, it gets me thinking about buying the TEC 160 or 180, or the TOA 150. There is just something about refractors that appeals to my aesthetic side. It's usually the mount size required for these bigger refractors that holds me back because it's not very practical for me.

This is why I usually try to have three scopes in my arsenal. I'm currently working on a replacement for the 14.5 I sold a couple years ago, but have not decided which way I want to go on that one yet.


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JimP
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Re: Using refractors for Deep Space Observing new [Re: Jon Isaacs]
      #5269400 - 06/13/12 11:45 AM

Quote:

Quote:

I DO believe a Refractor is the best scope there is.




I find that there is no one best scope.A 10 inch f/9 likely ok tor some objects in some situations but the 90 inch focal length makes for a narrow maximum field of view as well as a scope and mount that is difficult to transport and setup. Now if one is lucky enough to live in a black zone with excellent seeing, the manageability is not so important but for those of us who do transport our scopes to darker or more stable skies, there are
scopes that are more practical.

As refractors grow in size they inherently become longer because color correction scales with focal ratio/aperture so that while a 10 inchNewtonian is a reasonable scope to build, a 10 inch f/5 refractor is not
The best scope, the one I happen to be looking through at the moment.

Jon [/quote

Hi Jon,
I believe I answered in detail in my following post why I feel an apo is the very best scope (for me). You may not agree but then you are not me. :^)
The objects I view do not need a wider FOV than it provides. It is a Fantastic telescope and I would not trade it for any other telescope. Period.

Jimp


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JimP
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Re: Using refractors for Deep Space Observing new [Re: JJK]
      #5269410 - 06/13/12 11:58 AM

"Hi Jim,What was it about the Obsession 20" that you didn't like, compare to the 10" f/9 refractor? "


One of the problems with these forums is that we often speak from our own personal POV and people then try to apply it to their situation which may not apply.
My 10" F/9 TMB is in a roll off roof observatory which is large enough for additional scopes. It is at my Farm which I get to less often than I would like. The sky is dark compared to where I live but not very dark compared to what the committed Deep Sky observer would want. When I get there and the sky is clear I find myself having to choose between the 10" refractor and, say, a 20" reflector. In spite of plans I Always used the 10" refractor. Later, I tried again with an 18" with the exact same result. I Never chose the reflector.

best,

JimP


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Rich N
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Re: Using refractors for Deep Space Observing new [Re: JimP]
      #5269416 - 06/13/12 12:03 PM

My most frequently used scope is my AP 155mm f/7 EDFS on an AP 900GTO mount. It's fun to use visually. I can see lots of DSOs with it. But, for more detailed views of DSOs aperture, aperture, aperture.

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saemark30
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Re: Using refractors for Deep Space Observing new [Re: Rich N]
      #5269494 - 06/13/12 12:52 PM

Even for deep sky observing optical quality matters unless we are viewing wide angle objects at 30x.
Proper baffling is important and that is why refractors have an advantage over truss systems or reflective tubes.
But large dobs make up for that with lots of aperture.
Its amazing what a 10" or larger scope shows.
Even in the city Planetary Nebulas look good and OIII and UHC filters can work magic.
It would take a world class site to get the full resolution out of a 20" mirror.


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saemark30
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Re: Using refractors for Deep Space Observing new [Re: saemark30]
      #5269601 - 06/13/12 01:45 PM

To put things in perspective what I meant is stars look sharper in refractors than large dobs and likely to have a better/smoother figure over the exposed surfaces than a large mirror.

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JJK
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Re: Using refractors for Deep Space Observing new [Re: saemark30]
      #5270197 - 06/13/12 08:13 PM

Quote:

Even for deep sky observing optical quality matters unless we are viewing wide angle objects at 30x.
Proper baffling is important and that is why refractors have an advantage over truss systems or reflective tubes.
But large dobs make up for that with lots of aperture.
Its amazing what a 10" or larger scope shows.
Even in the city Planetary Nebulas look good and OIII and UHC filters can work magic.
It would take a world class site to get the full resolution out of a 20" mirror.




I use my (80 mm to 180 mm) and A-P 10" Mak-Cass at home (mag 5.8 skies at best), but the 20" Obsession was really quite impressive under mag 6.4 skies in WV when they were transparent (most often the seeing was good but not world-class). I never worried about wringing out the full resolution of that scope. The scope's light grasp and excellent optics provided bright views with tight stars and colorful nebulae. It was a pleasure to use. I need to find a place to use the 25" scope that replaced the Obsession 20".


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Re: Using refractors for Deep Space Observing new [Re: JJK]
      #5270279 - 06/13/12 09:18 PM

Sounds fantastic JJK. And, of course, when you head out to the Dark Sky site you only take your big dob. That helps. You don't have to decide which scope to use or what type objects to view. I'd love a peak through that 25"! I'm sure it is fantastic!!

JimP


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Napersky
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What is inherently flawed with Reflectors and why new [Re: JimP]
      #5587367 - 12/24/12 03:06 PM

Mirrors. Every time light reflects it doubles the error of the wavefront.

We all know that a 1/8 PV surface error is 1/4 wavefront error effectively doubling all abberations and this is just the primary!

Now the 1/4th wave hits the secondary and doubles the error again to 1/2 wavefront error. If the scope is a straight thru Cassigrain then that's what you get 12",14", 16" highly abberated wavefront. If there is a diagonal involved double the error again.

This is why I do not so much like "Folded Refractors."

Mark

I am not an optical physicist so show me where I am wrong.


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JJK
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Re: Using refractors for Deep Space Observing new [Re: JimP]
      #5587497 - 12/24/12 04:43 PM

Quote:

Sounds fantastic JJK. And, of course, when you head out to the Dark Sky site you only take your big dob. That helps. You don't have to decide which scope to use or what type objects to view. I'd love a peak through that 25"! I'm sure it is fantastic!!

JimP




The 25" is very nice. It really needs to stay at a dark site though. Perhaps I can coax one of my friends with places in WV to house it for me (and them).

I looked through John Vogt's 32" Dob-Newt at the 2012 Black Forest Star Party. The views were stunning. The Swan looked like it was fluorescent.

I was outside of Brussels this past August. One of the professors I had dinner with knows of someone who is making a 1.1 m scope. I think it'll be housed in France. Now there's four excellent reasons to visit there (the art, wine, food, culture, and the 1.1 m)!


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aa6ww
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Re: Using refractors for Deep Space Observing new [Re: JoeM101]
      #5590726 - 12/27/12 05:05 AM

Quote:

I have a question for all you refractor folks.. what would be the minimum aperture (for a refractor) to do decent DSO viewing?




I have plenty of fun using my TV-85 on deep space objects under dark skies. Lately however. I find my 6" F/5 Celestron Omni XLT is getting the most useage since its very compact and portable and 6" is no slouch!!

...Ralph


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aa6ww
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Re: Using refractors for Deep Space Observing new [Re: mikey cee]
      #5590727 - 12/27/12 05:10 AM

Quote:

All you really need is a 10" F/11 R30 with a little wide field help from a 6" F/8. Which deals with the photons in a way dobs can't.....sharp and to the point! Mike




Every time I see this picture, the mushroom cloud just keeps expanding. Very Nice!!

...Ralph in Sacramento.


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aa6ww
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Re: Using refractors for Deep Space Observing new [Re: Astrojensen]
      #5590730 - 12/27/12 05:19 AM

Quote:

Quote:

Aperture doesn't rule, looking up and observing does.....




Bravo!


Clear skies!
Thomas, Denmark





Triple Dog Bravo!!!

Ralph in Sacto.


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aa6ww
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Re: Using refractors for Deep Space Observing new [Re: aa6ww]
      #5590734 - 12/27/12 05:27 AM

I'm noticing now, with winter here and temperatures dipping down into the 30's and below, (that's about as cold as it gets out here where I'm at in calif,) my SCT's sit tight in their trunks and my refractors become the scopes of choice to use. The portability and cool down factor plays into this mostly. I wonder if more refractors are sold in the winter time than reflectors or SCT?

I do more solar observing in the winter than spring and summer also, again with refractors, and even my smaller scopes like my TV-85 becomes less of a piggy back scope and more of a main scope when the weather is colder.

...Ralph in Sacto.


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Astrojensen
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Re: What is inherently flawed with Reflectors and why new [Re: Napersky]
      #5590736 - 12/27/12 05:31 AM

Quote:

We all know that a 1/8 PV surface error is 1/4 wavefront error effectively doubling all abberations and this is just the primary!

Now the 1/4th wave hits the secondary and doubles the error again to 1/2 wavefront error.




If the secondary is of a higher accuracy than the wavefront that hits it, then the error of that wavefront won't be doubled, though it will still be affected. If both mirrors are 1/10th wave on the surface, then the final image will be 1/4th wave on the wavefront.

That is at least what my logic tells me.


Clear skies!
Thomas, Denmark


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Jon Isaacs
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Re: What is inherently flawed with Reflectors and why new [Re: Astrojensen]
      #5590768 - 12/27/12 06:47 AM

Quote:

Quote:

We all know that a 1/8 PV surface error is 1/4 wavefront error effectively doubling all abberations and this is just the primary!

Now the 1/4th wave hits the secondary and doubles the error again to 1/2 wavefront error.




If the secondary is of a higher accuracy than the wavefront that hits it, then the error of that wavefront won't be doubled, though it will still be affected. If both mirrors are 1/10th wave on the surface, then the final image will be 1/4th wave on the wavefront.

That is at least what my logic tells me.


Clear skies!
Thomas, Denmark




I think if both are 1/10th wave then the result would be 1/5th wave in one orientation and 1/7 wave in the other. This is because of the 45 degree angle on the diagonal.

Of course a refractor has at least 4 surfaces to figure. While the error for each surface is multiplied by n-1, usually a bit more than 0.5. Since there are a minimum of 4 surfaces this adds up to something greater than a factor of 2.

If high quality (or average quality) refractor optics were easily made, they would be cheap. The fact that a decent quality 8 inch achromatic objective from D&G costs about $2400 is indicative of the difficulty. An apochromatic objective is considerably more. For comparison, an 8 inch Zambuto mirror costs $990, a 14.5 inch costs about $2600...

Jon


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Asbytec
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Re: What is inherently flawed with Reflectors and why new [Re: Jon Isaacs]
      #5590790 - 12/27/12 07:46 AM

Sure, 1/8th on the primary surface is 1/4 P-V. Then, using a 1/8th diagonal might seem to add another 1/4 wave error to the wavefront making the wave 1/2 P-V before it strikes the eyepiece. Even in the simplest forms, the light must still transit 6 to 8 air to glass surfaces at the eyepiece. Then two more refractive surfaces in the eye. So, by the time the wave hits the retina, it appears to have more than 1 wave of aberration. No one sees this in any star test, which includes the eyepiece.

That level of aberration would make for a terrible view. And since this is not the case with almost every scope, there is a hole in this argument. I just cannot find a source to rebut it, yet.

The answer lies, I believe in the image forming optics as opposed to the flat diagonal. The waveform is made at the primary (reflectors have only one wave forming surface), that is where it varies from perfect reference sphere due to surface error. On the diagonal, the errors might be present, but they do not fundamentally reshape the wavefront. And if they do, it's likely a localized correction within the entire wavefront that may or may not be seen.

Accounting for the wavefront error between 4 to 6 optical surfaces of an APO, even at 1/20th wave smoothness, that would still add up to 4 to 6/20th's = 1/5th to 1/4th P-V error (depending on the type, coverage, and slope of the error, of course, but just assuming smooth SA.) Then that error travels through an eyepiece and they eye, too. So, if the math holds, even the best APO will be below 1/4 wave Raleigh limit.

Again, since this is not true, something is wrong with this argument. Jon may have hit on it above.

In any case, there is nothing wrong with a good parabola. In fact, it can produce the ideal spherical wavefront. Where as highly curved surfaces of APOs and my own Mak have a lot of higher order SA to deal with. Refractors deal with color on top of that.

There are no perfect scopes, just really darn good ones like a good quality refractor. However, reflectors probably have fewer inherent flaws in terms of correction.


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Re: What is inherently flawed with Reflectors and why new [Re: Asbytec]
      #5590980 - 12/27/12 10:57 AM

Quote:


Sure, 1/8th on the primary surface is 1/4 P-V.




I believe the precision of the mirror is typically reported as the wave front error rather than the surface error. Maybe Vla can help us here.

In terms of wave front error in a refractor, I believe Roland Christen uses a standard of 1/8-1/10 wave using an interferometer for his lenses.

The important wave errors are measured at the focal plane at the focal plane because the entire objective contributes to every point on the focal plane so the objective (and Newtonian secondary mirror) errors are summed at every point. The eyepiece only magnifies that image on a point by point basis, bringing your eye closer to the image, the eyepiece does not affect the overall wavefront error.

Jon


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doway1609
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Re: Using refractors for Deep Space Observing new [Re: Jon Isaacs]
      #5603653 - 01/03/13 08:17 PM

"Aperture rules???" Well, that is IF you have all the time and money in the world plus a DARK SKY, then it can be so, but not for all folks as we know, I live in mag 3.5 skies and i had an 8inch dob but it was to cumbersome for me to drag it down 3 stairs and out the backyard, plus i had to use it MANUALLY in light polluted skies which is VERY inconvienient so i had to sell it, i have 3 scopes and the biggest is my 4" F7.7 refractor and its a GEM! Its has medium size objective lens, space objects are crisp and sharp especially moon, planets and star clusters, and its not very heavy so i can use it on my DS 2000 go-to mount and serves me very well! So more aperture is better but thats for a rabid deep sky fan that has lots of time and money on their hands plus scopes more than 8 or 10 inches dont work very well in light-polluted skies and here in Jersey transporting a massive scope to a dark site is a MAJOR adventure!

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Re: Using refractors for Deep Space Observing new [Re: doway1609]
      #5604208 - 01/04/13 08:02 AM

Quote:

So more aperture is better but thats for a rabid deep sky fan that has lots of time and money on their hands plus scopes more than 8 or 10 inches dont work very well in light-polluted skies




I often use scopes 8, 10, 12.5 inches and even larger from my light polluted back yard... They definitely can out perform my 4 inch apo on the DSOs. Aperture is my friend when it comes to fighting light pollution...

Jon


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Scott BeithAdministrator
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Re: Using refractors for Deep Space Observing new [Re: Jon Isaacs]
      #5604881 - 01/04/13 02:06 PM

While DSOs are not my primary point of interest, I do enjoy checking out the showpiece ones when I observe. Since all of my scopes are refractors, I guess I qualify for this thread by default.

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csrlice12
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Re: Using refractors for Deep Space Observing new [Re: Scott Beith]
      #5605155 - 01/04/13 04:29 PM

Dob folks use refractors for finding DSOs all the time....

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coutleef
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Re: Using refractors for Deep Space Observing new [Re: csrlice12]
      #5605166 - 01/04/13 04:36 PM

wide DSOs benifit from a wide field refractor while faint DSOs benifit from aperture.

there is definitely a place for refractor for viewing DSOs


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Napersky
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Re: What is inherently flawed with Reflectors and why new [Re: Asbytec]
      #5606583 - 01/05/13 01:04 PM

Accounting for the wavefront error between 4 to 6 optical surfaces of an APO, even at 1/20th wave smoothness, that would still add up to 4 to 6/20th's = 1/5th to 1/4th P-V error (depending on the type, coverage, and slope of the error, of course, but just assuming smooth SA.) Then that error travels through an eyepiece and they eye, too. So, if the math holds, even the best APO will be below 1/4 wave Raleigh limit.

Again, since this is not true, something is wrong with this argument. Jon may have hit on it above.

In any case, there is nothing wrong with a good parabola. In fact, it can produce the ideal spherical wavefront. Where as highly curved surfaces of APOs and my own Mak have a lot of higher order SA to deal with. Refractors deal with color on top of that.

There are no perfect scopes, just really darn good ones like a good quality refractor. However, reflectors probably have fewer inherent flaws in terms of correction.






This doubling of the error only occurs with mirrors not with refractive surfaces. This might help explain why APOs produce such good images.

As far as the diagnonal, it's a mirror and should double the error but as Jensen mentioned if the diagonal were twice as good as the wavefront off the secondary then the error would be cancelled out. 1/4 wave off the secondary could be truely 1/4 wave to the eyepiece.

Mark


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galaxyman
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Re: Using refractors for Deep Space Observing new [Re: coutleef]
      #5607548 - 01/05/13 11:38 PM

Quote:

wide DSOs benifit from a wide field refractor while faint DSOs benifit from aperture.

there is definitely a place for refractor for viewing DSOs




Yep, use all 3 of my refractors for DSO's both wide-field and high power. In fact much of our video series (Galaxy Log) has refractors being used for many observations, particularly with the use of small and medium size scopes.


Karl
E.O.H.

Chesmont Astronomical Society - www.chesmontastro.org
Galaxy Log - http://www.youtube.com/user/GalaxyLog4565?feature=mhee
Telekit (Swayze optics) 22" F/4.5 Dob
Homemade (Parks Optics) 12.5" F/4.8 Dob
TMB/APM 8" f/9 Refractor”The Beast”. One great DEEP SKY achro
ES 6" f/6.5 achro. Good one
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