Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> Refractors

Pages: 1 | 2 | 3 | 4 | (show all)
Mark9473
Postmaster
*****

Reged: 07/21/05

Loc: 51°N 4°E
Re: What can I see with a 80mm refractor? new [Re: CounterWeight]
      #5942474 - 06/27/13 03:06 AM

In his thread above, Roland said "The smaller picture is similar to the view in an 8 mm ocular (150x magnification)." which I think is realistic. How small would you want to scale that down?

Of course a valid point is that you might not want to go to 150x in a 80mm scope, especially in an achromat.

Your computer monitor resolution settings could be another factor.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Astrojensen
Post Laureate
*****

Reged: 10/05/08

Loc: Bornholm, Denmark
Re: What can I see with a 80mm refractor? new [Re: CollinofAlabama]
      #5942498 - 06/27/13 03:40 AM

Quote:

when looking near the zenith where the seeing is the best, unlike the F/11+ refractors above (notice how they're NEVER pictured toward zenith?), you won't be groveling in the dirt or straining your neck or having to take out a huge mount that raises it so high it's comfortable to look thru at zenith (but a PiTA to look near the horizon, or move).




The trick to observe the zenith in comfort with a long refractor is called a chair, my friend. In my picture of my 80mm f/15 Vixen, the legs on the tripod are shown extended about halfway. That is all I need to observe the zenith, sitting quite comfortable on a low chair. And the lower latitudes aren't out of reach, either.

I find very short, small refractors a pain to observe with, since they sit so very close to the mount and tripod, that I almost have to sit inside it, to reach the eyepiece. I can't observe standing. My knees kill me within an hour and I lose two or three magnitudes from the strain and shakes.


Clear skies!
Thomas, Denmark


Post Extras: Print Post   Remind Me!   Notify Moderator  
Astrojensen
Post Laureate
*****

Reged: 10/05/08

Loc: Bornholm, Denmark
Re: What can I see with a 80mm refractor? new [Re: Mark9473]
      #5942503 - 06/27/13 03:49 AM

Quote:

Of course a valid point is that you might not want to go to 150x in a 80mm scope, especially in an achromat.




I often observed Mars and Saturn at 171x with my 80mm Vixen. The image was sharp and almost no false color was seen around Mars. Saturn shows no false color. The detail on Saturn was essentially identical to what Roland has captured in his 80mm Vixen (exactly the same scope, except for the color). It looked brighter and sharper visually. I could often see the STB on Saturn being split in a northern and southern part. I sometimes glimpsed the Crepe ring, when conditions were ideal.

Jupiter doesn't like nearly as much magnification, so I usually stayed at 133x. The Jovian satellites could be observed with much higher magnification and I could tell them apart on any night, based on their size and color differences, if the seeing was reasonably good.


Clear skies!
Thomas, Denmark


Post Extras: Print Post   Remind Me!   Notify Moderator  
Niklo
sage


Reged: 03/29/13

Loc: Bavaria
Re: What can I see with a 80mm refractor? new [Re: Astrojensen]
      #5942521 - 06/27/13 04:45 AM

Hi Thomas,
thank you very much for your comments. We enjoy our long refractors and others enjoy their short ED refractors. Both have advantages.

Hello Mark and others,
I don't want persuade anybody to buy a f/15 refractor. I just wanted to say that I have some positive experience with this long Vixen and have seen many details on Saturn. 150x on Saturn is no problem. Depending on the screen resolution Saturn might look smaller with 150x or bigger but I wrote that it looked similar (looking on my laptop monitor 14" 1600x900. I think it has about 5 dots per mm) and I should add that I look at my monitor from about 40 cm. So maybe that helps. OK let's go away from the size if it is not helpful for you. You can see the details what can be seen in the pictures and with good conditions you can see the details described by Thomas and it might look smaller in the ocular at 150x.

Kind regards,
Roland

Edited by Niklo (06/27/13 03:11 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
mrelliot
member


Reged: 05/17/13

Re: What can I see with a 80mm refractor? new [Re: Niklo]
      #5942917 - 06/27/13 11:06 AM

I have another question (sorry I'm flooding you guys with questions). What's the difference between an f11 scope and like an f6 scope?
Mrelliot


Post Extras: Print Post   Remind Me!   Notify Moderator  
GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: What can I see with a 80mm refractor? new [Re: mrelliot]
      #5942925 - 06/27/13 11:12 AM

Length is probably the biggest difference. But with that extra length comes some great advantages: Less chromatic abberation (purple haze around bright objects), less demanding on eyepieces, etc.

Biggest downside is dealing with that type of length of scope. Mounting, viewing positions (at zenith you may be on the ground), storage. Also you will not get a nice wide field view with an F11 scope.

Certianly pluses and minuses between the two. Planetary work seems to benefit the longer scopes. Wide field work would be the shorter ones.


Post Extras: Print Post   Remind Me!   Notify Moderator  
BigC
Carpal Tunnel
*****

Reged: 09/29/10

Loc: SE Indiana
Re: What can I see with a 80mm refractor? new [Re: Mark9473]
      #5942930 - 06/27/13 11:14 AM

"Of course a valid point is that you might not want to go to 150x in a 80mm scope, especially in an achromat."


150x is fine in a long achromat.

I have 80mm f5,80mm f11, and 80mm f15 ; each has strengths.

The f15 works much better with higher magnification than does the f5;the f5 excels in showing the "bigger picture".

Someone could no doubt place all three tubes on one mount for instant comparison or for personal convenience.


Post Extras: Print Post   Remind Me!   Notify Moderator  
t.r.
Post Laureate
*****

Reged: 02/14/08

Loc: Upstate NY
Re: What can I see with a 80mm refractor? new [Re: BigC]
      #5942981 - 06/27/13 11:55 AM

Quote:

This is why I think images are a terrible reference for someone who has no reference to begin with. It may make some sense to those of us with a lot of ep time within the possible intended reference - but I just see it as not a good thing for the OP who has no real idea?




Sketches made at the eyepiece however are very representative if done well I have found...go to that forum and take a look.


Post Extras: Print Post   Remind Me!   Notify Moderator  
BigC
Carpal Tunnel
*****

Reged: 09/29/10

Loc: SE Indiana
Re: What can I see with a 80mm refractor? new [Re: GOLGO13]
      #5943585 - 06/27/13 06:26 PM

"Biggest downside is dealing with that type of length of scope. Mounting, viewing positions (at zenith you may be on the ground), storage. Also you will not get a nice wide field view with an F11 scope. "

That is one aspect of a long tube scope ,but an adjustable height chair or even a tall stool and a low chair will solve the problem.

For zenith viewing the tripod legs need to be fully extended.It may also help to add a balancing weight near the rear of the OTA so the greater portion of the length be in front of the tube clamp.


Post Extras: Print Post   Remind Me!   Notify Moderator  
mrelliot
member


Reged: 05/17/13

Re: What can I see with a 80mm refractor? new [Re: BigC]
      #5943863 - 06/27/13 09:47 PM

Thanks for all your help!

Post Extras: Print Post   Remind Me!   Notify Moderator  
CollinofAlabama
Carpal Tunnel
*****

Reged: 11/24/03

Loc: Lubbock, Texas, USA
Re: What can I see with a 80mm refractor? new [Re: mrelliot]
      #5944016 - 06/27/13 11:36 PM

The Focal Ratio is the ratio of the primary (in this case an 80mm lens) and the number of times the primary's diameter the particular scope build needs to bring the image to focus. 80 x 7.5 = 600mm where the focal length of 600mm divided by 7.5 yields 80, of course, thus an F/7.5 instrument. One critical point not mentioned above is that the scope I recommend, the Celestron 80ED, uses Extra Dispersion (ED) glass in its lens design, rather than the 18th century crown and flint design of the achromats. The achromats CANNOT bring all the rays of light to focus at the exact same plane. This causes something known as chromatic aberration, or CA for short. The practical effect of this is a purple haze, particularly around bright objects like planets, brighter stars, and the moon. This purple haze can be mitigated somewhat by making the focal ratio higher, so that an 80mm F/5 achromat has an almost kaleidoscopic amount of purple haze, an F/8 something less, an F/11 somewhat less still, and an F/15 even less

ED refractors, however, do much, much better at aligning all the various wavelengths of light to the same point. They're not perfect, but they are awfully close to perfect, and much better than ANY achromat, F/15 and especially below.

But besides throwing up much less artificially colorful images, consequently representing the target in "true", magnified color, ED scopes achieve this at much shorter focal ratios. As a former Maksutov owner (a type of catadioptric that is essentially a reflector-type, but by design with long, F/13+ like focal ratios), I can tell you that finding a target, especially a beginner without a go-to mount, is much more difficult, due to the absolute lack of corresponding field of view. The F/ratio of any telescope is intimately tied to its True Field of View. They are inverse, the higher the F/ratio, the lower the TFOV. And the absolute focal length of the instrument is critical to TFOV, also. There's simply no way to compare the experience of panning about the Saggitarian Star Cloud, or the Virgo-Coma Markarian Chain in instruments at F/15 as opposed to one with 600mm of focal length (in the C80ED's case F/7.5). But even finding Uranus, e.g., in an F/15 scope without go-to is a difficult task for an experienced observer, but for a novice? The 600mm focal length instrument, here the C80ED, will not be a cakewalk, but it will be about 100x easier.

And then we get to the ergonomic issues of tube length, wind sail, looking at zenith, etc. And for the record, I have ALWAYS employed chairs in my basic observation gear. Rather than a fancy adjustable one, I own two distinct chairs: one that sits rather low, and one that sits about "normal" height. But I have also had to employ my derrière on the ground when using F/9 and longer refractors, and only such long tube refractors have ever required such uncomfortable groveling in my decades of astronomical observations.

Again, all these are my preferences, and there are clearly Maksutov and long focal ratio refractor owners who don't feel this way (of course, most Mak owners would agree with me about the ergonomic issues since Maks tend to be even shorter than ED refractors). However, achromatic refractor owners would have to concede that my preferences are certainly the more popular ones. That most telescope owners have: newtonians, which in their incredibly popular dobsonian incarnation eliminate the straining near zenith issue with their focusers positioned near the top of the scope; ED refractors; and Maks, as opposed to long tube refractors, should demonstrate something. Perhaps your preferences, mrelliot, are more like mine, more like the majority's, and not like the strained neck, narrow field loving long tube refractor crowd. Just something to consider.

I will concede they are attractive to look at, a long tube refractor, almost like a work of art. Sadly, art doesn't help much when you're trying to put a target near zenith in your eyepiece, and the narrow field makes putting ANY target, regardless of its orientation, into the eyepiece that much more difficult.

So, given all this, I stand by my original recommendation of the C80ED for your first true astronomical telescope. It's a very good place to start. Buena suerte.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Astrojensen
Post Laureate
*****

Reged: 10/05/08

Loc: Bornholm, Denmark
Re: What can I see with a 80mm refractor? new [Re: CollinofAlabama]
      #5944200 - 06/28/13 03:31 AM

Hi Colin

While I totally agree on your analysis of false color, I must respectfully disagree with you on a number of other points:

Quote:

But even finding Uranus, e.g., in an F/15 scope without go-to is a difficult task for an experienced observer




This is absolutely not true by any stretch of the imagination. First, finderscopes are invented for a reason, second, a long-focus refractor is often long enough to act like a sort of pointer on its own. I've used a 85mm f/19 (1600mm focal length) refractor for many, many years and have always been able to find what I wanted to see (if it was within the reach of the scope, of course). For most things, I just aim along the tube, like down a rifle barrel. This more than suffice for bright stars and planets, and for dimmer targets I starhop.

Quote:

And then we get to the ergonomic issues of tube length, wind sail, looking at zenith, etc. And for the record, I have ALWAYS employed chairs in my basic observation gear. Rather than a fancy adjustable one, I own two distinct chairs: one that sits rather low, and one that sits about "normal" height. But I have also had to employ my derrière on the ground when using F/9 and longer refractors, and only such long tube refractors have ever required such uncomfortable groveling in my decades of astronomical observations.




Funnily, I have only very occasionally needed to sit on the ground, while observing with one of my refractors, while on the other hand, I always find myself down in the grass, when I want to observe something low in the sky with my 12" dobsonian. And for most of the sky, I can't use my normal chairs with the dob, as the eyepiece gets too high in the sky. The dob needs a fancy, tall chair, the refractors don't. The dob is my most unergonomical scope by FAR. Compared to my 6" refractor, I find it very tiring to use, and I honestly consider selling it and getting myself a nice 8" f/12 refractor. It is also by far the most wind-sensitive scope I own, even de-shrouded.


Clear skies!
Thomas, Denmark


Post Extras: Print Post   Remind Me!   Notify Moderator  
Niklo
sage


Reged: 03/29/13

Loc: Bavaria
Re: What can I see with a 80mm refractor? new [Re: CollinofAlabama]
      #5944232 - 06/28/13 05:00 AM

Hi Colin,
I have not compared it myself but I heard from other people that the chromatic aberration of an cheap 80 ED and a Vixen 80L f/15 is quite similar. The ED should have a little less chromatic aberration but the difference should not be much.

I read from a good Zeiss AS 80/1200 which was tested as a half APO.
http://www.astro-foren.de/showthread.php?9295-Zeiss-AS-80-1200-ein-echter-Hal...

Of course the Zeiss AS 80 is better than the Vixen 80L but it is not a ED refractor, too and has an achromatic design.

Nevertheless ED refractors have advantages.

Kind regards,
Roland


Post Extras: Print Post   Remind Me!   Notify Moderator  
Astrojensen
Post Laureate
*****

Reged: 10/05/08

Loc: Bornholm, Denmark
Re: What can I see with a 80mm refractor? new [Re: Niklo]
      #5944284 - 06/28/13 06:36 AM

A Zeiss AS is close to being an ED, as it already have twice as good color correction as an achromat of the same focal ratio.

The Vixen 80L has good color correction, but the 80mm f/7.5 Synta ED's are better. That doesn't neccesarily make them better planetary telescopes, however, as there is more to a good planetary telescope than just color correction.


Clear skies!
Thomas, Denmark


Post Extras: Print Post   Remind Me!   Notify Moderator  
CollinofAlabama
Carpal Tunnel
*****

Reged: 11/24/03

Loc: Lubbock, Texas, USA
Re: What can I see with a 80mm refractor? new [Re: Astrojensen]
      #5944833 - 06/28/13 01:47 PM

Thomas, how much does the mount for your 6" scope weigh? Also, how high does all that weight stand? The Vixen Portamount, like Kenny has pictured above, is under 12 lbs and stands somewhere below yours, taking a wild guess. I believe if mrelloit finds a 10" dob off-putting, the large and heavy mount of your 6" refractor will not look appealing to him, either.

Additionally, I don't buy Thomas' apologetics of long tube achromats regarding the lack of TFOV in these scopes, especially as pertains to the use by a newbie. Of course, some will do better than others, but ALL would do better with an instrument with more TFOV, like the C80ED. There is no object you can name, even the moon, that will be easier to put into the eyepiece in an F/11+ 80mm refractor than the Celestron F/7.5 ED scope. Basic mathematics, no opinion involved. This is especially true for the newbie. If you've never seen the Eskimo Nebula in Gemini in a finder, you're long tube "gun barrel sight" is going to be much less useful than a shorter tube "gun barrel sight" with a wide field eyepiece in the focuser for that "wait a second" moment of catching the Eskimo for the first time in a low power eyepiece.

It is important for we more experienced astronomers to listen to the OP. He started the post. Let's try and address his needs above our own predilections.

Edited by CollinofAlabama (06/28/13 05:37 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Astrojensen
Post Laureate
*****

Reged: 10/05/08

Loc: Bornholm, Denmark
Re: What can I see with a 80mm refractor? new [Re: CollinofAlabama]
      #5944890 - 06/28/13 02:29 PM

Hi Collin

The mount for my 6" achro is an EQ-6, on a 115cm tall Baader tripod. It's quite heavy, yes. However, I didn't mention it because I wanted the OP to run out and buy one, but as an example, compared to my 12" dob. Both are big scopes and I guess the 6" is actually the heavier, but I haven't weighed them, so I am not sure. I simply mentioned both, because I felt that your comment that a dob was always ergonomically superior to a long refractor was far too generalized and those were the scopes I had experience with and they were about equal in physical size. With my 6" refractor on its EQ-6 mount, I can survey most of sky, sitting comfortably on a normal chair. The dob needs a special, tall chair, and the eyepiece end moves around A LOT. I need to constantly move around, when I use the dob, while I only occasionally need to move the chair, when I observe with the refractor.

The lack of TFOV in long focal length instruments is both real and not. It is real, if we think in terms of what TFOV any given eyepiece will give, but if we think magnification, then the lack of TFOV is not there, once we are above a certain threshold. A 80mm f/15 at 30x with a 40mm 70° eyepiece will give a TFOV 2.33° across. A 80mm f/7.5 with a 20mm 70° will do exactly the same. And an awful lot of our telescopic observing is done at more than 50x. A short focus scope CAN give more TFOV, but at the magnifications we typically employ, it doesn't do so.

The perceived difficulties of aiming a long-focus scope are similar. Suppose you want to find Neptune. It's not visible with the naked eye from anywhere. With any scope of, say, 1000mm focal length or more, you'll want some kind of finderscope on it. Finding Neptune with the 7x50 finderscope on a 80mm f/15 scope is arguably easier than finding it with a 80mm f/7.5 that doesn't have a finderscope. If the 80mm f/7.5 also has a 7x50 finderscope, there'll be no differences. And in the main scope at any magnification, Neptune will look completely identical. You just need very different eyepieces to get to the magnification you want.

And yes, there is no object that is easier to put into a long f/ratio scope than a shorter one, but that is why we attach small, short f/ratio scopes to our long f/ratio scopes, to act as finders.

Physical size differences aside, a long f/ratio scope really is no more difficult to observe with, compared to a short one, and may have intrinsic advantages, making their use well worth the added hassle of a bigger mount and taller tripod.


Clear skies!
Thomas, Denmark


Post Extras: Print Post   Remind Me!   Notify Moderator  
csrlice12
Postmaster
*****

Reged: 05/22/12

Loc: Denver, CO
Re: What can I see with a 80mm refractor? new [Re: Astrojensen]
      #5945009 - 06/28/13 03:22 PM

My dobs heavier then my refractor + EQ mount/tripod, but for quick "pull it out and look"...the dob will be up and running while I'd still be polar aligning the refractor. The weight differential isn't that much, and truthfully, speed of setup is more important for a quick look in the back yard then a few pounds weight difference. If I'm going to be in the back yard for awhile though, I'll use the refractor as it has tracking and I mostly view planets and the moon from my white zone back yard......

Post Extras: Print Post   Remind Me!   Notify Moderator  
Astrojensen
Post Laureate
*****

Reged: 10/05/08

Loc: Bornholm, Denmark
Re: What can I see with a 80mm refractor? [Re: csrlice12]
      #5945119 - 06/28/13 04:11 PM

My polar "alignment" consists of carrying the mount and tripod outside, plunk it down, roughly aimed at Polaris and that's it. I normally track manually, as if it was a sort of equatorial dobsonian. It's much easier to manually track with an equatorial than with an altaz. It's all I need at up to almost 400x.


Clear skies!
Thomas, Denmark


Post Extras: Print Post   Remind Me!   Notify Moderator  
mikey cee
Postmaster
*****

Reged: 01/18/07

Loc: bellevue ne.
Re: What can I see with a 80mm refractor? new [Re: CounterWeight]
      #5945354 - 06/28/13 06:40 PM

Hone your eyesight and observing technique for several years is my advice! Then when you finally get your 10" refractor you'll swear you can see canals on Mars!! Mike

Post Extras: Print Post   Remind Me!   Notify Moderator  
mrelliot
member


Reged: 05/17/13

Re: What can I see with a 80mm refractor? new [Re: mikey cee]
      #5945517 - 06/28/13 08:18 PM

Is it easier to learn the night sky with a dob or an 80mm refractor?

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | (show all)


Extra information
13 registered and 29 anonymous users are browsing this forum.

Moderator:  Scott in NC, FirstSight, panhard, star drop 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 3880

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics