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 >> Classic Telescopes

Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | (show all)
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Is bigger better?
      #6339086 - 01/27/14 04:07 PM

There is a lot of people in this forum with many years of observing and using many different types of telescopes. One thing I have learned over the years is bigger is not always better. This is not in reference to optics beeing used in varying conditions of seeing. this post is in reference to larger optics unless of good quality will not best a smaller scope of really good optics. You might get a brighter image in the larger scope, but the sharpness is just not there. My best example is the meade 16" starfinder that had decent optics was always outperformed by a 4" celestron refractor. The older C102 celestrons had really good vixen optics. It was not untill I got a reflector with a really good mirror that the rule aperture rules showed its teeth. wonder how many of you have experienced the same observations.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Chuck Hards
Post Laureate
*****

Reged: 05/03/10

Loc: The Great Basin
Re: Is bigger better? new [Re: starman876]
      #6339091 - 01/27/14 04:11 PM

The optical quality of both the larger and smaller scopes must be similar for aperture to rule. A large optic that is so-so will not necessarily outperform a smaller optic that is essentially perfect.

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

Reged: 04/17/06

Loc: Florida
Re: Is bigger better? new [Re: Chuck Hards]
      #6339117 - 01/27/14 04:21 PM

Thus the cartoons in the Unitron catalogs.
Bill


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sasa
professor emeritus


Reged: 11/03/10

Loc: Ricany, Czech Republic
Re: Is bigger better? new [Re: Chuck Hards]
      #6339135 - 01/27/14 04:29 PM

I had similar experience with my former Newton 150/750. The optics was supposed to be an excellent, it was Orion Optics with lambda/8 attest (in fact lambda/9). But still, I had much better success in seeing details on planets with my 80mm apochromat or later with 100mm ED.

I think it was more a problem of mechanics and thermal effects than optics. There was also probably some influence of 33% central obstruction.

My other former Newton 250/1600mm (again Orion Optics, lambda/8) was however always visibly better than 100mm ED scope. Here the aperture ruled. However, even with this scope there was certain class of DSO objects where 100mm ED refractor was giving better results - typically low surface brightness objects, like globular cluster NGC5033. This was probably due to sight light from all the nearby street lights.

Also, funny thing, I was able to push on stars the 100mm ED refractor below magnitude 14.0. While the faintest star that I saw through 250mm Newton was just 14.7. Theoretically, I should be able to go with 250mm telescope about 2 magnitudes lower than with 100mm one. I attribute this mostly to a better comfort I had with ED100. I was observing sitting and with mounts with fine motion and I could effectively shield my eyes. While with N250 I was observing standing, it was not easy to observe effectively at high magnifications.


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

Reged: 07/09/13

Loc: The Deep South, USA
Re: Is bigger better? new [Re: Sasa]
      #6339341 - 01/27/14 06:14 PM

"I was observing sitting and with mounts with fine motion and I could effectively shield my eyes."

Great point! Comfort affects perception; or, as Mister Spock might say, "So... Human."


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: Bomber Bob]
      #6339388 - 01/27/14 06:36 PM

emotions are not something we want to deal with here. Please stick to the subject matter

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

Reged: 08/09/08

Loc: Seattle
Re: Is bigger better? new [Re: starman876]
      #6339403 - 01/27/14 06:45 PM

We went to a tremendous amount of work to build the 200 inch Hale telescope and we already had a beautiful 100 inch. Resolution and contrast and planetary detail all of these things are dependent on aperture.
I'd say my unknown 10" newt reigns supreme in my collection. Nothing can touch it. I can see things with it direct vision that are invisible in my really excellent Optical Craftsmen 8" newt and I don't think the mirror in the 10 is anything special, its just a lot bigger.

Robert


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: actionhac]
      #6339440 - 01/27/14 07:08 PM

You guys need to read some of the articles of people having shoot outs between different scopes. In those articles over and over again bigger is not better. However, outstanding optics always triumphs over larger optics that just were not as good. There are a few mirror makers that make outstanding optics. There are also only a few that make outstanding refractor optics. And of course there is always the debate between obstructed optics versus no obstruction. I agree a 200" scope should win hand down on a good night of seeing. A lot of that has to do with image scale of the extreme focal length of a 200" scope. However, we are not talking about us setting up our 200" scope now are we

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

Reged: 05/29/12

Loc: Just South of the Mason-Dixon ...
Re: Is bigger better? new [Re: starman876]
      #6339519 - 01/27/14 07:52 PM

Better seems to be highly subjective term. I have repeatedly had what seem to be more pleasing, and certainly crisper views with my refractors than with SCTs and Dobs of 2 and 3 times the aperture at our club star parties. The refractors are definitely in the minority at our club star parties, often just mine. People come and look and are sometimes blown away by the extreme sharpness, the contrast, and that velvet black almost textured surrounding background they see through the refractor. They tell me star clusters look like tiny diamonds cast down on black velvet. I've seen it many times myself. Sometimes there is nothing like a refractor. A good Mak will come close, but still, there is something about that unobstructed view through a 4 to 6 inch refractor. And yes, on DSOs as well.

On the other hand, resolution and light gathering are aperture dependent. While I may present a very sharp and aesthetically pleasing view of Jupiter with a 4 inch refractor to other viewers who come by for a look, they are not going to see the detail at 160X that they see at 500X with someone else's C11 at the star party. The same goes obviously for a look at M31 with the 4 inch refractor compared to M 31 with a 14 inch dob. Routinely though the 4inch F11 produces nicer images than the C8s etc on the field. All this however is highly subjective and arbitrary.

Edited by terraclarke (01/28/14 12:46 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
photiost
scholastic sledgehammer
*****

Reged: 12/14/06

Loc: Montreal, Canada
Re: Is bigger better? new [Re: terraclarke]
      #6339642 - 01/27/14 09:01 PM

"There is a lot of people in this forum with many years of observing and using many different types of telescopes. One thing I have learned over the years is bigger is not always better. This is not in reference to optics beeing used in varying conditions of seeing. this post is in reference to larger optics unless of good quality will not best a smaller scope of really good optics. You might get a brighter image in the larger scope, but the sharpness is just not there. My best example is the meade 16" starfinder that had decent optics was always outperformed by a 4" celestron refractor. The older C102 celestrons had really good vixen optics. It was not untill I got a reflector with a really good mirror that the rule aperture rules showed its teeth. wonder how many of you have experienced the same observations."


Yes it depends on the quality of the optics.

I recall one evening the AP 180 f/9 and setup nearby the AP 155 EDFS f/7 and about 30 feet away the 10in Intes Micro Maksutov-Cassegrain (not sure which model) by if memory serves it was an f/15 system.

Anyway all 3 telescopes were observing Saturn and by chance we first walked up to the AP 180mm then the 155mm and finally the 10in Intes.

The images of Saturn through the AP's were excellent however our group of 4 all agreed that the planetary images of the Intes were "better" than the 2 AP refractors.

We kept going back and forth (to confirm) for a good 20 minutes or so.

Another night I remember observing Saturn with the 7in f/9 Astro Physics refractor and then with a 12.5in NGT spit ring EQ Newtonian and the views with NGT were better than the AP.

Not saying the AP was bad - only the NGT was better.

So if we are comparing premium quality optical systems then the bigger will also be better.



Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: photiost]
      #6339688 - 01/27/14 09:22 PM

There you go a correct answer

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Is bigger better? new [Re: Sasa]
      #6339727 - 01/27/14 09:39 PM

Quote:

However, even with this scope there was certain class of DSO objects where 100mm ED refractor was giving better results - typically low surface brightness objects, like globular cluster NGC5033. This was probably due to sight light from all the nearby street lights.




NGC-5033 is a galaxy, NGC-5053 is a globular cluster, is that what you were thinking of? I generally don't think of globular clusters in terms of surface brightness, I think of them in terms of resolution and can be resolved with a 4 inch scope while a 10 inch is much more capable in this regard.

As far as the question, "Is bigger better", this is complicated and there is no one answer. If one is going to step back from the seeing issue then the assumption would need to be that the seeing is good enough that the telescope's optics are the limiting factor and not the seeing.. That means excellent seeing.

The next issue is the thermal management and the handling of stray light. Like seeing, these are often gremlins that plague larger scopes. Thermal issues can be addressed but they still can limit the performance of a large scope, stray light, not an issue with planetary, not an issue if the skies are dark. Both these factors depend on the scope as well as the operator.

The final factor is the target in question, the factors that are important when viewing the planets are quite different than those that affect the deep sky. My experiences basically go like this:

The original poster assumed excellent seeing and I am going to assume, because it is something I pay careful attention to, a properly cooled and aligned scope. I am not one to roam star parties, my experiences are my own with my own scopes.

Under these conditions, my experience has been that bigger is better when it comes to viewing the planets and double stars. Contrast and resolution are a function of aperture and if the seeing permits a large aperture scope to perform, it will do so. It doesn't take exceptional optics for a significantly larger scope to outperform the smaller scope, just good optics. A 10 inch or 12.5 inch has such an advantage over a 4 or 5 inch, a small scope can only do what it can do.. The other night the seeing was quite excellent, the temperature had remained at 50F for several hours, the views of Jupiter were among the finest I have ever seen, the contrast and detail, like a photo.

Typically this particular scope is not my favorite for the planets, it has a 2 inch thick mirror and has a mirror that is large enough (25 inches) that typically the seeing will be causing serious issues. But that particular night, these were not problems and the scope was performing admirably and indeed bigger was most certainly better.

As far as deep sky objects, again it does depend on the object but resolution and optical quality are less important because the eye simply cannot see the details that are there at the focal plane, the dark adapted eye has poor resolution. Small objects are more easily seen in large scopes. If I am hunting down faint galaxies, I find that the larger the aperture, the more I see.. If I am looking at the details in a bright planetary nebulae like the Eskimo nebula, the larger aperture provides the superior view, essentially independent of optical quality. The same can be said of globular clusters and open clusters for that matter.. M30 in a top notch 4 inch is shows only the barest details, in a 12.5 inch, I can resolve many of the stars and in an even bigger scope, even more so...I never really saw M7 until I looked at it in my 16 inch. In a 4 or 5 inch scope it's a beautiful bright open cluster but in a significantly larger scope, one can see a multitude of stars and even other clusters both open and globular hidden within M7.

So, ignoring seeing and assuming a properly setup and cooled scope, in general, bigger is better.. There are some objects that are better seen in a smaller scope because the simply won't fit in the eyepiece of a larger scope. Large, low contrast gradient objects are better suited for smaller, shorter focal length scopes.

It is my experience that it is the seeing, the thermal management, the stray light control, that can result in a large scope not performing up to snuff. Larger scopes require more care and effort by the observer to get the most out of them.. In the few public outing I attend, I just don't quite see others paying the attention to the details that are critical in getting their scopes to perform up to snuff.. At a serious star party, this would not be the case...

That's how it works for me... If I want the best possible planetary views and the seeing is excellent, (which it can be in San Diego), I will startcooling either the 10 inch F/5 or 13.1 inch F/5.5 and hour before sunset and figure it will be at least an hour after sunset before the scope is ready...

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: Jon Isaacs]
      #6339738 - 01/27/14 09:44 PM

Another good answer. Thank you

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

Reged: 08/31/12

Loc: SC
Re: Is bigger better? new [Re: photiost]
      #6339827 - 01/27/14 10:21 PM

A good large optic is better. Most Newts are poorly collimated and not properly cooled down. That kills performance. My old 10" F6 had a premium mirror and would easily outperform a 6" AP. I've done a number of side by sides. Last year I set up the 3" F15 Jaegers, 4" F15 Jaegers, 5" F12 D&G and 6" F10 Jaegers. Each step larger was a real step up. The 4" is very nice on Jupiter, very little CA. The 6" F10 does have the best resolution but is a little compromised by the CA. The 5" F12 D&G is right in between.
I had a Vixen A102Mwt(Japan) a good scope. But the 3.25" Jaegers gave similar or better planetary images. The Vixen just didn't have as smooth or accurate figure. Still a good scope but the smaller Jaegers was just as good.
3" scope outperform a 6" ?? only if there are problems with the 6" or the seeing is terrible. It happens often though. My 4" Jaegers gave better images than a 10" dob and a C8 at a public event. The 10" dob wasn't cooled down and the collimation wasn't spot on. The C8 looked well collimated, but it wasn't well cooled. The others had potential, but had issues that really reduced performance. Terra's comment was spot on. Saturn is sooo sharp! was the oft comment. Under non optimal conditions, smaller refractors can perform better than a larger scope.


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: bremms]
      #6339894 - 01/27/14 11:04 PM

Good viewing of the planets is largely dependent on image scale. The longer the focal length along with larger optics is always a good winner. That is why so many F15 systems provide such excellent views of the planets. The C14 with it's 140 inch focal length is a good example. When you get a C14 with good smooth optics and it is dialed in correctly and the seeing is good the view is pretty good. However, no matter what you say a large refractor with good optics providing those pin point stars on a velvet back ground is about as close as to driving a 911 Porsche. There is no substitute.

Post Extras: Print Post   Remind Me!   Notify Moderator  
wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: Is bigger better? new [Re: starman876]
      #6340008 - 01/28/14 12:24 AM

Quality is always best. But its difficult to obtain.

But quality, with additional difficulty, can also be scaled.

All that matters then is the degree one copes with difficulty ... to obtain the desired, scaled, quality.

Some difficulties, like instrument optics/rigidity/stability, can be dealt with by obtaining better ones comprehensively.

Other difficulties, like seeing and thermal issues, cannot. One must absent them for quality to be present.

Compromise occurs when we're not aware of the flaws that injure quality. Which when scaled, happens more readily.

When bigger isn't better is when scaling fails to deliver quality.


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

Reged: 07/09/13

Loc: The Deep South, USA
Re: How do you choose? new [Re: wfj]
      #6340411 - 01/28/14 08:50 AM

"The optical quality of both the larger and smaller scopes must be similar for aperture to rule."

I was going to start a thread on 'What factors go into your telescope purchases?' but I think it can tie-in with this topic - especially when you think of all the choices we have with this hobby!

So: What guides your Classic Telescope purchases??


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: How do you choose? new [Re: Bomber Bob]
      #6340496 - 01/28/14 09:36 AM

Quote:

"The optical quality of both the larger and smaller scopes must be similar for aperture to rule."




This certainly depends on the object in question. For faint, small objects, the eye is the limiting factor, it cannot resolve the details that exist at the focal plane so that quality of the optics is not particularly important.

In terms of objects like planets, fine scale contrast and resolution are proportional (actually inversely proportional) to aperture so a larger scope need not be of the same optical quality to provide greater resolution and contrast... The optics in my 10 inch GSO Dob are almost certainly not of the same quality as those in my 4 inch apo refractor nor at they as good as those in my 60mm F/13.3 Asahi-Pentax. But for viewing the planets, for splitting double stars, it is by far the better scope because on an absolute scale, the optics are better.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sasa
professor emeritus


Reged: 11/03/10

Loc: Ricany, Czech Republic
Re: Is bigger better? new [Re: Jon Isaacs]
      #6340501 - 01/28/14 09:37 AM

Hello Jon, yes, I meant NGC5053, a globular close to M53. Sorry for the typo. I was chasing it for several nights with 250mm Newton but with no luck. To my surprise, I glimpsed it through ED100 just on the first try from the same location.

It is not important that it is globular. I meant it as a typical member of class of objects with low surface brightness. It was just a first one that came to my mind.


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

Reged: 12/02/04

Loc: Hockessin, De
Re: Is bigger better? new [Re: Sasa]
      #6340620 - 01/28/14 10:42 AM

Learn to test optics and post the data and this debate goes away. Now you know exactly what your comparing. You also be surprised at how many "1/10" wave telescope test out at 1/2 wave. Without knowing the optical quality you can't untaggle the issues of seeing, cool down time, eyepiece type, aperture, etc.
Learning to test optics is not hard and in many ways easier then many of the mechanical restorations present here. Also the types of errors I see are not small ones so your not going to have to worry about splitting hairs to see if you have 1/10 vs 1/12 optics. It is going to be that your "1/10" wave optics are 1/2 wave and the zones and other errors are going to jump out at you. So it is only going to take one look to tell that there is no way that your optics can be anywhere close to diffraction limited.

- Dave


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sasa
professor emeritus


Reged: 11/03/10

Loc: Ricany, Czech Republic
Re: Is bigger better? new [Re: DAVIDG]
      #6340761 - 01/28/14 11:30 AM

You are right Dave. Now I always try to perform star-test on newly required optics with green filter. One can definitely quickly recognize a lemon. In case of my current refractors it is splitting hairs. To my untrained eyes, AS80/1200 and AS110 are showing mild spherical aberration (I would say at the level of lambda/6-lambda/8, this is very hard for me to judge), Telementor (C63) is essentially perfect from this point of view but it seems to have very mild astigmatism. I don't recall any issues with my 250mm Newton but the first 150mm one was showing sometimes quite strange patterns with a bump at the edge of one side. I did not know too much about star-tests at that time, but now I interpret it as a sign of tube currents.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Ziggy943
Post Laureate


Reged: 08/11/06

Loc: Utah
Re: Is bigger better? new [Re: Sasa]
      #6340859 - 01/28/14 12:24 PM

When you say "better", better at what?

Jon gives good answers to the unasked question.

So much depends on the condition of the telescope, not just the aperture. The lack of thermal equilibrium will destroy an image in any telescope. Bigger telescopes take longer to reach that condition.

I have set up the 9" Clark next to larger telescopes many times. Sometimes the Clark gives a better view, i.e., Jupiter, Moon, double stars and sometimes it doesn't.

I don't mind seeing something better than what my 9" can produce.


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

Reged: 08/31/12

Loc: SC
Re: Is bigger better? new [Re: DAVIDG]
      #6341262 - 01/28/14 03:19 PM

Dave said it well, A lot large optics are not that great. Most C8's are 1/2 wave or worse. I've had some fine mirrors and a couple of duds. It's simple plop a small refractor down and just get a good image. Not so with a 6-12.5" newt. They take a long time to reach equilibrium. My 6" " F8 Newt has a good mirror and ALWAYS shows more detail than a 60mm, 80mm or 100mm refractor unless the seeing is dreadful. It must be cooled down for 1-2 hours. My 4" Jaegers puts up a little fight, but the 6" reflector has a small CO and no CA.

Bottom line is, alot of larger scopes don't have great optics and/ or have cool down and tube current issues.


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

Reged: 05/29/12

Loc: Just South of the Mason-Dixon ...
Re: Is bigger better? new [Re: bremms]
      #6341290 - 01/28/14 03:32 PM

That's why I am looking forward to getting my 6 inch F10 built. I have a beautiful set of 1/10 wave optics, the primary mirror has a beautiful parabola, I have a very small, elliptical 1/10 wave matched flat, nice cell, spider, focuser, and finder, all waiting for a tube and rings. That will be my summer project.

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

Reged: 04/17/06

Loc: Florida
Re: Is bigger better? new [Re: starman876]
      #6341507 - 01/28/14 05:30 PM

Quote:

Good viewing of the planets is largely dependent on image scale. The longer the focal length along with larger optics is always a good winner. That is why so many F15 systems provide such excellent views of the planets. The C14 with it's 140 inch focal length is a good example. When you get a C14 with good smooth optics and it is dialed in correctly and the seeing is good the view is pretty good. However, no matter what you say a large refractor with good optics providing those pin point stars on a velvet back ground is about as close as to driving a 911 Porsche. There is no substitute.




Personally I don't think there is an answer to you original question. There are too many variables and qualifications. I remember a night where I had one of my best views of Jupiter thru a C14. Next in fairly dark skies, M33. Very dim view the galaxy which filled the eyepiece field even tho it was long focus. The contrast was not impressive. So I move to my 4 inch f/5 refractor and look at M33. Perfectly framed, spiral structure much more evident and contrast superb. Your question is like asking the better of apples and oranges. But I enjoy the thread.
Bill


Post Extras: Print Post   Remind Me!   Notify Moderator  
photiost
scholastic sledgehammer
*****

Reged: 12/14/06

Loc: Montreal, Canada
Re: Is bigger better? new [Re: Bonco]
      #6341529 - 01/28/14 05:45 PM

"When you say "better", better at what? "

Better contrast, better resolution and more surface details were visible.

We were also able to see 2 more of Saturns moons with the 12.5 Reflector.

The observation was made around 2am and these scopes had been setup from 8pm so they had all reached thermal equilibrium.



Post Extras: Print Post   Remind Me!   Notify Moderator  
Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Is bigger better? new [Re: photiost]
      #6341600 - 01/28/14 06:24 PM

DaveG -- How would I begin to learn to test optics? I'd love to know how good or bad my scopes are! Maybe I should spare you the effort of answering, because I'm unlikely to take apart a scope to bench test it, although I am learning how to star test

Sasa -- Why do you star test with a green filter?

"Image Scale" -- Please could someone explain that? I think it means that, for the same aperture, the smaller field of view of a longer focal length means any given object fills more of the field of view, so more of the scope's resolution is naturally devoted to the object at the image plane. It's already bigger, so it looks bigger with less magnification from an eyepiece. This makes it resistant to becoming over-magnified. It could be (could it be?) that, for the same magnification, smaller aperture with longer focal length could thus get better resolution than bigger aperture with shorter focal length. If true, there should be equations for this.

As to what I buy: Aperture, schmaperture. If I can't lift it, I won't buy it!


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: Joe Cepleur]
      #6341648 - 01/28/14 06:55 PM

http://starizona.com/acb/ccd/equipbasicsscale.aspx

here is a good explination


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? *DELETED* new [Re: Joe Cepleur]
      #6341653 - 01/28/14 06:58 PM

Post deleted by RLTYS

Post Extras: Print Post   Remind Me!   Notify Moderator  
TCW
Pooh-Bah


Reged: 11/05/13

Loc: The North 40
Re: Is bigger better? new [Re: starman876]
      #6341666 - 01/28/14 07:07 PM

It also depends on what you are observing. Planets or wide field deep space objects, double stars or small, faint fuzzies. All telescope designs have certain compromises and design limitations such as long or short focal length or chromatic aberration. I don't think there is such a thing as the perfect-all purpose scope.

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

Reged: 08/31/12

Loc: SC
Re: Is bigger better? new [Re: starman876]
      #6341678 - 01/28/14 07:12 PM

Yes.. for what objects? Planets? M33 is a large LSB object. Sky transparency and large exit pupil are the key. To me, it looks best in a 8-10 inch reflector at 5mm exit pupil. I was observing M1 a good bit lately. It is better a higher magnification from my light polluted back yard. It's barely visible in any thing under 4" and I wasn't able to see it in a good 60mm.

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

Reged: 08/09/08

Loc: Seattle
Re: Is bigger better? new [Re: bremms]
      #6341725 - 01/28/14 07:35 PM

Sometimes the telescope choice is out of our control like right now I switched to a dew resistant newt because of dew.
All forms of finders have been useless lately and my 6" MCT was shut down and then my Edmund 4"f15.
I brought out my RV-6 and I'm OK now except no finder.
I've had some very strange weather.
The RV-6 is stunningly good, funny how we forget. Actualy I knew the RV-6 is very good but I was using a $1000 MCT why bother with the old RV-6? Now I'm scared to bring the Mak back out I think the RV-6 will beat the expensive exotic.

Robert

Edited by actionhac (01/28/14 07:41 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: actionhac]
      #6341740 - 01/28/14 07:43 PM

Nothing wrong with a RV6. Really good all around scopes.
Depending on what you are viewing determines the scope selection. However, throw in a high end 6" APO with a focal length of about F7 you have a really good all around scope that will provide detail that will require a lot more aperture in a reflector before you will be able to see the same detail. That is what I mean is bigger better. Also, that black velvet background that many of us love is so hard to obtain with a reflector. The Tak CN212 as a cassegrain provides that black velvet background. That is one fine reflector. That is the only reflector I have seen that in.


Post Extras: Print Post   Remind Me!   Notify Moderator  
wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: Is bigger better? new [Re: starman876]
      #6341886 - 01/28/14 09:06 PM

Quote:

However, throw in a high end 6" APO with a focal length of about F7 you have a really good all around scope that will provide detail that will require a lot more aperture in a reflector before you will be able to see the same detail.



Errm. If the CO is less than 20%, no difference on detail same size.
Scattering from the mirror coatings will limit the black background.

Best coatings on both, best baffling ... no diff.


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

Reged: 08/31/12

Loc: SC
Re: Is bigger better? new [Re: wfj]
      #6341931 - 01/28/14 09:33 PM

a 6" F8 or F10 Newt with a really good mirror and small secondary will surprise you. Really, I looked through a 6" F9 newt with a 1.25" Quartz diagonal an 1/12 wavefront mirror. It was a dead heat with a AP 6" F12. The AP was a tiny bit better. TINY. My 10" F6 kicked the 6" AP. You need to use a well collimated newt with a GOOD mirror. That AP was a fantastic scope, but I have to agree with WFJ. 6" APO will not best a very good quality 8"+ reflector. Don't compare an AP 6" to a Orion Dob. Compare it to a long focus Zambuto mirror scope.

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

Reged: 08/31/12

Loc: SC
Re: Is bigger better? new [Re: bremms]
      #6341937 - 01/28/14 09:37 PM

I will say, a 6" F7 AP would be a killer all around scope. It will outperform an average 8" or maybe a not so good 10" dob.
Nice wide fields.. No too hard to mount. Sure would trade my 6" F10 Jaegers for one.


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: bremms]
      #6341959 - 01/28/14 09:53 PM

Well, I had a 10" Royce dob with a protostar secondary and tuned to perfection and it could not outdo my 6" AP. The dob was good but not that good. Maybe if you have an exceptional mirror it would be good contest. Even the Intes MN76 I had would not outdo the AP. I have not had any of the other scopes out long enough to do a fair comparison. The Quantum 8 and the Tak CN212 should be a good comparison to the AP. The portaball so far has given me the best view of Jupiter ever. Must have been a rare night of good seeing. I would love to see Jupiter in a 25" dob on a night of good seeing with a great mirror. Yes, bigger is better on nights of good seeing as long as the optics are also excellent to allow seeing that fine detail that only good optics will provide.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Sasa
professor emeritus


Reged: 11/03/10

Loc: Ricany, Czech Republic
Re: Is bigger better? new [Re: Joe Cepleur]
      #6342309 - 01/29/14 03:25 AM

Quote:


Sasa -- Why do you star test with a green filter?





I'm not sure if one needs green filter for long achromats, probably not, for example star test of C63/840 lens looks good also in white light. But some of my former telescopes were pretty fast, like Stellarvue 80/480mm triplet or Vixen 130 ED SS. There is usually fair amount of spherochromatism in such fast refractors (dependence of spherical aberration on wave length). As a result, the defocused star pattern does not look like in textbooks and it is hard (at least for me) to judge the quality of the optics. With green filter you are checking the optics at the wave length at which the optics was optimized.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Is bigger better? new [Re: Sasa]
      #6342358 - 01/29/14 04:13 AM

Quote:

Hello Jon, yes, I meant NGC5053, a globular close to M53. Sorry for the typo. I was chasing it for several nights with 250mm Newton but with no luck. To my surprise, I glimpsed it through ED100 just on the first try from the same location.

It is not important that it is globular. I meant it as a typical member of class of objects with low surface brightness. It was just a first one that came to my mind.




It's been a while since I looked at NGC-5053 but it's pretty easy to find since it's about 1 degree from M53. I have to think it was an issue with light from a street light because it should be easy pickings in the larger scope..

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Is bigger better? new [Re: Bonco]
      #6342365 - 01/29/14 04:26 AM

Quote:

Personally I don't think there is an answer to you original question. There are too many variables and qualifications. I remember a night where I had one of my best views of Jupiter thru a C14. Next in fairly dark skies, M33. Very dim view the galaxy which filled the eyepiece field even tho it was long focus. The contrast was not impressive. So I move to my 4 inch f/5 refractor and look at M33. Perfectly framed, spiral structure much more evident and contrast superb. Your question is like asking the better of apples and oranges. But I enjoy the thread.
Bill




That is basically an issue with a large aperture, slow scope. Celestron specs the C-14 at F/11 so the wides possible field of view is about 0.66 degrees. M-33 is about 0.7 degrees x 1.1 degrees, it over flows the eyepiece. But in a similar sized Newtonian working at F/5, it can be properly framed against the dark sky and it can be quite impressive. I like to wander around M33 with my 16 inch F/4.42 (F/5.07 with the Paracorr), there are some interesting details to be seen.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
SpooPoker
sage
*****

Reged: 06/04/13

Loc: North Bay CA
Re: Is bigger better? new [Re: Sasa]
      #6342371 - 01/29/14 04:34 AM

It really is not impossible to make a Newtonian perform as well as an equivalent aperture APO Refractor. If both have equivalently well figured optics and the design for the Newt was on the stingier side in terms of diagonal size (i.e. below 20%), one would be hard pressed to tell a difference if the target was Jupiter or Mars. One would need to carefully collimate the Newtonian, flock / baffle the tube interior, have quality focusing components, anything is possible. A central obstruction of 30% is noticeable on the image (but not as awful as it has been made out to be), 25% is tolerable for all but the most fussy fusspots, 20% is barely perceivable by most people, 15% may only be perceived by the slenderest percentage of expert observers, 10% is absolutely impossible - I mean absolutely and totally and utterly impossible for the eye to detect a loss of contrast.

I have looked through a few Newtonians with obstructions of 12 - 15% - they may as well be considered the equivalent in image sharpness / contrast to a high end APO of equal aperture. It is a myth to talk of the APO >> Newtonian - they can in fact be very nearly equal. There is no question though that a Newtonian would give an equivalent sized Achromat a severe hurting (provided apertures >= 6" otherwise the Achromat is generally superior). A 6" achromat just cannot cope with good CA correction unless the tube was absurdly long. A 6" f/10 Newtonian can have a diagonal of 1" (even .75" if one used the scope exclusively for planetary / double stars) and thus give a very good contrasty image, a 6" achromat would have to be at least f/15 to give similar contrast if one is prepared to ignore the indigo/violet halo that surrounds bright objects. 6" f/10 is troublesome in size but manageable, 6" f/15 is a nightmare! 6" and above are magic numbers for the Newtonian and many 6" f/8 instruments are very fine, as is the 8" f/6.

However one thing a Newtonian cannot do: It will never match up, aperture for aperture with an APO when one factors in the focal ratio. A 6" APO could be very well color corrected down to about f/5. A Newtonian on that same focal ratio would get absolutely hammered in terms of contrast, fine resolution, details etc... To get a Newtonian to perform as well as the APO, pound for pound, aperture for aperture, would be if the design was for larger mirrors / objectives. At the small end of the scale, a refractor absolutely smokes a Newtonian out the water (particularly if one wishes to keep the focal ratio reasonable, i.e. f/10 or below). Once one hits around 6", particularly 8", the differences become academic rather than practical. The difference between a TEC 8" f/8 APO and an 8" f/8 Newtonian could be made negligible. The comparison between a 6" f/8 APO and a 6" f/8 Newtonian with a premium mirror errs in favor of the APO - the APO edging the Newtonian out slightly on contrast and fine color. At f/10 though, with one making a sacrifice on 100% illuminated diameter (perhaps down to a quarter inch or even an eighth of an inch), the 6" Newtonian would hypothetically rival the APO on planets. However, the APO would comfortably beat the Newtonian on illuminated area / field of view.

However, whatever the case one can make for good quality Newts, Maks, SCT's, Achromats and so on, there is something so utterly appealing about the APO. It is its mystique, its prestige, its poetry that makes all other telescope designs seem like something ugly to own and use. APO performance advantage over other telescope designs has been grossly overestimated by the majority of people, but lets face it, it's appeal extends far beyond the notion that it performs far better than anything else. We all know it does not, we all know it is a placebo type effect (it costs more, everyone says it is better, therefore my brain will say its better), we all know that even if it does perform ever so slightly better, it certainly is not worth $20K more.

Whatever the case, the APO versus everything else debate will go on endlessly. If low dispersion glass became dirt cheap and APO's end up costing as much as Achromats, most people would not get so hung up on them. The fact they are expensive means those that really spend a fortune will justify it's cost by whatever means possible - even ignoring basic optical theory / physics when a 4" APO is faced up against a Cassegrain or Newt of double the aperture. There are a plethora of threads along these lines "4inch APO better on planets than 8 or 10inch scope" etc... We all know basic optical theory should trump bias, emotion, or ignorance.

Peace.


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

Reged: 07/09/13

Loc: The Deep South, USA
Re: Is bigger better? new [Re: SpooPoker]
      #6342474 - 01/29/14 07:01 AM

"It really is not impossible to make a Newtonian perform as well as an equivalent aperture APO Refractor."

I haven't used APO's enough to know for sure, BUT Pre-APO / ED, amateurs on a budget built or bought Newtonian "Planet Killers" that I have looked through, and these were excellent performers. Even the "general purpose" Newts, like Jim Vice's 8" Cave, produced bright planetary images with truer color than an equivalent aperture ACHRO.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Bill Friend
super member
*****

Reged: 02/16/12

Loc: Maine
Re: Is bigger better? new [Re: Bomber Bob]
      #6342489 - 01/29/14 07:19 AM

I remember an article years ago in Reflector about taking a run of the mill 6" f/8, masking off the outer 1/2" of the mirror (where most of the error occurs) and installing a smaller secondary and low profile focuser. I believe the obstruction was below or around 20% and compared favorably to a 5" APO.

Cheers,
Bill


Post Extras: Print Post   Remind Me!   Notify Moderator  
clintwhitman
Caveman
*****

Reged: 01/01/07

Loc: CALI SoEasyACavemanCanSlewIt
Re: Is bigger better? new [Re: Bill Friend]
      #6342539 - 01/29/14 08:14 AM

Sorry to break the news
"All Things Being Equal" In other words any really well built telescope with optimizes optics, good seeing and optimal ground thermal conditions / control.
This not being a question of Newt Vers. Refractor, Acro / Apo or Cass.

"Always" is the answer to this "Resolution" question.


Aperture will always wins the race. No doubt about it. Why else would some of us drag around a 20" DOB!!
(aveman

PS:
Of course this is not taking into account my bias passions and the million reasons a well built large or small APO refractor will alway be my favorite to actually use!!

Edited by clintwhitman (01/29/14 08:28 AM)


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

Reged: 05/29/12

Loc: Just South of the Mason-Dixon ...
Re: Is bigger better? new [Re: Bill Friend]
      #6342586 - 01/29/14 09:04 AM



Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: terraclarke]
      #6342645 - 01/29/14 09:37 AM

So there we have it. The myth that bigger is better has been busted. We all agree the scope with the better optics always wins no matter what the size of the scope.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Chuck Hards
Post Laureate
*****

Reged: 05/03/10

Loc: The Great Basin
Re: Is bigger better? new [Re: starman876]
      #6342656 - 01/29/14 09:41 AM



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

Reged: 05/29/12

Loc: Just South of the Mason-Dixon ...
Re: Is bigger better? new [Re: starman876]
      #6342759 - 01/29/14 10:28 AM

So you are saying that a 50mm Ashai Pentax will best a run of the mill C8? I don't know that I would agree with that, though I do know that I would use my Zeiss Telementor or even my Russian Lomo Mak more than either and also enjoy the experience more.

As I have said time and again, my thresholds of aperture at both ends of the scale are determined by aesthetics and practicality.


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: terraclarke]
      #6342835 - 01/29/14 11:01 AM

OK let me reword that a bit
The scope with the better optics will alway better the scope of similar size or the unobstructed scope will most of the time beat a scope of similar or larger size. so the question of is bigger better has been busted. Bigger is not really better, take a coulter 17" for instance. We all know that they were not better. a lot of big meade newtonians were not better, well a lot of meade gear was not better I know that I kept talking about high end scopes and now I realize that I started this thread because of all the really bad experiences I have had with large cheap reflectors and refractors that I kept hoping would give me that thrill of large aperture cheaply. It only thought me a lesson that aperture comes at a cost and there is no substitute for quality.


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

Reged: 05/29/12

Loc: Just South of the Mason-Dixon ...
Re: Is bigger better? new [Re: starman876]
      #6342864 - 01/29/14 11:16 AM

And your last sentence I totally agree with. That being said, be careful not to re-kindle last week's firestorm. I am sure there are still glowing embers lying about.

Terra


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

Reged: 08/09/08

Loc: Seattle
Re: Is bigger better? new [Re: terraclarke]
      #6342879 - 01/29/14 11:23 AM Attachment (15 downloads)

Heres a photo of my 6"f13 Super Planetary.
This is a very special instrument which is not much fun to use as a general purpose telescope because of the sub one inch diagonal, less illumination for the focal plane and a very narrow field. Tube currents can be fearsome like a boiler flue pipe. And the extra trouble to set up the heavy mounting and observing with a ladder.
Its specialty is planets and I've seen Martians doing laundry along the canals with this scope, yes its that good.


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

Reged: 07/09/13

Loc: The Deep South, USA
Re: Is bigger better? new [Re: actionhac]
      #6342888 - 01/29/14 11:29 AM

"I've seen Martians doing laundry along the canals with this scope"

Hilarious!!

"not much fun to use as a general purpose telescope"

Ditto for my old D&G.

Tying in to Terra's comment: I think it boils down to what you want to observe, at what level of detail, and at what cost in time & treasure!


Post Extras: Print Post   Remind Me!   Notify Moderator  
tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
Re: Is bigger better? new [Re: Bomber Bob]
      #6342914 - 01/29/14 11:40 AM

This is fun while being a terrific planetary and deep sky scope. Most comfy, too.



I routinely rest my arm on the base of the equatorial head and lean on the scope while observing with it. Image doesn't move.

-Tim.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ziggy943
Post Laureate


Reged: 08/11/06

Loc: Utah
Re: Is bigger better? new [Re: clintwhitman]
      #6342924 - 01/29/14 11:45 AM

I don't know Clint, why do you drag around the 20" dob when you could be dragging out a 9" Pearl!?

Post Extras: Print Post   Remind Me!   Notify Moderator  
AllanDystrup
sage
*****

Reged: 09/27/12

Loc: Denmark
Re: Is bigger better? new [Re: Bomber Bob]
      #6342937 - 01/29/14 11:55 AM

Quote:

Is bigger better?



Depends:

-yes:
light gathering
(theoretical) resolution

-no:
collimation
portability
setup time
thermal equilibrium
stray light control
bad seeing tolerance
observation ergonomics
eyepiece requirements

I've held a sharper, crisper image of Jupiter in my 3" U*** compared to a nearby 20" Obsession Dob. on a night with so-so transparency and seeing;
On the other hand (eye), i've seen astonishing details in the Cygnus Veil Nebula in the very same 20" Dob. on a night with excellent seeing, that I could never hope to see in my 3" refractor.

Doing most of my observation from a light polluted backyard, in a costal temperate climate zone with very seldom excellent seeing, the answer is easy : Small is Beautiful! (ie. personally, I prefer small, high quality refractors).
In other, more ideal circumstances (dark skies, observatory, proper funding), I would chose another instrument profile.
It depends

Allan


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: actionhac]
      #6342977 - 01/29/14 12:13 PM

would it not be easier just to use an AP 6" F12. Should produce even better results and you would not need a ladder. just saying
I should talk, I bought that 10" F11 newt that has just sat in the corner since I bought it. Something about a 110 inch newtonian that just does not get used.


Post Extras: Print Post   Remind Me!   Notify Moderator  
A6Q6
professor emeritus


Reged: 05/31/11

Loc: Stroudsburg,Pa,U.S.A
Re: Is bigger better? new [Re: AllanDystrup]
      #6343011 - 01/29/14 12:24 PM Attachment (7 downloads)

My C5 is just as easy to take out as my fully assembled 60mm Bushnell Sky chief II, So bigger is better in that case. I can also take out my Quantum6 in one trip, but the C5 is soooo much lighter. The Meade 826 is a lot of work and not comfortable to use even if it had good optics. I had a RV-6 years ago, a great scope but I would take a good C5 over it anyday.

Edited by A6Q6 (01/29/14 12:33 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Is bigger better? -- Circular Logic new [Re: starman876]
      #6343041 - 01/29/14 12:38 PM

These discussions continue because the answer is analogous to being mathematical, and therefore is difficult to intuit. Aperture is one factor in the design of a telescope. Assuming perfect seeing, per the agreement in this thread, in theory, larger aperture always wins. No question. No contest. In practice, things get interesting: Can one make or buy a top-quality objective that big? Is it available; can one afford it? Will it cool before sunrise? Is it too heavy to transport to the viewing site?

Not to mention that the assumption of perfect seeing, while necessary in a theoretical discussion, is absurd. Clearly, all things considered, a better quality, smaller scope is often better than a lesser quality, bigger scope! So, why do the discussions continue? Because aperture *is* one important factor, and some kid's homebuilt 8" Newt may well trounce your $12,000 5" Astro-Physics on some objects, under some conditions!


Post Extras: Print Post   Remind Me!   Notify Moderator  
SpooPoker
sage
*****

Reged: 06/04/13

Loc: North Bay CA
Re: Is bigger better? new [Re: starman876]
      #6343051 - 01/29/14 12:42 PM

Quote:

OK let me reword that a bit
The scope with the better optics will alway better the scope of similar size or the unobstructed scope will most of the time beat a scope of similar or larger size. so the question of is bigger better has been busted. Bigger is not really better, take a coulter 17" for instance. We all know that they were not better. a lot of big meade newtonians were not better, well a lot of meade gear was not better I know that I kept talking about high end scopes and now I realize that I started this thread because of all the really bad experiences I have had with large cheap reflectors and refractors that I kept hoping would give me that thrill of large aperture cheaply. It only thought me a lesson that aperture comes at a cost and there is no substitute for quality.




The bigger not always better is too tricky to actually pen down in a way no-one can find fault with the reasoning.

Ultimately I look at it this way:

The telescope <-> observing paradigm is an optical chain.

- The first link in the chain is arguably the most important one - it is the plan wave light source from a distant object passing through around 100miles of atmosphere. This light source, now subject to temporal distortion, has to squeeze inside a tube. The tube diameter is much greater than the wavelength of the light, thus diffraction and atmospheric effects are the very first defect in the chain. All telescopes, irrespective of design fall within this yoke. No matter how good your optics, you are not going to beat this.

- The second link in the chain is important but its absolute necessity in forming a quality image has been grossly exaggerated. It is the quality of the objective / primary and secondary mirror / quality of corrector plates etc... A good designer / optician would naturally desire to get these components as perfect as possible, but reality suggests there is a cut-off beyond which few if any people would notice minor issues in the figuring of the glasses. The quarter wavelength rule (lamda/4) is derived only from the diffraction limit of the scope aperture and is taken as a rule of thumb for the minimum quality of the lenses/mirrors. Many mass market mirrors / objectives do their job within or at least close to this limit. They give good pleasing views. The views through a premium instrument are often slightly better - but a lot of that is also the telescope tube - the baffling, flocking etc... Naturally a better quality objective would lead to a better quality image, but I would be surprised if a person would notice the difference between, say, a 1/100 PV mirror versus a 1/20 PV mirror - or in the Strehl measure, the difference between .999 and .98. Many opticians consider the 0.8 Strehl to be a minimum target of sorts, and the difference between .8 and .999 is definitely noticeable but not earth shattering. The actual difference is 0.1999 and be left there, to talk about it aesthetically is probably meaningless - it will vary from scope to scope, observer to observer.

- Finally there is the eyepiece and the human eye itself. I prefer not to get into the premium orthoscopic / monocentric / plossl realm here, it is best left alone. Generally though, eyepiece aberrations often exceed that induced by the telescope objective. Have coma in your Newtonian? Many eyepieces hide it not through being superbly corrected but because they have defects > off axis aberrations.


Quote:

So you are saying that a 50mm Ashai Pentax will best a run of the mill C8? I don't know that I would agree with that, though I do know that I would use my Zeiss Telementor or even my Russian Lomo Mak more than either and also enjoy the experience more.

As I have said time and again, my thresholds of aperture at both ends of the scale are determined by aesthetics and practicality.




The enjoyment of using an instrument and appreciating its goodness - the real reason why we have preferred scopes! I will say I have often found my 60mm f/15 refractor giving one of my larger telescopes a good run for it's money. In choppy seeing conditions and better tolerance to eyepiece defects (nice narrow cone of light), a small quality APO / Achromat is an extremely fine instrument that can live with the big boys in some circumstances. I do 90% of my observing with a 60mm or 80mm refractor. I spend very little time at the eyepiece with a bigger instrument - and laziness in hauling that thing out is not a factor - it is practicality, enjoyment, and the fact that quite often, the big ol scope would be totally underutilized for the given seeing conditions.

The Zeiss Telementor? Lucky lucky. Very nice instrument it is one of the scopes on my list of must own desirables


Post Extras: Print Post   Remind Me!   Notify Moderator  
Bill Friend
super member
*****

Reged: 02/16/12

Loc: Maine
Re: Is bigger better? new [Re: SpooPoker]
      #6343096 - 01/29/14 01:04 PM

Quote:


The enjoyment of using an instrument and appreciating its goodness - the real reason why we have preferred scopes! I will say I have often found my 60mm f/15 refractor giving one of my larger telescopes a good run for it's money. In choppy seeing conditions and better tolerance to eyepiece defects (nice narrow cone of light), a small quality APO / Achromat is an extremely fine instrument that can live with the big boys in some circumstances. I do 90% of my observing with a 60mm or 80mm refractor. I spend very little time at the eyepiece with a bigger instrument - and laziness in hauling that thing out is not a factor - it is practicality, enjoyment, and the fact that quite often, the big ol scope would be totally underutilized for the given seeing conditions.




+1


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: Bill Friend]
      #6343172 - 01/29/14 01:41 PM

I agree with the above also. the seeing in this area severly limits aperture size. The Telementor routinely out performs anything larger. One night I had the Telementor out and the Zeiss AS100/1000 and the telementor was providing better views. One thing I will have to say about quality optics. The image quality does not break down as one increases the power. I have seen that over and over again. the 12.5 portaball has optics that are that good. Most dobs and newtonians I have had were merely light buckets and good for low power viewing. The Cave is also an exception to that rule. Cave made high quality mirrors. If you check through most sales for scopes the minute you see someone with a high qaulity mirror they do let you know about it. Not so with other scopes you see for sale. People in this forum when they have a scope they are proud of they let you know it and provide pictures. I would provide pictures, but I have never been much of an imager. Maybe I am too impatient by expecting istant results.

Post Extras: Print Post   Remind Me!   Notify Moderator  
SpooPoker
sage
*****

Reged: 06/04/13

Loc: North Bay CA
Re: Is bigger better? new [Re: starman876]
      #6343348 - 01/29/14 03:08 PM

There are so many variables with quality lenses or mirrors, I would take a lot of those quality measures (PV, RMS, Strehl and whatnot) with a large pinch of salt.

I do believe, if a mirror or lens produced errors that were truly below the diffraction limit, increasing the quality (lowering the errors) would be subject to law of diminishing returns - the image cleans up slightly better for every iteration but in a manner where the "relative gain" in bumping up the objective quality decreases. One could feasibly reach a limit where the human eye would no longer be able to detect the improvement in quality. Does the mirror or triplet or doublet lenses have to be perfect? Heck no!

Issues with most mirrors could include:
- not true parabola, mirror parabolic enough to work but spherical aberration would be present, but perhaps below lamda/4 from this effect.

- poor error performance from edges (could be masked off).

- poor secondary mirror partner (may be quite common, I took an underperforming 4.5" f/8 scope and it miraculously cleaned up when I switched secondary mirror).

- Regions of roughness, pits, and such. Causes scattering of light which affects contrast. Mirror needs to be smooth enough, but does not have to be perfect.

- Interfering light sources or scattered light due to hard edges / mirror roughness can affect the image contrast. This is particularly if the Tube is unflocked and unbaffled (quite common in the Chinese made scopes). Baffling / proper flocking helps the stray reflections quite considerably.

- Focuser issues: A common focuser even for a fast scope is the ubiquitous 1.25" 3.5" rack and pinion. Not a great focuser for the faster scope - and one that is unbaffled usually and introduces vignetting.

- The eyepiece itself. Ideally one would pick the best quality eyepiece, but more to the point, the eyepiece that would perform best for a given scope. A .96" Pentax Ortho may not be wisest choice for a 10" f/4.5 Newt - particularly if not coupled with a powermate/barlow. Similarly, a run of the mill Ultra Wide could introduce many aberrations to the optical path giving the illusion the Newt is performing poorly. Also fast scopes generally require assistance with a coma corrector - numerous under-performing Dobs I have looked through at star parties featured a run of the mill eyepiece and no coma correction in sight. No wonder the 6" f/8 Newtonian or 4" Refractor were giving the big old Dob the heave ho in image aesthetics!

I do believe that those folks left underwhelmed by the performance of their Newtonian, despite collimating and cooling down the mirror sufficiently, more than likely would run into any one of the issues above.

Usually the biggest issue though is seeing, cool down, and/or imperfect collimation - particularly for a faster scope.

With proper design, care to detail, and quality components, a Newtonian should perform beautifully. One thing it cannot do is beat the seeing and if there are thermal differences between mirror and outside, that alone will relegate even the most superbly designed instrument to one with 10 - 15X per inch limits.

I think all telescope designs perform beautifully once one understands what they are dealing with. A small quality instrument is an absolutely wonderful thing to own, as is a large instrument. They all good


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: SpooPoker]
      #6343424 - 01/29/14 03:34 PM

so it would be best to start with a quality product and that way the only thing left would be seeing, cool down, alignment and eyepiece qaulity. Alignment in most refractors should not be a problem. Cool down time is shorter and eyepiece selection should be easy to figure out.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Petrus351
sage


Reged: 12/17/12

Loc: Spain
Re: Is bigger better? new [Re: starman876]
      #6343487 - 01/29/14 03:54 PM

The laws of physics are the laws of physics, and the larger telescope has a bigger light gathering power and resolution.
Maximun magnification is related to aperture, and a four inch refractor, even being the most expensive in the world, can be used to a maximum of 200-250x at its best, while a 16 inch SCT can be used to a magnification of 800x.
I think the 16 incher, has to be a very, very, very bad a lemon, in order to show less than a 4 or 5 ich refractor.


Edited by Petrus351 (01/29/14 03:55 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: Petrus351]
      #6343490 - 01/29/14 03:55 PM

and when you find a night in Washington DC you can use 800X then I would say that I would be dreaming

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

Reged: 07/09/13

Loc: The Deep South, USA
Re: Is bigger better? new [Re: Petrus351]
      #6343498 - 01/29/14 03:57 PM

I routinely used 400x on my D&G 5" -- even pushed it to 500x when seeing was near-perfect.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Petrus351
sage


Reged: 12/17/12

Loc: Spain
Re: Is bigger better? new [Re: starman876]
      #6343503 - 01/29/14 03:59 PM

Quote:

and when you find a night in Washington DC you can use 800X then I would say that I would be dreaming




I donīt live in Washington, but that has nothing to do with the original question. If the seeing is bad, itīs better to play cards or to watch T.V. instead, as using a telescope in this case is not worth.
I have a C8, a C9.25 and a C11 EDGE, and I have used 500x many times with very good results, and I cannot imagine that with a 4 inch refractor.


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

Reged: 07/09/13

Loc: The Deep South, USA
Re: Is bigger better? new [Re: Petrus351]
      #6343509 - 01/29/14 04:01 PM

In fact: I consider 60x per inch the dividing line between average & above-average refractor optics.

Post Extras: Print Post   Remind Me!   Notify Moderator  
jrcrillyAdministrator
Refractor wienie no more
*****

Reged: 04/30/03

Loc: NE Ohio
Re: Is bigger better? new [Re: starman876]
      #6343513 - 01/29/14 04:02 PM

Quote:

and when you find a night in Washington DC you can use 800X then I would say that I would be dreaming




There will be nights when the larger telescope's greater resolution and magnification ability won't be used - but it will ALWAYS gather 16 times as much light and will present a much larger exit pupil at 250X or any other magnification.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Petrus351
sage


Reged: 12/17/12

Loc: Spain
Re: Is bigger better? new [Re: jrcrilly]
      #6343522 - 01/29/14 04:05 PM

A C14 with at least 1/4 wave, "eats" any 4" or 5" refractor, even the most expensive ones.
And nowadays, any SCT has 1/4 or better optics.

Go and search for the best planetary pictures in the world and see how many of them, have been made with 4" o 5" inch refractors, and at the same scale.
The best ones have been made with C14īs, or similar apertures.

Ask Damian Peach, please.



Edited by Petrus351 (01/29/14 04:10 PM)


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

Reged: 07/09/13

Loc: The Deep South, USA
Re: Is bigger better? new [Re: Petrus351]
      #6343535 - 01/29/14 04:12 PM

I bought my D&G 5" in 1988. At that time, a C14 with mount ran more then 4x the total cost of my kit (with Jaeger's pier mount). I think I did OK. I'll sacrifice some image size for a less budget-busting & hernia-inducing solution.

Post Extras: Print Post   Remind Me!   Notify Moderator  
amicus sidera
Post Laureate
*****

Reged: 10/14/11

Loc: East of the Sun, West of the M...
Re: Is bigger better? new [Re: Petrus351]
      #6343536 - 01/29/14 04:12 PM

Quote:

The laws of physics are the laws of physics, and the larger telescope has a bigger light gathering power and resolution.
Maximun magnification is related to aperture, and a four inch refractor, even being the most expensive in the world, can be used to a maximum of 200-250x at its best, while a 16 inch SCT can be used to a magnification of 800x.
I think the 16 incher, has to be a very, very, very bad a lemon, in order to show less than a 4 or 5 ich refractor.





Agreed, but it would appear that both the Refractors and Classic Telescopes forums have participants who have decreed that the laws of physics be held in abeyance.


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

Reged: 07/09/13

Loc: The Deep South, USA
Re: Is bigger better? new [Re: amicus sidera]
      #6343546 - 01/29/14 04:14 PM

Laws? We don't need no stinkin' laws!

Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: Bomber Bob]
      #6343595 - 01/29/14 04:35 PM

I agree with the laws of physics. My 6" AP is pushed to close to 500 power without an issue. So with that said how can I argue with the laws of physics. Many nights of veiwing I would have both out at the same time and the C14 and the 6" AP stay head to head at the same powers. So how can I argue with anything that is said here

Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: Petrus351]
      #6343606 - 01/29/14 04:38 PM

you really do need to look at pictures that smaller aperture scopes have taken. Pictures on Amart of the planets with high end APO's sure are awesome. I would have to argue that with some of them I have never seen anything better with a C14. Having a couple of C14's I know there limitations.

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

Reged: 06/13/10

Loc: Colorado, USA DM59ra
Re: Is bigger better? new [Re: amicus sidera]
      #6343617 - 01/29/14 04:43 PM

Quote:

Agreed, but it would appear that both the Refractors and Classic Telescopes forums have participants who have decreed that the laws of physics be held in abeyance.





I'm quite surprised that the Questar forum hasn't emptied to come over here and refute the laws of physics.


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

Reged: 06/13/10

Loc: Colorado, USA DM59ra
Re: Is bigger better? new [Re: amicus sidera]
      #6343619 - 01/29/14 04:44 PM

duplicate post deleted by rd

Edited by rdandrea (01/29/14 04:44 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: Is bigger better? new [Re: amicus sidera]
      #6343622 - 01/29/14 04:44 PM

Lately I've been culling my scope herd ...

I take out 1 "big" scope (at the moment 8" cAVE) and 1 "small" scope (62mm Nihon Sieko) along with the "unit under test".

Both "small" and "big" happen to be best in catagory, no optical issues, well tested and used, no thermal/environmental issues on site.

"Big" lets me check accurately seeing and "what's possible".

"Small" sets a lower bound on desired performance.

If I can see more than "small" that I can confirm with "big", I can accept this as an objective measure of pragmatic quality - that bigger than "small" is better.

I'll be selling some 80-130mm scopes soon. I also have a 152mm that has an issue I'm solving, and should I solve it, it will have a point and leave the "sell" category.

The practical reality is that for bigger to be better, it can't just be bigger, but at least as better as "small", for the first cut.

Survivor round 2: "how many "small","big" ... serves to suite this hobby". Tune in next week ...


Post Extras: Print Post   Remind Me!   Notify Moderator  
Dan /schechter
scholastic sledgehammer


Reged: 12/21/06

Loc: Long Beach, Calif.
Re: Is bigger better? new [Re: starman876]
      #6343637 - 01/29/14 04:48 PM

This is a great question that gets discussed from time to time. I enjoy reading the responses whenever it comes up again.

Is bigger better? If we can standardize the instruments, physics gives us the answer. If we compare instruments of excellent optical quality, build, eyepieces, cooling time and great seeing, then the answer is yes, bigger is better. My greatest aperture refractor is an AP 6" f/9 Starfire EDT. It almost performs as well or better than most instruments on the telescopes field. I can hardly count how many times I viewed thru larger aperture instruments, especially refractors, and did not get better views. However, on those once in a year nights with fantastic seeing, the owner of those larger instruments had to peel me away. Their superiority was easy to see.

Another way to phrase the question, on nights of poor to mediocre seeing, "Is Bigger worse?" Early in my viewing experience, I thought so. I read the statement that since the seeing cell is smaller for smaller aperture instruments, they will outperform greater aperture instruments on nights of so so seeing. It makes great sense. I have visited many observatories with BIG telescopes and had the guide explain that the 4" refractor over in the corner quite often outperforms the main instrument. Again, this makes sense.

Then Clint found his "Pearl". A 9" f/10+ AP triplet. I have had my 6" Starfire set up close to the Pearl somewhere between 5 and ten times with differences in seeing from lousy to nice. Not once did my 6" ever outperform Clints AP 9" no matter what the seeing or the power. When the power was the same, the Pearl always outperformed my 6" AP. In fact, as the power increased, the difference became even more apparent.

Last summer I set up a Clark 3" f/10 refractor next to Jack Eastman`s 6" f/15 Clark and had the same experience. When the powers were the same, his 6" outperformed my 3". Not only that, it did better as the powers were increased. It produced a mediocre image at higher powers while the 3" produced a blur. This was during a time of seeing being from a 2 to 4 out of ten.

I was surprised at the results since I was sure that my lesser aperture aperture telescope would outperform greater aperture telescopes in poor seeing.

That experience made me readjust the statement that bigger is poorer in poor seeing. I have not figured out the ratio between apertures that has to exist before that is true, but I think that the larger instrument must have several times the aperture of the smaller instrument for that statement to be true. Clints 9" Pearl is only 1 1/2" times as large as my 6". Jack`s 6" was only twice as large as my 3". Maybe, someone in this forum knows what the ratio has to be for the effect to be true.

Again, great topic,
Dan


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

Reged: 07/09/13

Loc: The Deep South, USA
Re: Is bigger better? new [Re: wfj]
      #6343642 - 01/29/14 04:49 PM

"I'll be selling some 80-130mm scopes soon."

You wouldn't happen to have one of the Meade 4" refractors from the 1970's would you? (They had a Unitronish look, IIRC.)


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: Dan /schechter]
      #6343663 - 01/29/14 04:58 PM

it is nice to hear opinions that are reasonable and not slanted in one direction or another. that is what I was hoping for when I started this post. I am not really interested in how my scope will beat yours. I am interested in the pure fact of how aperture, image scale and overall seeing conditions will guide us to picking the right scope for the right night. I doubt that many of us have looked through every scope that has ever been made. I am sure a good many of us have had plenty of scopes. However, only a precious few have had scopes that just are the best that can pull that last photon out of the night sky and provide that wow factor that many of us seek. This is not a contest of will your reflector outperform the refactor or the inverse. This is the question of how can one obtain the best performance possible from a scope on any given night. What would be the best scope to do that with.

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

Reged: 07/09/13

Loc: The Deep South, USA
Re: Is bigger better? new [Re: starman876]
      #6343685 - 01/29/14 05:06 PM

Terra had the answer: "All this however is highly subjective and arbitrary."

Post Extras: Print Post   Remind Me!   Notify Moderator  
Petrus351
sage


Reged: 12/17/12

Loc: Spain
Re: Is bigger better? new [Re: starman876]
      #6343697 - 01/29/14 05:11 PM

Quote:

you really do need to look at pictures that smaller aperture scopes have taken. Pictures on Amart of the planets with high end APO's sure are awesome. I would have to argue that with some of them I have never seen anything better with a C14. Having a couple of C14's I know there limitations.




Could you please show some pictures, made with 4" and 5" inch apos, please?


Post Extras: Print Post   Remind Me!   Notify Moderator  
Petrus351
sage


Reged: 12/17/12

Loc: Spain
Re: Is bigger better? new [Re: Bomber Bob]
      #6343717 - 01/29/14 05:21 PM

Quote:

Terra had the answer: "All this however is highly subjective and arbitrary."



Iīm not sure. What you can see with a scope is what you can see with a scope, and thatīs an objetive subject; not subjetive. If you can see some details with a scope, and the same details, cannot be seen with another one, is not subjetive.

Edited by Petrus351 (01/29/14 05:22 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Petrus351
sage


Reged: 12/17/12

Loc: Spain
Re: Is bigger better? new [Re: Petrus351]
      #6343735 - 01/29/14 05:28 PM

I think, the telescope was invented, in order to be able to see things, beyond the naked eye, so what really matters in a telescope is what you can see. This is not a subjetive matter, and thatīs why telescopes have been bigger and bigger as time passes by. When someone asks "is bigger better", I gess he means "what telescope you can see more with"?

Do you see more with a 4" apo than with a C14? In good seen conditions, I donīt think so.

Edited by Petrus351 (01/29/14 05:31 PM)


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

Reged: 07/09/13

Loc: The Deep South, USA
Re: Is bigger better? new [Re: Petrus351]
      #6343796 - 01/29/14 05:54 PM

"what really matters in a telescope is what you can see"

Yes, and I don't think anyone can argue with objective performance. The differences between us are about individual perception, which can be quite subjective, because what I see at the eyepiece is unique to my own neurophysiology, experience, and - yes! - emotional state.

Which is really a fancy way of saying: Lowell saw canals on Mars, but I only see blobs & smudges.


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: Bomber Bob]
      #6343816 - 01/29/14 06:04 PM

Those canals got removed because of urban renewal by NASA.

Post Extras: Print Post   Remind Me!   Notify Moderator  
SpooPoker
sage
*****

Reged: 06/04/13

Loc: North Bay CA
Re: Is bigger better? new [Re: Bomber Bob]
      #6343819 - 01/29/14 06:05 PM

Eeking details out of a small disc / extended object with lowish contrast is a challenge all in itself. It takes a special eye to resolve special details - and knowing ahead of time what to be looking for gives one a huge advantage.

Actually that is the one thing, the one huge advantage of using small aperture instruments to do observing - training yourself to see better. I learned observing skill far more from a 60mm refractor than I ever did with a DOB.

I regret passing up on a 40mm Unitron frac for a couple of hundred bucks - seeing detail with a 40mm would take some doing, and I have no doubt it could be done and would improve my viewing skills using one for a while. I may plump for the 50mm Unitron listed on eBay, but the price of $360 is plain nuts for that, hopefully the seller drops it to around the 200 mark and I will pounce on it.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Petrus351
sage


Reged: 12/17/12

Loc: Spain
Re: Is bigger better? new [Re: SpooPoker]
      #6343844 - 01/29/14 06:18 PM

What about pictures? Please donīt tell me that what you can see in a jupiter picture, for example, differs from what other people see in the same picture.

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

Reged: 07/09/13

Loc: The Deep South, USA
Re: Is bigger better? new [Re: Petrus351]
      #6343847 - 01/29/14 06:20 PM

Oh, I can definitely say that people have different perceptions of what they see, hear, smell, & taste -- regardless of the source -- how else to explain Nickelback fans??

Post Extras: Print Post   Remind Me!   Notify Moderator  
jrcrillyAdministrator
Refractor wienie no more
*****

Reged: 04/30/03

Loc: NE Ohio
Re: Is bigger better? new [Re: starman876]
      #6343906 - 01/29/14 06:41 PM

Quote:

Those canals got removed because of urban renewal by NASA.




The same thing happened to the Venus surface details he imagined and wrote about extensively. "Subjective" too frequently means "imaginary". Kind of like the Neptune and Uranus perturbations he imagined and then attributed to a nonexistent outer gas giant.


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

Reged: 10/17/09

Loc: Tucson, Arizona
Re: Is bigger better? new [Re: jrcrilly]
      #6344448 - 01/30/14 01:37 AM

What a loaded question.

Post Extras: Print Post   Remind Me!   Notify Moderator  
svdwal
Vendor (mBrain Software)


Reged: 03/10/13

Loc: Leiden, The Netherlands
Re: Is bigger better? new [Re: Datapanic]
      #6344504 - 01/30/14 03:19 AM

There is of course the quote from Suiter: "the best way to get a perfect 12" is to make a good 14".

If you look at the theory, the Modulation Transfer Function (MTF) captures the differences between different telescopes very well. For reasonable optics you can see how optical quality can be traded for aperture. The bigger optics will be better in resolving small high-contrast objects like very close doubles. But at the scale of details on planets there is much leeway, and smaller, better optics can compete with bigger and worse. But not with bigger and as good optics.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Petrus351
sage


Reged: 12/17/12

Loc: Spain
Re: Is bigger better? new [Re: svdwal]
      #6344528 - 01/30/14 04:14 AM

Quote:

There is of course the quote from Suiter: "the best way to get a perfect 12" is to make a good 14".

If you look at the theory, the Modulation Transfer Function (MTF) captures the differences between different telescopes very well. For reasonable optics you can see how optical quality can be traded for aperture. The bigger optics will be better in resolving small high-contrast objects like very close doubles. But at the scale of details on planets there is much leeway, and smaller, better optics can compete with bigger and worse. But not with bigger and as good optics.




Yes, but what are the margins???

I mean, weīre talking about a 4" refractor in comparison to a C14? or are we talking about a 6" vs 8" scope?
What you say, can be true between small differences in aperture, but not between important ones.

Edited by Petrus351 (01/30/14 05:19 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Petrus351
sage


Reged: 12/17/12

Loc: Spain
Re: Is bigger better? new [Re: Petrus351]
      #6344529 - 01/30/14 04:16 AM

Please show me the best Jupiter pictures made with a 4" apo.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Petrus351
sage


Reged: 12/17/12

Loc: Spain
Re: Is bigger better? new [Re: Bomber Bob]
      #6344532 - 01/30/14 04:18 AM

Quote:

Oh, I can definitely say that people have different perceptions of what they see, hear, smell, & taste -- regardless of the source -- how else to explain Nickelback fans??



At the end, weīll be talking about the sex of angels.

A good quality picture is the one that shows more detail, period.

I repeat: please show me the best Jupiter picture made with a 4" or 5" refractor.



Edited by Petrus351 (01/30/14 04:20 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Petrus351
sage


Reged: 12/17/12

Loc: Spain
Re: Is bigger better? new [Re: Petrus351]
      #6344550 - 01/30/14 05:06 AM

Take a 4" inch refractor, and try and capture jupiter at 60 fps in the blue channel, with a focal lenth of 8000mm, equivalent to a C14+2x barlow, and then you tell me. You will see thatīs simply impossible, because even if you increase gain to the top, the image will be too dark with a very poor histogram.
ŋWhy? Because the larger the aperture, the less you have to increase gain in order to get the same histogram, and a high histogram means noise.
With my C11 EDGE HD, I take captures of Jupiter in the three channels, always at 60 fps with a focal lenth of 5600 with a 2x barlow, with no issues.
Now try and do the same, with the same focal lenth with a 4" refractor. Even with my C8 is just impossible, having double the aperture of a four incher.
So aperture rules, period.

Edited by Petrus351 (01/30/14 05:21 AM)


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

Reged: 08/31/12

Loc: SC
Re: Is bigger better? new [Re: Petrus351]
      #6344710 - 01/30/14 08:57 AM

Yes it does. Beyond 6-8" only rare nights will allow full resolution. The photo of Saturn on the AP site with a 175EDF is exquisite. A nearly perfect 7" scope is going to be hard to beat on all but exceptional nights. One of the reasons I usually take the 6" refactor out vs one of my larger scopes.
Partly cool down too. My C11 shows more detail and contrast than my "6 refractor, but not when cooling or if the seeing is marginal. 4" scopes are just a bit small for most of my observing. Just the way it is, My 4" F15 refractor is easier to set up than the 6" F10, but the little extra effort is worth the gain in performance. The 4" is better for a quick look, and it does excel on the moon due to much less CA.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Chuck Hards
Post Laureate
*****

Reged: 05/03/10

Loc: The Great Basin
Re: Is bigger better? new [Re: bremms]
      #6344748 - 01/30/14 09:23 AM

Hey, after we resolve this question, let's talk about which classic eyepiece is best!

Post Extras: Print Post   Remind Me!   Notify Moderator  
clintwhitman
Caveman
*****

Reged: 01/01/07

Loc: CALI SoEasyACavemanCanSlewIt
Re: Is bigger better? new [Re: Dan /schechter]
      #6344822 - 01/30/14 10:11 AM

Re: Seeing conditions. Are smaller scopes better sometimes? Seem to be, but I am really starting to think it because you can see the bad seeing better at larger mags with more aperture. If you pump up the magnification to match the larger telescope (if possible) the smaller scopes usually looks just as bad or about the same, at least to me.

Dan you post is well said. Many of the nights we spent at Pinos with your 6" AP, Roberts 7" AP, A few dozen other refractors, Kennedy's 32" dob. dozens of C14s, 11s and all the other Newtonians at Pinos is why I,,,
#1 I am a Refractor lover,
#2 Feel that Aperture rules as to what you can see.The Telescopes setup at the Pinos parking lot are the best of the best with some of the best seeing. But nothing on the field ever made me wish I owned or was using any system other than the Pearl. Just mind blowing views.


Post Extras: Print Post   Remind Me!   Notify Moderator  
svdwal
Vendor (mBrain Software)


Reged: 03/10/13

Loc: Leiden, The Netherlands
Re: Is bigger better? new [Re: Petrus351]
      #6344915 - 01/30/14 11:11 AM

Quote:


Yes, but what are the margins???

I mean, weīre talking about a 4" refractor in comparison to a C14? or are we talking about a 6" vs 8" scope?
What you say, can be true between small differences in aperture, but not between important ones.




It depends a lot on the scopes. A Ritchey-Chretien with a big central obstruction will have to be bigger than a Newton for it to beat a refractor. And a mass-market SCT with 1/4 lambda spherical abberation will have to be bigger than one with 1/10 lambda.

Apparently the heuristic of subtracting the central obstruction from the objective diameter works quite well.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jim Curry
Pooh-Bah
*****

Reged: 10/29/07

Loc: STL
Re: Is bigger better? new [Re: Chuck Hards]
      #6345096 - 01/30/14 12:55 PM

I have the answer to that!

Jim


Post Extras: Print Post   Remind Me!   Notify Moderator  
Chuck Hards
Post Laureate
*****

Reged: 05/03/10

Loc: The Great Basin
Re: Is bigger better? new [Re: Jim Curry]
      #6345123 - 01/30/14 01:11 PM

Quote:

I have the answer to that!

Jim




Lol, you and everyone else!


Post Extras: Print Post   Remind Me!   Notify Moderator  
rcwolpert
professor emeritus
*****

Reged: 08/13/12

Loc: San Jose, CA
Re: Is bigger better? new [Re: Jim Curry]
      #6345165 - 01/30/14 01:25 PM

With 50 years of observing behind me and often pondering this question of "Is Bigger Better", I've come to the following 5 conclusions that seem to work for me:

1. A small aperture telescope out under the stars seems to always out perform a much larger aperture telescope in the garage.
2. Larger aperture provides better resolution of clusters and double stars.
3. Larger aperture provides better views of galaxies and nebulae.
4. On nights of bad seeing, both will perform about the same if the same POWER is used. If the same EYEPIECE is used, the small aperture scope may provide a much better view.
5. On nights of good seeing, both large and small aperture telescopes can have you totally awed all night long when viewing the moon, Jupiter, and Saturn.

- Bob


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

Reged: 09/29/10

Loc: SE Indiana
Re: Is bigger better? new [Re: rcwolpert]
      #6345203 - 01/30/14 01:41 PM

+1

Post Extras: Print Post   Remind Me!   Notify Moderator  
TCW
Pooh-Bah


Reged: 11/05/13

Loc: The North 40
Re: Is bigger better? new [Re: actionhac]
      #6345206 - 01/30/14 01:43 PM

That is quite a scope! Can it reach zenith?

Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: TCW]
      #6345488 - 01/30/14 04:05 PM

For the next post it will be is smaller better

Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: starman876]
      #6345493 - 01/30/14 04:07 PM

Of course all the data that has been presented are theories that were developed many years ago. I have always wondered if these same theories still hold true with all the advancements in lens making and the exotic glass that is used today.

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

Reged: 08/09/08

Loc: Seattle
Re: Is bigger better? new [Re: TCW]
      #6345789 - 01/30/14 06:49 PM Attachment (7 downloads)

Quote:

That is quite a scope! Can it reach zenith?




Yes I make sure the tube will reach zenith. You can see its close! I can roast marshmallows up at the other end of the tube. It settles down quickly once the sun sets. I've got a few more refinements to make to it. Its a ongoing experiment and I enjoy trying new ideas with it.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Is bigger better? new [Re: SpooPoker]
      #6346153 - 01/30/14 10:07 PM

Quote:

A 6" APO could be very well color corrected down to about f/5. A Newtonian on that same focal ratio would get absolutely hammered in terms of contrast, fine resolution, details etc...




Have you ever seen a 6 inch F/5 apo? They might exist but I don't know of any...

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
SpooPoker
sage
*****

Reged: 06/04/13

Loc: North Bay CA
Re: Is bigger better? new [Re: Jon Isaacs]
      #6346191 - 01/30/14 10:27 PM

Here is a 6incher on a short FL:
http://www.teleskop-express.de/shop/product_info.php/info/p5630_TS-PHOTOLINE-...


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Is bigger better? new [Re: SpooPoker]
      #6346525 - 01/31/14 05:24 AM

Quote:

Here is a 6incher on a short FL:
http://www.teleskop-express.de/shop/product_info.php/info/p5630_TS-PHOTOLINE-...




It's actually a 130mm f/7 with a field flattener that can be screwed into the focuser. It's a 5 inch along the lines of the NP-127 but less intergrated and possibly not capable of visual use .

I don't know of any "native" 6 inch F/5 apos. It might be possible but the ones I see are relatively slow and within range of focal lengths where a planetary 6 inch Newtonian is possible.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
Petrus351
sage


Reged: 12/17/12

Loc: Spain
Re: Is bigger better? new [Re: Jon Isaacs]
      #6346575 - 01/31/14 07:02 AM

"Only for some objects, although undermagnification is often a problem, even for experienced observers. The penalty for increased magnification is reduced field of view and brightness; faint objects grow fainter as the magnification is increased This is why larger aperture telescopes are so effective on faint objects; they provide enough light to stimulate the eye at high magnifications. For example, a 4-inch telescope will only view a globular cluster effectively at 80X, and it will appear as a blob. A 6-inch will resolve the outer stars at 130X, an 8-inch will resolve further in at 200X. 10 and 12.5-inch telescopes will make them glitter to the core at 300 and 400X".

Copy and paste from the Sky Watcher home web page.


Post Extras: Print Post   Remind Me!   Notify Moderator  
svdwal
Vendor (mBrain Software)


Reged: 03/10/13

Loc: Leiden, The Netherlands
Re: Is bigger better? new [Re: starman876]
      #6347128 - 01/31/14 12:23 PM

Quote:

Of course all the data that has been presented are theories that were developed many years ago. I have always wondered if these same theories still hold true with all the advancements in lens making and the exotic glass that is used today.




Those theories still hold, AFAIK. What has changed is that ray tracing is much faster on a computer.


Post Extras: Print Post   Remind Me!   Notify Moderator  
SpooPoker
sage
*****

Reged: 06/04/13

Loc: North Bay CA
Re: Is bigger better? new [Re: Jon Isaacs]
      #6347478 - 01/31/14 03:50 PM

Quote:


It's actually a 130mm f/7 with a field flattener that can be screwed into the focuser. It's a 5 inch along the lines of the NP-127 but less intergrated and possibly not capable of visual use .

I don't know of any "native" 6 inch F/5 apos. It might be possible but the ones I see are relatively slow and within range of focal lengths where a planetary 6 inch Newtonian is possible.

Jon






You are right, dunno where 130mm = 6" came from. Late night I guess. Yeah, it seems anything in APO world larger than 4" generally comes in f/7 - f/9 forms. I guess the reason would be correcting a 6" f/5 for visual would be prohibitively expensive or nigh on impossible to manufacture. A 6" f/5 on a crown flint form (achromat) would have phenomenal CA and there is only so much a triplet can do. I guess it is far easier to correct via triplet form a f/7 or f/8 than a f/6 or less.

In saying that, your TV 100mm f/5 APO does a good job on color correction - correct?


Post Extras: Print Post   Remind Me!   Notify Moderator  
CHASLX200
Post Laureate
*****

Reged: 09/29/07

Loc: Tampa area Florida
Re: Is bigger better? new [Re: DAVIDG]
      #6347962 - 01/31/14 08:02 PM

Bigger is always better until ya have to move it around or set it up.

Chas


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman876
Postmaster
*****

Reged: 04/28/08

Loc: VA
Re: Is bigger better? new [Re: CHASLX200]
      #6348242 - 01/31/14 11:02 PM

I would say bigger is better when you get around 20" and if it is your scope it is the best ever.

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

Reged: 10/17/09

Loc: Tucson, Arizona
Re: Is bigger better? new [Re: starman876]
      #6348372 - 02/01/14 01:01 AM

This thread belongs in the Beginners Forum!

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Is bigger better? new [Re: SpooPoker]
      #6348514 - 02/01/14 04:43 AM

Quote:

In saying that, your TV 100mm f/5 APO does a good job on color correction - correct?




It is excellent, even out of focus. But it's not really a 4 inch F/5.4, or at least the objective is not. It's a bit of a simplification but it's basically a long focal length apo double with a fancy ED focal reducer/field flattener at the rear of the scope. NP stands for Nagler-Petzval.

You could do a similar thing with a 6 inch apo but then you could do a similar thing with with a Newtonian but neither makes much sense.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
SpooPoker
sage
*****

Reged: 06/04/13

Loc: North Bay CA
Re: Is bigger better? new [Re: Jon Isaacs]
      #6350147 - 02/01/14 10:11 PM

Quote:


It is excellent, even out of focus. But it's not really a 4 inch F/5.4, or at least the objective is not. It's a bit of a simplification but it's basically a long focal length apo double with a fancy ED focal reducer/field flattener at the rear of the scope. NP stands for Nagler-Petzval.

You could do a similar thing with a 6 inch apo but then you could do a similar thing with with a Newtonian but neither makes much sense.

Jon




Cool sounds like an awesome scope.

Is the FOV just like a f/7 or f/8 frac or does the design get around that? I am seriously considering getting one of these for a big FOV, but if it has the same FOV as a regular 4" ED doublet, then I may sit tight on my money


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Is bigger better? new [Re: SpooPoker]
      #6352132 - 02/02/14 09:55 PM

Quote:

Quote:


It is excellent, even out of focus. But it's not really a 4 inch F/5.4, or at least the objective is not. It's a bit of a simplification but it's basically a long focal length apo double with a fancy ED focal reducer/field flattener at the rear of the scope. NP stands for Nagler-Petzval.

You could do a similar thing with a 6 inch apo but then you could do a similar thing with with a Newtonian but neither makes much sense.

Jon




Cool sounds like an awesome scope.

Is the FOV just like a f/7 or f/8 frac or does the design get around that? I am seriously considering getting one of these for a big FOV, but if it has the same FOV as a regular 4" ED doublet, then I may sit tight on my money




The TeleVue NP-101 is a 4 inch apochromatic with a focal length of 540mm and functions as 4 inch F/5.4. But the actual objective is not F/5.4.

Jon


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

Reged: 07/09/13

Loc: The Deep South, USA
Re: Is bigger better? new [Re: SpooPoker]
      #6354326 - 02/03/14 09:11 PM

I'll summarize my post from another forum: A city's heat dome will affect seeing, which will affect viewing options, and consequently the scope I use on a given night.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Is bigger better? new [Re: Bomber Bob]
      #6354380 - 02/03/14 09:28 PM

Quote:

I'll summarize my post from another forum: A city's heat dome will affect seeing, which will affect viewing options, and consequently the scope I use on a given night.




In my experience, the "heat dome" is localized so that if the object is at a reasonable altitude, it does not affect the overall seeing. But the localized heating effects are very important, viewing over trees and building, viewing on concrete or asphalt, these can make a big difference.

Jon


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

Reged: 07/09/13

Loc: The Deep South, USA
Re: Is bigger better? new [Re: Jon Isaacs]
      #6354389 - 02/03/14 09:33 PM

"In my experience, the "heat dome" is localized..."

What I've found in my current location (the city is in a Bowl) is that winds from the north make the dome much more unstable than the warm muggy air from the Gulf of Mexico. But, just 10 miles away, it's not a factor at all.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | (show all)


Extra information
25 registered and 26 anonymous users are browsing this forum.

Moderator:  Rich (RLTYS), Brian Risley 

Print Thread

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


Thread views: 2343

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics