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1 inch APO vs 12 inch SCT

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#451 sonny.barile

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Posted 28 January 2018 - 12:12 PM

One of the members who frequents the binoviewer forum.....eddgie.......has a theory that we are effecting our diffraction limited optics by hanging longer and longer equipment on the back ends of the moving mirror scopes. Stuff like 2 inch mirror diagonals and  Binoviewers......introducing SA.   This could equate to the bad views people claim to get. I view with my C8 and binoviewers 100 percent of time. Using the stock visual back and 1-1/4 prism diagonal stars looked a little bloated and duller. Not as sharp. I shortened the optical path on the back end by using a short SCT adapter and a T2 threaded Baader diagonal and coupled the binoviewer to the diagonal with a small adapter as opposed to the 35mm long eyepiece adapter. I chopped 136mm out of the focal length. The views with this shorter set up are sharp as a tack and the stars are no longer bloated looking. Focus just snaps in.     Some of these tiny aperture apo versus C8 contests may not have the C8 set up for optimal viewing. They might be using long mirror diagonals which optical path longer and not where it was designed to be.

A properly collimated C8 with a 1-1/4 prism diagonal (optimal designed length) should be able to take a 5 inch APO’s lunch money. 


Edited by sonny.barile, 28 January 2018 - 05:08 PM.


#452 yellobeard

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Posted 28 January 2018 - 05:14 PM

Partly you're right, but the amount of SA you introduce by adding a bino viewer is way less than the factory tolerances permit!
So if you happen to own a C8 with very good, diffraction limited optics, you could indeed see the difference.
But...There is also the fact that earlier SCT's mostly are tested at 632.8nm wavelength, which, when of exellent quality, makes them fully suited for bino viewing, as the green focus lies further away from the back of the tube than the red.

I also corrected my two C11's for a green 'sweetspot' some 8" from the back, to make them suited for a bino setup.

But as soon as optics are not of high quality, you will not see a difference between with or without bino viewer, simply because that difference is too small.

Edited by yellobeard, 28 January 2018 - 05:16 PM.


#453 sonny.barile

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Posted 28 January 2018 - 07:14 PM

Well.....I can’t take the credit for being any right at all. As I stated I’m regurgitating what I read from someone else. However, I took the advice and it proved to give a gain in viewing pleasure. I can definitely see it. Some of it may be attributed to a weak structured stock diagonal frame. I believe it was slightly sagging under the weight load of the binoviewers. The Baader T2 diagonal and adapters have axially threaded connections (like a pipe fitting) that have removed this from the equation.

I am also taking your advice on insulating my scope. I will be picking up some of the suggested material from the hardware store tomorrow. I have a 30/40 degree delta on most nights in this winter season. Anything that gets me viewing faster and more often is a big plus. 

 

 


Edited by sonny.barile, 28 January 2018 - 07:19 PM.


#454 Asbytec

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Posted 28 January 2018 - 08:50 PM

Actually, with back focus you add a tiny bit of overcorrection to an undercorrected, moving mirror system. So, if anything, the image should improve slightly if it's noticeable at all. 



#455 Reid W

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Posted 29 January 2018 - 04:45 PM

Planetary bino-views in my C11 are superb when using the Denk corrector.  Fine resolution is significantly improved when the corrector is in place.  

 

The other evening, I noted a significant improvement in double star resolution my 103 when I switched from my Baader prism to a TV 2" Everbrite mirror.  Just the opposite is noted in my 90mm.  Images with the Baader prism are superior to the mirror.  Go figure.

 

Is comes down to trying the combinations available.  

 

To that end, I have a 2" x 1.25" adapter inbound and will try the Denk 1.25" corrector in the TV 2" diagonal on the 103 and see how the bino-views shake out....  



#456 Bill Barlow

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Posted 29 January 2018 - 10:10 PM

I have compared 1.25" prism diagonals (Tak and Baader) against a dielectric one (TV Everbright) in the 6" MCT's and SCT's  and 3.5" and 4" refractors I have owned and found the prism's to be sharper on all objects and have more contrast on planets.

 

Bill 


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#457 luxo II

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Posted 02 February 2018 - 05:51 AM

Seeing limits all telescopes resolving power. The resolving power of a telescope is only its POTENTIAL resolving power not its guaranteed resolving power. And seeing can limit a larger scope’s potential resolving power to that of a smaller scope.

Bob

But you’re equally guilty of assuming seeing is the limit for all locations.

This would be true if you choose some random spot in the countryside without understanding how the air flows over the terrain, and where to find laminar flow (very good seeing) as distinct from turbulent flow (poor seeing).

In my case I’ve done a lot of work to identify what distinguishes some sites from others - and I have two sites that have a high probability of turning on sub-arc-second seeing - to the extent I have no problem cranking up my 9” mak to 450x and looking at very close doubles down to the Dawes limit, ie 0.5 arcsec seeing.

Can’t do it every time - obviously - as the jet stream often mucks it up. But it is possible to find sites that have an above average likelihood of excellent seeing - vs many other sites that invariably have dreadful seeing most nights.

The key here is an observing site which is on an elevated ridge or plateau with facing a very wide, low valley (700m below and 30km wide) with a 400m sheer cliff on the upwind side, so there is no low altitude turbulence over the site. The prevailing wind strike the cliff face and produces compression and a significant updraft, and the observing site has to be no more than 100-200m downwind of the cliff.

The reason I know the air is smooth is I’ve flown a paraglider over it many times in late afternoon - you can feel the air like a bird does through your fingertips - the slightest turbulence is evident. After sunset it’s even smoother.

Edited by luxo II, 02 February 2018 - 06:35 AM.


#458 mikona

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Posted 03 February 2018 - 11:21 AM

Hello Friends,

 

I am not nearly as smart or knowledgeable as many of you out here.  In fact, I am amazed by many of the posts here.  2 friends of mine who are brilliant indicated that I should concentrate on what I see in the eyepiece.  

 

I own 5 scopes... certainly more than I need.  2 cats (Mewlon 250 and C8) and 3 fracts (ES8OED, ES127ED, and  Tak FC100DF).  Here is what I can tell you from my perspective ... taking the science and math out of the equation ... only speaking through the emotions of my personal experience at the eyepiece. 

 

First... Fracts give routinely more pleasing views for me personally .  Second... The quality of optics in the Tak really do make a difference over the ES fracts.  Third... I find myself regularly willing to see less detail in favor of quality of image through fracts.  I will state that most of my viewing sessions are 2 to 3 hours, and I am often not patient to let the cat properly acclimate.

 

Now... when acclimated and seeing is good, my Mewlon produces jaw dropping images.  My best view of the Orion Nebula is through the Mewlon.  But... I had to let the Mewlon cool for 2 hours... I used my fract for the 2 hours patiently waiting...  And, even then, stars are not quite as pinpoint as the fracts.

 

And, interestingly enough, my friend and I preferred M82 in my ES127ED to his C11 just a few weeks ago.  It wasn't as bright... but it was certainly sharper and more aesthetically pleasing.   Although we had been viewing for 90 minutes, his C11 just couldnt acclimate fast enough to the changing temps.

 

I used to be a large aperture guy (16 to 20 inch dobs)... until Daniel Mounsey sold me a Tak FC100DF ... 4 inches of magic....  Now, due to my length of viewing time and lack of patience for acclamation, fracts are my most used scopes by far.


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#459 CHASLX200

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Posted 03 February 2018 - 11:32 AM

Hello Friends,

 

I am not nearly as smart or knowledgeable as many of you out here.  In fact, I am amazed by many of the posts here.  2 friends of mine who are brilliant indicated that I should concentrate on what I see in the eyepiece.  

 

I own 5 scopes... certainly more than I need.  2 cats (Mewlon 250 and C8) and 3 fracts (ES8OED, ES127ED, and  Tak FC100DF).  Here is what I can tell you from my perspective ... taking the science and math out of the equation ... only speaking through the emotions of my personal experience at the eyepiece. 

 

First... Fracts give routinely more pleasing views for me personally .  Second... The quality of optics in the Tak really do make a difference over the ES fracts.  Third... I find myself regularly willing to see less detail in favor of quality of image through fracts.  I will state that most of my viewing sessions are 2 to 3 hours, and I am often not patient to let the cat properly acclimate.

 

Now... when acclimated and seeing is good, my Mewlon produces jaw dropping images.  My best view of the Orion Nebula is through the Mewlon.  But... I had to let the Mewlon cool for 2 hours... I used my fract for the 2 hours patiently waiting...  And, even then, stars are not quite as pinpoint as the fracts.

 

And, interestingly enough, my friend and I preferred M82 in my ES127ED to his C11 just a few weeks ago.  It wasn't as bright... but it was certainly sharper and more aesthetically pleasing.   Although we had been viewing for 90 minutes, his C11 just couldnt acclimate fast enough to the changing temps.

 

I used to be a large aperture guy (16 to 20 inch dobs)... until Daniel Mounsey sold me a Tak FC100DF ... 4 inches of magic....  Now, due to my length of viewing time and lack of patience for acclamation, fracts are my most used scopes by far.

You can't beat the Taks. None of the cheaper APO will come close. And no mass made SCT's will come close to a well made Newt or high end Mak or SCT. But one out of a million SCT's do come kinda close. But finding one is the hard part.



#460 sonny.barile

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Posted 08 February 2018 - 07:34 PM

Wow!    This finally died down......lol


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#461 Daniel Mounsey

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Posted 09 February 2018 - 09:13 AM

This was from the valley with some slight winds so seeing over all was about 2-3 out of 5. We viewed last night through mikonas 8” SCT and my friend Darren’s 11” SCT. I had a 60mm frac since I was on a time crunch then Mike set up his 4” ED. Stars in the Trapezium in the SCT’s appeared like Pickering 3-4 while the little fracs looked more like 5-6. Certainly this is to be expected.

 

http://www.damianpea...m/pickering.htm

 

Since I was looking at stars at high magnification or doing widefield, I’m normally using fracs, but Hinds Crimson Star was fun to see in Darren’s 11” SCT and was Coke-can red. Also M42 looked bright and more detailed in the SCT’s particularly the darker structures. In the 60mm, mikona and I could make out dark regions much farther out all at once, better in the little 60mm. mikona got to see Collinder 70’s braided necklace the best in the little 60mm. All these scope worked wonderfully while looking at the various types of target each are suited for. NGC1907 and 2158 looked best in the 11”.

 

Btw, just to put this into perspective. To spend the time I need, setting up my open tube 10” DK, the  moons of Jupiter which are about mags 6-7 would need to appear as still as Pickering 8 or 9 to be considered a night the telescope deserves and needs to perform. Observers who take these scopes in bad seeing like last night are never going to see what any good reflective optical system can do like that.

 

Everything including the optical tube need to be as absolutely still as possible. Only then will great optical systems reveal ultrafine details. On those kinds of nights there are so many bands, details and colors on Jupiter it’s impossible to sketch it all. Even the polar hoods break up. 


Edited by Daniel Mounsey, 09 February 2018 - 09:32 AM.


#462 Lola Bruce

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Posted 09 February 2018 - 03:51 PM

I love my Celestron CPC 800 (C8). It is a gem of a scope package and happened to be the scope I was using on the best seeing night of my life. That was over five years ago, nights that good just don't happen often. I now own two Taks a 102 and Mewlon 250. Are they better, yes. Is the Celestron junk in comparison, no the Celestron compares very well but the Taks are just that little bit better. For reference the quality of seeing for any given night makes way more difference than the brand name on my tube. Now if only I could have another one of those majic nights with my TAK's.

Earlier it was asked who loves their CAT, well I do hand up.

Bruce


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