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Refractor vs SCT

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#76 Ed Holland

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Posted 24 September 2014 - 09:33 PM

What we have is diversity. That can be a wonderful thing, along with an incredible variety of optical instruments such as we see today. Oddly enough, this includes SCTs and refractors.



#77 Stephen Kennedy

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Posted 24 September 2014 - 11:25 PM

I found video astronomy very useful in taking really spectacular photos of the Moon, Saturn and Jupiter.  Attaching a digital camera to my 210 mm F/7 Newtonian on a tracking GEM I took about 10 second videos of these objects and then used the free online program Registax to process the video into a single picture.  The one of Saturn in particular looked like something taken by the HST. 



#78 AnakChan

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Posted 25 September 2014 - 01:18 AM

In the past month I've been researching and pondering about what scope to move to (from my VC200L) and I've looked at refractors (Vixen AX103S up to the Takahashi TOA-130NS), SCTs (9.25" & 11" EdgeHD), Cass & DK variants (VMC260L, µ-210, µ-250) and it's been a dilemma. After much reading, much thinking, much playing around with some simulations (this is a cool site BTW) I think I kinda feel more comfortable in the 2000-3000mm focal length range and it seems primarily the µ-250 gives the benefit of an APO-like contrasty image yet the light gathering capability of a non-refractor. Although I'm still looking at the VMC260L as an option, I'm concerned it's less contrasty than the µ-250 would just be larger but similar to my VC200L.

But this lead me to another (basic) question however of why refractors are popular with planetary (may it be physical or nebula) esp if their focal lengths are shorter than the SCTs/Cass/reflectors? In other words, this is a question of "short" focal length/high powered eyepiece vs long focal length/mid powered eyepiece. Is it because large primaries are more susceptible to atmospheric conditions than smaller primaries?


Edited by AnakChan, 25 September 2014 - 01:23 AM.


#79 rmollise

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Posted 25 September 2014 - 08:23 AM

Sky and Telescope ran their first article on video astronomy around 1966 or so... hasn't caught on yet.  Glen


You forgot the :)

Or you've never been to Chiefland. :lol:

#80 rmollise

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Posted 25 September 2014 - 08:27 AM

But this lead me to another (basic) question however of why refractors are popular with planetary (may it be physical or nebula) esp if their focal lengths are shorter than the SCTs/Cass/reflectors? In other words, this is a question of "short" focal length/high powered eyepiece vs long focal length/mid powered eyepiece. Is it because large primaries are more susceptible to atmospheric conditions than smaller primaries?


Some people believe a refractor gives the edge on contrast. Other people just like the way images look in a refractor. And some just like refractors, period.

It's not seeing. Even under the worst conditions, seeing almost always settles down momentarily, and when it does you will see more with more aperture. By the end of the evening, you will have seen more details with the larger scope, if not in the form of images that are as aesthetically pleasing as those in the smaller refractor.

So, you should always choose a larger CAT vice a smaller refractor? Yes, all things being equal. But all things are not always equal. ;)


Edited by rmollise, 25 September 2014 - 08:28 AM.


#81 Rick Huber

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Posted 25 September 2014 - 09:48 AM

This entire thread is basically like two anchors arguing who will hit bottom first.......... :confused:



#82 Sarkikos

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Posted 25 September 2014 - 09:54 AM

You're pulling my chain...

 

:grin:

Mike



#83 dpippel

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Posted 25 September 2014 - 10:08 AM

Ahoy matey! Arrrrrrrr...



#84 MB_PL

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Posted 25 September 2014 - 10:30 AM

And I was thinking about getting a 120ED!  One advantage I could see to the 120ED would be quicker cool-down time, especially in the cold months.  Maybe a 120ED would not be so bad for a winter planet/lunar scope?

 

Mike

Mike,

With a little bit of planning and/or a CAT cooler, cool-down is not much of a problem, at least for me, and in the winter I effectively get a temperature difference of approx. 40 degrees Celsius (from a room that is + 20 C to my balcony where the temperature will be approx. - 20 C). On weekdays, I set up the scope in the early evening (at approx. 7 p.m.) and observe anytime from 11 p.m. to 6 a.m. This would be my procedure regardless of the optical design of the scope I’d be using.
 

One important issue IMHO is focal length - the longer the better, as you will want to binoview and the longer the effective focal length of the system, the longer the focal length of the eyepieces you’ll be using (preferably goods orthos or plossles), which directly translates into more eye relief, which in turn means less fogging.
 

There are also other practical considerations, which speak in favour of a larger aperture, such as image scale, maximum useful magnification, exit pupil size at a given mag (I find floaters bothersome at exit pupils of less than 0.7mm).
 

I had also toyed with the idea of moving down to a 130 mm Apo. This would have given me less high contract detail, but pretty much the same amount of low contrast detail, less vulnerability to poor seeing and what some might call a more aesthetically pleasing view. In the end, I decided to stay with the C8 due to the issues mentioned above.
 

Clear skies


Edited by MB_PL, 25 September 2014 - 10:37 AM.


#85 Sarkikos

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Posted 25 September 2014 - 10:42 AM

I don't think a Cat Cooler would work with an EdgeHD telescope.  Also, I don't have a private area where I can set a scope out for hours unattended.  Well, I have a porch, but that is more-or-less open to the public.

 

I have enjoyed binoviewing planet/lunar, but so far only in my 8" and 10" Dobs. It is a possibility for my EdgeHD 8".  I wouldn't want to insist on binoviewing for the quick grab-n-go viewing that I'd intend for a refractor in the winter months.

 

Mike


Edited by Sarkikos, 25 September 2014 - 10:47 AM.


#86 MB_PL

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Posted 25 September 2014 - 11:00 AM

If you're looking for a grab-n-go/short-session set-up, then a 5" ED or APO does fit the bill :) (as mentioned in the last paragraph of my previous post).

 

Cheers



#87 Sarkikos

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Posted 25 September 2014 - 11:04 AM

:waytogo:



#88 StarWolf57

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Posted 25 September 2014 - 11:08 AM

Honestly, I can't imagine not having a small refractor if you have a big CAT. The two complement each other so well.

 

Back to the topic at hand, comparing a 120mm refractor to a C8 is a tough call. I was in the same position a month ago when I was looking for something to complement my C14. I was lucky in that I was able to compare both side by side at a star party. For me, the C8 was the hands down winner and I bought the Edge. The images were brighter and had more resolution. The FOV is less which could be an issue for some and there are still cool down issues with the C8 (although nowhere near as bad as the C14) so setup is faster with the 120. Imaging with a 120 is probably a little easier too because of the reduced FL, if that's your thing. There really is no "best", only what's best for your needs. I wouldn't be surprised if a 120 eventually made its way into my collection at some point :)



#89 Glen A W

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Posted 25 September 2014 - 11:13 AM

This entire thread is basically like two anchors arguing who will hit bottom first.......... :confused:

 

Mine will, it's smarter than yours!

 

Love,

Glen



#90 rmollise

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Posted 25 September 2014 - 11:44 AM

I don't think a Cat Cooler would work with an EdgeHD telescope.  
 
Mike

 
You don't need one for an Edge. It has vents, and, if needed, fans can be purchased for those vents.
 
http://www.deepspace..._4243_9331.html
 
;)


Edited by rmollise, 25 September 2014 - 11:44 AM.


#91 Sarkikos

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Posted 25 September 2014 - 11:47 AM

For me, the C8 was the hands down winner and I bought the Edge. The images were brighter and had more resolution. The FOV is less which could be an issue for some and there are still cool down issues with the C8 (although nowhere near as bad as the C14) so setup is faster with the 120. 

The TFOV is not really so bad for an SCT.  I was able to see both clusters in the Double Cluster with a Meade 5k UWA 24, and they were both very nicely framed with my Titan-II 40.  Sharp edge to edge and no appreciable vignetting.  This was without a reducer or FF/FR. 

 

Mike



#92 Sarkikos

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Posted 25 September 2014 - 11:48 AM

 

I don't think a Cat Cooler would work with an EdgeHD telescope.  
 
Mike

 
You don't need one for an Edge. It has vents, and, if needed, fans can be purchased for those vents.
 
http://www.deepspace..._4243_9331.html
 
;)

 

Yep, of course I knew about the vents, but wasn't sure if fans were available for them. Thanks.

 

Mike



#93 WesC

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Posted 25 September 2014 - 11:58 AM

 

For me, the C8 was the hands down winner and I bought the Edge. The images were brighter and had more resolution. The FOV is less which could be an issue for some and there are still cool down issues with the C8 (although nowhere near as bad as the C14) so setup is faster with the 120. 

The TFOV is not really so bad for an SCT.  I was able to see both clusters in the Double Cluster with a Meade 5k UWA 24, and they were both very nicely framed with my Titan-II 40.  Sharp edge to edge and no appreciable vignetting.  This was without a reducer or FF/FR. 

 

Mike

 

 

I disagree... in my Edge 11 with a 31mm Nagler I just barely miss out on fully framing the double cluster, I can't see larger structures like M31 and M45. The best I get is .91-degrees. But I can split the heck out of Delta Cygni!

 

In my SV105 with the same eyepiece I can frame all of that well, even the entire sword of Orion, or the Lagoon and Triffid nebulas becuase I get 4.6 degrees!  But Delta Cyngi's companion star is nearly lost in the first diffraction ring.

 

Complimentary brothuz!!!! :waytogo:



#94 ensign

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Posted 25 September 2014 - 12:00 PM

Right tool for the right job. The SCT has the edge with light gathering power, which is usually your numero uno requirement. However, a smaller APO can produce incredible views. You may not go as deep as with a C8, but the trip will be well worth it. And an 80 - 100mm APO can produce the tack-sharp wide-field images an SCT just can't deliver.

 

I'm sorry, y'all; I gotta be honest...the older I get, the more I appreciate my small refractors. Not that I will ever stop using a C8. ;)

 

The solution? "Both." :lol:

That's my experience too.  Sometimes I want to have a refractor session, sometimes a C9.25 session.  Each gives you a different perspective.



#95 Sarkikos

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Posted 25 September 2014 - 12:50 PM

 

 

I don't think a Cat Cooler would work with an EdgeHD telescope.  
 
Mike

 
You don't need one for an Edge. It has vents, and, if needed, fans can be purchased for those vents.
 
http://www.deepspace..._4243_9331.html
 
;)

 

Yep, of course I knew about the vents, but wasn't sure if fans were available for them. Thanks.

 

Mike

 

 

After reading the online PDF instructions, I have second thoughts about this. http://www.deepspaceproducts.com/docs/TEMPest_Instructions2-0.pdf

 

 Installing the fans requires threading a power wire through the back of the OTA.  Sounds like a dangerous mission.  I don't think I have the nerves for it.

 

Mike


Edited by Sarkikos, 25 September 2014 - 12:51 PM.


#96 dpippel

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Posted 25 September 2014 - 01:05 PM

It's really a no-brainer Mike. The TEMP-est fans are a snap to install and work great.



#97 Sarkikos

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Posted 25 September 2014 - 01:15 PM

Well, not exactly plug-n-play if you have to thread a wire from a hole on one side of the OTA, under the mirror and then out a hole on the other side.  A walk in the park would be much easier.

 

Mike



#98 dpippel

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Posted 25 September 2014 - 01:16 PM

Took me 10 minutes. A walk in the park would take significantly more time. ;)



#99 Sarkikos

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Posted 25 September 2014 - 01:31 PM

You don't know how fast I walk! 

 

:grin:

Mike



#100 dpippel

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Posted 25 September 2014 - 01:32 PM

:roflmao:




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