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Equipment Discussions >> Cats & Casses

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Classic8
professor emeritus


Reged: 04/12/06

Loc: Naperville, IL, USA
Re: SC 6 "vs. 5" Mak? new [Re: rmollise]
      #5820299 - 04/24/13 05:22 PM

Quote:

Quote:

The SCT may be easier to collimate, but aren't you more likely to have to collimate it, or have to collimate it more often? And when you do collimate it, is it as well collimated as it was when it came from the factory?




Not at all. When collimated properly they hold that collimation very well...as in "months or even years."




Just seems like most of the time in SCTs the image seems "soft" and it's hard to believe that so many people have telescopes that are not collimated, if they hold their collimation that well.


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KerryR
Carpal Tunnel
*****

Reged: 12/05/07

Loc: SW Michigan
Re: SC 6 "vs. 5" Mak? new [Re: Classic8]
      #5821699 - 04/25/13 10:03 AM

Quote:

Quote:

Quote:

The SCT may be easier to collimate, but aren't you more likely to have to collimate it, or have to collimate it more often? And when you do collimate it, is it as well collimated as it was when it came from the factory?




Not at all. When collimated properly they hold that collimation very well...as in "months or even years."




Just seems like most of the time in SCTs the image seems "soft" and it's hard to believe that so many people have telescopes that are not collimated, if they hold their collimation that well.




I suspect most folks don't tighten the collimation screws sufficiently. It's also often commented that scopes with Bob's Knobs don't hold collimation as well. It is surmised that this is because sufficient tightness is difficult to achieve with the thumb wheels.

Soft images in SCT's are most often due to a lack of thermal equilibrium in the tube, assuming decent seeing-- the top of the tube looses heat to the sky faster than the lower side, so there's a constant thermal battle inside the tube. Same thing happens in metal tubed Newts. Active venting helps a ton, as does thermal isolation of the interior space.

Edited by KerryR (04/25/13 10:03 AM)


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rmollise
Postmaster
*****

Reged: 07/06/07

Re: SC 6 "vs. 5" Mak? [Re: Classic8]
      #5821720 - 04/25/13 10:12 AM

Quote:


Just seems like most of the time in SCTs the image seems "soft" and it's hard to believe that so many people have telescopes that are not collimated, if they hold their collimation that well.





It may be hard for you to believe, but that is indeed just the way it is. The problem with collimation is that it's often not done or not done correctly. Over the years, people have--for no reason--been AFRAID to collimate their SCTs.

If an SCT is correctly collimated it will most assuredly hold that collimation, and its images will most assuredly not be "soft."


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Classic8
professor emeritus


Reged: 04/12/06

Loc: Naperville, IL, USA
Re: SC 6 "vs. 5" Mak? new [Re: rmollise]
      #5822464 - 04/25/13 03:59 PM

Quote:

Quote:


Just seems like most of the time in SCTs the image seems "soft" and it's hard to believe that so many people have telescopes that are not collimated, if they hold their collimation that well.





It may be hard for you to believe, but that is indeed just the way it is. The problem with collimation is that it's often not done or not done correctly. Over the years, people have--for no reason--been AFRAID to collimate their SCTs.

If an SCT is correctly collimated it will most assuredly hold that collimation, and its images will most assuredly not be "soft."




What about the comment above that with Bob's Knobs the collimation screws may not be tightened enough? I had heard that before....also, you can't collimate it until the tube has completely cooled down, correct? It would be easy to think it has cooled down completely when it really hasn't.


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rmollise
Postmaster
*****

Reged: 07/06/07

Re: SC 6 "vs. 5" Mak? new [Re: Classic8]
      #5822573 - 04/25/13 04:49 PM

Quote:



What about the comment above that with Bob's Knobs the collimation screws may not be tightened enough? I had heard that before....also, you can't collimate it until the tube has completely cooled down, correct? It would be easy to think it has cooled down completely when it really hasn't.




That has not been my experience with Bob's Knobs. Quite the opposite as a matter of fact. And I've had 'em on my Ultima 8 OTA for at least a decade...


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hottr6
Carpal Tunnel
*****

Reged: 06/28/09

Loc: 7,500', Magdalena Mtns, NM
Re: SC 6 "vs. 5" Mak? new [Re: curiosidad]
      #5822780 - 04/25/13 06:45 PM

Cannot comment on SCT vs MCT, but I am with others when they suggest "choose aperture".

My 6" Newt and MCT ALWAYS trump my 5" Newt on every object I have ever compared them with. The difference, e.g., is viewing M13 as a blob, or 100+ resolved stars.

The main reason to consider a 5" over a 6" is that the 6"-class demand more of a mount than the 5"-class. 5" cats will also cool faster than a 6".


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DJCalma
member


Reged: 01/17/13

Loc: Northern California
Re: SC 6 "vs. 5" Mak? new [Re: hottr6]
      #5823351 - 04/25/13 11:11 PM

My 5" Mak is an awesome scope. Beat a C5 in contrast and resolution, but not sure if the newer C6 would prove much better or not. Also tested my little guy against a couple 4" apos and it was closer than I thought.
I love the package size. My dream scope is a 5" Mak with the light gathering power and resolution of a 24". Yeah, I know all about the laws of physics, but I can dream.


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