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Questions for the optics perfectionists

Started by Wolfstar, 09/28/2018 02:02AM
Posted 09/28/2018 02:02AM | Edited 09/28/2018 02:14AM Opening Post
So in this thread or another I posted that I picked up a very little used Celestron Celestar C8. I ended up de-forking the optical tube so it can ride on a Skywatcher EQ6 Pro. I've used the scope quite a few times, and compared to other C8s that I've looked through it's probably one of the best that I've experienced. 

This is a completely stock optical tube. I have thought about doing hyperstar imaging with this scope, so I'm wondering how much of an improvement I can get in actual image quality by replacing the focusing mechanism. I have access to a hackerspace with any of the machining tools I could ever want to create a zero image shift mechanism for the primary mirror.

My question is, is it worth going through that trouble to create a zero image shift focusing mechanism for image quality? 

I haven't been on Astromart in a long time. Lots of changes in my life with losing my wife, so I'm trying to get back to my roots with the things I love to do. I would love any feedback to give me an idea as to how I should approach this..

It is what it is...
Posted 09/29/2018 07:40PM #1
Very sorry to hear about your wife.....

As to the mod you are talking about. It will keep you out of the bars, go for it smile

20" MidnighTelescopes f/5
8" f/16 Muffoletto Achro
Meade 6" AR6 f/8.0 Achro
Celestron C11
Parallax PI250 10" F/5 Newt
Vixen FL102S,NA140SS,R200SS
80mm Stellarvue Nighthawk with WO APOupgrade lens, 90mm f/16.67 Parallax Achro
LXD75/LX200, Mini-tower, GP-DX, CG5 ASGT, LXD650, GM-8, G11, GM-100, GM-150EX, GM-200 and a Gemini G40
4" portable AP convertable 44" or 70" pier
Stellarvue M7 Alt-Az, TSL7 Pier/Tripod
12.5" f/5 MidnighTelescopes DOB Swayze optics
Statham GA
Posted 09/30/2018 09:57PM #2
Originally Posted by Tony Aguire

I have access to a hackerspace with any of the machining tools I could ever want to create a zero image shift mechanism for the primary mirror.

My question is, is it worth going through that trouble to create a zero image shift focusing mechanism for image quality? 
Hi Tony,

Sorry for your loss. Forgive me if this old guy is misunderstanding, but wouldn't an accessory Crayford focuser accomplish zero image shift? 

Rebuilding the existing focuser mechanism is a serious design challenge. The original Celestron 8" Blue/White's came with a belt driven zero image shift focusing mechanism. It's quite a bit more complicated and requires precision machining that could be beyond the skill set of a hobby machinist. You might want to check out Robert Piekiel's "Celestron The Early Years" CD for pics of this focusing mechanism.

Forgive my ignorance but I'm confused about the "image quality" associated with a focusing mechanism.

Keith (Scopejunkie)

Scopejunkie



Restored Celestron C-14 with recirculating cooling
Celestron 180mm F/15 Maksutov
Posted 09/30/2018 10:21PM #3
Originally Posted by Keith Lawson

Hi Tony,

Sorry for your loss. Forgive me if this old guy is misunderstanding, but wouldn't an accessory Crayford focuser accomplish zero image shift? 

Rebuilding the existing focuser mechanism is a serious design challenge. The original Celestron 8" Blue/White's came with a belt driven zero image shift focusing mechanism. It's quite a bit more complicated and requires precision machining that could be beyond the skill set of a hobby machinist. You might want to check out Robert Piekiel's "Celestron The Early Years" CD for pics of this focusing mechanism.

Forgive my ignorance but I'm confused about the "image quality" associated with a focusing mechanism.

Keith (Scopejunkie)

So my thinking is to do hyperstar imaging with it, to that end the crayford focuser option is not viable. I've actually had a crayford focuser on my old C8. I really appreciated how well it worked, but I'm thinking if I could somehow replicate the design characteristics of a crayford into the movable mirror aspect of the C8, that's kind of where I'm trying to go. I know I'm going to have to machine a new rear cell for this project, and I've actually got quite a bit of mechanical knowledge and a couple of machinist /engineer friends that work over at the hackerspace to help me come together with something. They you Kieth, I appreciate your knowledge and insight on this.

It is what it is...
Posted 09/30/2018 10:29PM #4
A Crayford focusing mechanism for the primary mirror would be something to see! Let us know if you go this direction and please post your progress. 

Keith (Scopejunkie)

Scopejunkie



Restored Celestron C-14 with recirculating cooling
Celestron 180mm F/15 Maksutov