TheSkySearchers

Lady Fraktor wrote: ↑Mon Sep 16, 2019 7:13 pm For some reason my reply disappeared...
The CGE dovetail is a Losmandy style though slightly different.
Look at posting #6 for a diagram of how it will fit in the plate.
https://www.cloudynights.com/topic/4995 ... ce-or-not/

Bigzmey wrote: ↑Mon Sep 16, 2019 7:08 pm Stepping up to 8" is definitely a good move. You will go deeper on DSOs with still compact and lightweight scope. HD or vanilla for visual, I been agonizing over this for a while. It seems that opinions are fairly split on forums. Some saying "little improvement not worth the price" and some comparing HD vs plain to APO vs achro in refractors.

For myself, I figured out that if I ever need to replace my plain 8" SCT I would go with plain 9.25" SCT. It has different optics which delivers image quality closer to HD and gather ~30% more light than 8" SCT.

As for the focuser shift it does come from the fact that you are moving primary mirror while focusing. It seems that extend is vary from OTA to OTA. My newer OTA has hardly any. If it is an issue I would just get a helical focuser for the diagonal for fine focus adjustments.

Lady Fraktor wrote: ↑Mon Sep 16, 2019 7:18 pm To help get rid of the focuser shift focus towards the object and if you go to far bring the focus further back and focus towards again.
It helps take up some of the shift while focusing.

smp wrote: ↑Mon Sep 16, 2019 7:43 pm

Bigzmey wrote: ↑Mon Sep 16, 2019 7:08 pm Stepping up to 8" is definitely a good move. You will go deeper on DSOs with still compact and lightweight scope. HD or vanilla for visual, I been agonizing over this for a while. It seems that opinions are fairly split on forums. Some saying "little improvement not worth the price" and some comparing HD vs plain to APO vs achro in refractors.

For myself, I figured out that if I ever need to replace my plain 8" SCT I would go with plain 9.25" SCT. It has different optics which delivers image quality closer to HD and gather ~30% more light than 8" SCT.

As for the focuser shift it does come from the fact that you are moving primary mirror while focusing. It seems that extend is vary from OTA to OTA. My newer OTA has hardly any. If it is an issue I would just get a helical focuser for the diagonal for fine focus adjustments.

Thanks very much, Andrey! Much appreciated. Oh, no! Now you've given me even more to agonize about!

smp

stewe wrote: ↑Mon Sep 16, 2019 9:27 pm

smp wrote: ↑Mon Sep 16, 2019 7:43 pm

Bigzmey wrote: ↑Mon Sep 16, 2019 7:08 pm Stepping up to 8" is definitely a good move. You will go deeper on DSOs with still compact and lightweight scope. HD or vanilla for visual, I been agonizing over this for a while. It seems that opinions are fairly split on forums. Some saying "little improvement not worth the price" and some comparing HD vs plain to APO vs achro in refractors.

For myself, I figured out that if I ever need to replace my plain 8" SCT I would go with plain 9.25" SCT. It has different optics which delivers image quality closer to HD and gather ~30% more light than 8" SCT.

As for the focuser shift it does come from the fact that you are moving primary mirror while focusing. It seems that extend is vary from OTA to OTA. My newer OTA has hardly any. If it is an issue I would just get a helical focuser for the diagonal for fine focus adjustments.

Thanks very much, Andrey! Much appreciated. Oh, no! Now you've given me even more to agonize about!

smp

Hi there,

I agonized about the same thing some time ago, and after reading way too many posts about comparisons, I decided to acquire a C9.25 for visual instead of the C8 SCT or C8 Edge. If I also wanted to do astrophotography (at f/2), I would have opted for the 8" Edge, mainly because it is lighter (and its field is somewhat flatter). I have to admit that I have never had the chance to compare the two scopes side by side, but experts say that there is extremely subtle if any difference in the image quality visually (apart from the brighter image of the C9). Still, I can tell you that I did not regret my decision: the C9 is a superb scope, and for visual, aperture is (almost) always a winner. As a former 6"-scope owner, I am still amazed every time to see how GCs are resolved into thousands of pinpoint stars. The Moon and the planets are also amazing if the scope is well collimated and the seeing is good. I read that Damian Peach, a renown planetary astrophotographer uses a C9 after trying many different scopes, you might want to check out his blog to read more about the C9: http://www.damianpeach.com/c925review.htm . I use my C9 with an AVX and it is just fine for visual observation. I solved the (slight) mirror shift issue by attaching a Skywatcher dual-speed Crayford focuser to the SCT thread at the back of the scope. It costs a fraction of the price of the Feathertouch. Also, with its fine focuser, mount vibrations due to focusing diminished almost entirely. NB. the focuser adds some focal length, and the C9 effectively becomes an f/11 scope.

Happy contemplating!

Bigzmey wrote: ↑Mon Sep 16, 2019 10:18 pm
Good to hear Steve! Even with my 8" SCT getting 9.25" is tempting. Sharper optics and a bit more light in still manageable package. Going from 6" to 9.25" is no brainier. Unless you can handle 11". Used prices of 9.25" and 11" are about the same. 11" gathers twice more light than 8", so more logical choice for me. But 30lb weight of 11" is a bit more than I like to handle and I need to get a beefier mount. 9.25" has sharper optics, weigh ~20lb (my mounts can handle it) but gathers only ~30% more of light. Decisions, decisions.