DSO's at F/10 with a 200mm SCT and 294MC Pro

[DRCORTEX]

Hi All,

I have been imaging at F/6.3 with my C8, and thought I might jump off the deepend and have a go at something like the Pinwheel Galaxy at F/10. My image train works fine at F/6.3 with filter drawer, and I use a 60mm Orion and 120MM for guiding.

I read somewhere that the back focus length, is only required when using a focal reducer ?. If that is indeed the case, could I simply attach my SCT to T Adapter, then my filter drawer and camera ?

Cheers,

Lance

[AdamJL]

Hi Lance. I can’t speak for reflectors for but for refractors, back focus is a requirement with or without a reducer.

At least I’m my (limited) experience, if you’re off by a mm, it will have a big impact on the final image

[DRCORTEX]

I thought as much, I use 105mm at F/6.3, The Celestron site says 5" ( 127mm ) at F/10.

I really doubted what I had read, but who knows. For planetary at F/20, I simply use a barlow, straight into the the visual back.

Cheers,

Lance

[floyd_2]

Interestingly, there seems to be two camps re back focus using a Celestron f/6.3 reducer. Mostly it seems to be 105mm, however there is mention of 85mm as well. For example, Bintel states that the back focus is 85mm for this reducer.

I'm using 85mm with the Celestron f/6.3 reducer on a C9.25 after much research and it seems to be perfect. I'm guessing that the scope is forgiving, but the results seem good. Mind you, I'm in the EAA camp using a Sony A6000 so your mileage may vary.

[The_bluester]

Regards using it without the reducer, to an extent it is just a matter of plonk the camera on, find focus and go. Apparently the way the two mirrors interact means that as you move the primary mirror up and down the cell, the effective focal length changes slightly, but I never noticed any significant difference.

I eventually found the reduction in coma with the reducer more valuable than the extra focal length without it so most of the imaging I did prior to selling my C925 was with the reducer.