Spacing question

[Black Knight]

Spacing is not something I've really had to worry about in the past, imaging with a DSLR only, but now I have a new shiny red round thing (and filter wheel), I guess it is something I'm going to have to get to grips with.

My question is, how do I tell if the spacing is out? Does it show in my images in some way, for example, like not being able to focus correctly? Or does it manifest in another way?

[Uranium235]

When you mention spacing, are you using a corrector/reducer? If not, then there is no spacing as such - just bung it on the focuser (maybe a 2" extension will be required, same as DSLR).

If you are using a corrector/reducer, then the correct(ish) spacing is important. You can check whether its working by inspecting the corners of your subs, if you can see coma or distorted stars then its not right. When testing for flatness/roundness its best to work in a good starfield (anything in Cygnus will do), be careful though - getting flat images and round stars can become a bit of an obsession!

Forgot to add, CCDs are much less forgiving of bad focus. The great thing now is that you can pop your b-mask on and zoom right into the diffraction pattern using artemis capture (0.5s, 1x1 bin, sub framed) to get a really close look at it.

[Black Knight]

When you mention spacing, are you using a corrector/reducer? If not, then there is no spacing as such - just bung it on the focuser (maybe a 2" extension will be required, same as DSLR).

If you are using a corrector/reducer, then the correct(ish) spacing is important. You can check whether its working by inspecting the corners of your subs, if you can see coma or distorted stars then its not right. When testing for flatness/roundness its best to work in a good starfield (anything in Cygnus will do), be careful though - getting flat images and round stars can become a bit of an obsession!

Forgot to add, CCDs are much less forgiving of bad focus. The great thing now is that you can pop your b-mask on and zoom right into the diffraction pattern (0.5s, 1x1 bin, sub framed) to get a really close look at it.

I'll be using the Skywatcher coma corrector on my Quattro, and the Skywatcher 0.85 reducer/flattener on my ED80. So I need to be looking for coma and distorted stars in the corners of my subs, got it! . I'll try and remember what your tip about using a b-mask and subframes as well.

Ta muchly