Spacing of a Atik 16hr

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Hi Guys,not too sure if this is in the right section but here goes.. I have an old atik 16hr and using it with a William optics ZS80D...ive tried a few times  with different spacing and can achieve focus with almost all the different spacing.. the further out (longer) I go the  star looks huge...the shorter the star looks smaller but using a mask I can achieve focus..my question is what's the right distance from the reducer to sensor and should I be using the extension..i need it to focus a DSLR.. anyone with the same setup? The camera has the same chip as a 314 so I'm told..

[newbie alert]

Sorted now thanks