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WO GT 71 II + Flat6A III + Nikon D5600 Spacing question

25 Mar, 2020 19:50
Hello there,

I have a problem of finding out correct spacing on Flat6A III for my Nikon D5600.

firstlightopticsoptics suggests 7.1mm:

williamoptics suggests 9.1mm:

Which one is correct and is there any ways to check if its correct 100%(I can get focus with bahtinov mask by using  telescope focuser, should I see something strange by using bahtinov mask if the spacing is not correct)?
Edited 25 Mar, 2020 19:51
25 Mar, 2020 21:48
I had already replied to your previous thread earlier today also. I assume WO has the correct spacing since they designed it, but I would suggest you email them directly ( wo -AT- ) and get them to verify the correct spacing? They do seem to answer quickly the couple times I have emailed them.

Then post their answer here so we all have the benefit of the right value? I think my images look reasonable in the corners in general, but I’d like to know if I’m 2mm off too!
26 Mar, 2020 05:57
Just got an reply from WO:
DEar Lukas.Flattaner settings should be - 9.1mm
Matthew you were correct smile

I wonder is there any software I could use and verify the spacing is correct by giving my sample image?
26 Mar, 2020 09:45
I do not know of any software, but I think that you could probably use the Bahtinov mask to at least check the flatness next time you set it up - if you put a bright star in the center of the field, line up the diffraction spikes, and then rotate that star to each of the four corners, the spikes should stay lined up if the field is completely in focus. I bet it will be close.
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