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

William Optics Flat6A III Nikon D5600 Equipment Flattener DSLR
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Lukas Šalkauskas avatar
Lukas Šalkauskas avatar
Hello there,

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

firstlightopticsoptics suggests 7.1mm:
https://www.firstlightoptics.com/reducersflatteners/william-optics-adjustable-flat6a-iii-08x-reducer-flattener.html

williamoptics suggests 9.1mm:
https://williamoptics.com/2019-all-new-adjustable-flat6aiii-t-mount-not-included

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)?
matthew.maclean avatar
matthew.maclean avatar
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- williamoptics.com ) 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!
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Lukas Šalkauskas avatar
Lukas Šalkauskas avatar
Just got an reply from WO:
DEar Lukas.Flattaner settings should be - 9.1mm
Regards,
Tim
WO
Matthew you were correct

I wonder is there any software I could use and verify the spacing is correct by giving my sample image?
matthew.maclean avatar
matthew.maclean avatar
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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