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How to achieve 'perfectly flat' field with WO Z61A field flattener and DSLR?

Nikon D5300 Equipment Flattener Coma
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Photon_Collector avatar
Photon_Collector avatar
Hi all, 

I just bought a Zenithstar 61 along with a field flattener (Flat 61A) and tried imaging last night with my Nikon D5300 DSLR. I was able to get perfect focus with a bhatinov mask but when looking at subs there was a lot of coma/stretching of the stars immediately outside the center of the image. 

How do I get things in focus and achieve a flat field? It seems like I have to choose one or the other with this set up...

See example image below (Bode's galaxy and Cigar galaxy were the DSOs)...

Well Written Engaging
Dan Vranic avatar
Dan Vranic avatar
That flattener is the wrong distance away from the sensor.

If you're able to move it forward or backward, use trial and error to find the correct spacing.
Well Written Concise
Photon_Collector avatar
Photon_Collector avatar
Dan Vranic:
That flattener is the wrong distance away from the sensor.

If you're able to move it forward or backward, use trial and error to find the correct spacing.

Thanks, but if I move it forward or backwards then I get out of focus. I'm just confused as to how to find the right spacing while maintaining focus.
Well Written
Dan Vranic avatar
Dan Vranic avatar
Refocus after every adjustment. 1mm will not throw it out of focus.
Jens avatar
Jens avatar
Hey, I hope I'm not to late. So you have a scale on the Flat 61, you have to put your adjustment ring on 12.9 to get a perfectly flat field. They mentioned it on their website. I have the same setup and it works perfectly for me 

https://williamoptics.com/new-adjustable-flat61-for-z61