SVBONYSV209 Field Flattener, 0.8X Focal Reducer, Corrects The Field Curvature and a Wider Field of View, Telescope Accessories for SV550 122mm APO Refractor Telescope

Personally I did not notice any difference in resolution at the edge of the field. Both uses of direct capture and field flattener capture produced the same result.

If you want to delve into Astro photography, this is a must have. It gives you a flat field for round stars across the frame without sacrificing focal length. If you want to use the scope for visual only, this is still a must have. It’s hard to describe the difference it makes to have the full image flat but it’s like the difference between looking at fish in an aquarium and on a 4K TV. The quality of what you’re seeing isn’t better, it’s just different on how it gets to your eyes.Great product!!

I can't be more happy. Good quality, well made.

Having focusing issues because of backspacing contradictions in the documentation. SvBony shows the back spacing can be 55MM, 91.5MM or 103MM. Removing the extension tube changes the back spacing length more than the length of the tube. Not sure how removing the 48x.75MM tube that measure at 34MM long can change the focal length from 55 to 91.5. 55MM + 34MM comes out to 89MM not 91.5MM back focus. but going the other way from 91.5MM and adding the 34MM extension tube is 57.5MM not 55MM like the documentation shows. I have wasted a lot of time/money ordering different length extensions trying to get a flat sharp stars all the way out to the edge of this flattener and cant find it. extending or reducing the extension by 2.5MM has not helped to match the 91.5MM or 55MM back spacing. I am still getting stretch stars using my EOS 6D. Either my extension that came on the flattener is wrong and should Measure 36.5MM not 34MM or I got a pre-production unit with some type of custom extensions that don't match the documentation. The second extension/reducer measure out to be what i think is correct. I get 11.5MM using my calipers to measure making me think the 91.5mm to 103MM is correct. The issue is getting down to 55MM. I dont have a way to connect up with the 63x1MM threads to test that requires ordering more extensions.

Well made reducer, works exceedingly well on my SVbony refractors. I have both the 80ED and the 122 APO, each with it's own SVbony 0.8x reducer.