Astro Tech focal reducer/flattener spacing recommendation

[Fivel]

Hello to all.
I just bought an Astro Tech (AT) .8 focal reducer/flattener model ATR8 for my scope, and ZWO camera.
I have the AT 80mm/F480mm ED triplet scope and the ZWO1600MC-C camera.
The FR/FF is apparently made by GSO. The manufacturer recommends a spacing (FF rear shoulder to camera sensor) of 55mm.
I tried some images, but that spacing seems to much. The stacked images show a large central bright image circle surrounded by a more normal brightness. Also the stars are showing coma. So it seems that the image circle isn't covering the sensor properly.
Is anyone familiar with this FF/FR and the actual spacing needed for this scope and camera combination?
Thank you for any help with this.

Fivel

[Frank the Troll]

From what I was told when ordering a reducer,  just the camera t-ring will provide the spacing you need, your FR might b the same

Edited February 26, 2020 by Frank the Troll

[Fivel]

Thanks Frank for that info.

I thought that the (now sadly deceased) owner of Astronomics, may have said that several months ago, when I was asking about spacing.

I think he said that no additional spacers are needed. Yet, the info that comes with the reducer says to use the 55mm spacing.

I am not using a "T" ring, but have some spacers of the same length. I hope that solves my issue.

Dark skies for you.

Fivel