ASI2600MM ZWO Filter Wheel Setup with Antlia 36mm Filters 

Hello, this is a great question! When it comes to backfocus distance, every mm counts. If you have all of the spacers and everything is adding up to 54.5 mm and you need only .5mm you can purchase shims in various thicknesses that can take up that .5mm spacing. Something to keep in mind ,if you are using a field flatter and once you have your 55mm back focus if your stars I. The corner are not round you may need to add or remove additional spacers. Also you need to account for the thickness of your filters. You divide the thickness of your filters by 3 to get the additional length you need. For example if your filters are all 3mm, and your setup requires 55mm backfocus. You will actually need 56mm backfocus. (3mm filter tickness/3) + 55 = 56.

I have not had a chance or the clear skies to thoroughly test this setup out other than for a few short imaging sessions. So far, I have not noticed any vignetting in the images except possibly in the very edges at the corners. I am still working on fine-tuning my back focus spacing as I am getting some oblong stars in the corners. These filters have been highly regarded by other astrophotographers, and there is quite a price difference when stepping up to a 2" filter. I also have not noticed any halos around stars with the oxygen filter either. It is possible that the star field has not had any stars bright enough to cause any haloing. I will post a video once I get several images completed on my thoughts about this camera and filter combination. (So far, I am very impressed)

Thank you for the tip! When I was placing the luminance filter I was thinking it may have been easier to line everything up if I would have taken the carousel out. Hopefully someone will see your comment if they are setting up their filter wheel, and they won't struggle like I did.

You are correct these are unmounted filters, I am using Antlia 36mm unmounted filters.