fielderda

Thanks souls33k3r -  Good luck with your new purchases and Clear Skies!

Here's a first light with my ASI1600MM-Cooled and my EDGE HD 8. Not great, but a good start in my opinion for a newbie.

Full downtown light pollution; LRGB; 30 sec exposure; RGB binned at 2x2; stacked with Nebulosity and finished in PS

Still lots to learn!

I'm a newbie at mono CMOS astrophotography but the LRGB filters for the 1600MM are a good entry level but I've been pleased with them. 

The EFW is excellent is smooth and quiet. The only caution is getting filters that thread properly and are not to thick to impede movement of the wheel. I'm plenty pleased with my ZWO products!

This seems a correct calculation since my ZWO EFW (5 POS) is only 10mm accounting for the difference between your 8 POS and mine.

Mea culpa!

ZWO ASI1600MM-cooled is a CMOS camera

This fall, I bought my first CCD camera for my Celestron EDGE HD 800  -  a ZWO ASI1600MM - Cooled, with their 5 POS EFW  (since they didn't have a 8 POS at the time). Since I'm new at astrophotography, I bought their LRGB filters specific for the 1600MM-Cooled.

I had the same questions as you have and came up with the calculations as follows:

With Celestron 0.7x reducer :  105 mm

Celestron T-Adapter:  50mm

Adapter extension (comes with Celestron T-Adapter): 28.5mm

ZWO ASI1600MM-cooled: 6.5 mm

EFW: 10mm

Total back focus: 95mm

I bought a set of different T-ring extensions from Telescope Camera adapters for about $USD30. They are really well made and used a 10mm extension ring to make up the needed space (Total 105mm).  Note I have no affiliation with this company but like you were assisted by other astrophotographers.

I've just bought a OAG to assist in eliminating flexure from my setup.

Good Luck with your ZWO camera - it's great!