Thanks for your comments. The reason for going to the TS2.5Flat from Teleskop-express in germany was for me two fold. Firstly as you pointed out I was worried about the clear apature of the smaller flattener this being 2.5" I felt was better. Second was that I got a specially made VERY low profile 2.5" focuser from Ron at Moonlite
www.focuser.com, I needed this focuser to be low so I could pull focus. The standard height Moonlite focuser will not focus with this flattener (needs 11mm more infocus), Ron made one from a few different parts, same cost, no extra machining needed. This focuser has a M68 threaded top used to screw in things in like 2", 1 1/4", STL, T adapters but it is also the same thread that the TS2.5Flat has on it's telescope facing end! Then they made another adaptor from the M69 thread on the other end of the flattener to STL thread for my camera. So I have a fully threaded solution with perfect spacing. So far I'm very happy with the flattener. I now just have to solve a issue with the ~3" baffle tube on the primary mirror not being long enough causing light spill directly onto the chip. This makes it almost impossible to flat field correctly and causes a few internal reflections as well. Early days :-)
