I am looking at connecting an AO-X to a TEC reducer/flattener, and Precise Parts says it can't make an adapter from the TEC reducer to an AO-X with the dovetail adapter or with a "bolt to AO-X" side (the adapter would be too wide to be able to get to the bolts on the AO-X adapter). Precise Parts CAN make this TEC reducer adapter to AO-X thread: If I got that adapter, what adapter would I use on the AO-X? This adapter appears to have threads inside, so I assume it's the correct adapter: Is that the STX 3.5" OD / 3x24 threaded adapter? Using the threads, will there be any vignetting with the AC455 camera? Its web page (Aluma AC Adapter Plates - Astronomy & Scientific Imaging Solutions) says when using the threads the backfocus is 17.02 mm, but the BackfocusCalculator.xlsx has 17.0688 mm. Which is correct?
That is the standard 10018 STX style adapter, with 3-inch x 24 tpi internal threads, and that is what comes with our camera. No Vignetting with an AC455 or AC4040. I will have to check into the backfocus difference on Monday. That said, it's a small fraction, your focuser should be able to take care of it, and the adjustment range of the SC-4 is likely more than sufficient.
