Common imaging train

Askar SQA85 + ASI2600MC Pro + filter drawer

The SQA85 is an f/4.8 Petzval with a wide tolerance on its M48 rear adapter — Askar quotes a range rather than a single figure, so a few tenths either way are not the problem they are on a fast flattener. One-shot colour usually runs a single dual-band filter in a drop-in drawer instead of a wheel. The M42 drawer threads straight onto the camera and leaves a gap that one of the extenders in the camera box closes — once the filter glass is accounted for. Same stock-extender answer as every 55 mm M48 optic, with the filter glass nudging it by a fraction.