Common imaging train

Askar SQA55 + ASI2600MC Pro + filter drawer

The SQA55 is a 55 mm f/4.8 Petzval with a 44 mm image circle; Askar quotes a connection range with 55 mm recommended, measured behind its M48×0.75 rear adapter. 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. At f/4.8 the drawer's M42 output is the narrowest point; the tool shows how close it runs to the APS-C cone.