Common imaging train

Askar FRA300 Pro + ASI533MC Pro + filter drawer

The FRA300 Pro has a built-in flattener, so there is no fixed spacing: Askar publishes a maximum connection length from the M48 thread with the focuser fully racked in, and the focuser takes up anything shorter. 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. Because the figure is a maximum, the drawer plus camera simply need to be shorter than it — the focuser does the rest.