Common imaging train

WO Ultra Flat 91 + ASI6200MM Pro + EFW 7×2"

The Ultra Flat 91 is the 0.79× reducer for the Fluorostar 91 with an M54 T-mount and a slightly non-standard spacing; William Optics marks it discontinued, but plenty are in use. Full-frame mono: ZWO only recommends 2" wheels for the 43 mm diagonal, the camera wears its M54 tilt plate, and the wheel and OAG-L bolt on with screws rather than threads. Every bore in this train has to clear the diagonal. Its M54 T-mount goes straight into the 2" wheel; an OAG-L would need a step-down ring that costs too much length here.