This William Optics Flattener Reducer for the Zenithstar 61 OTA is adjustable so you can get the proper spacing in your imaging setup without needing extension tubes.
Suitable for several camera types including CCD and CMOS astronomy cameras, Nikon, Sony, Canon, and more.
Has a backfocus of 56mm.
M48 thread on the camera side.
M54 thread on the telescope side.