Variable M48 Extension 17-23 mm

M48 extension tubes are intended for reaching the optimal back focus when using correctors like field flatteners or reducers. They are also needed for eyepiece projection. This variable M48 extension allows you to fine tune the distance by a fraction of a mm. The threads (male and female) are the international used M48 threads (M48x0,75)

Turn the connection part as long until the desired length is reached. Then, tighten the counter ring. Now you have a fixed M48 extension which is exactly the right length.