William Optics M48 Nikon F T-Ring - Black - TM-NK-F-M48 threedaysale It works on the difference

It works on the difference between Ambient Air Temperature and the temperature of your optics

The Calcium K modules line is centered at 393

Optical Design: Includes one ED element

About the Celestron Cheshire Collimation Eyepiece - 1

Unique features such as an electronic friction break and power down memory allow the mount safely stop and resume a GoTo slew or continue tracking even after an abrupt power loss (No need to realign and start from the beginning)

William Optics M48 Nikon F T-Ring - Black - TM-NK-F-M48 threedaysale It works on the differenceWilliam Optics 48 mm T Ring for Nikon F Cameras Use this aluminum black anodized T ring to attach your Nikon F camera body to an imaging accessory, etc. with M48 threads.