Astro-Tech AT60ED Field Flattener

This thread on field flattener for the AT60ED is a must for full frame photography.The Astro-Tech 60ED 1x flattener easily threads on to the focuser of your AT60ED after your remove the standard compression ring eyepiece holder. The flattener produces wonderful flat fields as well as a 41mm image circle. The threads on the t-ring side of the flattener are 48mm male. Make sure your t-ring will work with this particular flattener. The standard for years has been 42mm and not 48mm, so please double check your equipment. Backfocus from the rear shoulder of the AT60FF to the image plane is 54.8mm, so you may require some additional spacers to reach focus.