Field Flattener for f/7 Telescopes with 2" Focusers (SFF7-21)

Description

This is our most popular modular flattener designed for all Stellarvue telescopes that operate at a certain focal ratio. The lens inserts into the 2” focuser and uses a tapered insert tube to more accurately seat the flattener in the focuser. The spacing distance from the T-thread on the flattener is 55 - 56 mm, so it will work as-is with any DSLR camera that has a t-adapter. For other cameras including all ccd cameras, consult us. Usually, a thread extension is all that is needed. This flattener is designed for use with cameras having an APS or smaller chip. This is the majority of cameras on the market.

The Importance of proper spacing: The photographic field flattener must be placed at a precise distance from the camera’s internal ccd sensor. If the spacing is incorrect, the performance will be compromised. Our stock flatteners are made to work with DSLR cameras. The distance from the t-ring to the internal ccd sensor on a DSLR camera is about 55 mm. This distance from the thread on the front of the camera to the sensor is also known as its “backfocus.”

Non DSLR (ccd astro cameras) are not made to the same specifications. The distance from the thread on the front of the camera to the chip varies and if often much less than 55 mm.  

If the distance from the camera's chip to the front thread is less than 55 mm, you must purchase threaded extension tube(s) and/or spacer rings in order to maintain a distance of 55 mm from the back of the field flattener to the cameras sensor. 

This field flattener has a standard M42 X .75 t-thread attachment.