Designed for their Evoguide 50ED and 50DX guidescopes, this Sky-Watcher Field Flattener allows you to use the guidescope for astrophotography. It virtually eliminates spherical aberration in the objective lens system which, if left uncorrected, causes blurry, defocused, and distorted areas in astrophotography or CCD images. Standard T-threads and a 1.25" holder allow you to use most styles of cameras and eyepiece imaging systems with the scope. The flattener has a 28mm imaging circle, a 17.5mm back focus, and a 5.33 x 3.57° field of view when using an APS-C sensor.