Flatteners clean-up focus away from the center of an image. The 0.8x Reducer/Flattener for 102 Scopes reduces telescope focal length by 80 percent while flattening the field for up to 35mm frame formats. Although optimized for TV102 scopes, it also works with any non-flat-field refractors (such as doublets or triplets) from 800-1000mm focal length.