Orion 8893 Field Flattener for Short Refractors
Eliminate field curvature in short, optically fast refractor telescopes with this handy 38mm clear-aperture, fully multi-coated field flattener. Designed for use with 400mm to 650mm focal length refractors with f/5 to f/7.5 focal ratios. Optimizes your fast refractor telescope for astrophotography. Preserves focal length attributes of the attached refractor telescope while flattening the field of view. Requires 55mm of refractor telescope backfocus, weighs 7.5 oz.