The Vixen Optics SD Flattener HD Kit is designed for a flat focal plane to produce crisp images of stars with Vixen's SD series of APO refractors. The kit consists of a high performance flattener lens, a spacer ring for the SD81 telescope, and an EX Tube 66 extension.
High Performance Flattener Lens
The SD flattener HD lens improves off-axis image quality greatly with a minimum change of the focal length. It covers a 44mm photographic field that is sufficient for full frame DSLR cameras.
AS Anti-Reflection Coatings
The same anti-reflection AS coatings that are used for Vixen's high-end VSD100F3.8, renowned for extremely high light transmission (99.9% per surface), are provided on each of the lens surfaces of the SD Flattener HD. Matte finish eliminates internal reflections and loss of light.
Used with Optional Reducer
If combined with an optional Reducer HD, the focal length will be reduced by 0.79 times (f/7.7 to 6.1) without diminishing the image circle of 44mm. The result is a sharp image throughout the photographic field of view.