Stellarvue Field Flattener for f/7 Telescopes with 2" Focusers
This is Stellarvue's Field Flattener for f/7 Telescopes with 2" Focusers, the most popular modular field 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. The photographic field flattener must be placed at a precise distance from the camera’s internal CCD chip.
Stellarvue 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 was standardized because of the standard adopted for optics for interchangeable-lens reflex cameras. For other cameras including all CCD cameras, consult Stellarvue or your dealer. Usually, a thread extension is all that is needed. This flattener is designed for use with cameras having an APS or smaller chip, which covers the majority of cameras on the market.
A field flattener lens is normally required to provide a completely flat focal plane to match the flat surface of a CCD or other electronic imaging chip in a camera. Even though a particular telescope is designed to be Apochromatic and has the highest possible theoretical image resolution, its focal plane will usually exhibit some curvature of field. While this is not an issue for visual observing, it would be a problem for imaging.
It is essential that the flattener be placed at a precise distance from your camera's CCD chip. This is referred to as the camera's "backfocus." When using a CCD astro camera, spacer rings and/or extension tubes may be required, depending on the exact location of the CCD chip behind the front attachment component of that camera. Some cameras have a short back focus. If you are not sure about your particular requirements please contact your dealer or call Stellarvue to discuss this matter in more detail.