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Condition:
This is a used Astro-Tech 2" field flattener in great condition! The optics are clean and the body has a few marks that can be seen in the provided pictures. Any dust you see in the photos is easily removable. Two dust covers included!
Description:
The Astro-Tech 2" zero-power field flattener improves the image sharpness at the corners of the field with Astro-Tech and TMB apo refractors, but will also work well with any other f6 to f/8 refractor.
The Astro-Tech zero-power field flattener reduces the normal field curvature inherent in all refractors to provide you with images that are sharply focused out to the very corners of your 35mm or large format CCD imager frame. Stars look sharp and point-like all the way across the field. You don't have to worry about photos that are sharp in the center but out of focus at the edges.
The Astro-Tech 2” field flattener has been designed to optimize the flat-field imaging performance of Astro-Tech and TMB apochromatic refractors, even the very fast f/5.5 focal ratio TMB-92. However, the field flattener will also work well with any other brand and type of f/6 to f/8 focal ratio refractor, and can even improve the imaging performance of refractors with focal ratios somewhat outside these limits.
Designed to work purely as a field flattener, and not simultaneously as a focal reducer or telecompressor, the 2” Astro-Tech does not change the focal length or focal ratio of your telescope.
A review in Sky & Telescope magazine of the Astro-Tech field flattener and the Astro-Tech AT106 refractor said the field flattener was “extremely easy to use with any SLR camera. You simply screw on the appropriate T-ring, connect your camera, and slip the flattener into the AT106’s 2-inch focuser. Daylight shots made two things immediately apparent – the field flattener does not change the telescope’s focal length (it’s a true zero-power flattener), and it sharpens images at the edge of the field . . . At night, star images in the corners of my Nikon D300’s APS-format frame, while vastly better than those recorded without the flattener, still showed a slight elongation . . . By focusing at a point slightly off center, thus balancing the imaging performance between the center and edge of the field, I could fill the frame with nice, round star images. For photographers shooting day or night, the flattener is well worth its current $150 price.”
While not specifically designed to work with Ritchey-Chrétien astrographs, field tests by adventurous Astro-Tech R-C owners have shown that the Astro-Tech 2” field flattener works remarkably well with these advanced coma-free reflectors as well as with refractors.
The 2” barrel of the fully multicoated dual-element Astro-Tech field flattener inserts directly into your scope’s 2” focuser drawtube. A groove machined into the field flattener barrel engages the thumbscrew or compression ring of your focuser to act as a safety stop. This prevents the field flattener and camera from falling to the ground should the thumbscrew or compression ring accidentally loosen during use.
Standard 42mm x 0.75mm pitch T-2 photographic T-threads on the observer/camera side of the black anodized field flattener accept a standard T-ring for connecting a 35mm or DSLR camera to the field flattener. They also allow direct connection to many CCD camera/color filter wheel combinations. Optimal spacing from the field flattener lens to the imaging sensor or film plane is 60mm (57mm from the shoulder of the field flattener body to the imaging sensor) +/- 4mm. Some experimentation with spacers may be necessary to achieve optimum performance.