2 inch to male T-2 thread zero-power field flattener for f6 to f/8 refractors
The Astro-Tech / ProStar 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.
This field flattener works optimally with refractors f/6 to f/8 focal ratios but can also improve edge performance of refractors slightly outside these limits.
Designed to work purely as a field flattener, and not simultaneously as a focal reducer or telecompressor, the 2 inch Astro-Tech does not change the focal length or focal ratio of your telescope.
The Astro-Tech field flattener is extremely easy to use with any SLR camera. You simply screw it on the appropriate T-ring for your camera and slip it into the telescopes 2-inch focuser.
While not specifically designed to work with Ritchey-Chretien astrographs, field tests by some adventurous R-C owners have shown that the field flattener works remarkably well with these instruments as well as with refractors.
The 2 inch barrel of this fully multicoated dual-element field flattener inserts directly into your telescope 2 inch 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 DSLR camera to the field flattener. They also allow direct connection to many specialized CCD camera s and colour 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.
Is threaded to take standard 2 inch filters.