One of many things I like a lot about the TEC 140 for imaging is the dedicated field flattener. Other vendors make dedicated flatteners too of course, but I only have experience with TEC's offering. The TEC flattener is very large, with about a 3.5" aperture, so vignetting is a non-issue. The flattener housing is threaded to screw onto the drawtube of the Feather Touch 3545 focuser; it is very secure. I use Astro-Physics part A-1261 to couple the flattener to the camera, wheel and focuser assembly I use.
If you scroll through the attached, you will see that I am getting a very flat field and minimal tilt with this set up, across the entire surface of a 35mm chip. This attachment also demonstrates that it is important to get the specified field flattener to chip distance right, within a mm or so.
http://home.comcast.net/~jameslbrown/flatteneranalysis.pdf
Jim
If you scroll through the attached, you will see that I am getting a very flat field and minimal tilt with this set up, across the entire surface of a 35mm chip. This attachment also demonstrates that it is important to get the specified field flattener to chip distance right, within a mm or so.
http://home.comcast.net/~jameslbrown/flatteneranalysis.pdf
Jim
