[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]
RE: [APML] new telecompressor
I had
wanted to use this on my C8 for 35mm. The Baadar says field is flat.
Do you have any comments on photog use?
-Bill
In
a message dated 6/10/2002 11:40:11 AM Central Daylight Time, wclark@cdic.ca
writes:
Any one heard of this? Looks like a good idea? Any
good?
http://www.alpineastro.com/optical_accessories/optical_accessories.htm#alan%
This is an old design that goes back to the 1980s. We
can sell these through Astro-Physics if anyone is interested.
They are
most useful for visual work with SCTs and Baader Binoviewers. As you may know,
a Binoviewer requires quite a bit of back focus, something achieved in SCTs by
moving the mirror forward. However, the action of moving the mirror forward
causes the F-ratio of the SCT to increase, with the result that the field of
view decreases and the power goes up. An F10 SCT can easily become F14 or
longer when the mirror is moved to achieve the required back focus. In order
to bring the F-ratio down to a reasonable value, the Alan Gee telecompressor
was developed by Baader (actually I designed the optics for this device). The
result is a wider field of view, but with a consequent vignetting at the edges
due to the limited size of the optics and barrel size that can be stuffed
inside an SCT's central hole.
Photographically, the optics do not
produce a very flat field - there is astigmatism and field curvature over a
35mm field. For the limited aperture of a Binoviewer, this compressor works
quite well.
Roland Christen