Re: [APML] new telecompressor

[Chris1011@aol.com]

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