Re: [APML] (OT) IC1396 CCD with Schmidt-like FOV

[Chris1011@aol.com]

In a message dated 8/5/2002 10:22:11 PM Central Daylight Time, tan@cox.net writes:


> The other issue with widefield CCD imaging is the need for short focal
> length well corrected optics. I am sure they are out there so this is
> just a matter for finding the right one. 


The problem with short lenses designed for film photography is that they are not made to the level of accuracy as astronomical optics. They are machine made optics with on-axis aberrations exceeding many waves, whereas an astronomical optic is on the order of 1/4 wave or better. As a result, the smallest image spot sizes rarely get less than 25 microns with film optics. Furthermore, even ED and "fluorite" film lenses do not really have the color correction of real astronomical apo lenses. I dare say that you could take the finest Nikon or Canon ED lenses and not be able to resolve the Cassini division with them, neither would you have a pure color-free view of Vega showing one diffraction ring at high power. If you are looking for true Schmidt-like optical performance you will need a hand corrected lens made to astronomical precision.

Roland Christen