ATM A corrector for huge, fast, photovisual Newtonians

[Aplanatic@aol.com]

As some of you may recall, I have been working on a corrector for a 42" f/3.3 
paraboloidal mirror.  (It is not my mirror!)  My goal for the corrector is 
diffraction limited performance on-axis (for visual use) and spot 
characteristics suitable for a large CCD camera off-axis.

I have optimized the performance of the system and achieve the stated goal 
for a CCD array having 25 micron pixels, 1" on a side, in other words, a 1 
megapixel array.

The following are the spot characteristics over wavelengths of 0.67, 0.5, and 
0.42 microns at off-axis distances of 0, 10, and 17.5 mm:

Distance | Size(all rays) | Size(RMS)

0 mm      |   2 um           |     1.2 um
10 mm    |   4X16 um      |     7.3 um
17.5 mm |   20X20 um    |     11.4 um

Amazingly, the design continues to work well down to about f/3, opening the 
way for 1 meter plus amateur systems with excellent optical performance in a 
reasonable size.

The back focal length, i.e., the distance from the last glass surface to the 
focal plane is 40 mm, which should be sufficient for all CCD cameras and 
eyepieces.  Comments on this aspect are welcomed.

In quantities of 10, it should be possible to make this multi-element 
corrector for 1K to 2K dollars, at cost, including the mechanical assembly 
and fully coating all optical surfaces.  The outer diameter of the corrector 
will be on the order of 85 mm.  Longitudinal positioning and collimation will 
be very important, so the mechanics of the OTA and mirror cell may require 
considerable additional design work.  I suspect that graphite-epoxy 
structures will be required.

As I have previously stated, I am looking for potential interest in this 
corrector from other amateurs in order to amortize the tooling cost over a 
few units.  The schedule for producing units is on the order of 9 months to a 
year.

At the moment, I am not in the position to release the design, but it will be 
released some time in the future (before it is fabricated, I think).  The 
design will be thoroughly checked by several professional opticians, a 
tolerance analysis will be performed and an iterative method of controlling 
manufacturing tolerances will be employed.

Dave Rowe
Torrance, CA