From: "Richard F.L.R. Snashall" 
To: ATM List 
Reply-To: "Richard F.L.R. Snashall" 


I have added a simple 100 mm f/15 normal glass Clark type achromat at:

        http://users.rcn.com/rflrs/comdoub1-09x.len

This is quite close to the results straight out of Bob May's gsum program
(a little thicker elements).

Looking at the performance has me a bit confused. The F-C difference is
only 1 part in 1180, and it looks, to me, like the correction is not really
that great. Still, it has a photopic Strehl ratio is between .83 and .84
across the field, actually a little better than others I've tried at that
aperture and speed.  The tolerances here, except the air space (25 micron
tolerance), seem to also be relatively loose, so I don't think its some
form of singularity.

Is there something I'm missing here?  Is something artificially improving
the Strehl ratio?  Why does this one seem better than it should perform? 
Is it at the threshhold of some boundary condition?

        Rick S.

--- BBBS/NT v4.00 MP