Re: Picking a Mark IV Lens/Film test?

[Chris Albertson <chrisa@wavenet.com>]

aah@nofs.navy.mil wrote:
> 
> Tom gave an informative (as always) description of a comparison between the
> Mak 350mm f/4 solution and the 400mm f/4 solution.
>   Texereau, in How to Make a Telescope, 2nd ed., page 141, gives a table of
> how the relative obscuration of a cassegrain secondary modifies the point
> spread function of the telescope.  In particular, for a ratio of 40%
> (approx 38mm/90mm), you get about 40 percent of the light in the diffraction
> rings instead of the central disk.  This means that the optical system does
> not come close to providing the kind of images you would get with the
> 400mm refractive solution. 

Two comments:

1) We can test this Mak mirror/lens system and understand it before
   we have a working MkIV camera.  Film will work well for this.
   Just shoot a light bulb at 100 meters, shoot a clear blue sky
   or shoot a gray card on an overcast day. then scan the film.
   Film scanners can work at a better spatial resolution then Tom's
   CCD.  I can process and scan film but the commercial cost is
   pretty low, about $10 for a PhotoCD transfer at 3600x2400 pixels

2) I just can't forget those radar systems I worked on as a
programmer.
   On these systems the transmitter would modulate the pulse
specifically
   so that the PSF would be recognized by an auto collation function.
   They would convolve the returned signal with the expected PSF.  It
   seems that PSF fitting is like this and could make a cruddy but
well
   sampled PSF usable.  Is the PSF of  the Mak bad enough that it is
   well sampled?  

   Film test would help here too.  We could have an image in a week
   to look at.  Yes film can be non-linear but you can plot the film
curve.
   Many photography books go to lengths to tell you how to plot
curves.

   
-- 
   --Chris Albertson             home: chrisa@wavenet.com           
     Redondo Beach, California   work: chris@topdog.logicon.com