Re: [ATM] Ghosts

["Richard F.L.R. Snashall" <rflrs@rcn.com>]

Richard F.L.R. Snashall wrote:
>
> While the ghosts from the first two groups do not have
> problems, the ghosts from the image plane and the last
> group are getting small.
Back of the envelope calculation -- the 50% encircled
energy point on a perfect Airy disk for the e-line at
f/4.2 is about 1.14 microns radius.  Ignoring diffraction
effects, the RMS spot radius of the ghost reflection
between the outer surfaces of the last group is about
94.6 microns.  Assuming a 4% reflection at each
surface, the ghost loss is then:

   ( 1.14 / 94.6 )^2     -->     9.59 magnitudes
 +    ( 0.04 )^2         -->     6.99 magnitudes
                                -----
                                16.58 magnitudes

A full moon ( mag. -12.6 ) would then have a ghost at
about magnitude 4.0.

On the other hand, in another design:

    http://users.rcn.com/rflrs/calcn-78x.atm  ATMOS input file
    http://users.rcn.com/rflrs/calcn-78x.len  OSLO input file
    http://users.rcn.com/rflrs/calcn-78x.txt  TEXT prescription
    http://users.rcn.com/rflrs/calcn-78x.zmx  ZEMAX input file

where I thickened the larger concave lenses and thinned the
smaller lenses, the RMS ghost spot radius is 579.9 microns.  The
loss here is:

   ( 1.14 / 579.9 )^2    -->    13.53 magnitudes
 +    ( 0.04 )^2         -->     6.99 magnitudes
                                -----
                                20.52 magnitudes

and the full moon ghost would be about magnitude 7.9.

Would this be enough; would the original loss be sufficient?
_______________________________________________
ATM mailing list http://www.atmlist.net/