Re: [ATM] A Null Test

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

Richard wrote:
>
> I'm commenting in the dark a little, Richard, as I didn't see
> your original post, only Donalds follow up. This looks like an
> OIffner Null test, but with three lenses rather than two. What
> does the extra lens do?
The difference is the positioning of the lenses.  I have to admit,
I would not have thought of putting them outside the primary CoC.

I was originally looking for a way to reduce the lens diameter in
a Ross null test of a faster primary.  It looks like the major gain
here is the second direction reversal in the longitudinal error.
>
> Here's the Offner setup I traced for a 16" RC primary :
Interesting test.  The lenses are small and the final cone angle is
also small.  Makes me kind of wonder why someone didn't recommend
that as an alternative (on the "other" list).  Is there any price
to be paid?

I guess an equivalent in the three lens form might be something
like (Isn't green a pretty color?;-):

Surf     Radius   Thickness    Glass   Diameter       Conic

 OBJ   44.18282         500                   4           0  MG LLP117
   1   Infinity           6      BK7         40           0
   2    -51.872    18.02549                  40           0
   3   Infinity           6      BK7       55.6           0  MG LFF349
   4   86.36324    73.56343                55.6           0
   5     154.79         4.8      BK7         42           0  MG LDX203
   6    -154.79    82.89377                  42           0
   7   Infinity    2391.669            2.760186           0
 STO   Infinity    8.331249                 400           0
   9      -2400   -8.331249   MIRROR        400   -1.144162
          ...

>  A good merit function operand to use is RAID on the mirror, and
>  TRAX, after using PMAG to ensure unity magnification.
Was you goal value on RAID zero?

_______________________________________________
ATM mailing list http://www.atmlist.net/