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Re: [ATM] barlow lens

Saqib Sajjad wrote:

>hello everyone,
>
>
>due to non-availability of barlow lens in local
>markets i have no choice but to custom make a barlow
>lens. i have
>talked with a vendor and he is willing to make me one
>if i provide him with schematics. so can anyone help
>me
>in providing any info on its structure/power/shape
>etc.
>any help/article in this regard would be apperciated.
>
>
>Saqib
>
In ATM 2, Gee suggests that this is nothing more than a object distance
optimized negative doublet with a focal length somewhere between [minus] 4
and [minus] 8 inches.  Under that assumption, and starting with something
like -150 mm f.l. and f/5 with a 75 mm distance to the initial virtual
focus, I came up with the following 2x:

Surf    Radius  Thickness  Glass  Diameter
 OBJ  Infinity      -1000               25
 STO  Infinity        925         201.0076
   2     -2407        5.5     F2        40
   3    -73.81     1.6825               40
   4   -65.506          3  N-BK7        40
   5    65.506      131.5               40
 IMA  190.4286                     50.1298

In R&vV, the picture of the Barlow looks cemented.  I wonder where the
trade-off point is... don't know if this one is good or bad, either.
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