Re: [ATM] Finder

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

Richard wrote:
> Hi Richard,
>
> Wednesday, February 28, 2007, 6:34:00 PM, you wrote:
>
> RFLRS> The objective itself can use two OTS lenses.
>
> What are their part numbers please Richard?.
>
> Looking altogether more doable now :)
Or, you could wait for the sequel:-)


Title: Ptz08-13x
72 mm f/6.96 Refractor
VS: 0.7547 at +0.009 mm shift
VS: 0.7289 at 2.4 Degrees
Min: 543.665 nm
Sugg: MG LDX221, MG LPX286 and Coherent 43-2542

Surf    Radius   Thickness   Glass   Diameter

 STO  Infinity   -3.173151                 72
   2     205.8         9.8   N-BK7         75
   3    -205.8       0.593                 75
   4    -205.8           3    N-F2         75
   5  Infinity       306.1                 75
   6    129.68         4.4   N-BK7         50
   7  Infinity      47.232                 50
   8    -129.5           2   N-BK7         38
   9     129.5    90.30412                 38
 IMA  863.4799                             42

The field is more convex, but that may actually match
some eyepieces better.  There is a touch of vignetting,
but OTS is OTS.  The field is now only 4.8 degrees, but
the Strehl ratio seems to hold up well across the field.

The last lens may be more expensive than you might want
(I don't know the price, only guessing.).  It wouldn't be
too hard to get one that mates the third lens convex surface,
I think.  Then too, given adequate measurement, it might
not be difficult to do this with any 200 mm f.l. isoconvex,
250 mm f.l. planoconvex, and -125 mm f.l. isoconcave BK7
lenses (given they reasonable diameters and thicknesses, too).

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