Re: [ATM] Cassegrain vs. Gregorian (secondary testing) Best of BothWorlds

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

Kevin Whitefire wrote:
> I am working on a 13.25" f/3.12 primary that will
> become a 4-way telescope.  Here's the plan:
> 
> 1. Prime-focus CCD.  Let's let my computer do the
> looking so I don't have to put my eye to a cold
> eyepiece barrel.
> 
> 2. Visual-photo Newtonian.  I like galaxies and
> faint-fuzzies.
> 
> 3. Cassegrain.  I think the f.D will be about 18 here.
>  I like the moon and sun, with the right filters. 
> Great Orion also fits in here, as do several star
> clusters.
> 
> 4. Long-focus Gregorian.  I like planets and cheap,
> longer-focus eyepieces.

Since you don't list any correction lenses for the Newt,
I assume you've decided on the Classical Cassegrain.
Assuming also you want a Cassegrain/Gregorian focus
behind the primary of about 3/4 aperture, that would
make the primary RoC of 2100 mm and the Cassegrain
secondary RoC of 465.5 mm with a separation of 857.6 mm.
The secondary conic seems to be -2.026 or so.  The
secondary is smallish (paraxial relative diameter of
18.3%), about 68 mm with a 2 inch field (you said you
wanted long focal length eyepieces, so I thought
2" ones???).

In my ZEMAX lens catalogs, Rolyn Optics lists 22.0375,
a 72 mm diameter, 400 mm f.l. BK7/SF5 achromat.  Turns
out it looks like a good pair to test this system with;
the knife/source 337.28 mm from the pair of doublets.
The moving source zonal delta looks to be only about
1.75 mm.

> Kevin of Eastern Iowa
> Seeker of the Darkness


-- 

Rick S.

http://users.rcn.com/rflrs

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