Re: ATM Slevogt figuring method and results

[astrojoe@erols.com]

Thanks Dave. I think I'll will toss this to the ATM list. Specific
interest would be placing the corrector between the primary and
secondary of a short focal ratio (F/3) sperical mirror.

Joe





DROWESMI@aol.com wrote:
> 
> Hi Joe,
> 
> > Let me pass this by you. To keep the focal length of a large mirror for
> >  a DOB to a short length, say F/3 which would have a spherical curve, and
> >  a corrector of some type work ? To correct the image could a schmidt
> >  corrector in front of the secondary flat between the primary and
> >  secondary work ? Would a Celestron schmidt corrector from an 8" work ?
> 
> If you put the corrector skyward of the secondary mirror, in a place where the
> secondary can be held by the corrector, then you have a short tube variation
> of the Wright-Newtonian.  This design is not bad at all, coma is reduced
> considerably from that present in an equivalent Newtonian.  The drawback is
> that the primary is not spherical but an ellipse.  The Schmidt-Newtonian uses
> a spherical  primary but places the corrector at the radius of curvature of
> the primary, i.e., at twice the focal length, making the telescope very long.
> Howver, this configuration has nearly perfect images across a wide field.  Bad
> news about the Schimdt-Newtonian is that the focal surface is strongly curved,
> as in a Schmidt camera.
> 
> There are some strange variants that have optics between the primary and
> secondary but I don't know anything about them.
> 
> Yes, you can take a "pre-owned" corrector plate and use it with a spherical
> primary that has the right focal length for that corrector.  The corrector
> will have to be measured to determine the right mirror to make for it.  You
> will then have a Schmidt camera.  Or, that same corrector can be used with an
> elliptical mirror of the right focal length and deformation constant (SC) to
> make a Wright-Newtonian.
> 
> Dave.