Re: ATM - Help finding materials for cassegrain project.??

["Frank Ward" <thewards@mindspring.com>]

Ken,

I didn't imply a Schmidt, nor did you mention one.  I was just
wondering where the 10" BK-7 was going to be used in a Cass.

Now I see.  The correctors are 10" each. One is double convex
and the next is double concave. You are attaching the convex
secondary to the inside of the concave corrector.

So, if I have this right.  You are going to make R1 R2 R3 R4 Primary
R5 and for a f/6.3 you will add a R6 the meniscus.

I personally have never heard of this design.  What are it's advantages
other than the spherical figures for  null testing?

Frank Ward
Atlanta, GA
----- Original Message -----
From: Noesgaard,Ken <Ken.Noesgaard@siemens.ca>
To: 'Frank Ward' <thewards@mindspring.com>
Sent: Monday, December 13, 1999 6:17 PM
Subject: RE: ATM - Help finding materials for cassegrain project.??


> Frank,
>
> you must be thinking of ATM Vol.1 (Ingalls)
>
> I was referring to ATMT Vol.1 (Mackintosh) (Advanced Telescope Making
> Techniques).
>
> The project in question is not a SCHMIDT cassegrain. It's more along the
> line of a Maksutov without the hideously expensive and difficult to make
> maksutov corrector. The corrector is instead a double convex lens followed
> by a double concave lens. The primary is a pyrex mirror polished to a
sphere
> at about f/3. The secondary is a convex first-surface mirror about 80mm
> diameter for an f/10 telescope, or a 80mm meniscus lens made into a
> second-surface mirror for an f/6.3 telescope. The secondaries could even
be
> exchanged to switch from f/10 to f/6.3 - like an SCT with a focal reducer!
> All surfaces in this design are spherical, so NO zone testing. Everything
> nulls out.
>
> Ken.
>
>
>
> > -----Original Message-----
> > From: Frank Ward [mailto:thewards@mindspring.com]
> > Sent: December 13, 1999 12:22
> > To: Noesgaard,Ken
> > Subject: Re: ATM - Help finding materials for cassegrain project.??
> >
> >
> > Ken,
> >
> > Your post confuses me.  Would you add more information?
> >
> > First, Vol 1 ATM page 192 gives instructions for making a
> > spectrohelioscope.
> >
> > Second, if you are making a Cass why would you need a 10"
> > piece of BK-7
> > 1" thick.  If it is for a window Tex has all that worked out.
> >  If it is for
> > a primary
> > you sure don't need BK-7.
> >
> > Frank Ward
> > Atlanta, GA
> > ----- Original Message -----
> > From: Noesgaard,Ken <Ken.Noesgaard@siemens.ca>
> > To: <atm@shore.net>
> > Sent: Monday, December 13, 1999 12:33 PM
> > Subject: ATM - Help finding materials for cassegrain project.??
> >
> >
> > >
> > > Merry Christmas to all!
> > >
> > > I'm starting on a 10" cassegrain similar to the design
> > shown in A.T.M.T.,
> > > Vol. 1, p.192 (Mackintosh) and I'm having a little trouble
> > locating BK-7
> > > blanks. Most places I've tracked down are wholesale
> > suppliers, and Newport
> > > hasn't even provided me with a price.
> > >
> > > I need 2 pieces of BK-7 roughly 10.5" x 1" circular would be vastly
> > > preferable, although trepanning is an option.
> > >
> > > If anyone could steer me in some direction to procure this
> > glass, I would
> > > really appreciate it.
> > >
> > > BTW, I plan to publish my ATM diary of this project once I
> > have completed
> > > it, if anyone wishes to check it out. The design work is by a local
> > > professional optical designer who previously worked on satellite
> > telescopes
> > > and interferometry, Doug Miller. He is planning on offering
> > his services
> > via
> > > the net as an optical consultant. I'm finding him
> > particularly handy in my
> > > projects as if your optical element is slightly out of
> > spec, he can adjust
> > > the design to optimum using the specs of the element on
> > hand. A nice plus
> > > for a guy who grinds and polishes on his kitchen table.
> > >
> > > Any tips on making correctors or general large lens work
> > would also be
> > > gratefully accepted.
> > >
> > > Thanks much,
> > >
> > > Ken Noesgaard.
> > >
> > >
> > >
> >