[ATM] Flat Field Cass with Hougthon subaperture corrector. WAS: corrected dall-kirkham telescope

[mauritz andersson]

This reminds me, a few years ago I played around with adding a subaperture
Houghton type corrector to design an astrograph with a flat field.
See the following page:
         http://hem.bredband.net/mauritzandersson/atm/FlatCam/
The secondary is spherical, and only the primary is aspheric so I guess it
could be called a corrected Dall-Kirkham. (But to be picky it is not a
strict DK , since it does not have the same conic constant for the primary
as the DK.)

Since the corrector has two lenses of same glass type and has pairwise same
curvatures, it simplifies construction.

If anyone is more interested in the design I'm happy to adapt it to a
desired aperture and f-number!

As four your question
Did you refer to the following site?
http://www.astronomical.com/TelescopeOptics.htm
However there are no references to the type of corrector...

Also Celstron has/had a similar scope the C20, I think it had a three lens
corrector. There is nothing on their homepage anymore unfortunately. But
found a russian site where you can see the simulated spot sizes, which seems
very good. http://www.celestron.ru/prod_c20.shtml

Very best atm regards,
Mauritz Andersson


2007/2/5, Guy Brandenburg <gfbrandenburg at yahoo.com>:

    Anybody care to comment on the 'corrected dall-kirkham telescope'
design?

    see
    Corrected Dall-Kirkham
    Employs a spherical secondary and a primary with a conic constant around
0.8  together with a flat field corrector.  Produces a beautiful wide-field
(2°).  Can be used from very fast (f/3.5) to moderate (f/9) systems.   Has
the distinct advantage of a spherical secondary which is very easy to
collimate and stay in collimation.  Many R-C systems, although in theory
produce diffraction limited images, are incapable of doing so due to
misalignment of the primary-secondary with tube flexure or due to tube
currents  in closed- tube OTA designs.  All ACE telescopes use open-tube
truss  designs.