Re: [ATM] Super compact Houghton camera

["Chris Dalla Piazza" <dalchri@hotmail.com>]

I am currently working on a 6" f/4.5 myself and am hoping it works
practically as well as it sounds on paper.

One thing that I was warned about from someone else that made one is the
collimation.  He wouldn't specify which degree of freedom or if all combined
were troublesome.  I have heard that centering the corrector lenses is
important and that misalignment can lead to astigmatism. 

I have completed the Pyrex primary and have started polishing the BK7
corrector lenses.

>From my personal experience so far, I would like to say that the extra work
beyond the mirror for the 5 optical surfaces is not as bad as it might sound
at first.  This being my first experience with BK7, I have found the effort
required to grind both of the matching concave and convex lens surfaces to
be no worse than the effort for grinding the Pyrex primary owing to the
softness of the BK7.

The softness of the BK7 gets me two sides of my concave lens for the effort
required of one Pyrex mirror and because the "tool" becomes the convex lens,
I actually get 4 BK7 optical surfaces for the effort of one Pyrex mirror
surface.

Of course, I now face polishing 4 lens surfaces separately.  However, they
won't require figuring, only polishing to a sphere.

The new skills that I had to learn beyond the creation of single a Newtonian
primary thus far have been:
1) Construction and use of a spherometer
2) Measurement and elimination of wedge in the corrector lenses
3) Trepanning the corrector lenses and reseating the cores

The last thing I need to tackle is how to test the figure of the convex lens
surfaces.  Although I've had zero to minimal trouble arriving at a sphere
after polishing in the past, I just don't want to commit to removing my
cores from the corrector lenses until I am sure they are ok.



-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
vladimir sacek
Sent: Tuesday, December 12, 2006 6:31 PM
To: atm@atmlist.net
Subject: [ATM] Super compact Houghton camera

These past couple of days I've been playing with the Houghton corrector.
Incidentally, I realized that by putting the corrector - the type consisting
of a pair of plano-concave and plano-convex element - half way between the
mirror and the focal plane (single-mirror arrangement) the system becomes
aplantic, with the field practically flat and with relatively low
astigmatism. In fact, both astigmatism and chromatism are comparable to that
of the Wright camera, only in an all-spherical system.

What makes me curious is that I never heard of this type of camera before.
If it is about as good performance-wise as the Wright, much easier to build
and twice as compact, why isn't it at least mentioned here and there? I've
put more details about the camera at:

http://www.telescope-optics.net/Houghton.htm

Vlad
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