Re: [ATM] Loveday alternative to Cassegrain

["vladimir sacek" <vlad@copper.net>]

Woodchuck wrote:

> This, of course, is a very attractive system :-) !
>
> But by tweaking the Schwartzschild constants, you've lost the
> correction of the prime focus, no?  (I.e. without some sort of field
> corrector).

I don't see it as much of a loss, an f/3 parabola having less than well
corrected field itself. A field corrector od some kind would be needed 
anyway,
and hyperbolas are easier to correct. I didn't post the complete data since
I was concentrated on figuring/performance characteristics, but
here it is: a 400mm f/3/8.1 aplant:

primary: R=-2400mm, K=-1.096, 800mm to secondary
secondary: R=-900mm, K=-1.927,
primary to final focus: 843mm

The room behind the secondary is a bit too tight for mounting a camera,
but it can be easily corrected. In this particular system, the diagonal 
would
have to be placed in between the two mirrors, somewhat closer to the 
secondary.
This (front) diagonal location is necessary for faster systems; slower 
systems
can have it on the beck of secondary. Either has good and not so good 
points,
but nothing really disadvantageous.

Not just any out-of-hat system is feasible, either due to relative size of 
the diagonal
in the cone reflected from the secondary or, alternatively, size of the 
secondary perforation needed
for the standard field size, but the design is flexible enough to make it 
possible overcome this obstacle.
Nevertheless, at smaller apertures it would likely have somewhat more of 
field limitations than the Cassegrains.

I went through the '99 threads. Seems that the accent was on long-focus 
systems, similar to the original Loveday.
But the design is about as flexible in respect to relative aperture as any 
Cassegrain.

Vlad







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