Re: [ATM] Loveday alternative to Cassegrain

["Richard F.L.R. Snashall" <rflrs@rcn.com>]

vladimir sacek wrote:

> Woodchuck wrote:
>
> 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 

840??

>
>
> 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.

How does this change the original complaint about the Loveday, i.e.:
the ratio of the light diameter at the second pass into/to/upto the
secondary to the secondary is roughly limited by the ratio of the
secondary shadow on the primary to the primary?

One disadvantage; you can no longer ignore that hill in the center
of your primary;-)

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