[ATM] Classical Cassegrain Design Tradeoff Help Needed

[atmmessages at infinichron.com (Gerald Boutin)]

I am (slowly) moving ahead on design of a Classical Cassegrain telescope.
The design is for a 350 mm diameter F/14.5.

I am somewhat stalled out at trying to make the final decision of the actual
mirror ROCs. My present dilemma is trying to decide what tradeoff to make
between field curvature and minimizing the obstruction.

What it boils down to is that I don't have a good feel for what effect
varying the flatness of the focal plane has on visual observing. In other
words, how flat of a field curvature do I need to get nice sharp points over
the maximum 1/2 degree field? Although I have done a bit of Googling on eyes
and accommodation, I haven't been able to come up with any hard and fast
guidelines that I can go by. I do have a commercial 8 inch SCT and a 102 mm
MCT and I am reasonably satisfied by their sharpness using 1.25 inch EPs.
However, I don't have any experience with 2 inch EPs, which are going to be
required with a focal length of over 5 meters to get any kind of FOV. 

I am considering the following range for the primary: f/4.0 to f/4.59.

The f/4.0 primary gives a field curvature radius of -390 mm and obstruction
of 29.3%.
The f/4.59 primary gives -495 mm and obstruction of 31.5%.

The f/4.0 is as fast a primary as I would want to try (just in case this
ends up being a Newtonian after all.) The f/4.59 case is about the maximum I
want to go for overall OTA length.

The obstruction figures are based on 0% field fully illuminated and 46 mm
fully shielded. I am also still working on the baffling design to help keep
the obstruction down for planetary viewing, possibly using swappable
baffles, but so far I haven't come up with any clean ideas on how to
implement this.

I would like to end up with a telescope that provides very good to excellent
planetary performance, but I also want to be able to use it at its lowest
magnification around 100X and get a sharp edge-to-edge view.

--
Gerald Boutin