Ultimate Mars scope on order

I'll be replacing my 25-year old 10" classical cassegrain this summer with a Royce planet killer 16" f18 class. cass. Conical mirror, totally open design, aluminum square-tube lower truss and carbon fiber upper truss. This will be one rock solid OTA. I'll keep you posted on installation and first light.

Bob,

I just saw the optics at the Royce website. Are they building the whole scope for you or are you having it built elsewhere? This really does sound like a killer scope assuming the Cass optics match the Royce reputation for Newtonian mirrors.

Paul Maxson

Bob Schnitzer said:

I'll be replacing my 25-year old 10" classical cassegrain this summer with a Royce planet killer 16" f18 class. cass. Conical mirror, totally open design, aluminum square-tube lower truss and carbon fiber upper truss. This will be one rock solid OTA. I'll keep you posted on installation and first light.

Bob,
Wow, that should be a fantastic scope, let us know all about it.

Bob, sounds like an awesome instrument, please keep us posted, and don't forget about pics as soon as you get some!! 8)

I feel myself turning green with "telescope envy"!

Classical Cassegrain has field advantage, but for an ultimate planetary scope what matters more is the mid-field quality. In this department, Dall-Kirkham is likely to have practical advantage, due to its lover sensitivity to misalignment.

Assuming an f/4.5/18 system, the DK would have 8.1 times smaller quality linear field than the CC. But this is still at the level of linear field of an f/9 system, with about 16mm diffraction limited field diameter (7.6 arcmin). With good tracking,
more than necessary.

On the other hand, as little as 1mm decenter of the secondary would induce 0.23 wave of center-field coma with the CC. That alone would push its Strehl down to 0.83. Add 1/10 wave from despace (about 6mm, with ~1/60 wave per mm), and the wavefront is just at the diffraction limited level.

At the same time, the DK would have 2.65 times smaller error from the decenter (1/11.5 wave, or ~0.97 Strehl), and four times smaller error from the despace - entirely negligible. A tilt error (to which both are equally sensitive) which would knock DK's Strehl down to diffraction limited level (about 1/14 wave RMS), would have the CC down to 0.66 Strehl (1/2.9 wave s.a. level) in the very middle of the field.

Vlad