Re: ATM RE: 12" refractor

[astrojoe@erols.com]

Hi Roger,

 snip>
> Personally, I suspect that a very well-made Cassegrain of f/25-30,
> employing a small secondary, aluminum tube that's well ventilated, and
> capped with an optical window will perform as well or better than your
> proposed refractor. 


Why an optical window ? What benefit would the OTA gain. I have owned
both a  C-9.25 & C-14 and found the trapped air to be a major problem in
cooldown time. Wouldn't the additional diffraction from a spider be the
lesser of two evils ?

Joe Castoro








 It will also be cheaper, lighter, probably shorter,
> and totally apochromatic.
> 
> Good luck, whatever you decide on!
> 
> Roger Ceragioli