Re: Joel's Christmas list

[Brian Reynolds <reynolds@xxxxxxxxx>]

Greg wrote:
I wrote:
> >It would be a lot cheaper to buy a 8 inch telescope mirror grinding
> >kit and telescope making book and build a pair of 8 inch Newtonian
> >binoculars.
[snip]
> 
>   :)
> 
>   Yeah but you can't stop down to f32 to
> get more DOF with a telescope. :)
> 

Sure you can.  People use sub-aperture masks all the time.  Usually
it's to mask off a bad edge, or because seeing conditions are too bad
for the full aperture.  One of the really neat focusing methods is to
use a mask with a pair of holes on opposite sides of the aperture.
This turns the telescope into a rangefinder.  When the double images
are lined up you're in focus.

If all you want to do is adjust exposure (without changing DOF) you
can just use neutral density filters at the focuser.

:)

-- 
Brian Reynolds     | "Dee Dee!  Don't touch that button!"
reynolds@xxxxxxxxx | "Oooh!"
NAR# 54438         |    -- Dexter and Dee Dee
                   |       "Dexter's Laboratory"