Re: ATM turret telescope

[Anthony Stillman <atmer@flash.net>]

>>...the russel turret...appears...unobstructed... Is this so?
>
>No, the porter turret is obstructed.  The "obstruction" is a hole...

It was kindly pointed out, off list, that perhaps I was a little unclear in
my definition of obstruction.  I do not mean that the hole in the flat
vignettes the light cone.  I'm told it does not, and I can't imagine that a
Porter design would.  What I meant to say is that the presents of the hole
in the flat means no light is reflected from the center of the aperture
toward the primary.  Hence, from the primaries perspective, the light cone
is obstructed just as if it were shadowed.  With more or less the
equivalent effects.

Thankyou Gary for keeping me honest.

Anthony