William Optics 2" Mirrored Diagonal...

...came in yesterday.

It's been cloudy so I haven't had a chance to try
it out; plus I've been working long hours.

My God! It's ENORMOUS! It dwarfs even an 1.25"
diagonal, not to mention my 4" refractor's focusser,
and to the point that it looks like I have a 60mm or
an 80mm refractor instead.

It is almost flawless in its all-metal construction, and
with no detail left unattended, as far as I can see.

Now, if only it were available prismed...

Alan

Now, if only it were available prismed...


Hi:

Why? Prism diagonals of _any_ kind usually produce poorer images than mirror
diagonals of any kind.

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

On 08 Oct 2003 02:09:20 GMT, (Rod Mollise) wrote:

Prism diagonals of _any_ kind usually produce poorer images than mirror
diagonals of any kind.

I must respectfully disagree. The statement is true if qualified to
read "when used in short FL instruments." In longer FL 'scopes (F10 &
up), a good prism will be the equal of the many mirror diagonals, and
often will have greater throughput. Their known tendency to introduce
CA is muted by the less steep light cone, and the losses at the
air-to-glass interfaces are less than those of most first-surface
mirrors.

Problem is, its doggone expensive to make a *good* 2" prism, so that's
where the price/performance ratio turns around.

Wayne Hoffman
33° 49" 17' N 117° 56" 41' W
"Don't Look Down"

http://home.pacbell.net/w6wlr/

WayneH wrote in message . ..
On 08 Oct 2003 02:09:20 GMT, (Rod Mollise) wrote:

Prism diagonals of _any_ kind usually produce poorer images than mirror
diagonals of any kind.

I must respectfully disagree. The statement is true if qualified to
read "when used in short FL instruments." In longer FL 'scopes (F10 &
up), a good prism will be the equal of the many mirror diagonals,

Howdy Wayne:

Well, I did weasel-out with "usually". :-)

And you're right, I've got a 1.25" prism diagonal that I use with my
SCTs occasionally that works quite well. The thing is, as you mention,
it's just easier to do a good mirror 2" diagonal for a "reasonable"
price.

Peace,
Rod

On 08 Oct 2003 02:09:20 GMT, (Rod Mollise) ...reflected:

Now, if only it were available prismed...


Hi:

Why?

I have this persistent brain cramp that insists that a prism
diagonal is truer to a straight-through unobstructed observance
than that employing a mirror, and by virtue of the former's, at most,
semi-reflective mode of transmission, if not an outright denial that
a reflection takes place at all. Perhaps, rather, a refraction of
the light cone is effected, and at a 90 degree angle, that is,
perhaps...

Prism diagonals of _any_ kind usually produce poorer images than mirror
diagonals of any kind.

Intellectually, I am aware of the pros and cons. Still...

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

Alan

On 8 Oct 2003 06:16:38 -0700, (Rod Mollise) ...reflected:

WayneH wrote in message . ..
On 08 Oct 2003 02:09:20 GMT, (Rod Mollise) wrote:

Prism diagonals of _any_ kind usually produce poorer images than mirror
diagonals of any kind.

I must respectfully disagree. The statement is true if qualified to
read "when used in short FL instruments." In longer FL 'scopes (F10 &
up), a good prism will be the equal of the many mirror diagonals,

Howdy Wayne:

Well, I did weasel-out with "usually". :-)

And you're right, I've got a 1.25" prism diagonal that I use...

What brand is it, please?

...with my SCTs occasionally that works quite well. The thing is, as you
mention, it's just easier to do a good mirror 2" diagonal for a "reasonable"
price.

Peace,
Rod

Alan