Re: ATM Adding a Prism Diagoanal

[lifedata@vol.com]

"Frank" <thewards@mindspring.com> said:

>A prism acts exactly like a secondary mirror......it is a surface at
>45 degrees to the axis.  You won't have to change the length of the
>tube because of the actions in the focal path.  You will have to
>change it to accommodate the prism.  You can't just stick a prism
>diagonal into a focuser and add an eyepiece.  The body of the prism
>will take up enough room necessitating shortening the tube.

Perhaps the elementary points are being left unsaid here, but what
I've seen so far on this thread seems rather unclear.  So I'll post
what I think is what has not been said.

The point I haven't seen specifically covered is whether the
questioner is considering the difference between a mirror and a prism
or the difference between a diagonal and no diagonal.  Maybe Frank is
referring to this in his last two sentences, but if so the word
"prism" could be exchanged for "mirror" could it not?

That is, "You can't just stick a [?] diagonal into a focuser and add
an eyepiece.  The body of the [diagonal] will take up..."

Frank, correct me if I'm wrong.

Jim L
Lawbreakers will all suddenly obey the law if you write more gun
laws!