Re: [ATM] RE:anealing

["David Harbour" <scarab2@cox.net>]

Bob, all:

This is reasonable, Bob, and I hadn't thought of it.

I did think of the possibility of the departure of the field from perfectly
flat; this seems inevitable. I dunno; it worked for Ritchey; but maybe only
to a "first approximation", which, I guess, considering the skies over the
Potomac River, which never let the telescope (40") run "flat out".  Dr.
Osterbrock says that's why the RC Cassegrain took so long to be validated:
there was only the one, the one metre; no one wanted to take a chance on the
new curves elsewhere. I wish the old guy (Ritchey) was still around. Don't
you?

Dave

----- Original Message ----- 
From: "Bob May" <bobmay@nethere.com>
To: <atm@atmlist.net>
Sent: Thursday, May 26, 2005 8:35 AM
Subject: Re: [ATM] RE:anealing


> Ah, I missed the autocollimation word in the question!  That indeed does
> make the paraboloid without a toroid condition.
> Now, as to using subdiameter flats, that is going to be a bit difficult
but
> can be solved by putting an EP near the focus point and locating the
flat's
> return in the image from the EP.  Note that when you subdiameter a
> telescope, the off-axis image ends up producing a large spot of light
where
> the aperture is in what would be called the star test image. You won't see
> the full star test image but only the part that is returned from the
mirror
> and you can explore the location of that spot in the image and get the
spot
> into the right location.  How accurate you ucan do so, I don't know but
I'd
> suspect that you can do this good enough to berify that the surfaces are
> right or not.  Needless to say, the bigger the subdiameter flat, the
better
> it will be as you will quickly be able to see the center hole in the image
> and be able to locate the flat more accurately as a result.  For example,
a
> flat 1/2 the diameter will end up with the central hole showing 1/2 of
it's
> diameter in the image.
> Other than that method, I don't think that it would be possible to
> accurately focus a telescope unless you do so against the real world and
> then put the flat in the path for the actual testing.
> Bob May
> bobmay@nethere.com
> http://nav.to/bobmay
> http://bobmay.astronomy.net
>
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>


_______________________________________________
ATM mailing list http://www.atmlist.net/