Re: [ATM] plate glass blanks

["Bob May" <rmay@nethere.com>]

That answer tends to be variable for several reasons.
First off, are you going to slump the glass?  If so then you can
go a lot larger than an unslumped glass.
Second, are you going to do a built up mirror?  If so, you can
really go berserk with the diameter.  I've got some 11" mirrors
that are built of  quarter inch plate.  I've seen Bob Goff's work
and have seen a 32" mirror with that same thickness for the front
and rear plages.
Now back to reality.
I'd not do a mirror that ihas a center less than three quarters
the thickness of the edge.  This means that you have about a
quarter of an inch for sag so the larger the mirror, the longer
the focal ratio that you need to do to stay uner that spec.
Lastly, I'll note that the larger the mirror, the less likely it
will perform well due to atmospheric disturbances  and thus, the
less likely that you'll ever be using the scope at higher powers.
Longer focal length telescopes do have one interesting advantage
in that they do provide larger image scale so not a short a fl
EP is needed to see something of a certain size.  However, they
also end up needing larger diameter EPs to get some field of
view.  I did three inch eyepieces on my two hundred inch
refractor for just that reasonn as I wanted to be able to see the
full moon in the EP. Unfortunately, an eight inch focal length EP
has an enourmous amount of eye relief!
Bob May
Due to the large volume of SPAM thaat I'm getting, add an open
square bracket to the subject line or my spam filter will reject
your post~
rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net
Replace the obvious words with the proper character.

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