Re: [ATM] 8" F/4.2 progress

[Mike Lockwood <melockwo@uiuc.edu>]

Jason,

Jason Hissong wrote:
> Here are some pictures of the scope close to being fully assembled:
> 
Very next looking scope.  With it to allow star testing, you are about
to learn star testing under almost ideal conditions - you get to test
the mirror whenever you like.  Try it before you start figuring if you
can.

> I need to take a break from the building part because I am starting
> to get pretty fried.  There were a couple of nights where I did not
> get any sleep thinking of how to do various things with the
> design...

Typical symptoms of the disease.  There is no cure.  Beer may help.

> My mirror was slightly oblate (as you may recall) and the edge was
> a little turned down.  Well, I think I fixed the edge.. and after
> once around the turntable, my mirror is just about a perfect
> sphere... As you can see, I got the edge cleaned up.  It is amazing
> to see the difference in just one pass around the barrel.

Once around the turntable?  How many minutes did that take?  For me
it's a minute or two.  I would be surprised if it shaped up that
quickly....

> I have read and re-read Mike Lockwood's material and it has really
> assisted in understanding this. (Thanks agian Mike).

You're welcome!  If there's any place where it could be more helpful 
or clear, let me know.

> So now I got this thing looking this good... I don't want to mess
> it up into a parabola... !!   But then I cannot use it as a scope!!
> It's a catch 22...  :-)

Why not?  You can learn what LOTS of undercorrection looks like.

> I think I figured out why it is difficult for me to use the couder
> mask: the entire mirror nulls out at once!  It took me a little bit
> to realize that (I think I am right about this..)

If you can take some pictures with a knife edge tester that would be
useful.  It will probably tell more than the ronchi image, at least 
for me.

	Mike Lockwood

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