From: "Dwight K. Elvey" 
To: atm{at}shore.net
Reply-To: "Dwight K. Elvey" 


Hi
 Nils Olof did some calculations for me once, a while
back, on least material removed. It showed that the same amount of material
would be removed, regardless of the method used ( a surprise ). It also
showed that one could remove about only 20% as much material if you removed
stuff from the center and outer zones in equal amounts ( 70% being the high
zone ). This typically doesn't happen with just MOT.
 I feel that the reduced chances of developing TDE
are the main reasons. Still, if I were doing a really large mirror or a
really fast one, I might consider the balanced method, part MOT and part
TOT, since it works the glass the least.
 This isn't the case for the convex mirror. You need to
remove material in the 70% zone. This is a little trickier than working the
concave surface we do for mirrors. The point is that the same stroke is
used to make anything form a ellipsiod to a hyperboloid. It is all a matter
of amount.
Dwight


>From: klowther{at}cisnet.com
>
>I think this method is based on a 'least glass removal' theory and the fact
>that we seem to
>have a simple process to do it.  Long strokes deepen the center and turn
>the edge.  Result, if
>you are lucky, is a parabola.
>
>Ken
>
>----- Original Message -----
>From: Dwight K. Elvey 
>Sent: Wednesday, May 07, 2003 12:43:00 PM
>To: 
>Subject: Re: ATM dumb question, maybe
>
>>
>> >From: "Bianco Giuseppe" 
>> >
>> >Even if I've a PhD in Astronomy and reasonable knowledge in optics, I'm
>puzzled
>> by something which will be certainly solved by somebody in the list.
>> >Textbooks on mirror making say that, in order to
"parabolize" a concave
>> spherical mirror, one should dig into the center of the surface;
>conversely, in
>> order to "hyperbolize" a convex spherical mirror, one
should depress the
>outer
>> zones of the surface. To me, both those action lead straight to an
>ellipsoidal
>> figure. In fact, in the case of a concave surface, a paraboloid results
>from
>> flattening the outer zones with respect to the center, and even more so
>in the
>> case of an hyperboloid.
>> >Where's the trick? Thank you all in advance.
>> >
>> >Dr. Giuseppe Bianco
>> >Centro di Geodesia Spaziale "G. Colombo"
>> >Agenzia Spaziale Italiana
>> >75100 Matera (MT), Italy
>> >phone:+39-0835-377209
>> >fax:     +39-0835-339005
>> >e-mail: giuseppe.bianco{at}asi.it
>> >
>>
>> Hi
>>  You need to think of these shapes as a continuum of shapes.
>> An ellipsoid is just a stretched shpere. A paraboliod is a
>> particular one that has been stretched to infinity. The
>> hyperboloid is a continuation to the stretching.
>>  To modify a sphere to any of these shapes, we can progress
>> the same way. The suggestions for where to remove the most
>> material can be used to change the shape from a sphere to
>> ellipsoids, to a paraboloid and then to hyperboloids. It
>> is more a case of how much, not where. The where is the
>> same for all of them.
>> Dwight
>>
>>
>>
>>
>
>

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