Re: [ATM] Recognising TDE

[Mike Lockwood <melockwo@uiuc.edu>]

James,

James Mulherin wrote:
> Any way, here goes. A TDE spreads light radially outward from the star's
> image causing spikes and causing loss of contrast. On the other hand, a TUE
> causes light to come to focus ahead of the light coming from the good part
> of the mirror. In fact, this light crosses the focus point and then
> continues on radially outward. I suspect that the effect of a TUE is
> essentially the same as a TDE, although I doubt that anyone could produce in
> a TUE the kind of extremely steep slope that can be produced in a TDE.
> 
> Can any one else comment on this. Is a mild TUE effectively the same as a
> mild TDE in the star test? 

A point of terminology - I define the edge as the outer ~1/16" of the 
mirror, and I have never seen a true TUE by this definition.  However, 
I have seen plenty of "turned up outer zones", or undercorrected outer 
zones, 1/4" and wider.

James, you've made more mirrors than me - ever seen a true TUE by that 
definition?

You might try the "Star Test" feature of FigureXP to simulate the star 
images of a mirror with a narrow undercorrected outer zone.

A turned up outer zone will often masquerate as a good outer zone when 
the mirror is cooling!

	Mike Lockwood


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