RE: ATM Anti reflection coatings and TDE (not related)

["Bertapelle, Ken" <Bertapelle.Ken@tci.com>]

Hello Balaya,

My recollection of the discussion of TDE in Suiter's book is
that the light from the edge is scattered all over the places
where light from other portions of the mirror is focusing.  This
is what causes the general degradation of the image.  If you 
can get a copy of his book ("Star Testing Astronomical Telescopes")
it's easy to see from the diagrams how this happens.

- KenB

> -----Original Message-----
> From: Ashish, Balaya (IE10)
> [mailto:ABalaya@meghadoot.hiso.honeywell.com]
> Sent: Friday, July 30, 1999 5:33 AM
> To: atm
> Subject: ATM Anti reflection coatings and TDE (not related)
> 
> 
><snip>
> 
> 2) TDE : How does it degrade the image? By definition, TDE 
> means that part
> is slightly convex so light coming in must, after reflection, 
> be diverging
> away from the cone that is being reflected (converging to 
> focus). So how can
> this diverging part interfere with the converging part and 
> spoil the image.
> Of course I know it does spoil the image because doing a star 
> test on my
> telescope (I'm hooked. The star test is wonderful and its 
> amazing how well
> it works. It showed me I have TDE. Thanks to all who 
> encouraged me to try
> the star test) shows me but the explanation eludes me.
> 
> Clear skies,
> Balaya
>