From: "Martti Koskimo" 
To: 
Reply-To: "Martti Koskimo" 


You could use transverse  ray error example to clarify this.

Lets take a 2000 mm focal length . If at the Objective (mirror) surface
error causes a 3 arc second displacement, then at the focal plane the
displacement ( transverse error) is  2000* tan(3 arc sec)=about 50 Waves.
If the error is 10 millimeters from the focus the error is error is
10*tan(3 arc sec)=0.25 Waves.  The error is 200 times smaller. Use simple
college geometry with triangles.
The film at the focus can have clump errors that are as bad as focusing
tolerance and you still have 'sharp' picture.The quality  tolerance for
field flattening lens near the focus has thus very relaxing tolerances. If
you have Optical Design program , you can run a tolerance analysis to get
exact numbers for each particular case.

Martti Koskimo



----- Original Message -----
From: 
To: 
Sent: Sunday, April 06, 2003 8:54 PM Subject: Re: ATM How Good Does a
Diagonal Need to Be?


>
> >The Quality of the diagonal, if it is located at the objective(
> >mirror), needs to be the 'same' as the main mirror tolerance. This
> >tolerance is reduced to the same as the focus tolerance at focal plane.
>
> It seems to me that a given surface error near the focal plane would
> effect a greater "percentage" of the total image, therefore have a
> greater effect.  What's wrong with this logic?
>
> Jim L
>
>
>

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