Re: [ATM] Ronchi challange

[Dominic-Luc Webb <dlwebb@canit.se>]

On Fri, 3 Feb 2006, Dale Eason wrote:

> http://home.comcast.net/~doeason/rc/100lpi_outside_p150.jpg
>
> I'm curious what the ronchi experts can tell me about
> the mirror in this image.

Maybe I could try and give this a stab after a long hiatus
from ATMing?

I am not an expert, but do toy with these. I guess
this 16" is about F/3.5, obviously a challenging project.
The straightness of the two outer lines immediately bending
into a new line or curve at about the 33% zone leads me to
suspect you have at least two distinct curves on this
surface with a major deflection at the 33% zone. In other
words, I think you do not have a nice smoothe curve running
from center to edge. What kind of surface were you after?
Whatever it is, I fear you are bit off the mark, so far.

Not sure about a better grating. What did you use this time?

I think you will need more images, as you have already suggested,
to determine exactly how serious this is. My own experience with
much faster systems often lead me to go back to grinding at about
#600 SiC, after I decided my flaws, which at first did not seem
too bad on these single shot pics, represented errors exceeding
20 microns. With such deep sagitta on the faster systems, you can
easily have such large errors that they cannot be polished. Best
to leave anything more to experts.


Dominic-Luc Webb




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