RE: ATM parabolizing-long

[BOB PRABOWO <BOB@bahana.co.id>]

Hi Guys,

I spent the whole weekend reading Tex' and Berry's books, the chapter on
Foucault test. Confusing at first, but I think I got it. I desperately
hope I got it!

Here's my understanding after reading the books over and over again, I
need your verification whether I understand it right. 

A.The objective of Foucault test is to measure the ROC of the mirror
(the measurement of the Spherical Aberration) and then compares the
result of the measurement with the theoretical value. This is done
without the Couder mask. In Tex book, the theoretical value of the
longitudinal aberration is: 
delta p'=h^2   (the triangle symbol reads as Delta, right?)
        R

In Berry's book, since the tester using a moving light source, the
theoretical value is 
delta R= r^2/2R.

B. The Couder screen is used the isolate a certain zone of the mirror,
and measure the longitudinal aberration of the zone than compare the
result with the theoretical value. 
In the Couder Test Data sheet, the  value is hm^2/R (according to Tex)
or, hm^2/2R (according to Berry). Actually Berry's book use r eff. and
for hx he uses r out.

Now, questions time :-)
 
1. Regarding the longitudinal aberration measurement. 
I place the KE at the COC, move the KE toward the mirror to get inside
COC (the right side of the mirror dark), note the number read on the
micormeter dial. And then I move the KE away from the mirror to go
outside COC (the left side of the mirror dark) and do the same
procedure. I calculate the KE travel distance and the number is the
Longitudinal Aberration (delta p'). I compare the result with the
theoretical value. And then what? If it's less than the theoretical
value, what should I do? and if it's more?

2. For the Couder test, I do it exactly the same way as I do the
Longitudinal aberration measurement, except this time with the Couder
mask in place. 
I place the KE at the COC of zone 1, do the same steps as mentioned
above, and take the measurement. And then go to zone 2 , do the same
procedure, take measurement and continue to, say, zone 4 of the mirror.
Is that correct? I haven't tried it yet, my wife complaint about me
spending so much time on the mirror :-(
And after the measurement, what do I do? For instance, if the readings
in zone 1 is higher than the theoretical value, what shoud I do? I guess
this is called figuring, right?

3. Couder Screen
I tried to make the Couder screen myself, using calculator, compass and
Exacto knife. My first try was using the list in Berry's book. No
problem, I could make the screen. But when I tried to follow Tex's
instruction, I had a problem. I could determine the ouside radii of zone
4 (it's the optical diameter, right?) BUT I do not know how to determine
the inside radii of this zone. I do not know how to determine the width
of the zone, is there a formula for it, i.e., the width of the zone has
to be determine following the formula? or is it left to our discretion
to determine the width of the 
zone ?

I hope I understand it right. 

Bob P. Sumitro
Jakarta, Indonesia
the new land of the free

"To be able to express your opinion freely, free of fear, ain't that
great!" 

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