Re: [ATM] Calculate Astigmatism

["john sherman" <atm@mail.johnspics.com>]

>> I don't understand the need to not disturb the apparatus 
>>over a mirror rotation.  

>Another alternative would be to use a pinhole, 
>and rotate the direction
>that the KE moves to intersect the image.  
>If pinhole and mirror are not moved, 
>then one might measure on-axis astigmatism this way

Hi Dave,

That's a good suggestion. If you make the slit two-dimensional by using a pinhole, then the test setup becomes more robust, requiring less rotations. What if you also replaced the knife edge with a 2D edge, a small, round spot? Could you then test for and measure astigmatism without having to disturb or rotate the mirror, the mask, the knife, or the light source? You could use the four-way mask described by Herb Kasler a while back to check both horizontal and vertical zones at the same time. Then rotate the mask only and you can check both diagonal zones at the same time. 

You like?

John



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