Quote:
Originally Posted by Stefan Buda
Yes the spacing between the interference fringes represent 1 lambda on the wave front regardless of the relative tilt between the two surfaces. In other words they show the size of the air gap between the test plate and the optic. If the two surfaces have the same shape, the fringes are straight.
It is very easy to see a deviation of 1/4 spacing, especially if one spread out the fringes. I kept the fringes rather tight for the pictures as it was easier to photograph them.
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So the test plate has to be perfect? Did you make it as well?