Thank you very much for your blog, I learn more from it. But, I am confused about the Fig.2 in this blog. How it the formula y=0.0188x+0.409 got from the curve. Thank you very much!

best wishes!

pi

My original point still stands, though: the slanted edge method will measure the correct MTF even if the edge is at a 44 degree orientation — you will just have to replace the 1D sinc MTF with the appropriate cross-section taken from the 2D sinc MTF to obtain the reference MTF curve.

The reason, I suspect, for recommending angles between 2 and 10 degrees are twofold: a) it completely avoids the undersampling at the critical angles of 14 and 26 degrees, and b) it makes it simpler to remove the photosite aperture MTF if you want only the lens response (i.e., just divide by the appropriate 1D sinc).

]]>For big angles,you will start to measure the mtf in the diagonal direction, which is worse since the square photosite of the detector are “widder” on the diagonal. ]]>

Other than those two critical angles, you should be able to obtain decent results with anything between 0.5 degrees and 44.5 degrees.

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