That is an interesting target--an alternative to the dead leaves model?

Hi Bill,

Well they allow to do similar things, e.g. determine MTF curves, but they are also different in how they achieve that. The type of target that I suggested has several very interesting characteristics (sub-pixel oversampling accuracy is just one of them) that are not as available to exploit in the dead-leaves version. The symmetry allows to additionally do distortion calculations at the points where the patches intersect. A single target shot therefore delivers multipurpose data. The target also allows to check for uniformity of lighting, and by comparing the patches at different positions it is possible to judge whether the target was shot square, all usefull for test quality control.

Anyway, how would one use this target? You have already presented your web based method employing a slanted edge target to determine the optimal sharpening radius. How does this relate to the new target?

It has been researched that the slant angle of 5-6 degrees versus the horizontal or vertical axis provides the best quality for SFR/MTF calculations. The only (minor) drawback is that it restricts the outcome to 2 orthogonal axes. The proposed new pattern has edges at all 360 degrees, not just 2 orientations. This allows to produce MTFs at any rotation angle, which makes shooting the target 'rotation invariant'.

For the simpler task of just determining the PSF, it also offers different benefits. It does not only allow to determine a simplified elliptical PSF (where only the hor/ver sigma dimensions can vary), but also an even more accurate PSF for more complex blur shapes (e.g. astigmatism with a more diagonal elliptical shape towards the corners).

The required math is a bit more complex, but that's why we use computers. The same calculation principles can be used to analyse regular images which also have edge detail at various orientations. Depending on the required accuracy or calculation speed it is possible to use different calculation methods, but they all require a more complex software application than my current webtool.

Cheers,

Bart