Narrow DOF

[mgrayson3]

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Your analysis is wrong.

 

<Pointless discussion redacted>

Edited May 17, 2018 by mgrayson3

[alan.y]

Peter Karbe talked about the rapid contrast falloff of the apo 50 explicitly with Overgaard, in relation to the correction of aberrations within each element (as opposed correction between elements, so in a way it is the opposite of an FLE?)

 

“Yes!” Peter points a finger in the air and I feel like the student who finally got it, “the contrast has to fall off very fast in terms of depth of field. That’s it. That is the idea – and the ideal. The fall off has to be very fast!”

 

“You point the lens and shoot, and where the focal plane is, the contrast should be high. The front and behind should fall off very fast. That is the difference between the older Summicron lenses and the APO-Summicron. Not in terms of sharpness but in terms of contrast behavior.“

 

http://www.overgaard.dk/leica-50mm-APO-Summicron-M-ASPH-f-20.html

Edited May 17, 2018 by alan.y

[mgrayson3]

I photographed a tape measure running away from the camera with two lenses of different philosophy - The 120/2.5 APO-Makro and the 100 Summicron. The 100 isn't quite as soft a rolloff as the older designs, but I loaned out my v2 50 Lux, so it's the best I can do.

 

Sure enough, there is a marked difference in the point spread as a function of distance. The real function is too high-dimensional to visualize, but if we assume symmetry (reasonable on axis), then we get a surface plotting brightness vs. distance from the axis and distance from the plane of focus. The APO-Makro does, indeed, have a non-linear spread vs. distance near the plane of focus. The older design 100 is more linear.

 

Here's an example of the sharp rolloff of the 120 APO

 

Unfortunately, I don't have a direct comparison with the 100, 

 

 

I'll try for a direct comparison when I can get someone to sit still for it.

Edited May 18, 2018 by mgrayson3

[pico]

When this concept is accepted we should expect a revival in spherical aberration where there are two planes of focus.