This is the twelfth in a series of posts about the Nikon 70-200 mm f/2.8 S lens for Nikon Z cameras. The series starts here.
Yesterday, I told you about the quantitative differences that Imatest and I found between the Nikon 70-200 mm f/2.8 S and E lenses using a slanted edge and a Siemens Star target. Now I’m going to show you two more sets of results, one fairly conventional and one that I’ve never seen before.
The fairly conventional one is a contour plot of MTF contrast levels in polar coordinates by slice angle. Here’s what Imatest has to say about that plot:
The plot… shows MTF70 through MTF10 displayed in polar coordinates. Spatial frequency (cycles per pixel in this case) increases with radius. (This is the opposite of the image itself, where spatial frequency is inversely proportional to radius.)
This plot is most similar to the spider plot shown in Image Engineering digital camera tests and Digital Camera Resolution Measurement Using Sinusoidal Siemens Stars (Fig. 15), by C. Loebich, D. Wueller, B. Klingen, and A. Jaeger, IS&T, SPIE Electronic Imaging Conference 2007.
Here it is for the two lenses in the center:
Those look similar.
In the corner:
The differences are again not striking, with the E lens more symmetric.
Now for the novel approach. In this year’s version of their analysis program, Imatest has introduced a metric to gladden the heart of any computer scientist: the Shannon capacity. Here’s one of the plots associated with that metric.
The information capacity of the S image is 3.03 bits/pixel, and that of the E image is slightly higher at 3.10 bits/pixel.
In the corner:
The information capacity of the S image is 2.57 bits/pixel, and that of the E image is slightly higher at 2.78 bits/pixel. Both are lower than the center images, which agrees with my visual impression.
It’s going to take some time to see how the Shannon capacity squares with image sharpness in general, but it is an interesting new metric.