Tom Droege made some experiments on the Mark IV camera lenses, as described in E-mail sent out May 18-May 20. He attached two examples of stellar images near the corners of the field of view.
I show each new image side-by-side with an old image from the same corner of the camera; I took the old images from V-band image V1265_920.fts. New image on the left, old image on the right.
Stellar image near X=140, Y=40 (upper-left corner)
Stellar image near X=52, Y=1904 (lower-left corner)
I measured the concentration of light within each stellar image with radii 1 pixel, 2 pixels, 5 pixels, and 10 pixels. Here are the fractions of light falling within circles:
1-pix aper 2-pix aper 5-pix aper
---------- ---------- ----------
10-pix aper 10-pix aper 10-pix aper
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old upper left 0.149 0.394 0.765
new upper left 0.194 0.490 0.802
old lower left 0.152 0.447 0.765
new lower left 0.160 0.447 0.817
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These measurements should really be done on a bunch of stars, since they vary slightly with stellar brightness. It appears that Tom's adjustment of one lens does help signficantly to concentrate light, especially in the upper left corner.