I took the plunge and picked up the Nikkor T ED 360mm, 500mm and 720mm lenses recently, and did a quick test for all three on 8x10. The results are below. The executive summary is: the 360mm covers a bit more than 5x7 as per the specifications, the 500mm covers more than 6½x8½ and the 720mm fully covers 8x10. The 360mm and 500mm images were made with the lens closed 2 stops from wide open, while the 720mm was only closed one stop.
I did a quick measurement of the circles of illumination and the 360mm lens covers about 230mm and the 500mm lens covers about 280mm. The limits of the circle produced by the 720mm lens is well outside the 8x10 film area.
Made with a Toyo Field 810MII using Shanghai GP3 100 film, developed in replenished ID-11 using continuous agitation 10 minutes at 20˚C. Exposure times were 1/4, 1/2 and 1 second (the light was fading so I gave the last image with the 720mm an extra s. These were my first three photographs using the lenses and they were made from the walkway of a road bridge, so overall image quality (focus, sharpness etc) may not be optimal due to deficiency in my technique and vibration from traffic – particularly the 720mm lens.
Hopefully these images will answer definitively what the coverage of these lenses in actual use are.

Nikkor T ED 360mm f8 at f16

Nikkor T ED 500mm f11 at f22

Nikkor T ED 720mm f16 at f22
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