I’m trying to figure out if I can use a Nikkor 480mm f9 for some experiments. I already have the lens so hoping I can make it work. Does anyone know the size of the image circle of this lens when stopped all the way down to f128? When looking at the specs, it’s listed as having an image circle of 820mm @f9 and 1:1. Is there a formula that can be used to determine the size of the image circle at different f-stops and magnifications? If there’s a formula, that would be hugely useful. Alternatively, does anyone know the size of the image circle at infinity @f128. I’m not concerned here with resolution, corner sharpness, or anything that we typically use to determine if a lens makes an acceptable image i.e. I’m not looking for the “usable” image circle. I’m just looking for the actual image circle (illumination not resolution) at f128. Any help would be appreciated.