Nikkor 480mm f9 image circle at f128?

[Fragomeni]

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 (http://www.savazzi.net/download/manuals/Apo-Nikkor.pdf), 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.

[ic-racer]

Send it to me and I'll check it :)

[Tin Can]

pencil and paper

draw the cone of light

Macro is possible

[Len Middleton]

it’s listed as having an image circle of 820mm @f9 and 1:1.

Well, given its original intended usage for photo-mechanical reproduction, the image quality within the specified image circle would be high, but uncertain of image circle quality fall off out at the circle of illumination.

At 1:1, your bellows draw is twice it would be at infinity, and as the cone of light the lens throws would be identical in geometry, but only half the 1:1 size, your image circle would be half that at infinity.

I do not know what the impact stopping down would have to the image circle.

For a darkroom enlarger, for magnification and dimensions, there is the following formula:

u=v*F/(v-F)=F*(M+1)/M or v=u*F/(u+F) , where u = lens to negative distance (inches), v = lens to baseboard distance (inches), M = Magnification, F = lens focal length (mm), and u+v = negative to baseboard distance (inches)

You will need to put a 25.4mm to one inch conversion factor in a couple of places, as required.

I used the formula to calculate maximum print size for a big Durst enlarger with limited head room, but physics should be same for a camera....

Hope that helps,

Len

[Maris Rusis]

Easy to measure.
Stop the lens down to f128 and place a ruler or tape measure 480mm behind the lens aperture and at right angles to the optical axis. Now walk left and watch when the exit pupil of the lens cuts off. Note the point where the line between your eye and the exit pupil crosses the ruler. Then go right and do the same thing. The difference between the two distances on the ruler or tape is the diameter of the illuminated infinity image circle as restricted by mechanical vignetting.

[Fragomeni]

Easy to measure.
Stop the lens down to f128 and place a ruler or tape measure 480mm behind the lens aperture and at right angles to the optical axis. Now walk left and watch when the exit pupil of the lens cuts off. Note the point where the line between your eye and the exit pupil crosses the ruler. Then go right and do the same thing. The difference between the two distances on the ruler or tape is the diameter of the illuminated infinity image circle as restricted by mechanical vignetting.

This is gold. Thank you. Thanks to the other who responded as well. This is the kind of method I was hoping to find to figure this out. It’s essentially the same as looking down through the corners of the ground glass to check your coverage. My issue there is I haven’t finished building the rear standard get so this solved it for me. According to the approximation I got from this method, the 480mm f9 Nikkor definitely won’t cover 20x24 even stopped all the way down to f128 — image circle at that aperture looks to be around 660mm, a fair bit short of the 793-ish needed to cover 20x24. I did end up finding that my Zeiss 60cm f9 Apo-Tessar will cover with room to spare at f90 (I forget already but I think it was around 1080mm circle. So I’ll be using that and I’m considering a 450mm Nikkor M that I know covers from conversations with Sandy King.

Very much appreciate the help folks.