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Remember what the definition of the f-stop number is. The aperture is written as a fraction with a numerator of the focal length, f, and with a denominator of the f number.

If there is no way to change the distance from actual pinhole to film, then all three have the same focal distance and the f/number is just the distance from pinhole to film divided by pinhole diameter. With 30mm, this would be f/150, f/100 and f/75.

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It's possible that the writer of the instructions was thoroughly confused. The information quoted is at least confusing.

In truth, you aren't restricted to a particular focal length for any given pinhole, although there will be a point where it produces a sharper image. The focal lengths you have for the various pinhole sizes are not too far from optimal, but you can use the pinholes at any focal length. The f/stop will change with the focal length.

The term "f/stop" is just what it looks like: a fraction -- "f" is the focal length, and "stop" is the diameter of the aperture. The focal length divided by the aperture size gives the numerical f/stop.

Pinholes will cover a very wide cone of view. So you just have to experiment whether the darkening of the corners (vignetting) will be obnoxious when the film area exposed covers 6 x 12 cm with 20mm pinhole, etc etc. It is fun to experiment with 1 or 2 films, Joe. Make, take note and then you will know what focal lengths work in which format for you. Good success and luck!

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If the camera is somehow set up to zoom, or has different spacers, or if the different pinholes have mounts that change the distance from hole to film, then it would be different. If you can use three different focal distances, then they probably mean for you to use the smallest pinhole for the smallest focal distance, largest pinhole for largest focal distance. There are formulas for calculating optimal pinhole size, and they would give you this kind of a result (IE, use larger pinhole, giving smaller f/number, at larger focal distances).

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If you put the .2mm pinhole at the same distance from the film as the .4mm pinhole, then indeed the .2mm hole will have a numerically larger f number, by two stops.

The camera must have been constructed with 3 positions for the pinhole (bellows of sorts, or inserts ,,,) at different distances (20, 45 and 80mm) from the film plane:

I would not be surprised if the shortest focal length wouldn't cover the larger negative sizes due to geometrical considerations.

If you want to place a pinhole at a focal length of 30mm, then the .2mm will give you an aperture of 30mm/150, or the .3mm will give you an aperture of 30mm/100, or the .4mm will give you an aperture of 30mm/75. Best sharpness is probably around f/150, or .2mm, but experiment. The bigger pinholes will give faster exposure times, of course.