RUFLI – the pinhole unit of measure

Pinhole photography is an excercise in the art of approximation and imprecision, a venture into the realms of serendipity.


Everything to do with pinhole photography is measured in RUFLIs: The diameter of the hole made by the pin can be fairly accurately measured but in reality a regular pin, for instance, makes a hole that is RUFLI 0.5 mm across, the distance from the pinhole to the image plane might be RUFLI 75 mm making the aperture RUFLI f/150. On a sunny day with regular photo paper the required exposure would be somewhere in the region of (i.e. RUFLI) ten seconds or so.

RUFLI should be pronounced ‘roughly’.

My mobility of late has been hampered by a torn calf muscle and photography has had to take a back seat. However, today I hobbled out with a tin can punctured by a pin, the hole sealed by a piece of electrical tape, and the screw-on lid sealed from light leaks by a strip of sticky-backed felt. Inside the can was a sheet of 5″x7″ Ilford MGIV RC Silk photo paper. My mission was to make a shoreline exposure of the paper in the can. Mission completed, here’s how it went.

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The observant may notice a few things in these photographs of the coffee-tin pincam:

  • The pinhole is positioned about three-quarters of the way up the can, not dead-centre as might be expected. This is not a mistake! When the pinhole is centred, so will be the horizon. By positioning the pinhole as I have I can raise or lower the horizon giving greater emphasis to sky or foreground depending on whether the can is upright or upside-down.
  • I’ve labelled the pincam with what look like accurate measurements of P.D., diameter and aperture, ignoring the RUFLI unit of pinhole measurement. This is merely an illusion created by the number of decimal places used. Had space on the label permitted, each parameter would have been prefixed ‘approx.’.
  • I refer to P.D. – Projection Distance. All too often the distance between the pinhole and the image plane is erroniously referred to as the focal length. However, ‘focal length’ correctly refers to the distance from the nodal point of a lens to the plane of focus of the lens. In a pinhole camera there is no lens and therefore there can be no focal length. Light projects through the aperture of the pinhole and continues to the image plane. ‘Projection Distance’ is simply the use of accurate terminology and is RUFLI correct.

For my image of the shoreline I wanted more foreground than sky so I turned the can upside-down.

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I developed the paper negative in Ilford Multigrade diluted RUFLI 1+9 at RUFLI 17ºC until it looked OK-ish in the darkroom safe-light. I only took RUFLI 35 seconds or so.

Once dry I scanned the paper negative and inverted it to a positive in software. After a bit of tweaking of levels, these are the scanned negative and positive images.

shoreline negative
shoreline positive

There. I’ve hobbled happily with a pincam and my leg is so much better now an image has been made.

I’m thinking the paper is a bit fogged and could do with a tad more contrast. That might be due to light bouncing around the exposed shiny interior of the can. A quick spray of the inside with flat black paint should solve that for next time. Or it might be that the bedsheet I used to create a dark space in which to load the paper into the pincam was only RUFLI effective …


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