how to translate exposure factor figures into reality?

[DWThomas]

... Even a quarter-stop anomaly in your initial reading will be grossly exaggerated by the time you get to f333. ...

Hmmmm -- actually, since stops are ratios, I believe after the extrapolation, you'll still only be off a quarter stop. But the basic situation is true that there are enough variables tangled up here that some simple tests are likely the quickest way to get there.

The fudged metering works pretty well for me with film, but since paper doesn't normally spec an ISO and may have some spectral issues as well, it would be necessary to figure out an ISO from tests to get any real precision.

Myself, once I start pinholing, I tend to toss precision out the window.

[Chan Tran]

I wouldn't use the exposure factor at all since the aperture is known (i.e. f/333) the film speed or rather paper speed is known as ISO 3.2. What else does one need except for the reciprocity characteristic of the paper?

[DWThomas]

I wouldn't use the exposure factor at all since the aperture is known (i.e. f/333) the film speed or rather paper speed is known as ISO 3.2. What else does one need except for the reciprocity characteristic of the paper?

I doubt many meters can give a direct reading for f/333 or f/256. My Digisix stops at f/32 and my Sekonic L-508 ends at f/128. Pinhole Designer can actually output a table (Excel spreadsheet compatible) with a list of settings compensated for the exposure factor and optionally, reciprocity. The latter is only for some films and a bit suspect in at least one case I've tried.

One notes the shutter speed indication for f/22, uses that to index the table and get a value of how long to hold the button down. Such a table easily fits on a small card. Obviously one can mentally diddle the f/22 and shutter speed values by stops and come up with a new shutter speed, but the chart is simpler (based on my one day a year experience!)

[Tom Miller]

I wouldn't use the exposure factor at all since the aperture is known (i.e. f/333) the film speed or rather paper speed is known as ISO 3.2. What else does one need except for the reciprocity characteristic of the paper?

Reciprocity failure is a big problem. Each paper and film has different reciprocity failure characteristics. Tech specs for film usually include reciprocity compensation factors; but since they are not needed for enlargements onto paper, the manufacturers don't publish them. The easiest way around the dilemma it is to test. Also, the 3.2 ISO mentioned in the original post seems to be little golan's light meter's lowest setting. People usually rate paper anywhere from ISO 2 to ISO 6. One advantage of testing is that when the basic daylight exposure for the tested camera / paper or camera / film combination is known, adjustments to the it, like giving three or four more stops of exposure, are linear. For practical purposes, doing the test in the pinhole range incorporates reciprocity in determing the basic exposure and no further compensation is needed.

[RalphLambrecht]

Reciprocity failure is a big problem. Each paper and film has different reciprocity failure characteristics. Tech specs for film usually include reciprocity compensation factors; but since they are not needed for enlargements onto paper, the manufacturers don't publish them...

In the absence of testing, paper typically has a reciprocity failure of 1/12 stop per stop of exposure.