Photography by Wesley R. Elsberry

Last update: 980730

Time exposure
B+W development
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Time Exposure

The time exposure is one of my favorite ways of manipulating an in-camera image. Having time to move around in the frame and alter the way things record themselves on film opens another dimension of expression.

A problem encountered in time exposure is that of "reciprocity failure". This term indicates that the usual way that film responds to light fails for long exposure times. One cannot simply exchange one unit of f-stop for one unit of time and expect the same image density on the developed film when the time is longer than about 1/4 second.

Adjustment for reciprocity failure

The following table is one that I have used as a starting point for black and white time exposures. Use with color film is fairly rough. Expect to experiment a good bit...

Time on meter   Factor       Time to expose

1/2s              2            1s
1s                3            3s
2s                4            8s
4s                5           20s
8s                6           48s
16s               7          132s
32s               8           ~4min
60s               9            9min
120s             10           20min
240s             11           44min

44 minutes is the longest exposure that I've attempted in this way, and the adjustment worked fine for Tri-X Pan Professional Sheet film, developed in HC-110 Dilution B.

Black + White development

Getting from exposed film to good negatives isn't - or shouldn't be - a matter of luck. Planned development is the key to consistent results, and consistent results can lead to superior results.

POTA - another developer for Technical Pan film

Going from memory, here is the formula for POTA, a developer to produce low contrast images on high contrast film, like Kodak's Technical Pan film.

1.5g 1-phenyl-3-pyrazolidone (Ilford's "Phenidone")
30g sodium sulfite
Water to make 1 liter
Mix at warm temperature (120 F) until ingredients completely dissolve. Cool to 68 F. Use immediately. This developer oxidizes rapidly when exposed to air.
Base development time: 20 minutes. Expect to experiment a good deal.

Like I said, that's from memory. It has been some years since I've used that formula, mainly due to getting involved in these computers.

If you are exposing Technical Pan for continuous tone development with POTA, base your exposures at ISO 20, and bracket. Tech Pan does not hold detail in highlights... once you overexposure a detail, it is gone. This contrasts with the case for Tri-X Pan, where with sufficient patience, one can extract quite a bit of grainy but recognizable features out of negatives with three stops worth of overexposure.

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