BetterPhoto Q&A
Category: New Questions

Night photos

Many thanks, Will, 20/05/01

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May 20, 2001

Some of the newer cameras have electronic shutter releases without this threaded socket for a cable release. If yours is like this, is there a socket for an electronic equivalent of the mechanical cable release that can be used to hold the shutter open in the "B" setting? If this is the case, you will undoubtedly have to get the camera maker's electronic device for this.

With very long exposures, close counts. For an exposure of 10 seconds, 5 seconds is one stop less and 20 seconds one stop more. If you expose for 9 or 12 seconds you won't notice the difference between that and 10 seconds. In the past I've simply locked the shutter open with a cable release and counted out loud ("One-one-thousand, two-one-thousand" etc.).

Now for a very, very, very old trick:
If you have any way of locking the shutter open, but are still afraid of camera shake doing so with long timed exposures:
Cover the lens by holding an opaque hat over the front of the lens. 50 years ago I would have advised using your "felt fedora," but a heavy ball cap . . . without vent holes . . . works nowadays. Lock the shutter open, wait a second or so, then remove your hat from in front of the lens and start counting the exposure. When you've finished counting it, place your hat back over the lens front, then close the shutter. Just hold it over the lens front, don't hang it on the lens or you'll induce shake with it.

Ancillary issues:
1. Reciprocity Failure:
Check your specific film data sheet. At long exposure times over about 1 to 10 seconds the film speed rating plummets. This means you must increase exposure time even longer to compensate for this. At what shutter speed this occurs is very dependent on the film. All of the major film manufacturer sites (Agfa, Fuji, Kodak, and Ilford) have the film data sheets on-line. Find the sheet for your specific film and look for the "reciprocity failure" section in it. It will give exposure compensation recommendations for long exposure ranges. Also an issue with some color films is a shift in color response. The data sheet will give color compensating filter recommendations along with the exposure compensation.

2. Diffraction Limiting:
The first thing that caught my eye was using an f/32 aperture to maximize depth of field making a night city-scape:
a. An f/32 aperture in 135 format (35mm cameras) is typically found only on some long telephoto lenses (200mm and up). It's more common on larger film format lenses (see "b").
b. For 135 format cameras, aperture diameters smaller than f/16 bite into resolution "diffraction limiting" with nearly all lenses. This effect is caused by the light "spreading" when it passes through a small circular opening. In general, apertures tighter than f/16 will degrade resolution in the overall image, losing what you are trying to gain in maximizing the DOF with it. Because of this I recommend f/11 if possible and no tighter than f/16.
Caveats: a specific lens design may allow it (some long telephotos); the aperture at which it diffraction limiting occurs also depends on film format (size).

-- John

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May 20, 2001

The Kodak Pocket Photoguide has a section on "existing light" for estimating long exposures using examples of different types of situations. In it is a wheel that helps estimate combinations of aperture and shutter speed for a given film speed. It doesn't compensate for film reciprocity failure; you have to do that after using the wheel in the guide. Don't have one here with me, but I believe the larger Kodak Professional Photoguide has a similar section. If the desired aperture is beyond the range of times shown on the wheel, increase time for increased aperture stop-down, stop for stop, then do any reciprocity failure compensation required.

Remember they are guidelines; experience with low light photography helps. Take a guess, shoot some film and record what you did. See what happens and adjust from there. Bracketing exposure with several shots (if possible) is recommended.

-- John

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May 20, 2001