Alley in Pisa, Italy

by Lars Kotthoff

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One of my favorite techniques of photography is "long exposure", night photos that take minutes or more to complete. The usual problem with these is picking the exposure.

Built-in luxmeters of most cameras will give you a flat zero or a noise around it, and even if they don't, that gets seriously biased by point light sources that will remain similar bright dots whether I set exposure to 30 seconds or to 10 minutes. It's the dark background that matters and that I want to be visible.

Currently, I'm working by trial and error, which is problematic considering 3-4 tries to get the exposure just right, each try taking 15 minutes or so.

I wonder though, are there any fault-proof (and not budget-destroying) methods of sure-fire adjustment of shutter time for night photos that don't take hours? For example cameras / firmware hacks, where you could obtain "exposure progress" to show? Like, I watch the screen, where the image gets gradually brighter following the light gathered by the lens, then I decide "it's enough", press the remote button and the camera finalizes making the photo?

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I'm going to vote to close also but strongly encourage you to edit and rephrase, sort of along the lines of "how can I determine the proper exposure for insanely long exposures." –  Paul Cezanne Aug 26 '13 at 13:19
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As I read it, the other question asks about a series of individual snippets during long exposures to deal with issues of composition during light painting. In other words each interval shown without the previous interval retained. This question deals with the total cumulative image constantly updated to deal with exposure. –  Michael Clark Aug 26 '13 at 14:08
    
"Partial" as in "not complete" — I don't think that the other question meant individual segments. In any case the accepted answer to the other deals with a cumulative image. –  mattdm Aug 26 '13 at 16:30

1 Answer 1

up vote 15 down vote accepted

The Olympus OM-D EM-5 can display the cumulative collection of light in a long exposure. But there is another way to test long exposure that takes much less time and works with almost any digital camera.

Start out by setting your camera to the highest ISO setting it has, open the aperture of your lens as wide as it will go and start with short exposures until you find the correct exposure. Then reduce the ISO and aperture to what you desire and increase the exposure time by the same number of stops. Remember that ISO and shutter speed double/halve for each one stop interval up/down. Aperture is multiplied/divided by 1.4 (the square root of two) for each stop up/down, so every two stops is double/half the previous one.

For example, if you find that ISO 12,800 @ f/1.4 requires a 1 second exposure, then to use ISO 100 @ f/8 you would need to increase the shutter speed (Tv) seven stops to compensate for the ISO difference and another five stops for the narrower aperture. Increasing Tv 12 stops from 1 second yields a Tv of 4,096 seconds, or roughly 68 minutes.

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The Olympus OM-D E-M5 has this feature. See the question this is marked as a duplicate of. Your suggestion for testing is also good as an alternative. –  mattdm Aug 26 '13 at 13:03
    
Does the OM-D E-M5 display a cumulative image (i.e 1-5 sec, 1-10 sec, 1-15 sec, etc.) or does it display a series of snippets from each interval (i.e 1-5 sec., 6-10 sec., 11-15 sec, etc.)? –  Michael Clark Aug 26 '13 at 15:55
    
Cumulative. Watch a demo: youtube.com/watch?v=Rz4g-MFW_t8 –  mattdm Aug 26 '13 at 16:28
    
This is what i usually do for low light photography in caves :) –  NULLZ Aug 27 '13 at 1:27
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@Apalala If you want a dark scene to turn out averaged to 18% gray you can. –  Michael Clark Sep 25 '13 at 1:44

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