How to Calculate Camera Equivalent Exposures for Night Photography
Nighttime photography requires that you shoot with a fast lens or use flash to capture a moving subject. However, if a subject is not moving, for example, in a nighttime cityscape shot, you need only a steady tripod, and a reciprocity failure chart if you are shooting film, and you can take well-lit shots with exposure times longer than 30 seconds. Because all film suffers from reciprocity failure, where the film does not stay accurate to its box speed in long exposures, it adds an additional element that you will need to calculate in finding the correct exposure time.
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Things You'll Need
- Light meter
- Tripod
- Reciprocity failure chart
- Calculator and notepad (optional)
Instructions
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Instructions
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Mount the camera on your tripod. Take a meter reading using either the camera's meter or a hand-held light meter.
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If the exposure must last a second or longer and you are using film, consult your reciprocity chart to find the correct exposure time. For instance, Kodak Tri-X 400 suffers from reciprocity failure at one second or more exposure. According to the chart, Tri-X has a reciprocity failure factor of 1.5 at one second and 2 at two seconds. That means that if the meter reads a two-second exposure, you must multiply the meter's reading by the reciprocity failure factor of 2; so Tri-X 400 requires a four-second exposure to get the same exposure level as a digital sensor would get at just two seconds. Digital sensors do not suffer from reciprocity failure.
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For longer exposures continue to calculate the proper exposure length using the meter reading and checking that against your reciprocity failure chart.
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Take the exposure. If you are using a digital SLR, check the exposure by previewing the image to see if the results are bright enough and take another exposure if you need to.
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Tips & Warnings
Digital nighttime photography presents its own challenges. When a digital sensor is left on for multiple seconds, it will heat up and this will show up as noise in your photography. Today, many DSLRs have "long-exposure noise reduction" features. Be sure to select this when shooting exposures longer than a few seconds.
For very long digital exposures, it might be helpful to also take a quick shot with the lens cap on and the aperture set to f/22 and then layer that shot with the properly exposed shot in post processing to reduce some digital noise in the black parts of the sky.
If you don't have a tripod, or see a particular shot that you want to take while your tripod is at home, you can also set your camera on any solid surface and use the camera's self-timer function to avoid blurriness in your photo caused by camera shake.
Always bring warm clothing when out shooting at night. This will keep you warm and extend your shooting session.
References
Resources
- Photo Credit ancient light meter image by jimcox40 from Fotolia.com
