How do aperture and shutter speed affect car light trails in night street photography?
Asked 1/29/2013
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If I photograph a night street scene with moving cars, what changes if I use:
- a wide aperture with shutter time t, or
- a smaller aperture with a longer shutter time chosen so the overall exposure stays about the same?
Will both settings record the car lights, and how will the light trails look different?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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1) Open diaphragm will result in a shallow depth of field, which means that a lesser portion of the image will be in sharp focus. Like this shot of the Blue Mosque (notice the further away from the camera the more blurred the image becomes). You will see car trails if cars move fast enough and you expose long enough. 2) Closed diaphragm will bring up the so-called star trails on lights. Like here on the bridge. Car trails will be longer than in the first case, because with a lesser apperture you exposition time increases to compensate for the reduced portion of light.
What you describe as the lights of the cars, the car trails will be longer the longer the exposure time you choose. The trails appear as the camera captures light spots over time. If cars move during exposure, their lights will move from pixel to the next, which is how the trails appear.
If shooting in RAW, you can always overexpose your scene by 1 stop and then recover details in bright areas in Adobe Camera Raw or Lightroom. In that case, you will get even longer car trails. Or the other way round, i.e. underexpose.
Originally by user4807. Source · Licensed CC BY-SA 4.0
user4807
13y ago
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Generated from our catalog & community — verify before relying on it.
Yes—both settings can record the car lights. The main difference is not whether the lights appear, but how motion and depth of field are rendered.
With a wide aperture, you can use a shorter shutter speed. That means less time for the cars to move during the exposure, so light trails will be shorter or may appear more like bright points if the shutter is fast enough. Depth of field will also be shallower.
With a smaller aperture, you need a longer shutter speed to keep overall exposure similar. Because the shutter stays open longer, the moving headlights and taillights will produce longer streaks. A smaller aperture also increases depth of field, so more of the scene can appear sharp.
Bright point light sources at small apertures can also show starburst effects.
In practice, the exact result depends on how long the shutter ends up being, how fast the cars are moving, and how bright the ambient scene is. But in general: same exposure does not mean same look—aperture affects depth of field, and shutter speed affects the length of the light trails.
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