Do I need long exposure noise reduction when shooting at ISO 100?
Asked 3/7/2014
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I usually shoot long exposures at ISO 100. Does low ISO mean I can leave Long Exposure Noise Reduction turned off, or is it still useful? I know it doubles the time because the camera has to process after the shot, so I’d like to know when it’s worth using.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
12y ago
2 Answers
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The long exposure Noise Reduction takes a "dark frame" after the real shot, and then uses the noise pattern from that image to reduce the noise generated by the sensor. That's why the exposure takes twice as long as this NR were disabled.
Long time exposure can increase the sensor temperature, and increased temperature also means more noise. So you should generally leave that feature on, and disable only if time is a critical issue.
The dark-frame is (depending on the camera manufacturer) also used to identify and map out any hot pixels during the exposure.
Originally by user26144. Source · Licensed CC BY-SA 4.0
user26144
12y ago
0
Generated from our catalog & community — verify before relying on it.
Yes, it can still be useful at ISO 100. Long Exposure Noise Reduction is typically dark-frame subtraction: after the exposure, the camera makes a second exposure with the shutter closed and uses that frame to reduce sensor noise and hot pixels.
With long exposures, noise is affected not just by ISO but also by exposure time and sensor heating. Even at low ISO, longer exposures can produce extra noise or visible hot pixels, so this feature can help.
The downside is that it usually doubles the capture time, since the camera needs a matching dark frame after each shot. If timing is critical or you’re shooting many frames, you can turn it off and instead capture a dark frame manually later using the same exposure settings and conditions, then subtract it in software.
So: low ISO alone doesn’t mean Long Exposure NR is unnecessary. Leave it on when image quality matters most; turn it off when speed matters and handle dark-frame subtraction later if needed.
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