Is the in-camera Long Exposure Noise Reduction necessary when using a camera in cold weather? This is a question I have wondered about for a long time so I finally did a more specific test.
First of all, what is Long Exposure Noise Reduction? Here is the scoop: When LENR is turned on, the camera makes the exposure and then re-energizes the sensor again, for the same amount of time, basically taking a second picture with the shutter closed. The camera then compares the two and performs a noise reduction algorithm before writing the file to the card. Supposedly, long exposures can increase heat on the sensor, resulting in possible noise. While this is a good feature, should potential noise be a problem, it creates a delay when shooting since you have to wait for the same amount of time as your exposure before you can preview the file. The only time I have used it is when shooting the northern lights, but the delay is annoying.
The following comments is based on my experiment with the Canon 5D Mark III camera, so if you have a different model, I suggest testing it.
At -30 degrees (F) below zero, I shot hundreds of consecutive frames of 30 second exposures at ISO 1000 with LENR turned off. There was no sign of noise or hot pixels in any of the images. Now that is a pretty cold temperature, but my other less specific tests at +20 degrees (F) showed similar results, but I will need to do a more aggressive, repeated exposure test to be sure. In the future, when it is below zero at least, I will no longer turn on LENR!