Caution with Long Exposure Noise Reduction


Today’s Question: Do you need to hold the camera steady during the second half of the long exposure when using long exposure noise reduction?

Tim’s Quick Answer: No, you don’t need to continue holding the camera steady during the second exposure created when you have enabled long exposure noise reduction in the camera.

More Detail: When you enable long exposure noise reduction your camera will actually capture two images for each photo you capture. The first exposure is the actual photo, and the second exposure is a “dark frame” that is created to measure the actual current noise behavior of the image sensor, so the noise can be subtracted from the actual photo.

During that “dark frame” exposure, the camera is not actually recording any image data through the lens. It is instead taking the equivalent of a photo captured with the shutter remaining closed. That would theoretically produce an image that is completely black. In reality there will be noise in that capture, and so the noise is known to have been generated by the sensor and can therefore be subtracted from the photo.

Because there is no image data being captured through the lens during this “dark frame” exposure, there is no risk in moving the camera during that exposure. You’ll just want to be sure that the real exposure has indeed completed, before moving the camera.

You may obviously want to keep the camera in the same position in any event, so that you can capture another photo of the same scene, perhaps with different camera settings, as soon as the long exposure noise reduction capture is completed. However, after the initial exposure and during the “dark frame” exposure you could certainly start moving the camera into a different position for your next shot.