known as dark frame subtraction to remove noise. When it is enabled, LENR creates a dark frame after each exposure, which is essentially a second exposure of equal length, except that the shutter is not opened. The dark frame contains the same noise as the original exposure. The two frames are combined together, and the noise is subtracted from the image. This process results in a doubling of the exposure time, which can cut down on productivity in the field. With LENR enabled, a 10-minute exposure means that the camera is inoperable for about 20 minutes. LENR also has features that help to minimize random noise. Most cameras have either an on or off option for LENR, but some have a third auto setting that analyzes the image on the fly and determines whether or not LENR is needed. It can be left on all the time, and it will be applied only when noise is detected. The performance of in-camera LENR varies from camera to camera, and whether or not to use it involves an evaluation of the trade-off between lost shooting time and improvements in the image. There is considerable debate about whether noise reduction is best achieved in-camera, in postproduction, or a combination of the two. Testing your own camera can facilitate making the decision of which approach to take. To do this, make a series of exposures of varying lengths from 1­30 minutes both with and without LENR, both in summer and winter. When you process the images in your RAW conversion software, you may find that you only need to use LENR over a certain temperature or exposure length and that postcapture software is adequate most of the time.