Noise is something we pretty much all try to minimize in our photos, and we know that one of the best ways to avoid it is to shoot at as low an ISO as possible. But even at low ISO values, you can still see noise, particularly as you shoot longer exposures. This great video will show you what long exposure noise is, why it happens, and how you can fix it.
Coming to you from David Bergman with Adorama TV, this informative video will show you what long exposure noise is, why it occurs, and how you can fix it. Long exposure noise occurs due to your sensor heating up during an exposure. You will see it show up as random "hot" pixels scattered through the image that can be rather distracting. You can always clone these out (and dedicated astrophotography setups will often actively cool the sensor), but another method is to use your camera's long exposure noise reduction. In this mode, after you take an exposure, your camera takes an equally long second exposure with the shutter closed, resulting in a dark frame with only the hot pixels shown, after which it automatically eliminates them. The drawback is that this doubles the amount of time for each shot, which can be significant when you are shooting long exposures. Check out the video above for the full rundown from Bergman.
While this only works if you have AC power available, you can reduce internal camera heat by using an AC adapter instead of the camera's battery. As the battery is being used, it also generates heat.