Long Exposure Noise ReductionThis filter, found on Shooting Menu 3, goes after the type of noise that's caused by a slow shutter speed. The settings work as follows:
- Off: No noise reduction is applied. This setting is the default.
- Auto: Noise reduction is applied when you use a shutter speed of 1 second or longer, but only if the camera detects the type of noise that’s caused by long exposures.
- On: Noise reduction is always applied at exposures of 1 second or longer. (Note: Canon suggests that this setting may result in more noise than either Off or Auto when the ISO setting is 1600 or higher.)
So your shot-to-shot wait time is twice what it would normally be. For some scenes, that may not be a problem, but for shots that feature action, such as fireworks, you definitely don’t want that long wait time between shutter clicks.
High ISO Speed Noise RemovalThis filter, also found on Shooting Menu 3, attempts to do just what its name implies: eradicate the kind of noise that's caused by using a very high ISO setting. You can select from these settings:
- Low: Applies a little noise removal.
- Standard: Applies a more pronounced amount of noise removal; this setting is the default.
- High: Goes after noise in a more dramatic way.
- MultiShot: Tries to achieve a better result than High by capturing four frames in a quick burst and then merging them together into a single JPEG shot. Although this mode can be effective, it comes with several caveats: flash isn’t possible, you risk having image alignment issues between the exposures, and you don’t get a Raw image. When enabled, the same symbol appears on the Shooting Setting screen and in the LCD panel. For more fine print, look up this feature in the camera manual.
- Off: Turns off the filter.
It’s also important to know that High ISO noise-reduction filters work primarily by applying a slight blur to the image. Don’t expect this process to eliminate noise entirely, and expect some resulting image softness. You may be able to get better results by using the blur tools or noise-removal filters found in many photo editors because then you can blur just the parts of the image where noise is most noticeable — usually in areas of flat color or little detail, such as skies.