A friend who bought a Nikon D800 found a note in the owner’s manual that says: “Resolution can be improved by disabling high ISO noise reduction particularly at low ISO.” Would that also apply to my Canon EOS 7D and my sister’s Nikon D5100? In other words, do all DSLR cameras apply noise reduction even at ISO 100 or 200 and should everyone disable that feature?
There’s no way to be certain that every DSLR applies some noise reduction (NR) at low ISO but that is probable based on my research, Mario. Typically, it’s very mild at ISO 100 and 200, a bit stronger at ISO 400 and more intense at each higher ISO level. It works by blurring the digital noise pattern and that also blurs fine details to some extent. That’s why Nikon recommends disabling NR at low ISO with the D800 to get the maximum resolution. Most other DSLRs also provide a High ISO noise reduction item in the menu; that allows you to set a desired intensity level or at least to turn this feature Off.
Noise-reduction processing is definitely useful—even with the best DSLRs—at ISO 800 and especially at ISO 1600 and above. The higher the ISO the more digital noise you would get without this feature: obvious “graininess” or mottled colour specks that can obliterate fine detail. With some older DSLRs that use less sophisticated sensors, digital noise can be problematic even at lower ISO, making the default level for noise reduction the best setting.
Since I own the latest DSLRs, I set NR to Off at ISO 100 to 400, to Low at ISO 800, and to the default at higher levels when shooting JPEGs. Does that provide better resolution? Yes, slightly better, although there is also a very slight graininess by ISO 400 and more visible graininess at ISO 800. Before you use the same tactic, check out the sample images from the Canon EOS 7D (made at all ISO levels, with the various NR options) . Sample images from the Nikon D5100 are available here. All of the recent DSLR reviews on the Imaging Resource website provide this type of visual illustration.
Note: When setting a low level (or Off) for noise reduction, make sure that you do not underexpose your images because that would lead to obvious digital noise when lightening the photos in software. (Use + exposure compensation when necessary.) And remember to set the menu item back to the default before you start shooting at high ISO to prevent problems caused by digital noise.