ISO Settings and Digital Noise

by Bob Singer

Posted: August 8, 2012

One question often asked is “How high can I set my camera's ISO without experiencing excessive digital noise in my images?”

The answer: “It depends."

Photographing dark-colored, poorly lit, or fast-moving subjects means you'll be favoring really fast shutter speeds. In the days of film cameras, that meant using your largest lens opening and highest shutter speed with a reasonably fast film (ISO 200 or 400) and, well, praying a bit. Of course, faster film meant larger film grain, but that was fine in order to get the shot. Strangely, what was fine in film days to those photographers stopped being 'fine' with the advent of digital cameras.

Until relatively recently, digital shooting in low light situations or with fast subjects required using your biggest lens opening and fastest shutter speed and praying a bit. Many older DSLRs were limited to ISOs in the 200 to 400 range before the level of noise in a picture became quite noticeable. (And, of course, every photographer has a different tolerance level for acceptable amounts of noise.) To compound matters, each individual digital camera has varying capabilities  - even camera bodies of the same brand and model that were made in the same factory in the same week. That's because of small manufacturing variances from one body's sensor to another. Two sensors from the same manufacturer can create different amounts of digital noise at the same camera setting.

The latest DSLRs have amazing low-noise capabilities that were unheard of just one or two camera generations ago. My new Nikon D7000 can capture virtually noise-free pictures at ISO 3,600, where my old Nikon D100 would produce noise at any ISO over 200. In fact, I have taken quite acceptable streetlamp-lit night pictures with my D7000 at ISO 12,500. New Canon models offer similar capabilities.

Keep the lens cap on when you take your noise test exposures!

Noise Tests

So, how do we find out if our camera's ISO settings will produce pictures with acceptably low amounts of noise? We conduct a series of simple and quick tests, ones I encourage you to do at home because it takes a fairly big computer display to see the results. You can't really see them on the small LCD screen on the back of your camera.

Step-by-step, here's how you do it:

• The lens you have on your camera body doesn't matter for these tests. Put your lens cap on your lens. You are intentionally blocking light from entering the lens.

• Put your camera in Shutter Priority or Manual mode. Set your shutter speed for 1/60th of a second.

• Noise test image at ISO 200. Enlarged 2" x 2" section of exposed test image (Photoshop magnification set to 100%). This is how an excellent low noise exposure test image should look. Note the absence of white or colored flecks of noise.

  Set your DSLR for its lowest ISO setting (probably either ISO 100 or ISO 200) and press the shutter button. Make a note of the exposure number and the ISO speed.

• Move your ISO up to the next highest ISO setting and press the shutter button. Make a note of the exposure number and ISO speed.

• Repeat this procedure, moving up through each next highest ISO. Note each exposure number and ISO speed.

• Noise test image at ISO 1,600. Enlarged 2" x 2" section of exposed test image (Photoshop magnification set to 100%). This is how little noise a current generation DSLR generates at ISO 1,600. While there are some random bits of noise present (white flecks), they're minimal and quite acceptable for good quality, low noise images.

  Download these exposures from your memory card into a folder on your computer desktop

• Next, open the folder's picture files using any image viewing program you have. (Adobe Lightroom or any editor/viewer with a dark background is especially good for this.)

• Observe the black image area in each exposure (remember, your lens cap has been on all through this procedure). In your image Edit setting, zoom in to 100% (Actual Pixel Size in Adobe Photoshop or Adobe Photoshop Elements). As you move up through each picture in the series, at some point, you will begin to notice digital noise on the black exposure. Luminance noise (which is most like film grain in character) will appear as white flecks or dots. Low levels of luminance noise are generally not problematic. A different kind of noise, chroma noise, will appear as red, green and blue flecks or dots. Chroma noise is the one you want to avoid the most.

• Noise test image at ISO 25,600. Enlarged 2" x 2" section of exposed test image (Photoshop magnification set to 50%). This is how much noise even a top current model DSLR generates at ISO 25,600. Yet, although heavily 'grained' in its appearance, a picture taken with this much noise still provides a passable, viewable snapshot. But, it wouldn't be used by most professional or serious amateur photographers for anything else.

  Make a note of the ISO numbers at which luminance and chroma noise are minimal, tolerable, or disturbingly obvious and heavy.

• You have now identified the ISO ranges for your specific camera at which you can take pictures that are relatively noise-free, those at which noise is tolerable, and those at which unacceptable levels of noise will appear.

That said, always remember one overriding truth: in the end, it's capturing the picture that counts, not how much noise is in it. I'd rather have a picture of an airborne snowboarder than not have one at all!

Bob Singer is a Cape Cod and Florida-based juried fine art photographer. He has been honored with hundreds of awards for his highly styled contemporary and beautiful traditional images which have appeared in national and local publications, in advertising, and hang as signed limited edition prints in galleries, homes and offices across the United States and Europe.  A popular judge-commentator, instructor and speaker at photo conventions and camera clubs in New England and in Florida, Bob also gives seminars, leads workshops and teaches classes at the Cape Cod Art Association in Barnstable, MA and at the Venice Art Center in Venice, FL. He can be contacted at:bob@singercreative.com