Q and A: Why does my camera produce severe underexposure in dark locations?


Question

Can you help me solve the exposure problem with my new digital SLR camera? It’s fine when I use the fully automatic modes. But I tried taking photos in a church during a wedding (without flash) and all my photos were underexposed. I was using ISO 400 and set the shutter speed to 1/500 sec. in Shutter Priority mode to make sure the photos would be sharp. But they are all too dark. D.M.

Answer

This is also a common problem among students in my BetterPhoto courses when they first try night photography. The answer is simple, but you need to fully appreciate how this semi-automatic mode works. In theory you can set any shutter speed and the camera will set a suitable aperture for a good exposure. If you change the shutter speed, the camera will change the aperture to maintain the same exposure.

That often works well, especially in outdoor photography in daylight. However, in a very dark location, you need to use a much higher ISO – and a much longer shutter speed – for a good exposure. If you set 1/500 sec. at ISO 400 in low light, the camera cannot find an adequately wide aperture to provide a good exposure. (The same would apply if you set a small aperture in low light when using a low ISO level.) When your settings cannot provide a good exposure, most cameras will provide a warning in advance: blinking numerals in the viewfinder.

Note: Instead of providing a warning, some cameras will actually change inappropriate settings when that’s necessary to avoid a grossly incorrect exposure. For example, certain EOS DSLRs can provide this feature when the Safety Shift AV/TV or the Safety Shift ISO custom function is set to On. Do note, however, that neither custom function is available with all EOS cameras.

When you get a warning in low light, start by setting a higher ISO, such as 1600. If the blinking still continues, you must also set a longer shutter speed, such as 1/125 sec. If it’s really dark, you may need to use an even longer shutter speed, such as 1/15 sec. When the blinking stops you should be able to get a well-exposed photo. Granted, at the long shutter speed, the photo may be blurred: from camera shake or from movement of your subjects. If your camera offers even higher ISO options, try those. They will allow you to shoot at a faster shutter speed but your images will be more “grainy” due to digital noise.

If numerals blink in your camera's viewfinder, be sure to change the ISO and the shutter speed or the aperture until the warning signal stops. You should then be able to get a good exposure. Photo Courtesy of Canon Canada

If numerals blink in your camera's viewfinder, be sure to change the ISO and the shutter speed or the aperture until the warning signal stops. You should then be able to get a good exposure.


During this ceremony, I needed to use ISO 1600 and a 1/40 sec. shutter speed because of the low light conditions. The image is grainy due to digital noise at the high ISO but the exposure is fine. There's no blurring because I used a lens with an image stabilizer and braced my elbows on a solid object. (86mm focal length.)  ©2010 Peter K. Burian

During this ceremony, I needed to use ISO 1600 and a 1/40 sec. shutter speed because of the low light conditions. The image is grainy due to digital noise at the high ISO but the exposure is fine. There's no blurring because I used a lens with an image stabilizer and braced my elbows on a solid object. (86mm focal length.) ©2010 Peter K. Burian




Comments

  1. In low light conditions I generally use Aperture priority, ISO 800, set a prime lens to wide open (f/1.4 or f/1.8) and let the camera choose the shutter. It’s a simple technique that works very well for me. :) If still too dark, I bump up ISO.

  2. Peter K. Burian says:

    Bob: Yeah, when you have a lens with such an extremely wide aperture, ISO 800 is probably fine even in a dark location.

    But if someone is using a zoom lens, with a maximum aperture of f/4, he would need to use something between ISO 3200 and ISO 6400 in the same circumstances.

    And yes, bumping up the ISO is the solution with any lens in a dark location …. if you have already set the widest aperture (smallest f/number).

    Peter http://www.peterkburian.com

  3. It would seem to me that all your reader’s exposure questions could be solved very easily: STOP USING AUTO EXPOSURE! If photographers would just learn how to use manual exposure they could quit obsessing about photo too light/photos too dark. It has never been easier when you can review every photo instantly and make the appropriate exposure corrections. In my experience auto exposure has only gotten worse as it has become more complex. Center weighted was just about perfect. Besides, where is the satisfaction in taking a great photograph when you have to share credit with your camera’s computer. I learned photography with a meter-less Leica IIIF guessing exposure for slide film. I think every photographer should have this experience.

  4. Peter K. Burian says:

    Well, Sanford, sure … if everyone learned to use Manual mode and really appreciated exactly how it works …. and how to use it to get a correct exposure, for a snowy landscape *and* for a black cat in a coal bin.

    Especially with Center Weighted metering, that is not as easy as all that. I doubt that 90% of digital camera owners will ever reach that level of understanding.

    And I’m not sure they need to. They can use Aperture Priority or Shutter Priority mode — with Matrix metering providing a good exposure very often — and with Exposure Compensation as necessary. Minor exposure errors can be fixed often with something as simple as Auto Contrast in Adobe Elements. The result may not be perfect, but close enough for most folks’ needs.

    I do teach those aspects in my on-line digital courses. And most students seem to understand the concepts quickly, especially after shooting the assignments. Of course, when they set 1/15 sec. to shoot a waterfalls on a very bright, sunny day at ISO 400, they run into problems. Or when they decide to shoot at 1/500 sec. in a dark arena at ISO 400 to freeze a moving subject.

    Once they understand the problem and then solution, they do just fine.

    Cheers! Peter http://www.peterkburian.com

  5. J. Littlebear says:

    I agree with all four of the above comments. But the last one gives me pause. If 90% of digital camera owners will never reach the level of understanding needed to make good captures under unfavourable conditions, that is a sad commentary upon those owners. A sophisticated camera gives the user much power, which is why the user spent a lot of money. But cash is only part of the owner’s investment. Effort devoted to learning about the camera is even more important.

    That someone would spend so much cash and then refuse (and I do use the word “refuse” deliberately) to read and understand the users’ manual, and even pursue supplementary education about that camera so as to learn how to use their investment effectively, astounds me completely. I know such people. One complaint commonly made by them is that they don’t like to read!!!!! A sophisticated camera needs more than an investment of cash. It also needs a large investment in self education, which requires considerable reading, and experimenting with the camera. This needs time and focus and discipline.

    Some of the cameras I have been privileged to own have required years of learning on my part. I am hardly unique among serious photographers in that. If one elects not to learn and to self discipline, well what can one say and what can one do for such people? There is an old saying in the high tech fields, “RTFM.”

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