Use ISO to Take Low-Light Photos
Published by Dave April 10th, 2007 in Digital photo
Light is both a photographer’s best friend and worst enemy. Consider what happened to me recently, for instance. I visited a wild animal park with the hope of taking some pictures of wolves, cougars, and bears. Unfortunately, it had rained all morning, and the sky was dark and overcast when I arrived at noon.
As I prepared to take my first photo, I found that the camera was so starved for light that it wanted to set the exposure at about 1/10 second–far too slow to get a sharp image of active animals, especially since I was hand-holding the camera.
So what did I do? I increased the ISO.
ABCs of ISO
As you might recall from the days of film cameras, film comes in a variety of speeds. Film speed is measured using a numbering system called ISO (sometimes also referred to by its geezer name, ASA). Lower ISO numbers are known as “slow” films, which are less sensitive to light, while higher ISO numbers are more sensitive to light. It’s pretty typical to shoot with ISO 100 or 200 in normal daylight, and use 400 film for lower light photography. Super-fast films like ISO 800 and even ISO 1600 are available for photography in near darkness.
Here’s the secret code that governs film speed: doubling the ISO number of the film doubles its sensitivity to light. So ISO 200 film needs half the light to take the same picture as ISO 100 film. ISO 400 film needs a quarter of the light that ISO 100 needs. In other words, if your camera would try to capture a particular low-light scene with a shutter speed of 1/15 second at ISO 100, you could capture it at 1/60 second at ISO 400. That’s an incredibly powerful capability that means the difference between getting a blurry mess and a sharp photo.
What ISO Means for Digital
Big deal, right? This is the world of digital now, not film. We don’t buy memory cards with ISO speeds marked on them the way we used to pick film boxes for their ISO numbers. So what does all this have to do with us?
As it happens, you can control the sensitivity of your camera’s light sensor by changing the camera’s ISO setting. By default, most digital cameras have an ISO somewhere around 100. If you need more film speed for low light conditions, getting more sensitivity out of your camera is as simple as selecting a higher ISO from the camera’s menu. Most digital cameras offer a range of ISO values, such as 100, 200, and 400. Some cameras go much higher–all the way to 3200, in fact. Just dial in the ISO you need. By increasing the ISO, I was able to get pictures like this wolf at the animal park–but at the default ISO, everything would have just been a blurry, slow-shutter mess.
The Dark Side of Film Speed
That sounds great, right? So I know what you’re thinking: If higher ISO film is more light sensitive, why not always use a high ISO number?
Unfortunately, light sensitivity brings its own baggage. High speed film was notoriously grainy. As you increased film’s sensitivity to light, the light-sensitive grains of silver halide in the film emulsion got bigger and more noticeable. In the final print, that manifested itself as grain–irregular, pixel-like elements in the photo that took away the photo’s smooth, high-resolution look. Ironically, in the world of digital, we have almost exactly the same effect when choosing ISO values. Increasing the sensitivity of the camera’s light sensor introduces digital noise into the picture. Similar to film grain, noise is random pixels of color.
You may not notice noise from a distance, but if you zoom in on a digital photo on the computer screen or look closely at a print, it’s hard to miss. All digital images have some amount of noise, but it gets worse as the ISO goes up. Check out the small detail of a high-ISO photo, for instance. The noise–appearing in the form of colored speckles–is quite apparent.
ISO Advice
So what should you do about ISO? I suggest shooting at the lowest possible ISO all the time. In ordinary shooting conditions, stick with the camera’s lowest ISO level, since that’ll give you the least digital noise. But when you notice that the camera is recommending a really slow shutter speed, crank up the ISO. Just remember to drop it back down to the lower value when you’re done, so you don’t accidentally capture a month’s worth of pictures at ISO 800.
Another thing to keep in mind: most digital cameras don’t allow you to adjust the ISO (or any other setting for that matter) when you’re in Automatic exposure mode. To tweak the ISO, you’ll want to be in Program, Shutter Priority, Aperture Priority, or a Scene mode.
Want to learn more? Check out my recent Digital Focus newsletter on minimizing the effects of digital noise.
33 Responses to “Use ISO to Take Low-Light Photos ”
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How do you know when your camera is “recommending a really slow shutter speed”? Mine just turns on the flash when it’s dark. (Which I hate because then all the highlights are blown out and the darks go darker).
Great article. Any chance we can see the same images taken in different iso’s side by side? I’d love to be able to see the difference with someone who knows what they’re doing.
Nice article, now I know!
I’m gonna go grab my S5600 right away..
Jim,
You are probably using a compact camera, or at least one that is usually fully automatic. This article is meant for cameras that have manual features that let you chang the iso speed, such as DSLRs or DSLR-like cameras (there are many other cameras that have ISO speed settings, but these are camera styles that you will definitely find them on).
To change the setting on a fully auto camera, try turning the flash off. That usually forces the camera to use a higher ISO speed with low light.
hope that helps.
answer to Jim:
I use the following rule to know I’m not too low in the shutter speed
Don’t go under 1/focal length
So if you have a 50mm lens, the minimum speed is 1/50 of a second
for a 100mm, 1/100 of a second.
This is aproximative and valable only for fix subjects.
Pay attention, digital camera’s have a focal length multiplicator (1.5 or 1.6)
So a 100mm equals 150mm (1/150 sec).
Thanks. Yes, I’m using a point-and-shoot Canon A90.
I’m shopping for a new camera and this is good information to have while looking.
Hi Jim,
I used to have a A80 before getting my 350D. Even with the A80 you can set the camera into P or Av (or Tv or M) mode. I favor Av mode, which lets you set your own F stop (aperture). If you set a desired F stop in Av mode, the camera will then “suggest” a shutter speed. A shutter speed that’s too low will increase the likelihood of blur (through camera shake or subject motion).
On the A80 I could turn the flash off and/or adjust the ISO setting in any mode other than auto. Again, this would enable you to shoot in lower light with a faster shutter speed for sharper (if noisier) pictures, as per this article. Check the manual on your A90 - I’m sure similar functionality exists if you want to play with this setting.
-Andrew
Thank you for this great information. I will go and play with my point and shoot and see the differences.
One tip when shooting digital with very high ISO: switch to B&W. The resulting grain from using a high ISO will look “arty.”
Piggy-backing off of Pépé, I just wanted to point out that aperture/focal length is also very important in low-light situations. If you’re set your camera to a low f/stop, you can use a lower ISO, which means less noise in your photos.
Thanks for your tips. I am just not getting into photography and this will help tremendously.
When shooting at higher ISO, some camera’s offer High ISO noise reduction feature. If this feature is set on, graininess of the pictures can be reduced!
Great article, thank you! I have Rebel-G XTi and suffer from blurness in low light conditions.
Dear Dave,
Your suggestion was excellent and given in a very simple way. Though I am not a photo enthusiast, I thoroughly enjoyed your discourse. Why didn’t you give the full form of ASA/ISO? Please write more to enlighten us.
A good thing to keep in mind is that these suggestions are for when you are hand holding your camera. If you are on a tripod, table, or the like AND you are not shooting something that moves… then keep your ISO as low as possible. It won’t matter that you have a longer exposure time and you won’t get the extra grain/noise.
Aperture is also critical for low light situations. Whenever possible, I try to shoot in aperture priority mode and lock it at f/1.4 (and whenever I can find that f/1.0 lens, I’ll shoot even wider!). The narrow DoF is great because it gives you something closer to what your eyes actually see.
I don’t really care about grain from shooting at a high ISO unless I’m trying to get artistic shots. Generally, the low light situations I shoot in end up being candid portrait shots, and the grain is an acceptable tradeoff for the sharpness. Also, with a good SLR, the grain even at 1600 is minimal.
Personally I love the noise / grain of high ISOs, particularly in monochrome mode. Turn the ISO up to 1600, turn on monochrome mode, put on a lens with a nice big aperture, and my DSLR takes some great, grungy black and white night photos. I guess it’s all about what you’re into - I have to admit the noise you get in colour mode with high ISOs doesn’t look nearly as nice.
“Just remember to drop it back down to the lower value when you’re done, so you don’t accidentally capture a month’s worth of pictures at ISO 800.”
You nailed it with this line. I’ve wasted tonnes of pictures this way.
Thanks so much. I was at NW Trek in WA this past week where the light was very low due to cloudy and dark conditions. I was using a 70-300 lens with the aperture wide open. My pictures were a blurry mess. I’m new to manual settings and didn’t even think about the ISO. It’s currently set for 200. I’m planning to head back tomorrow bound and determined to get decent shots. I feel more confident that I will now. Thanks so much!
I would like to see a continuation of the topic
Thank you!!!… Finally I got a clear idea os ISO…
Really a good article :).
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