Dim Light? Raise the ISO Speed
Just like film cameras, digital cameras provide a choice of ISO speeds that adjust your camera's sensitivy to light: the higher the ISO number the more sensitive your camera becomes to light. Most digital cameras have a default ISO of around100 or 200--the same as if you were using an ISO 100 or ISO 200 film. These moderately slow speeds are fine for outdoor work where there is a lot of ambient light and when you want image quality to be its best. You can also use speeds in this lower range for flash photography since the flash will provide most of the light.
If you're shooting in very dim lighting (room interiors, concerts, sports events, etc.), however, the camera probably won't have enough light to get a good sharp photograph at safe handheld shutter speeds. If you switch to a shutter speed that's too slow, of course, you'll end up with camera shake--the main cause of unsharp photos. Some cameras may even refuse to take the picture in dark situations or might force you to use flash when you don't want flash.
Why not just give in and use the flash? The trouble is that in a lot of situations you can't use flash, it's just not allowed (in museums or stage events, for example). But even if you are alllowed to use flash,the hard blast of direct light from flash will not only ruin what might be interesting available lighting, but it will certainly destroy the intimate mood of many low-light situations--photographing your daughter blowing out her birthday candles, for example.
The solution is to raise your ISO speed high enough so that you can safely shoot handheld and capture, not eliminate, the interesting ambient lighting. I shot this photo of the contortionist at a traveling tent circus (the Cole Bros Circus), for instance, by bumping the ISO up to 1600. The lighting in the tent was incredibly dim and because the performer was quite a distance away using flash wasn't an option even if it had been allowed (it wasn't). So, as an experiment I raised the ISO on my Nikon D70 to its highest setting and I was able to shoot at shutter speeds of about 1/60 second. That's not as fast a speed as I would like to use since I was handholding a 300mm lens that with the cropping factor was a whopping 450mm, but that was all the ISO I had available (newer DSLR cameras have much higher speeds. I think the new Nikon D700 will go to ISO 6400 or higher).
When I downloaded the images from the circus, I was really surprised at how sharp and "noise" free the images were. Digital "noise" is similar to the grain (that kind of sandy looking pattern) you get when you use very high speed films. The higher you raise the ISO, theoretically, at least, the more obvious the noise becomes. To the Nikon's great credit, there is virtually no digital noise with my D70s.
Because I shoot a lot of concerts (see the show of blues singer Miss Marie, below), I'm often forced to work with very dim stage lighting and flash is never allowed--so I must shoot at very high ISO speeds. Similarly, to get the shot of the candles in Notre Dame Cathedral in Paris, I used the same high ISO of 1600. You can't use either flash or tripods in Notre Dame (and most churches or cathedrals) so raising the ISO speed is your only option.
By the way, my book Exposure Photo Workshop (published in April 2008 so it's very up-to-date) provides very comprehensive coverage of night and low-light photography, as well as self-assignments that you can shoot and then post to www.photoworkshop.com to share with other serious photographers. I rarely hawk my books much, I let them speak for themselves, but I think my exposure book is the best book on the subject and you will learn a lot from it.
So next time you're confronted with lighting that's dimmer than you'd like, try cranking up the ISO speed and see what happens. I am usually very pleased with the results I get and often the only alternative is not to shoot any pictures which is hardly an option worth considering.
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