BetterPhoto Q&A
Category: New Answers

shooting timed exposures

To love this question, log in above
December 20, 2005

First of all, the moon is a special exception. Don't treat the moon as a low-light subject. It is actually reflecting sunlight and is bright. A good rule of thumb is to shoot the moon at f/11 or f/16, and set your shutter speed to match your ISO setting (ISO 100 = 1/100 sec, ISO 200 = 1/200 sec, etc.) Since the moon is usually much brighter than the night sky, longer exposures will usually result in the moon being a burned-out white blob.

For other scenes, I'm assuming your problem is that your camera's shutter speed only goes to 30 seconds, but you want to take longer exposures. You need to get a starting exposure with your camera meter, then "shift" it to where you want it.

For example, you want to take a landscape scene at f/22 to get the most Depth of Field. But when you meter the scene at f/22, the camera indicates that 30sec will still be underexposed. Meter the scene at a larger aperture, like f/4. Let's say at f/4, your camera indicates a shutter speed of 4 seconds. For each shift in f-stop, you need to double the exposure time. So f/4=4sec, f/5.6=8sec, f/8=15sec, f/11=30sec, f/16=60sec, f/22=120sec.

You can also shift your ISO speed if you need to in order to get a starting exposure. If you meter at ISO 1600, you will double your exposure time for each shift to ISO 800, 400, 200, etc.

Be aware that some digital cameras have serious noise problems with long exposure times. You'll just have to try it to see how well your camera does.

Have fun,
Chris

To love this comment, log in above
December 20, 2005