Apart from all the composition requirements, there are basically three technical factors behind a correct capture: aperture, ISO and speed. Like a tripod, if you alter one leg, you have to compensate in the others, and this is what most digital cameras do for you automatically, but rarely very well. This “Biff” note is about the third leg on the tripod: speed. It seems like an easy one, but we all get it wrong. When your subject is blurry, when there’s camera shake, the usual suspect is the wrong speed setting.
Cameras with a PASM (program-aperture-speed-manual) mode dial can let you set the exposure time and work out the other factors. Why? Because sometimes we want to capture moving subjects.
Speed (not to be confused with film speed or sensitivity, a.k.a. ISO) means how long you expose your film/sensor for a capture. When there’s less light hitting the sensor, you need either a wider hole (aperture) or more time
, which is why the S is replaced by Tv (time value) on some cameras. It’s measured in a range that goes from “B” for “bulb” (in the early days of film, you grasped a bulb), that equates to as long as you want to hold the shutter open, to 1/8000th of a second, that’s 0.000125 of a second.
If you’re shooting sports images, you’re going to need a long telephoto lens that captures a lot of light (and a lot of money to afford it) because to capture people, machines, animals moving, it has to be done in hundredths or thousandths of a second, otherwise it’s blurry.
Before image stabilization (vibration compensation/reduction, etc.), you had to shoot fast with telephoto lenses because even the slightest blur at the long end of your telephoto zoom. The simple rule was (and remains) that to guarantee any sharpness your speed had to be the focal length as a fraction of a second, i.e., a focal length of 300 mm meant that you really be shooting at 1/300th of second or faster. IS helps enormously, but people forget that it helps reduce your camera shake, not the blur caused by the moving object.
Compacts usually get this very wrong. Shooting children and other pesky, moving subjects in low light (say, indoors) asks too much from a camera whose high ISO performance is poor, takes time to focus and doesn’t offer a decent grip. Even so, other cameras always promise more than they deliver. My rule of thumb is simple: anything less than one-third of a second is going to be blurry. If I use a tripod to compensate, then subject is going to move. The only solution is to increase the ISO (if you can), widen the aperture or insist that photographer and subject take up Zen yoga breathing exercises.
This is the main reason why flashguns were invented: to increase the amount of light so that you can shorten the exposure. We’re usually disappointed by the result, because the camera’s built-in flash creates a harsh, unforgiving contrast and sinister shadows. You can attenuate this by sticking a cigarette paper over the flash. If your camera has a hot shoe for an external flash unit, bounce the flash above (or even behind). Even better results can be obtained by moving the flash off the camera with a cable, but that’s another story.
Sometimes we want blur. Try this next time you’re near moving water (beach, river, fountain, etc.): using a tripod, set your speed to half a second or longer to give the water a silky smooth effect that contrasts nicely with the solid, sharp lines of whatever’s around it. If your camera’s flash unit features something called “second curtain sync” (which means the flash goes off when the camera shutter closes after the exposure, not when it opens at the start), try shooting cars; you’ll see an agreeable motion blur.
About "Biff" notes:
Brenda referred to the last post as "Cliff" notes, something my limited knowledge of American education equates to "crib sheet for getting through Shakespeare 101". I almost like the idea, but I think "Biff" is closer to the mark. Anyone who's seen
Back to the Future will know what I mean.
A note to the more technically proficient:
These notes are kept at an intentionally simple level. Please don’t confuse readers with very valid, but rather complex, additional information. However, feel free to correct / simplify my notes. I will edit accordingly and credit you.