Monday, September 26, 2011

shutter speed

Nearly Everything You Ever Wanted to Know about Shutter speed

Shutter speed seems pretty straight-forward, right?  It's how long your shutter is open for, from 1/8000 of a second to minutes, hours, or even days (months in some cases!).  Some specialty cameras even have wider ranges.

Shutter speed, in and of itself, is that simple, however, in a larger sense, to speak to the complete exposure process, there is a bit more to know.

Shutter speed and the motions of your subject matter

Are you shooting inanimate objects?  If so, are you shooting COMPLETELY inanimate objects?  For instance, a flower is basically an inanimate object, right?  Well, not really if it is moving around in the breeze.  So, let's start with truly inanimate objects.  Maybe a bowl of fruit in the kitchen window.  Are you using a tripod?  If so, shooting an inanimate object couldn't be easier.

Set your aperture based on the depth-of-field you desire (we address this in a future post) and then select absolutely any shutter speed that will give you the right (or desired) exposure according to your in-camera or in-eyeball meter.  Easy peesy!

What if you don't have a tripod?  This changes things.  Now you are introducing your own motion to the camera (we'll talk more about this and in-camera or in-lens stabilization in a minute). I personally know that I cannot handhold a camera without stabilization any slower than about 1/40 of a second.  So this limitation would affect my available shutter speeds (which in turn affect my choice of aperture and ISO).

What if you are shooting moving objects?  For people, you will probably want at least 1/100 of a second (keep in mind that we are not talking about every situation -- for instance, in a vrey dark banquet hall where you are using flash, you may want a shutter speed as slow as 1/15 of second to capture some ambient light and the flash will freeze your subjects).  For sports, somewhere between 1/500 and 1/1000 of a second.  For airshow jets zooming by, more light 1/2000 to 1/3200.  All depends on the speed of your subject and whether or not you want to completely freeze their motion, or introduce some motion blur to give the photograph a sense of the motion that was happening.  This can be important for images of people dancing.  Dancing people frozen in time without a visual sense of the motion often look static, flat, and lacking in visual appeal.

With some moving objects, you can utilize a somewhat slower shutter speed than normal, if you pan with your subject.  A classic example is shooting a racing bicyclist.  If you smoothly pan your camera with the bicyclist at exactly the same rate, you can capture the biker reasonably crisply while leaving the background in speedy streaks of colorful blur.  This requires some practice but can be well worth the effect.

Shutter speed and light

Every time you adjust your shutter speed, you change the amount of light hitting the sensor.  A faster shutter speed allows in less light (so you'll adjust aperture accordingly, but now you are changing depth of field -- also, you might change ISO, but you will be affecting digital noise -- thirdly, if working with flash, you can add or subtract light).  A slower shutter speed allows in more light, but can introduce digital noise and may not work with many moving subject matters.

Shutter speed and image stabilization

Many lenses and some cameras have image stabilization features (depending on brand it can be called optical stabilization, image stabilization, vibration compensation, etc.).  This moves elements in your camera or lens in an opposite direction from those small moves, jerks, spasms, and heartbeats in you that get transmitted through the camera.  Stabilization only compensates for small motions and has no bearing whatsoever on the motions of your subjects.  It will allow you to handhold up to two or three stops slower, and that can be a godsend, but it is not a miracle worker.  You still need to practice stable handholding techniques.

There are also times when you should shut off stabilization.  Working on a tripod?  Turn it off.  It can actually add vibration in that scenario, because it really doesn't understand "no movement".  Also, if you are working at shutter speeds of 1/1000 or faster, turn it off.  It's not helping you any.

Shutter speed and flash

In some situations when using flash, shutter speeds becomes less intuitive.  Want to freeze the action of a bursting balloon?  The obvious choice is to use a fast shutter speed.  But most cameras, while allowing for fast shutter speeds (often 1/8000 or better) cannot compete with the speed and action-freezing power of the flash gun.  For the balloon situation, you will be better served by shooting in a dark room, a slower shutter speed, but having your flash set at a low power.  This can yield an action-freezing pop of light with a duration of as little as 1/50,000 of a second!  There is a bit more to this situation as you will need a special sound or laser trigger, but you get the idea.  As fast as your shutter can be, the flash can be much, much faster.

Shutter speed and post processing

If you shoot in RAW you may find that the margins you are allowed in post-processing can affect your shutter speed.  Say your ISO is maxed out (or as maxed out as you are comfortable with due to noise issues) and your aperture is wide open.  Furthermore, you are hand-holding and your meter wants you to shoot at slower than 1/40 and you just know you can't be stable at that speed.  If you are a RAW shooter, you can bump your speed by as much as two full stops and recoup the light in your RAW processor!

Shutter speed is one-third of the classic exposure triangle (with aperture and ISO) and can be though of as one-fifth of the modern exposure triangle (with aperture, ISO, flash power, and flash to subject distance).  It is all a balancing act, but if you consider the nuances of your subject and the ambient light, you can begin to build the perfect exposure. With practice it begins to get intuitive and you'll be adjusting all your settings appropriately faster and faster.  Good luck and good shooting.

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