Saturday, February 18, 2012

Tutorial - Shutter Speed

Shutter speed - it's probably the easiest photographic concept to grasp, yet it seems camera companies pour lots of research into this very aspect of photography - allowing your camera to attain higher shutter speeds under a variety of photographic conditions while producing great quality photos.

Not paying attention to shutter speed is also the bane of many a beginning photographer - who hasn't made a blurry photo before?

Shutter speed (sometimes abbreviated SS) is typically expressed in seconds or fractions of a second.   But before we get into shutter speed talk, let's review a bit of simplistic math.

Since SS is many times expressed in fractions, we must remember one of the rules of a fraction - the bigger the bottom number, the smaller the value!
 Here are two shutter speed readings - which one is smaller?  Faster?   
1/125s  or 1/250s
The answer to both of those questions is 1/250s.  Since 1/250 is smaller than 1/125, when it comes to a shutter speed it's also faster - it means it took your camera only one-two hundred-fiftieth of a second to create a proper exposure.  1/125s, while fast in human terms, is still twice as slow as 1/250s.

Now that is out of the way, let's get to business - Why do we care about shutter speed?  Glad you asked!  To (help) make our photos look the way they do!  Proper shutter speeds ensure we get the exact image we're looking for in a given situation, assuming we've done our part in the other areas of making a great image.  Sometimes we want (or need) a slow shutter speed, whereas other times we need all the speed we can get.

But first, we have to know how shutter speed is determined.  In a typical situation, the shutter speed is calculated by the camera, like the following:

1) The camera meters a scene.  This is the part where basically the camera "sees" what's ahead of it and says "you know, I think the image needs to have X amount of light in order to make a proper exposure."

2) Knowing how much light the image is going to require, the camera then checks to see the aperture of the lens.  If the user has set a wide aperture (meaning a big opening, like f/1.4), that means the camera is going to get lots of light in any given time period.  Conversely, if the photographer has chosen a small aperture, something like f/8.0, then the camera is going to require more time to leave the shutter open in order to catch all the light it needs.  Check out the aperture tutorial for more on this.

3) So the camera has read (or metered) how much light it's going to need, and it has also glanced at the aperture the photo is going to be take at - the final piece of the puzzle is the ISO.  This is basically the sensor's sensitivity to light - the higher the ISO, the more sensitive it is, and the less light it needs to acquire an exposure.  (there's actually a lot more to it, but for now let's keep it simple).

Let's look at a photo, shall we?

Julia-Pfeiffer Burns State Park, CA
ISO 200, f/9.5, 0.7s
Ever see a waterfall or stream photo, like the one above, and wonder how the heck they "blurred" the water like that?  When I was starting out, I used to think photographers would do this in Photoshop - boy how wrong I was!

By using a slow shutter speed (and a good tripod), a photographer is able to smooth out details of moving elements in a photo.  In the case of moving water, it usually calms the look of the water, giving the photograph a more serene feeling.  In the photo above, I used a shutter speed of almost one second, which is actually fairly short for some moving water shots, but still long enough to get the effect I wanted.

Here's another water example I like - this one uses a 2-second exposure, yet still retains the turmoil and action of the crashing water:

Beach in California
ISO 100, f/45, 2.0s

Slow shutter speeds can also add a sense of movement, chaos or energy to the photo:

Kids at play
ISO 100, f/19, 1/3s
On the Bike
ISO 400, f/18, 1/10s
Important Note - Notice how on each one of these photos, small apertures are used?  f/9.5, f/18, and even f/45!  That's because in each of these photos, I was in shutter priority mode - This lets me tell the camera what shutter speed I'm looking for, and the camera figures out (based on the ISO rating) what aperture to set the lens.

Since 1/10th of a second (on an overcast but bright day) is fairly slow, as in the photo above, my camera decided it needed to stop down to f/18 (which is  very small) in order to give me the long shutter speed I was looking for.

Now on to part #2 - Let's speed it up!

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