Monday, April 4, 2011

Photo Tip #9 - Aperture and light...

When I first started in Photography, it seemed like it took me forever to understand the difference between shutter speed and aperture...especially aperture. Quite frankly, it is one of those concepts you learn that seems exactly opposite of what it should be. I'll do my best to keep this simple.

When dealing with aperture (built into the lens), you are basically dealing with 2 things...how much light comes into your camera, and depth of field. We already discussed depth of field in Photo Tip #8.

In this Photo Tip, let's take a look at our aperture graphic once again and see how aperture and light go together.

Picture a hose and water. The lower numbers (f2) to the left have a great big hole in the middle. The higher numbers on the right (f16) have smaller holes. That was always confusing to me. I would have preferred the big holes on the left having BIG NUMBERS! Oh well...I had to get over that. :)

Now let's imagine filling up a bucket of water with these different hoses. If you shot water through the f2 hose on the left, you'd fill up the bucket way faster than if you used the f16 hose, assuming the water pressure was the same. It's the difference between using a fire hose and a swizzle stick straw.

Now let's translate this illustration over to "light". Your camera needs a specific amount of light to properly expose photos. There are a few different ways to get light into your camera, but for now let's focus on aperture.

If you have a lens that can adjust down to f/2 or below, you'll be able to grab a bunch of light much faster than if your lens only has an f4 or higher aperture setting. Most kit zoom lenses start somewhere around f3.5 on the low end, and progress to f5.6 on the low end as you zoom in.

Let's make that a little more simple. If you have an 18mm-200mm zoom lens that has a range of f3.5 to f6.3, when you are zoomed out at 18mm, your aperture will be f3.5. If you are zoomed in at 200mm, your aperture will be f6.3. At 100mm, your aperture will be somewhere in the middle. As you can see, kit lenses will have some light limitations relating to aperture.

Now let's look at your camera's shutter. Your shutter is like a lid on a box that opens up to let light into your camera, then closes when you have enough light to properly expose your image. If you use an aperture of f2 (the big hole), you'll let a lot of light in quick and your shutter won't have to stay open as long when you take a picture. This is helpful for reducing blur from moving objects.

On the other hand, if you use a aperture like f4 or higher, your shutter will have to stay open longer to grab the same amount of light as an f2 setting. The higher your aperture number, the smaller the hole, the longer your shutter has to stay open to properly expose the image. The longer your shutter stays open, the more chance you have for blurring objects. Sometimes this is a good thing if you are looking to take a long exposure shot. Most times, blurry is not that helpful.

Let's look at the water illustration again. If you use an f2 hose, your shutter will open up and fill the bucket of water quickly. If you use an f16 hose, your shutter will have to stay open longer to fill up the bucket.

So, you've been wondering why your images always turn out blurry when you zoom in with a kit lens and don't use a flash? Well it's because your kit lens probably has a f5.6 aperture (at best) when fully zoomed in. As you can see from the diagram above, the f5.6 hole is pretty small so your shutter will have to stay open pretty long. If anything moves in the photo, or your hands move, your image will be blurry. You can work around the hand shaking thing by using a tripod, but that won't keep people or other things from moving in your shot. They will still turn out blurry if they move. Now you know why those f2.8 zooms are so expensive! F2.8 zooms are often used in sports applications, where there is always movement...especially in low light settings.

On a bright day with lots of sunlight, almost any lens will work. The dimmer the lighting, the more you need a lower F-stop lens. There are some work around as we'll discover in future Photo Tips so stay tuned in.

Keep sending those questions and have fun practicing!

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