Tips And Tricks

The Aperture

Over the past couple of weeks, we’ve taken a look at the dSLR photography system. We’ve taken a look at how point-and-shoot cameras stack up against dSLRs (see: Buying a dSLR – Part I), the similarities and differences between film SLRs and dSLRs (see: Buying a dSLR – Part II), and took a brief look at all the additional accessories that make-up the dSLR photography system (see: Buying a dSLR – Part III). This week (and for the next several weeks), we’ll take a look at one of the most important parts of your photography system: lenses.

Before we can even take a look at the wide varieties of lenses available, I’m afraid we’ll have to do a quick math lesson. It’s fairly simple if you promise to read carefully – trust me! Now, if you’ve started to take a look at lenses when you were shopping for your dSLR camera body, you were probably inundated with a bunch of letters and numbers about the various lenses that you could buy with your dSLR camera body. Focal length this and f-stop that, 50mm-180mm here and f/1.4 there, L or DX, EF-S or IS… Yikes! Don’t worry, though. Let’s take a couple of minutes and learn what all these terms actually mean, and soon, you’ll be a lens pro.


Tips and Tricks

The main focus of a lens is to collect light, and the aperture is the hole or opening through which light is admitted and then projected onto the sensor. In photography, the aperture is the diameter of the lens opening where the larger the diameter of the aperture, the more light that is allowed in to get to the sensor. The aperture is expressed in what is commonly referred to as an f-stop (f-stop is short for field stop), and this is where it can get a little confusing – the smaller the f-stop number, the larger the aperture. So f/2 lets in more light that f/4. Therefore, f/1 lets in a lot of light, where f/32 lets in very little light.

Math Alert!

Tips and Tricks

Now, you may have noticed that the f-stop is being displayed as a fraction (yikes, here comes the math stuff!). The f-stop is expressed as a ratio of focal length to effective aperture diameter. It may not be immediately obvious (except to extreme math geeks), but each f-stop is actually measured in a factor of 2 relative to each other. Therefore, f/2.8 would allow twice as much light as f/4, and f/2.8 allows half as much light as f/2. The relative association of the f-stops becomes even more apparent when you notice that each stop is the square root (well, the rounded square root) of their ratio to the focal length of the lens (we’ll cover focal length more in-depth next week). Since the standard range of apertures is 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22 and 32, the numbers can be squared which gives us a range of numbers which vary by a factor of 2 relative to each other (therefore the result would be 1, 2, 4, 8, 16, 32, 64, 128, 256, 512 and 1024).

Tips and Tricks

If math isn’t for you, all you really need to take from the above paragraph is that each stop lets in twice as much as the stop after it, and each stop lets in half as much as the stop before it – f/2.8 lets in twice as much light as f.4, and f/5.6 lets in half the light as f/4.Think of the aperture like a faucet on your sink – the faster the water is running (the larger the aperture), the shorter amount of time it takes to fill the glass (properly expose the photograph) – the slower the water is running (the smaller the aperture), the longer it takes to fill the glass (properly expose the photograph). So the faucet (aperture) controls how much water (light) gets into the glass (reaches the sensor) over a certain period of time (the shutter speed).

Aperture is usually expressed in 2 different ways when referencing camera lenses: max aperture (f/1.4, for example) and aperture range (f/2.8 – f/8.0, for example). The maximum aperture is usually the most important aspect of the aperture when looking at camera lenses. Tips and TricksThe larger the aperture (the smaller the f-stop number), the better it will perform in low-light situations (because you’re allowing more light to hit the sensor). A large aperture also allows you to use a faster shutter speed to “freeze action” (because you’re allowing more light in, you can use a faster shutter speed but still expose the photograph properly). A smaller aperture is also useful, though it is usually a less-important factor when looking at lenses. A smaller aperture (larger f-stop number) will help for longer exposures (letting less light in, allowing you to use a slower shutter speed to create effects like smooth water and motion blur).

The aperture is also used to influence depth of field (the distance in front of and behind the subject which appears to be in focus). The larger the aperture (smaller f-stop number) the more shallow the depth of field (DOF) – meaning with a large aperture you can have your subject in sharp focus, but have the foreground and background all blurry (think: macro shots or portraits). The smaller the aperture (larger f-stop number), the greater the DOF, which means you can have more of the frame in focus (think: landscape photographs).

The aperture, of course, is only part of the equation when it comes to lenses. The actual size of the aperture at a specific f-stop is determined by the focal length of the lens. So the actual diameter of the aperture at f/8 could be 4mm or 10mm or 50mm or more, depending on the focal length.

Next week we’ll take a closer look at focal length, as well as other designations that you see when shopping for the various lenses to add to your photography system. Once we’ve learned how focal length fits into the equation, we’ll be ready to look at the variety of lenses for our dSLR photography system.

Henry's Photo Tips are brought to you by Tim L. Walker, owner of the popular photography resources site

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