Monday, November 17, 2008


Here we are again, and we've got some thing fun to talk about. We're talking about aperture today. I promise that by the time you are done reading this post you are going to know exactly what an aperture is, and not just because you are going to see a picture of one. We are only going to cover the affect that aperture has on how long it takes to take a photograph today. There are lots of other things you can do with different aperture settings thought that will make for many more posts.

At its most basic level, an aperture is the hole in your lens that light has to pass through on its way to the sensor. A larger aperture in your lens will allow more light to get through the lens and onto the sensor, while a smaller aperture will allow less light to get through. You might be asking why some one would want less light to get through? Well there is a reason but we'll get to that in a second here.

When we talked about ISO we saw that increases in sensitivity were higher numbers. Well with Aperture its the reverse. If you want to increase the size of the aperture in your lens, you have to use a setting with a lower number, and if you want to use a setting with a smaller aperture you have to select a higher number.

As an example lets look at one of the lenses that I use a lot, my 50mm f1.8 lens. The number after the f is the aperture and most lenses will usually have the largest aperture they are capable of printed on the side.

My 50mm (and we'll talk about focal length some time too) has an available range of aperture settings from f1.8 to f22. F1.8 is the largest aperture it is capable of while f22 is the smallest. Lets take a look at an example so we can put this in perspective.

Here you can see a picture of my 50mm lens with the aperture set to f22. The hole in thecenter of the lens is the aperture and controls how much light can pass through the lens to the sensor. Put your mouse over the picture and you can see the same lens set to f2.8. You can see that the aperture is much larger which will allow much more light to pass through to the sensor.

Now that we've established exactly what aperture is we can talk about one of its affects on how you take pictures. For today we are going to focus on the apertures affect on shutter speed and why we might want less light to get through the lens at a time.

If we are taking pictures of things that are moving fast and we want the shutter to go fast enough to capture it we could use a high ISO setting like we did with the chess board. But we also saw that doing that can decrease the quality of our images. Instead we can use a wider aperture and the shutter speed will increase without the graininess of a high ISO. The other thing to consider is, what if we are using a low ISO, but there is still too much light for what we are trying to do. Some times we want a slow shutter speed. There is equipment you can buy to accomplish this, but you could just use a smaller aperture. To illustrate what I am talking about I have a couple examples.

You see here a picture of a helicopter that I took some months ago. It looks ok. Its all inTQ-1593.jpg focus and there isn't any blurriness. But in this case thats actually part of the problem. I want a little bit of extra blur in the spinning rotor blades on top to give a sense of motion. The easiest thing I can do to solve that little problem is use a smaller aperture, and you can see the result in the next image.

So I hope this has been a pretty good explanation of what aperture is. As always if you have any questions drop me a line, and I'll be back soon to finish off the basics with shutter speed.

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