Monthly Archive for November, 2006

The pics below were taken with the same point of focus. The first picture is exactly what I saw through the view finder on every picture. The only change from one picture to the next is the aperture (f stop) setting.

The pics were taken at f- 2.2, 3.2, 5.6, 9, and 22 respectivly

Depth of field, and aperture explained:

It’s been too long since I’ve written anything about real photography, so I thought I would start back up with a discussion about aperture and how that effects the depth of field and focus. It’s my hope that you will be intrigued by the different types of effects and images you can get when you venture outside of the fully automatic modes (like the famous “Green Box”) on your SLR cameras. Once you start using the manual modes, you will be able to make the picture in your minds eye something that you can actually capture, even if it is not at all what you see through the view finder.

So what is aperture? I guess there are just a few easy things that you need to understand when you think about aperture. First of all, aperture is usually expressed as “f”, or “f-stop”. When you take a picture, the lens of the camera has circular window that it closes down for a split second to restrict, or allow a specific amount of light into the digital sensor or onto the film. It can make a very small hole to allow almost no light in, or a larger hole to allow maximum light through. Each full “stop” changes the amount of light it lets through by a factor of 2. Most cameras will allow you to adjust your f stop by 1/3 stop increments. Concerning the aperture, in general the lower the f stop setting the lower the depth of field, and the higher the f stop setting, the higher the depth of field. In general, wider glass will generally will have greater depth of field, and longer lenses will have more shallow depth of field. That is, a picture taken at f22 will have a higher depth and more of the picture in focus than a similar photo taken at f2.8, and a 24mm lense will generally have a greater depth of field than a 200mm lense shot in a similar situation. See the pics at the top of this blog for an example. The size of the hole, along with the speed of the shutter works to make sure that the image is properly exposed. This hole is the aperture (see pics below). When you leave you camera on the fully automatic settings (like “P” or the green box” the camera figures out your exposure for you and sets the “f” and shutter speed for you.

The pics below show the window that creates the aperature. I held down the aperature preview button at f2.8, f 16, and f22 to get the pics below.

Next we move on to depth of field. This is actually a really simple term that just refers to how much of the image area is in focus. Pictures that have everything in focus are said to have a high depth of field, where pictures that have a small area in focus, and a lot of blurry back/foreground are said to have a narrow depth of field. The length (zoom) of the lens and the aperture are two of the biggest factors that determine the depth of field. With out getting too teched out, if you understand how a pinhole camera works, you will understand why a higher f stop (thus a smaller hole) creates a greater depth of field. Basically when you have a small hole the light comes straight in and doesn’t have to be bent to be focused. If you are near sighted, take your glasses/contacts out/off and make a tiny hole (i mean tiny!) with your hand and hold it up next to your eye and look through the hole (or could be like Ronald Regan and make the pin hole in a piece of paper). Look through the small hole, and if you are blind like me you will be able to clearly see much better than you can without your glasses. You are only looking at the light that is comming straight in and doesn’t need to be bent/focused. Thus it is in foucus. The same idea holds true with cameras.

Now, if you are ready to step outside of the green box, you can do some really cool things with your photographs. My first recommendation is to try out the aperture priority setting on your camera. On most cameras, this is the Av setting. This setting allows you to dictate what “f” you want to use, while the camera figures out the correct shutter speed to properly expose. The lower the f stop you set you camera up for, the more light it will let in. Lower aperture numbers will also give you photographs that will have a depth of field that is very similar to what you see when you look through the view finder because the lens isn’t closing the window. Now it’s time to play and experiment. When I was teaching myself about all of this I burned a roll of film by taking pictures from the same spot with the same focus at 20 different apertures to find out what the effect would be. Today with digital cameras you can learn and experiment in seconds and not cost yourself anything. Go outside on a sunny day and play around. Keep an eye on your shutter speed to make sure that you are exposing properly. If it is too bright outside, you camera may need a faster shutterspeed than it is capable of at low f numbers. Most cameras will blink the max shutterspeed if this is the case (and your pics will be washed out). On higher f settings, make sure that your shutter speed is high enough for the lense you are shooting and your shooting conditions. If your camera is slowing your shutter down too much, you will have less crisp, or blurry pictures. Play around with different lenses, and different settings. Focus on different parts of your view and see how your depth of field changes. You can also use your aperture preview button on bright days to actually see through your viewfinder what your film or sensor will “see”. This post is getting a little long, so stay tuned. I think I’m going to write a few other posts soon about how to use aperture to get better party pics indoors, and how to choose a lense for low light/indoor shooting without a flash.

I’ll finish this post with two more pics. These are similar to the opening pics, but the point of focus was my shoe, not the backgorund. The first pic was taken at f2 and has a very narrow depth of field. This is what I saw on both pics when I looked through the view finder. The second pic looks nothing like it looked like in the view finder because it has a HUGE depth of field with the shoe and the background in focus. To get everthing to be clear, I just used the Av setting to crank the aperature setting to f22.