Sunday, January 17, 2010, 2:44 AM
[
General]
Capturing Alaska
with Wayde Carroll
Effective Use of Aperture
Someone sent me an image recently in which a person in the photo was clear and sharp while the foreground and background were out of focus. This person really liked the look of the photo and wanted to know how they could emulate the style.
The answer is aperture. For those of you who don't know, when you press the shutter release on your camera three factors come in to play to give you your proper exposure. The shutter speed, your ISO, and your aperture.
The shutter speed simply determines how long the shutter remains open and is one way of controlling how much light is allowed on to your sensor when you take an image. The darker it is the longer shutter speed you need etc..
Your ISO (same as "film speed" in the old days!) determines how sensitive the sensor is to the light coming in. A photo taken at a lower ISO of 100 needs more light to give a proper exposure than a photo taken at ISO 400. There are good reasons and times to use both but that's another post!
The aperture determines the size of the opening that is allowing light in during the exposure. The smaller the aperture opening, the less light gets in and the more time needed for your exposure. Thus, with a larger aperture opening the less time needed.
Sounds similar to the shutter speed right? Well, not exactly. The size of the aperture opening also determines your "depth of field" or range of apparent sharpness. The smaller your aperture opening, is the sharper your image appears. This is referred to as being "stopped down". If you have a large aperture opening, less of your image appears to be sharp. This is called "shooting wide open".
To make it a little more confusing the aperture numbers are sort of counterintuitive. The larger the aperture number ( F16, F22, etc.) the smaller the aperture opening. The smaller the aperture number (F2.8, F4, etc.) the larger the aperture opening.
I get clients to think about it this way; "The larger your aperture number, the larger amount of your image appears sharp, the smaller your aperture number, the smaller your amount of apparent sharpness is."
So, in general, if you want to isolate a subject with a shallow depth of field- a small range of apparent sharpness- then set you camera's aperture on the smallest number you can. Focus on your subject and let the rest fall out of focus. There are various factors that effect this technique as well. The closer you are to your subject the greater the effect will be. Using long telephoto or zoom lenses compresses a scene so things appear closer and thus diminishing the effect. The best thing to do is experiment with the lenses you have at various apertures and various distances. Soon you'll have a good feel for what works well with what you have.
Here are a couple of examples to show you the difference between photos taken "wide open" (larger aperture number) and "stopped down" (smaller aperture number.

Aperture "Stopped Down" to F16

"Wide Open " Aperture of F2.8

Aperture "Stopped Down" to F16

"Wide Open " Aperture of F2.8
Of the top two images I prefer the wide open exposure. Of the bottom two I prefer the stopped down image.
Here is a typical scene that required a small aperture of F22 to get the canoes and the mountain to appear in focus.

Here is a scene where I wanted a large aperture opening to blur the distracting foliage behind the leaves.

Thanks Wayde, it was a very fun way to spend a Saturday. I think my next adventure will be to the beaches in the Winter!
denise6:58 PM