Photo by Alex Thorne I wanted to draw your attention to an in-depth article by Todd Vorenkamp at B&H on aperture.  It’s part of a three-part series covering exposure.  In this post, I’ll touch briefly on how I think about using aperture in my photography, but I encourage you read Vorenkamp’s detailed article on how aperture is used to adjust exposure, depth of field and image quality.

There are three ways the camera can control light to obtain a proper exposure: aperture, shutter speed, and digital ISO (or film speed).   When thinking about how I’m going to expose an image, ISO has become less of a concern for me because of the fantastic high ISO performance and auto-ISO settings of today’s DSLRs.  Except for extreme lighting conditions or long exposure shots, it really comes down to just thinking about aperture and shutter speed for me.

The subject matter dictates whether to focus on shutter speed or aperture when thinking about how to capture the image I want to create.  In my previous blog post of the images I shot at Cornerstone Gardens, considering what aperture to use was my primary focus.  In this case, isolating individual elements in the image was important to the composition.  To do this, I needed a prime lens with a large aperture to isolate the subjects in the image.  You can see the affect setting the aperture wide open has on the image below. Photo by Alex Thorne

When considering how to set the aperture, you need to ask yourself, “what do I want to be in-focus in this image?” For example, if the shot is a landscape where everything needs to be in clear sharp focus, then I need to shoot with a small aperture to create a very wide depth of field.  Maybe I just want to focus on a single subject like a flower and needing to blur out the background.  To create a shallow depth of field, I’ll need to open up the aperture.  However, you need to be careful not to set too large an aperture or else some of you subject may be out of focus.

Photo by Alex Thorne

I run into this issue sometimes with my outdoor or natural light photo shoots where I’m only using available light.  I’m also trying to make the background very blurry by setting a large aperture.  I do most of my natural light headshots with an 85mm lens and set the aperture to f/2.0, which, depending on how the subject’s head is turned, can cause one of the eyes to be slightly out of focus.  You can see in the headshot image on the left how a large aperture only keeps the eyes and face in focus, blurring out everything else.  The large aperture comes in handy but I need to make sure the eyes parallel to the digital sensor to ensure that they are both in sharp focus. 

Large aperture prime lenses are also extremely handy when capturing images in low light situations such as parties, weddings and family snapshots.  You can see how useful this can be in the following image.  We were doing some shopping in downtown Sonoma and I found a backroom in one if the stores where I quickly posed my daughter for quick portrait on an antique tricycle.  The lighting was terrible, but I was able to get the shot because I had a large aperture prime lens.

Photo by Alex Thorne