Mostly, It's an Aperture Thing

In my last blog post "Mostly, it's a Shutter Thing", I talked about how important shutter speed is to capture great shots of wildlife and other action genres. In this post, I will talk about how important aperture is and how it can be used creatively in wildlife photographs.
A Quick Aperture Primer
Shutter speed controls how long the shutter stays open and exposes the sensor or film to light. Aperture also controls how the light hits the sensor, and it does this by controlling the amount of light coming through the lens. Back when film was popular, the lenses had an aperture ring on the barrel measured in stops of light. The higher the f-stop number, the smaller the aperture and the smaller the amount of light getting through to the sensor.  The lower the f-stop number, the larger the aperture and the greater the amount of light getting through to the sensor.  In modern cameras, the f-stop is controlled electronically and for the most part there is no f-stop ring on the lens, but all the concepts are still the same.
  So that handles the exposure part of controlling aperture, but there is also another benefit to your photography the aperture can provide.  This benefit is called depth of field.  Put plainly, depth of field is the area in sharp focus in front or behind the subject to which you have focused the lens.  High f-stop numbers give you greater depth of field and lower f-stop numbers give you a shallow depth of field.  So that photograph of the flower you like, that has a very dreamy and blurred look on the petals, but has  a sharp center was created using a lower f-stop.  By using this f-stop, the photographer allowed the viewer to see a very small depth of field accentuating the pistil or stamen of the flower.  Conversely, that beautiful scenic you love where the entire image is in focus from the foreground to the background is using a large f-stop number like f16. 
Turning Aperture into Art
In wildlife, the primary way to artistically use your aperture is by using the depth of field to isolate the subject.  What, isolate the subject?  How does that work?  Remember the flower mentioned above and how the stamen was and the flower's petals were out of focus? The same principle applies here except you are going to use the shallow depth of field to blur out the background and remove the distracting elements.  To do this, open up your aperture as far as it will go.  On most large lenses this will be between f4 and f5.6.  Now, here is the big secret that many people get wrong.  The distance between the camera lens and the subject matters a lot, as does the distance between the subject and the background.  Let's run through a scenario...
Close Subject Less than 10 Feet Away
In this scenario, we are usually in a blind or photographing a bird or mammal who has tame qualities.  Maybe you are on your belly at the beach photographing a plover for instance.  In this case, even at f5.6, you are so close to the subject, your background only needs to be a 15 to 20 feet behind the subject and you start to see quite a bit of background blur.  This is one of the main reasons photographers, even with 600mm lenses, get as close to the subject as practical.  As the distance from the lens to the subject increases so must the distance from your subject to the background to maintain the blurred background. The house finch below was shot only 5 feet from the lens giving the background a nice gradient blur.  Even at f8 the background is blurred because of the close proximity to the subject.

What does it look like when you don't quite nail it?
Although, not a failed image by any means, this image below shows what happens when the distance from the lens, to the subject and subject to the background is too great.  Note how we have blur, but not significant enough blur to simplify the background.  In this image, I had to actually burn in the background to try to simplify.  I really did not have a choice here and often times you won't, but I always try to simplify it whenever possible.

Aperture can be use to control your exposure, but also to creatively control the depth of field in the image.  This is one of the oldest and most used tools in the wildlife photographer's back of tricks.  Give it and try and see what happens.  Oh and above all, have fun!


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