You're Smarter Than Your Camera - Effect of Aperture and Depth of Field

February 13, 2015  •  Leave a Comment
You're Smarter Than Your Camera - Effect of Aperture and Depth of Field
Hi everyone and welcome to my second blog.  
We are getting to understand aperture and this blog will continue with exploring the concept of changing aperture on your camera.  Thanks for reading and enjoy the blog.
Tracey
From the last blog, we know that aperture relates to the size of the opening of the lens and so determines how much or how little light gets to the sensor in our camera.  But, other than letting light in, why do we care?  Well, we care because aperture is one of the aspects that controls how much of our image is in focus.  'But don’t we want all of it in focus?' I hear you say!  Well, sometimes, but sometimes not. Take a look at these images below of our beautiful magnolia as it is just blooming.  Both images are of exactly the same flower and from the same viewpoint.  
Which do you like more?  Which one makes the subject stand out?  For me it is the one where the background is blurred.  If the background is in focus, it is far too busy to allow the viewer to narrow in on the main subject in the image.  So how do we achieve this?  There are a couple of things we can do.  One is to set our lens aperture as wide as we can.  The second is to get as close to the subject as possible without compromising the composition.

The type of lens you are using will determine where you need to be located physically in order to frame your subject in the way that you want.  Plus, the lens will also determine how large you can make your aperture, remember the smaller the aperture number, the wider the actual aperture and the more light that gets into the camera to record the image.  If you aren't able to get down to the low aperture settings such as 2.8 or 3.2, try going closer to the subject to try to force the background out of focus more. 
Try to think of lenses focusing on a plane or a slice of what you see in front of you.  Here is our cartoon camera below taking pictures of funky colourful trees.  If we set the aperture to be large, there will only be a slice of the image in focus - that is shown in yellow highlight.  Everything in front and everything behind the yellow slice will be out of focus.
Aperture, (along with camera type, lens type and distance to the subject,) controls the ‘Depth of Field’.  The area of the image that is in focus is called the ‘Depth of Field’.  It is not that everything immediately goes out of focus outside this, but rather that there is a gradual reduction in the focus as you move away from the depth of field.  It is a little subjective, but in general, the depth of field is agreed as the area that is considered acceptably sharp. 

Have a look at this photo of the dining table from the 'Great Hall' from Harry Potter.  There is actually very little in focus and this is shown as the 'depth of field' on the image.  You might say that it has a 'shallow depth of field'.  Everything in front and everything behind this yellow line is out of focus.
Your Challenge –
 
Continue with using aperture priority on your camera - so the camera takes care of everything other than setting the aperture.  Use a similar subject as you did for the first blog on aperture, but this time, change your distance from the subject so you are able to see how this also affects how much of your image is in focus.
You could also try moving the subject away from the background or closer to it to see what effect that has on focusing the viewers attention on the main subject in the image.
Next Time – Focus stacking and circle of confusion; hopefully you wont be!  Also how lenses differ.
Until then, enjoy taking your pictures and get out there in the sunshine.  As always, do get in touch if you don’t understand anything or if you would just like to comment.
Thanks again,
Tracey
 
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References
 
http://en.wikipedia.org/wiki/Depth_of_field
Complete Guide to Digitial Photography by Rick Sammon
http://www.cambridgeincolour.com/tutorials/dof-calculator.htm
http://www.imagemaven.com
 

 


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