Focus: Depth of Field

Focus: Depth of Field


So I mentioned Depth of Field (DoF) earlier in Part I, on exposure using aperture.  Changing your aperture settings of your lens changes the depth of field in your photos.  Now, what is depth of field?  It is the width of area in your photo that is in focus.  The larger your aperture (or smaller the aperture number) the smaller DoF you have.  So I demonstrated this using my portrait shot of my friend at f/1.4 (wide open/large aperture) with my 50mm f/1.4:

Portrait - 50mm f/1.4 D

So, I mentioned that the area of focus is just on her eye that is closest to the camera.  That is a very small or "shallow" DoF.  Another example of this would be some of my hand held macro work.  I need to use a wide open aperture to allow the most amount of light in to allow myself to have a fast enough shutter speed to not have any blur.  Some of my macro photos demonstrate a very small DoF which happens when you shoot macro photos with a wide open aperture.  This example of the dragonfly demonstrates just how small of a DoF we are talking:

Dragonfly - 105mm Macro VR

The depth of field in this photo is roughly the width of this dragonfly's head.  And when you look into the background it is completely blurred out.  This blurred out background is call bokeh.  Bokeh is not so much a cool hip trait for dragonfly portraits but more so for people portraits.  The photo above has very nice creamy bokeh.  The bokeh or out of focus background allows portraits to pop out a little more.


In landscape photography, as I also mentioned in Part I, needs a small aperture (or large aperture value) to create a large DoF so everything in the landscape is in focus.  Here is an example:

Boardwalk - 17-55mm

This photo just demonstrates that the depth of field is good because you can still make out the grass in the background and the boards going off into the distance.  In landscape photos you want the most detail you can get usually.  However in this photo the background isn't completely sharp because I focused more on the foreground because I wanted that area of the photo to be sharpest.  This was so that you looked at the bottom of the boardwalk first because it was sharpest, and then were led to the top of the photo.  The boardwalk gave your eyes a path, literally through the photo.  So you don't always have to follow photography rules especially if you have a game plan with what you are doing.

Depth of Field can be changed by Tilt-Shift lenses.  These flatten the DoF a little so that the DoF is more horizontal than just vertical.  This allows landscapes to have more detail because the DoF is flatter to the horizontal axis.  I personally have not used a TS lens so I have no examples and the photos would just look like a very sharp landscape photos from the foreground to background.  

Other manipulation of optics or in post-processing can blur the photo more to make the aperture effect on the DoF different.  Lensbaby lenses alter the effects of the DoF to blur areas of the photo while keeping certain areas of the photo in focus.  Again I have not tried one of these lenses so I am not an expert witness but that is the gist I have gotten from seeing the photos from those lenses.

So DoF can be a factor that makes or breaks a photo.  But just like most rules in photography, they can get tossed out the window from time to time.  It's art, who cares.  I am sure you can find an audience to like your photos even if you don't do the normal things with DoF.  But more often than not, DoF is a good thing to pay attention to since it is a large-ish part of photos.  

And with that I will wrap up my focus on DoF, I hope that helps and again if you have any questions or things you would want me to cover on my blog, do not be afraid to send me off a e-mail @ tomhouston7@gmail.com.