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Introduction to Depth of Field control
A fun question to ask fresh new photography students is “What makes a good photograph stand out to you?”, and while there’s a bunch of answers ranging from subject, emotions, and more, it doesn’t take long before someone points out that sometimes it’s as simple as the subject is in focus and everything else just starts to blur. In photography this background blur is caused by controlling Depth of Field (in this case the lack of Depth of Field). Controlling depth of field is extremely important for a photographer to know, as this is how we place an emphasis on our point of focus. This blog post breaks down the 4 major factors that control depth of field, and also gives tips, suggestions, and comments concerning equipment, techniques and more that will further enhance your ability to control depth of field.
What is Depth of Field?
When your camera focuses on a point it creates a linear zone of focus. When you focus anything that is exactly to the left, right, above, or below your point of focus is in focus. From that point expands out the depth of field, which is a zone of focus that is in front and behind your subject. When you have a shallow depth of field your zone of focus is small and things start to blur behind your subject and also up front (this is important to note). When you have a deep depth of field more of the background and foreground show up in your image.
Depth of Field – By giving our viewers less, they see a lot more.
Before we get much into the technicalities of Depth of Field, I wanted to share my opinion about DOF. Its apparent people love shallow DOF in portraiture and such because of how abstract it makes the background. Your subject should be sharp, and by blurring the background you take away competitive elements that would detract from your subject. Furthermore, when we give our viewers an abstract background due to shallow DOF they also begin to reconstruct the place in their heads from their memories. If you take a pretty picture of a couple in a field for their engagement photo, but you keep the trees and field a little blurry, than the viewers see the happiness of the couple yet with the abstract nature of the background they subconsciously reconstruct that setting in their head from their experiences. I personally believe this helps our viewers “Read” our photographs rather than just stare at them like it’s a snap shot. As the subtitle states, it really is giving our viewers less to see, but in the end they see a lot more.
Photographs are more than just shallow depth of field, there are some really wonderful photographs that have extremely deep depth of field. The purpose of this post is to help you know the best ways to achieve your depth of field goals.
Depth of Field Control – Breaking it down to the basics
Most everyone on the web will tell you that if you want a blurrier background, than get a lens with a wide aperture. This tends to be something like the 50mm 1.8 that Nikon and Canon both offer really cheaply. Those people suggesting that are absolutely right. That 1.8 lens wide open is so much different than the 5.6 their kit lens would be at 50mm that the results are striking. Yet its more than just aperture that controls depth of field though, it’s actually 4 major factors, and here they are:
These 4 elements make up your depth of field, and if you control them you can get results you aren’t expecting like a shallow depth of field at F11, or a deep depth of field at 5.6 with a wide lens.
So let’s get into a little more detail about those 4 elements
The aperture of the lens is how much light it lets in. Aperture is a fraction and is measured in what’s called Fstop. Fstops are displayed in numbers such as 1.2, 5.6, 11, etc. Since it’s a fraction when you see a smaller number you actually have a bigger opening which lets more light in. Since you are letting so much light in you don’t have to use a long shutter speed to get the shot. When you bring your aperture down (and get a higher fstop number) you get a larger zone of focus in front and behind your point of focus. Since you aren’t letting as much light in, be aware that your shutter speed has to be longer. Lenses have a maximum and minimum aperture they can reach. If a lens has a really fast maximum aperture, there’s a good chance your minimum aperture will be small such as F16. This actually isn’t a bad thing as photographs can actually start looking worst if you go past f16 due to something called Diffraction. This website is an EXCELLENT write up on how diffraction affects image quality: http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
Here is an example of DOF changing via aperture.
Now here’s a major factor that many people seem to not consider when it comes to the depth of the field formula. Simply put, the closer you are to your subject the shallower your depth of field zone becomes. This is why Macro lenses have CRAZY shallow DOF, because you can get really close to your subject with them. This is also something that’s extremely important for lens selection as each lens has its own minimum focus distance (MFD). For example Canon’s old legacy 70-200 2.8L had a MFD of around 59” which wasn’t bad, but a few years later the 70-200 4L came out with a MFD of 47.2” and people were able to really get close in comparison with that lens, and you could really tell the DOF difference. Fortunately Canon recognized this situation and made the new 70-200 2.8L II IS MFD the same distance as the 70-200 F4L, and mixed with the faster aperture you have a crazy DOF control lens. Newer lens out now such as the Canon 40 2.8 STM and the newly announced 24-70 F4L IS really take advantage of minimal focal distance.
Here is an example of changing DOF via subject distance.
Interested in modifying the MFD of your lens for cheap? Look into extension tubes for your lens. Read about extension tubes here : http://www.slrphotographyguide.com/camera/lens/extensiontube.shtml
Focal length of your Lens – MM
Part three of the DOF equation is the mm length of your lens. The larger the focal length the shallower DOF you have. Having a different focal length does change your composition. Have you ever seen a professional nature portrait of a bird flying, or a professional football player, more than likely you are seeing a 300mm+ lens being used and the background is completely obliterated into a mass of colors and abstract shapes. This is caused because the MM length is higher.
Here is an example of DOF differences using lens of various focal length.
Distance of foreground and background elements
This one seems pretty obvious, but it is a major part of the DOF equation. The closer an item is to your plane of focus, the more in focus it will be. So if you have too sharp of a background, one of the best things to do is move your subject further away from it.
Here are examples of moving a subject away from a background, and a foreground element. Note that the background is physically either close or far from the subject. (Foreground also)
Putting it all together
These four factors are what makes up depth of field. So if you want MAXIMUM depth of field combine all the factors together to achieve that result (larger aperture, wider lens, further from the subject, and get the elements closer together). If you want the minimal depth of field, get in closer to your subject, user a smaller aperture, use a longer lens, and lastly get your subject away from foreground and background elements.
By picking and choosing what four options you want you can really affect the final results. Good luck and happy shooting.
A term aspiring photographers may have heard is “Bokeh” which is close to the Japanese word for blur (Boke). Bokeh is the quality of the blur in the shallow DOF area. Bokeh can have it’s own unique personality and quality which people see exist in certain brand of lenses such as Leica (A.k.a the Leica Look). For further research on the web for DOF be sure to look up the term bokeh also.
Bokeh (Wikipedea) – http://en.wikipedia.org/wiki/Bokeh
Leica Look – http://www.leicalook.com/
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