Lessons from the Shot: Shallow Depth-of-Field


 by Stanley Leary

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“I bought a Canon ƒ/1.4 50mm prime lens last year and I love it.  My only issue is that when set to automatic the depth-of-field can be so narrow that a nose is in focus and an eye is out of focus.  I’m assuming that the aperture is just too open.  Is there a rule of thumb when taking portrait-type shots as a minimal (or max – not sure which is which) aperture?  Maybe I just need to stay on aperture priority and ƒ/1.8, or something.  What’s your recommendation?”
One of the most popular lenses being bought today is the 50mm ƒ/1.4.  The reason for the popularity is the silky smooth shallow depth-of-field obtained when shooting at ƒ/1.4.  You will see a lot of wedding photographers using these to not only get that look, but also used because you can use it to make photos when flash is not allowed—like during the ceremony. 
Often dark inside lighting conditions require a lens with an aperture of ƒ/1.4 or ƒ/2 to get photos.  Slow shutter speeds can only help up to a point before the camera and subject movement becomes an issue.  If you were photographing objects and not people then you could take a photo with a shutter speed of 1 second, but with people you need to be shooting at least at 1/30 of second or faster to avoid subject movement, which will produce blurred images. 
When using the lens for portraits wide open at ƒ/1.4 and filling the frame with someone’s face will very quickly give you the desired shallow depth of field results.
Items that affect depth of field.
1) The ƒ-stop/aperture.  
As you already know the lower the number the less depth-of-field. 
2) Distance to subject.  
The closer you get to a subject the shallower the depth-of-field when the ƒ-stop remains the same.  In macro photography, if you get as close as 1:1 ratio you often have to be at an ƒ -stop minimum of ƒ /11 to appear in focus.  When I do macro photography the aperture is quite often at ƒ /45 and it still appears like a shallow depth-of-field.  
See how the eye is out of focus.  You would think at ƒ /45 everything would be tack sharp, but it isn’t.  
My suggestion, the closer you get, a greater ƒ /stop to keep the facial features of the eyes, nose and mouth in focus.  I personally don't mind the ears out of focus.  
I occasionally will shoot with my 85mm ƒ /1.4 wide open, where only the persons eye in focus. I usually shoot between ƒ /4 and ƒ /5.6 for headshots to keep the head in focus.
When doing group photographs, people are often two or three rows deep in the photo.  In these situations one needs to be shooting at ƒ/8 or greater aperture or the people on the front or back will not be sharp. 
If you own a shallow depth-of-field lens like ƒ/1.4, just remember the silky smooth, out of focus look requires an ƒ/1.4 setting.  On many of the new cameras you can move the focus point around in your viewfinder.  This will help you maintain your focus and composition.  Focusing in the center of the frame and then recomposing the photo will often give you poor results since the tolerances are so critical. 
Practice by making portraits at ƒ/1.4, and then do some at ƒ/4 and then some at ƒ/5.6.  Get comfortable with the look of each aperture and when you want a certain look you will feel confident that you can deliver, because you have practiced.