Portrait Photos

In previous posts, I've explained the impact of aperture upon depth-of-field.  When taking portrait photos, a commonly desired featured is a blurred background, as shown in the following photo:

My daughter, Tess, before her senior prom.
1/125 sec, f5.7, ISO 125, focal length 155mm

There are still more features in the background than I prefer, but they are fairly blurred so that the focus is literally upon her.   Better yet is the following image in which the background is completely blurred:

My daughter, Tess, before a previous prom.
1/1600 sec, f5.7, ISO 1250, focal length 300mm

Notice that in both cases, the aperture was f5.7, not extreme.  Instead, the shallow depth-of-field and resulting blurring of the background was due to using a longer focal length, 155mm in the first and 300mm in the second.  In both cases, I was using a Canon T6 with a zoom lens.

This narrowing of the depth-of-field is a strong reason for using a longer lens for portrait images.  A second reason is that the photographer need not be very close to the model.  I was probably 20 feet or more from my daughter in both cases and could take multiple candid shots without her being painfully aware of my presence.  Depending on the comfort of your model with being photographed, this may be a tremendous advantage.

The weakness of using a long lens is the general need for better light or a more expensive lens.  Many photographers who specialize in portraits will spend the money on a fixed-link lens (prime lens) of 80 or 90 mm.

Another reason for using a long lens is simply to take photos at a distance, such as when my older daughter was on the field at a track meet:

Ananda (left) and her friend, Kat.
1/500 sec, f8, ISO 400, focal length 300mm

Notice the lack of detail in the grass behind them.  That said, if you depend on the camera to do the focusing, the shallow depth-of-field may result in something other than your intended subject being in focus.  We'll leave focus issues for another post.

Shutter-Priority Effects

In my previous post, I showed examples of how by changing aperture settings the photographer can alter the depth of field.  In this post, I'll show the effect of setting your camera to Shutter Priority (Tv on Canon cameras) and experimenting with fast and slow shutter speeds.

When you set your camera to Shutter Priority (instead of fully manual), your camera will automatically set aperture and iso.  So, as in the previous post, the depth of field will change.  But by setting the shutter speed very fast or very slow, you can stop or blur movement, respectively.

With a very fast shutter speed in the image in the left below, individual drops of water are visible.  With the very slow shutter speed on the right, the water falling is blurred, as are the resulting ripples. (Both images were shot while using a tripod and a 50mm lens.)

left: 1/2000 second exposure, f1.8, ISO 400                  right: 1 second exposure, f23, ISO 100 

Note also the difference in the shadow on the rock in the upper-right of each image and the difference in detail in the water upstream.

Sports and live-arts photographers may also wish to use fast shutter speeds to capture images without blurring.  Note, however, that the price of high shutter speeds is either small f-stop values or high ISO values.  Very small f-stop values (large aperture) generally mean expensive lenses.  Very high ISO values generally mean graininess in images.  Such are the tradeoffs.