Wednesday, June 20, 2012

Fundamentals of Photography - Aperture

Copyright Monica L. Shulman
Portrait of my baby having her favorite "bubbly agua" right from the bottle.  You try prying that bottle of water away from her when she's got her hands on it!  Aperture f/4.5 and focal length 44mm.

So after sharing a few tutorials and receiving a number of emails from readers I got to thinking that it might be time to write a series of posts about the fundamentals of photography.  This is the first one and it's about what I think is the most important part of taking a picture: Aperture and depth of field.

What is aperture?

A photographer who taught the one and only course I've ever taken in photography explained aperture in the simplest way: you have to think of the camera's aperture as the pupil of the camera's eyeball.  On a very bright day your pupils become smaller in order to prevent too much light from reaching the back of your eye.  When it's dark your pupils dilate to allow more light in. 

Similarly, the aperture controls the light that can reach your camera sensor (or film...remember that?)  It refers to the size of the hole in between your camera lens and the sensor (or film) that can be made larger or smaller in order to allow different amounts of light to reach the sensor.  Combined with the shutter speed (look out for the post on this) the aperture size regulates the sensor's exposure to light. 

How is aperture measured and what do those numbers mean?

The camera's diaphragm controls the aperture (the diameter of the opening of the lens) and the aperture setting refers to the size of the opening and the size of the opening is measured in "f-stops". 

The lens aperture is usually specified as an f-number (the ratio of focal length to the aperture diameter) and a lens has a set of marked f-stops that you or the camera can set the f-number to like f/1.4, f/2.8, f/4, f/5.6, f/8, f/22.  Moving from one f-stop to the next doubles (or halves) the opening in your lens (and the amount of light getting through).  I know this is a lot of technical information but I think it's really helpful to try to understand it since measuring light is basically the most important aspect of capturing images and once you learn how it works you'll really have creative control over your photographs and most importantly, finally take your camera off Auto (yay!).

It can be confusing to new photographers (myself included!) because large apertures (where lots of light gets through) have smaller f-stop numbers and smaller apertures (where less light gets through) have larger f-stop numbers.  So f/1.4 is a much larger aperture than f/22. 

What is depth of field?

Depth of field is used to control how much of an image is in focus.

Large depth of field just means that most of the picture will be in focus and small (shallow) depth of field means that only part of the picture will be in focus and the rest will be fuzzy or creamy or have those lovely little bokeh circles.  You can read a bit about depth of field and choosing aperture settings in my portraits tutorial.  Shallow depth of field is really useful when you want to highlight a particular portion of a photo or photo just on one subject.  I like to use it too just because it gives photos a really pretty and creative look that you just don't get when everything in the frame is in focus.  The thing to remember is that large aperture (smaller f/stop number) decreases depth of field and small aperture (larger f/stop number) gives you larger depth of field.
When depth of field is really important to me, like for a portrait for example, I usually put my camera on Aperture priority (admittedly my favorite setting after shooting manually) so that I can set the aperture and let the camera choose all the other settings like shutter speed.

Copyright 2008 Monica L. Shulman
Somewhere in New York City.  Aperture f/5.6 and focal length 200mm.

I Happen to Like Purple.
This has the same aperture and focal length setting as above but I physically moved away from the scene so that I could fill the frame with the flowers but still get that creamy background.  Also the post-processing was obviously different with the colors of this one being a bit warmer.

Beets and carrots at the farmer's market.  Aperture f/4.0 and focal length 50mm.

Copyright Monica L. Shulman
Vintage bags at one of my favorite flea markets in NY on the Upper West Side.  Aperture f/5.6 and focal length 150mm.

Now get out there and practice!

Do you have any tips?  I'd love to hear in the comments.

Copyright Monica L. Shulman
A butterfly flew right into the photo and startled my girl who for once was actually standing still and posing - these days she's always on the move.  Aperture f/5.3 and 90mm focal length.  I love the bokeh in the background.  This was shot in aperture priority.  

Copyright Monica L. Shulman
The "after" to the "before" just above.  She noticed the butterfly.  Aperture f/5.3 and 90mm focal length.

Also, check out tips for photographing people in public and tips for taking pictures of babies.  You can see all of my tutorials here.

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