In our second session of Seriously Fun Photography, we reviewed what we learned in Week One by considering how we would shoot in various situations and discussed what aperture, shutter speed, ISO setting and lens focal length might be appropriate in each situation. This type of thinking is good to do before any photo session.
Then we decided to start applying our general knowledge about the relationship between apertures and depth of field. While we start to get the idea when we say "f/2 -- shallow depth of field and f/22 - deep depth of field" actually trying this out in with some real world shots is always a good experiment.
So we set up an experiment that can be repeated at home: set your camera on a table or a tripod, and in front of it arrange people or objects in a receding line. Put the first person or thing just 3 feet away from the lens, and have the furthest be at least 12 feet away. Now set the widest aperture you can -- I used a lens that goes to f/1.4 for this session -- and focus on the closest person or object. You'll probably find that the people / objects behind that are out of focus. Now run through the whole series of aperture settings you have available (you'll probably want to be in "aperture priority mode" so that the camera sets the corresponding shutter speed for an acceptable exposure. Or you can set that yourself). Try this and compare each shot -- more and more will be in focus until you should be able to get everyone in focus.
Now, keep in mind there's one other factor here -- the focal length you shoot with. Usually the effect of getting a main subject in focus and the background out of focus is much easier to achieve if you use a lens of at least 50mm or set as zoom to 50mm focal length or a more telephoto setting.
Many photographers think that "telephoto lenses have shallow depth of field and wide angle lenses have deep depth of field" -- it turns out that isn't exactly true, but for pragmatic purposes it isn't a bad way to think. If the goal is a sharp subject and a blurry background -- grab a 90mm or set your zoom lens about there.
(For a discussion on why the wide focal lens = deep depth of field idea isn't precisely true, read Do wide-angle lenses give you greater depth of field than long lenses?.)
Another thing that comes up at this point: some lenses allow your camera to reach to f/1.4 or f/2 or f/2.8, but many times the "kit lens" zoom that comes with a DSLR or the zoom lens built into a compact camera will not go to that wide-open an aperture. And to further add to the confusion: many common lenses that go from 18mm to 55mm (or 70mm) let you go to f/3.5 when using the widest focal length (18mm) but only to f/5.6 when you are using the long end of the lens (55mm or 70mm). That's just how those lenses are built.
Now, once we know a technique to control depth of field -- go towards f/2 to get a sharp person, blurry background or toward f/22 to get subject and background both focuses -- we want to think about why we would do it. Well, it's that kind of control that lets us emphasize or deemphasize what a viewer sees in a photograph, so we want to master it so we can control our images. Need to photograph a person against a cluttered, distracting background? Use selective focus. Need to show that a person has kids but keep the emphasis on the person? Use selective focus to make the kids visible but de-emphasized.
In this same mode of thinking, we then went on to begin the long and complicated process of thinking about composition. We started with the idea of framing. Putting a subject within another shape is a very usable technique -- and one that is worth studying in Robert Frank: The Americans. So we tried a bit of that, and then began to notice that -- in looking at such a shot -- we need to notice what is happening at the edges of our frame. Are the edges including and excluding what we choose? Can we align the edges of our frame with the lines that invariable exist in rooms and other spaces?
From this we began thinking about compositional strategies. For example, we introduced the "rule of thirds" -- which I have posts on here and here and here.
We also started asking questions like -- how could we arrange two people in the frame?
By the way, it looks like they are offering a second summer session of this course starting July 17th: Seriously Fun Photography. I'm hoping enough people sign up -- Thursday night is turning out to be a good time for the class.