Lesson 107: Depth of Field Through the Lens

I taught a Beginners class on macro and close-up photography on Saturday.  Macro teaches us a lot of great skills as photographers.  Because shooting subjects life-sized or bigger magnifies the mistakes we might get away with if our subjects didn’t loom so large on our sensors, macro serves to remind us and help really bring home some basic photography concepts in a whole new way.

Depth of Field is of primary concern with macro photography.  When you’re shooting practically on top of your subject, DOF is reduced to fractions of an inch–sometimes DOF is so tiny that it’s easier to think of it in millimeters, even for metric-adverse Americans.

One of the things that often confuses beginning (and even more experienced) photographers is that the depth of field you see when you look through the lens is not the depth of field you’ll get when you create the image (unless you happen to be shooting with your aperture wide open).

For example, during class, I was shooting with the Canon 100mm f/2.8L IS macro lens.  When I looked through the lens at a dandelion, this is what I saw:

The inside of the dandelion (f/2.8)
The inside of the dandelion (f/2.8)

Pretty cool, huh?  When you are looking through the lens, the aperture is wide open regardless of what aperture setting you have selected for exposure.  This allows the maximum light through the lens for you to see as well as for functions like autofocus to work better. 

Some cameras have a DOF preview button that stops the aperture down to what you’ve set it at so you can theoretically tell how much DOF you’re actually going to get.  I find this button to be only marginally useful.  I rarely can tell how much DOF I’m getting by pressing it, partly because of the loss of light.

Instead, I tend to take a shot and use a magnifying loupe to look at it on the LCD.  I may also zoom into the image to enlarge it for more careful viewing.  Then I decide if I like the DOF I’m getting and adjust if not.

In the next example, I shot the same dandelion at f/16 instead of f/2.8 (as in the first example).  Notice how we see the full ball of fluff instead of getting a horizontal view of the inside of the dandelion seeds?  That’s because there is enough DOF for the foreground portion of the seed ball to not blur completely out of view.

Same Dandelion at f/16
Same Dandelion at f/16

Personally, I find the very shallow depth of field more interesting in this case–it’s like having a view of the inside of the flower.  However, if I wanted a shot of dandelion that looked more like what we see in life, the second example would be my pick.  In fact, I’d probably want a little more depth of field to keep the tufts of the closest seen “fronds” sharp.

Lesson 102: DSLR Macro Photography

Since I answered a question about macro photography with the iPhone on our Facebook page yesterday, thought I’d do a more detailed follow up on macro with a DSLR version–my apologies for using the iPhoneography blog for a DSLR example.  For the iPhone version, check out Lesson 37:  Small Subjects.

Macro (in Canon terminology; micro if you’re a Nikon shooter) photography is probably best understood as getting really close-up to small subjects.  So close that the subject is life-sized or larger on your camera’s sensor.  It allows us to capture details that are often surprising to those of us who can’t see that well without our reading glasses.

The challenge is that all lenses have something called a minimum focusing distance.  Macro (or micro) lenses have short enough minimum focusing distances to allow you to get up close and personal with a 1:1 ratio, meaning if the subject is 10mm wide, it occupies 10mm on your sensor.

If you don’t have a macro lens, you can use extension tubes to make your minimum focusing distance much smaller, allowing you to get much closer.  Extension tubes can also be used with a macro lens to get larger than a 1:1 ratio.  Extension tube sets run from about $20-200 with the low-end being full manual and the high-end supporting the lens electronics.  With the low end version, you are likely to be stuck with a wide open aperture as the camera and lens won’t be talking to each other.

Since this blog is normally used to post simple lessons on photography you can do with your iPhone, I’m going to try to minimize the tech talk here.  But, depth of field is important in macro photography.  Depth of field refers to how much of the image is acceptably sharp in the 3rd dimension of your image–that is, front to back of the scene.

Getting up close to a subject means your depth of field is minimal even with the aperture stopped all the way down.  Sometimes backing up a bit and going more for a “close-up” shot vs a true macro image yields a more pleasing image as a result.  I frequently use a very small aperture opening (f/22ish) and opt to go “close-up” rather than true macro to increase depth of field.

Your Assignment:  I’ve included some examples of my own experiments.  There are many better examples out there from serious macro photographers.  Google macro photography in Google images and see what you get–it’s like a whole new universe living right under our lenses.  Check it out and see if this is a form of photography you’d like to experiment with.  If so, for iPhone shooters, consider getting a macro attachment lens (see Lesson 37).  For DSLR shooters, check out extension tubes as a cheap way to turn a lens you already have into a macro lens.  If you have an advanced point-and-shoot, you may also want to check out whether a macro attachment is available for your camera.