Depth of Field

On the previous page, photographic image clarity was affected by the slightest movements and vibration. A stable setup and camera shutter options resolved most of the issues. However, there is a physics limitation related to focus that significantly affects macro photography. Fortunately, it can be largely overcome by modern software.

The last time you used a magnifying glass, do you recall how much you had to move it back-and-forth to focus on a particular spot? The amount you can see near and far distances simultaneously is called “depth of field”. The more you magnify, the shallower (more limited) the depth of field.

Below is a contrived example, where focusing on any particular minifig makes it sharp, but the others are out of focus.

Example of depth of field with Lego minifigs

Example of depth of field with Lego minifigs

Artsy fartsy photographers manage depth of field to direct the viewer’s attention to particular aspects or to intentionally hide busy backgrounds. Technical photographers often prefer to present as many details as possible, and therefore struggle with the limitations of depth of field. (A shallow depth of field is not always the enemy of the scientist, though, as researchers adjust focus in a microscope to see through slices of microscopic creatures.)

Recently, some very smart people figured out how to combine the sharpest portions of multiple photographs. This is called “photo stacking”. Such capabilities are available in high-end digital editing software or specialized application, such as Helicon Focus.

I chose Helicon Focus, because it is incredibly easy to use:

  1. Take a bunch of photos (say 20) with a large aperture (such as f/4), but adjust the focus from near to far over the course of the shots.
  2. Drag and drop the photos onto Helicon Focus
  3. Press the Render button and you’re done!
Stacking photos in Helicon Focus 6

Stacking photos in Helicon Focus 6

The software does all the work for you. Look at how clear each of the mini figures turned out in the composite photograph.

Stacking overcomes depth of field limitations

Stacking overcomes depth of field limitations

Rather than stacking, you could decrease the aperture, say to f/16, to increase the depth of field in a single shot. However, you are trading degradation due to diffraction for focus. For example, here are the same minifigures with all in focus in a single shot (no stacking).

Increased depth of field with f16 aperture

Increased depth of field with f16 aperture

It looks a little less clear than the stacked photo, right? If it isn’t immediately apparent to you, look closely at the hat, glasses, and zipper of the policeman.

Comparing details of stacked and reduced aperture photos

Comparing details of stacked and reduced aperture photos

The stacked photo wins because it takes that portion of the image from the photo with a larger aperture (less diffusion) and targeted focus. Other parts of the stacked photo come from each of the best portions from a bunch of photos. Now you see why the technology is so amazing.

To speed the process of taking photos with different focuses, you can purchase an automated rail system, discussed on the next page.