Effect of Aperture on

Single Frame Depth-of-Field and Resolution

Rik Littlefield (email rj.littlefield at computer.org)
Page written May 11, 2005,
Revised August 19, 2005,
Typo correction December 27, 2005,
Last minor edit May 22, 2007.

Background (from the parent page)

Shallow depth of field is a problem when photographing small things.  Stopping down the lens is not a complete solution.  Beyond some optimum point, stopping down the lens reduces geometric blur but makes the entire image fuzzy due to diffraction effects.  When photographing something the size of a housefly, the optimum point is typically f/8 or wider, and the useful depth of field ("depth of detail") for a single picture is often 0.1 mm or less.  The problem becomes more severe with smaller subjects.

Illustration

Shown below are typical results, obtained with a Sigma 105 mm f/2.8 macro lens at 1:1, on a Canon Digital Rebel camera (22.2 x 14.8 mm sensor size).  The subject is a Small Pearl-bordered Fritillary (Boloria selene), tipped at roughly 45 degrees to the optical axis.  A single full frame is shown at right; crops showing more detail appear in the series below.

If the goal is maximum detail, then the optimum aperture for this lens under these conditions is only around f/8-f/11 (see series below).  Stopping down farther results in progressively less detail.  Resolution is obviously degraded even at f/16 and becomes worse with smaller apertures. At f/45 the image would be noticeably fuzzy even in a 4x6 inch print. 

Unfortunately, at f/8 the depth of best resolution in a single frame is only about 0.015 inch (0.375 mm).

Extended-depth-of-field software, such as Helicon Focus and CombineZ5, allows high resolution to be achieved over great depths.  The images labeled "f/8 + EDOF" result from compositing 35 frames spaced at 0.015 inches, resulting in a total depth of field of 0.525 inch (13.1 mm). 

References and Credits

To the best of my knowledge, the earliest solid technical discussion of this topic is a June 1960 article by H. Lou Gibson, "Magnification and Depth of Detail in Photomacrography" (J. Phot. Scty. Amer., 26, 34-46).  It includes a detailed mathematical analysis.  An extended and much more approachable discussion can be found in the venerable Kodak Technical Publication N-12B, "Photomacrography", copyright 1969, now out of print but still commonly available through used book sellers.  In Kodak's N-12B, Figure II-82 provides "A photographic demonstration of depth of detail ... [using] a butterfly wing tilted away from the camera at 45 degrees".  That figure served as the model for the illustrations appearing in this web page.

The work presented here is a personal publication of capabilities and techniques developed by the author.  You may link to this page, but please do not reference in archival publications; contact the author instead.  All images and text are copyright Rik Littlefield, 2005.

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