Anti Bokeh

Bokeh (derived from Japanese, a noun boke ぼけ, meaning "blurred or fuzzy") is a photographic term referring to the appearance of out-of-focus areas in an image produced by a camera lens using a shallow depth of field.^[1] Different lens bokeh produces different aesthetic qualities in out-of-focus backgrounds, which are often used to reduce distractions and emphasize the primary subject.

Wikipedia

Almost everyone who has put a camera in manual mode, or who has used a manual-only camera, has played with depth of field. A shallow depth of field produces the bokeh effect described above. A wide depth of field brings more of the frame into acceptable focus.

But there are limits to what you can do with an aperture ring. Close down too much, and diffraction at the aperture starts to work against you, blurring out the picture. So what do you do with a shot that has a lot of range to cover?

One solution is to use a large format camera with motions and take advantage of the Scheimpflug Principle. I won't go into the details here, but the upshot is that you can tilt your plane of best focus by tilting the lens or film holder. If, say, you're photographing a field of flowers stretching from your feet out to infinity, it would be impossible to bring the entire field into sharp focus using the aperture ring alone. But you could tilt your lens and shift your plane of best focus until it coincided with the field of flowers. The entire field would be in focus, but everything above it or below it would begin to go out of focus. This is partially the reason why photographers like Adams and Weston were able to get incredibly sharp sweeping landscape shots, and it's the reason why many landscape photographers continue to use large format cameras to this day. (Including me!)

But what if you need everything above and below that field of flowers to be in focus as well? You can still stop down, and broaden your depth of field somewhat above and below. But again, there are limits. Eventually diffraction begins to work against you, and you start to fuzz out the overall image. Where can you go from here?

Back in 2000, I ran across GRAFICA Obscura, a web site written by Paul Haeberli of SGI. It described a method of taking a stack of images shot at different focus distances, and selecting only the sharpest bits of each image in order to combine them into a single, sharpest image. Paul used an edge-finding filter to build his layer masks, a technique that worked, but not perfectly well. I made some attempts to use his technique, but I ran into a number of problems and no real successes.

Skip forward to 2008 when I swapped out my Nikon Coolpix 5600 camera for a Canon A650 IS. One of the reasons I chose the A650 was that it could run CHDK, a scripting language that can run on top of the Canon firmware in many of their compact cameras. I was interested in running CHDK for several reasons, one of which was a bracketing script that was far more flexible than the bracketing available in the Canon firmware. Among other things, it let you bracket your focus.

All of this would've put me in no better position than I was already in with Paul Haeberli's technique, but times change. At some point in those intervening years, Alan Hadley wrote a package called CombineZM that automates and improves on the technique Paul Haeberli described. The combination of CHDK's bracketing script and CombineZM's ability to stack the images yields a tool to get infinite depth of field out of a scene.

Anti-Bokeh

It's not for every photographer, and certainly not for every situation. But it's one more tool to add to the tool belt. And now that that tool is there, it's something to think on when heading out into the field.

Tom