"The Minox is my life."

-- Walter Zapp

BOKEH

Peter Zimmerman

The image from a well-designed, built and focused lens is "sharp." A mathematical point of light in the subject becomes a mathematical point of light on the film; mathematical lines are 'lines' with no width. Of course, represented on film a mathematical point image must acquire some size since film grains are finite, and images of the mathematical line acquire a width for the same reason. This irreducible size on the film to 'reproduce' an image of a point or line is what defines the ultimate resolving capabilities of the lens. In practice we deal with subjects and images with finite size. But the definition of 'in focus' is not changed by the fact that in real life we can never photograph a line with no width and obtain a picture of it on film, also without width. Squares, rectangles, and circles in the subject become squares, rectangles, and circles on the film, and if they are evenly filled in, the image of the filled-in color just fills the outline on the film and is even from edge to edge with no spill-over into the rest of the picture.

When a point subject in a picture is in focus, 'all' the rays of light go through a single point on the film. Let that point subject go out of focus, and the rays of light begin to spread over the image depending on whether they strike the edge of the lens, the center, or part-way out -- whether they go through the top or bottom, left or right, of the lens. The most striking form of Bokeh, the one most photographers recognize, is the rings of light produced by an out-of-focus mirror telephoto lens. The secondary mirror on the front element of the lens blocks the central rays of light, so only those passing near the circumference of the lens can reach the film, which means that the out-of-focus image of a point of light is a ring of light.

For the photographer, the important thing is the quality of out-of-focus images, not the cause which can be coma, over- or under-corrected spherical aberration, astigmatism, or any of the other lens aberrations which designers work so hard to eliminate for in-focus images. Bokeh can turn a point of light into an evenly filled-in circle or to a circle bright in the middle and fading at the periphery or to one dim in the middle and harsh on the circumference. It can turn single straight lines into two closely spaced parallel lines. This doubling of lines I find particularly annoying. For me the best result is to turn points and lines into even blurs and not to distort them. The accompanying pictures show the Bokeh from the Complan lens in a Minox B. The pictures were taken on Kodak Technical Pan film and printed with a Minox enlarger onto Ilford Multigrade IV paper.

The Complan generally gives a gentle, even departure from sharp focus with a transition to uniform blurs. But points of light reflected from objects farther away from the point of sharp focus show a slight tendency to give a blur circle which is more intense on its circumference than in the middle. This, I think, accounts for the somewhat craggy shapes of out-of-focus tree limbs and other hard-edged objects in the background of a picture which is sharp in the foreground. I can't pretend it is my favorite form of Bokeh, but now that I know the behavior of the lens, I can plan my Minox photography in order to de-emphasize some kinds of backgrounds.

Since the depth of field of a Minox is very great, just a little thought can ensure that background objects are rendered cleanly. So long as an object is near enough to the point of focus that it is within the 'official' Minox depth of field, the Minox Bokeh, even in large prints, is of little importance. But when the background starts to fuzz out, watch out.

A later test will study the Bokeh of the flat focal plane Minox lens on more modern cameras.

The following images show Minox B Bokeh at several different distances.

The cameras are aligned as follows:

• 8" -- Minox C
• 10" -- Minox C
• 12" -- Minox IIIS
• 18" -- Minox III
• 24" -- Riga Minox attached to a Riga Minox tripod head which is in turn attached to a Leica mini tripod.
• 36" -- Minox C (vertical)
• 6' -- Leica M3; Summilux 50mm
• 12' -- Nikon F/Photomic FTN with a white body cap; no lens

Note that out of focus areas beyond the focus point tend to have slight brightening at the periphery of the blurred area, but that out of focus areas closer than the focus point (bok6larg) have uniform brightness.

The first 3 cameras from above. Focus at 8"

The first several cameras from a point just a bit above them.
Focus at 8"

2.5x enlargement of out of focus areas on the Riga;
camera focused at 8"

Focus at 10"

Focused between the Riga and the vertical C,
both of which are about equally unsharp
showing one should NOT rely on depth of field to save your picture.

Focused on the Leica M3

A 2x enlargement of out-of-focus areas
on the Riga at 24" and the III at 18".