American Cinematographer - June 2021 - 10

Shot Craft By Jay Holben
Specified Lens Tests

The isolated flare from a Leitz
Summilux-C 50mm prime lens
test reveals slight onion ring in the
pink flare orb, a light ring flare, and
gentle diffraction spikes.

In our April issue, we covered the
methodologies of a generic lens
test. This month, we'll take it a step
further and look at more specified
testing techniques that examine
particular characteristics of a given
lens.

Bokeh
The out-of-focus portion of the
image can be a leading factor in
defining a feel and look, arguably
more so than many other attributes
or aberrations. It's therefore not surprising that so much ado has been
made about bokeh in recent years.
The bokeh of a lens can really stand
out.
While people often discuss
bokeh as out-of-focus highlights,
in actuality, bokeh describes all of

the out-of-focus image - all points
in the frame that are larger than
the circle of confusion. It is merely
that the out-of-focus highlights are
where we can more easily discern
what is happening with a lens'
bokeh.
One of the best methods for
revealing the bokeh of a lens is
holiday twinkle lights. These small,
bright point sources are excellent
for providing the highlights that,
when rendered out-of-focus, can
reveal much about the character of
a lens.
I prefer to use the " net " variety
(see Shot Craft in AC April '21)
instead of just a strand, as you get
more spread-out sources for your
buck - and the nature of a lens'
bokeh changes over the field of

view that you're looking at. It's also
important to use actual incandescent filament holiday lights, as the
LED variety can cause problems
with flicker at various frame rates
and even weird color bias or sensor
clipping.
Place the holiday twinkle lights
in front of a black background for
the cleanest representation of the
bokeh. Positioning them about 8'
away from the lens tends to be
ideal, and allows for the ability to
test both intra-focus (in front of
the focus plane) and extra-focus
(behind the focus plane) characteristics. You can do this by focusing
the lens at minimum focus first, and
then at infinity, to examine different
qualities of spherical aberration,
chromatic aberration and coma, and

even to magnify design issues such
as aspheric " onion ring " patterns.
When shooting the test, I'll start
with the lens wide open and compensate for exposure by adjusting
the camera's shutter angle (see
the chart in April's Shot Craft), so
that the holiday lights are exposed
between middle gray and about a
stop-and-a-half above. If they go
too hot, you'll lose details and the
ability to see the character you're
looking for.
I'll begin with minimum focus
and then roll the camera. After a
couple of seconds, I'll slowly pan
the camera so that the holiday
lights move past the edge of frame
- then slowly pan back in the
other direction so the lights cross
the entire frame to the other side.

10 / JUNE 2021

p.10-17 Shot Craft_v4.indd 10

5/9/21 5:40 PM



American Cinematographer - June 2021

Table of Contents for the Digital Edition of American Cinematographer - June 2021

Contents
American Cinematographer - June 2021 - Cover1
American Cinematographer - June 2021 - Cover2
American Cinematographer - June 2021 - 1
American Cinematographer - June 2021 - Contents
American Cinematographer - June 2021 - 3
American Cinematographer - June 2021 - 4
American Cinematographer - June 2021 - 5
American Cinematographer - June 2021 - 6
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American Cinematographer - June 2021 - 8
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American Cinematographer - June 2021 - Cover3
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