American Cinematographer - July 2017 - 15

critical focus marks make it considerably
easier to find focus and smoothly hold and
adjust focus as your subject moves. Note
that there isn't a difference in the amount
the optical elements within the lens actually travel; there is just a compression or
expansion of the amount of travel of the
focus control. Think of it like a gear system
where the full rotation of a small gear
might move a larger gear only a fraction
of its full circumference.
The next great advantage in
cinema-style lenses is the speed. Many
modern still lenses are f2.8 or slower; it's
not uncommon to find a short-range still
zoom in the f3.5-4 range. This is not such
a detriment to still photographers, as they
can more readily adjust their shutter speed
to compensate for slower lenses. In addition, still photographers often work with
flash units that provide extraordinary
amounts of light for the fraction-of-asecond exposure - light levels we cinematographers only dream of! As cinematographers can't readily change the
shutter angle without affecting the
motion artifacts of the moving image, we
need to rely on faster lenses.
And faster means bigger. For a
given focal length, the f-stop value is
determined by the focal length divided by
the diameter of the aperture. To get an f2
on a 100mm lens requires at least a
50mm-diameter front element. To open
that up further to an f1.4 requires at least
a 72mm-diameter front element.
In addition, as the modern trend in
cine lenses is to match the sizes of all of
the lenses in a set in order to facilitate
quick changes from one focal length to
another during production, the speed and
size of the entire lens series are often
dictated by the longest lens in the family.
Because larger equates to faster, and
because of the benefits of an expanded
focus scale, most cine lenses are significantly larger than their still-lens cousins.
Cine lenses also feature gears integrated into the lens design for followfocus systems or motors. The standard
gear size is 0.8-module 32-pitch, and
most cine-style lenses will have gears for
focus, iris and, if applicable, zoom. A trend
for modern lens design is to position the
gears at exactly the same distance from

Top: CW Sonderoptic's Leica Thalia primes
are designed for the larger-than-full-frame
sensors in such cameras as Arri's Alexa 65.
Middle: A Fujinon MK 18-55mm (T2.9)
cine-style zoom lens; note the 0.8-module
32-pitch gear rings for focus, zoom and
iris. Bottom: A Nikon Nikkor 50mm (f1.4)
lens designed for still cameras.

the rear of each lens in a series to enable
fast lens-changing on set.
Many still lenses, especially modern
lenses designed for DSLR cameras, don't
have manually adjustable iris rings. This
isn't a problem when you have the proper
electronics communicating with the lens,
but when you put the lens on a camera
that doesn't have such functionality, you
lose control of your iris. Cine lenses will
always feature a manual iris control ring
and, generally, a smooth iris with no
"click-stops," allowing for iris changes inshot, if necessary.
Now we can finally start to talk
about the optics inside the lens, although
we'll continue to avoid discussions specific
to the glass - contrast, resolving power,
color reproduction - as these are all
completely independent of the particular
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lens housing. For a still lens, considerations of the movement of the subject in
the frame and the movement of the optical elements aren't an issue, as you're only
dealing with one still image independent
of any other frame before or after that
individual photograph. In motion pictures,
though, we're typically dealing with 24
frames per second, and differences
between frames can be very distracting.
One such distracting optical anomaly is lens breathing. As you adjust the
focus on a lens from close to far or vice
versa, you're actually moving the focusing
group farther from or closer to the sensor,
and that change in distance results in a
change in magnification of the image,
evidenced by a "zooming" effect as you
rack focus from foreground to background and background to foreground,
July 2017

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American Cinematographer - July 2017

Table of Contents for the Digital Edition of American Cinematographer - July 2017