Cinema Lenses; What’s the Big Deal?
Standard DSLR lenses of the type you already own for your DSLR cameras work quite well for shooting video, both with DSLR bodies, and with the next step up: Cinema cameras such as those from Black Magic and Camera Red, if the lens mounts are compatible. However there are also dedicated cinema lenses designed specifically for shooting video. This may leave you wondering just what is unique about these lenses, and why might you consider acquiring one or more of them.
A Short List; and Likely to Get Shorter
The list of advantages of Cinema lenses over their DSLR brethren is relatively short, and the justifications may sound minimal as well; but they may add up to justify adding one or more dedicated cinema lenses to your collection, if you find yourself shooting an increasing amount of motion.
The Inverse List
Keep in mind that there is a flip side to this coin: dedicated cinema lenses may not be as convenient for still photography, and may best be thought of as motion-specific. And a final caveat: as the major DSLR manufacturers move forward, they will be keeping their eyes ever more closely on the motion category, so newer lenses from them are likely to offer increasing optimization for video work, while still being eminently usable for still imaging; so with the exception of any areas where there is an unresolvable conflict between the two, future DSLR lenses may well be optimized for both.
The adjustment rings on DSLR lenses are typically ridged, for positive grip when rotating them. However those ridges are not usually in the form of standard 32 pitch geared rings. This means attaching any type of follow-focus or follow-zoom device will require trusting a friction band (read: rubber band) or installation of a third-party geared ring for use with standard motion rigs. Cinema lenses tend to come with gear rings already in place. It will be interesting to see if any of the major DSLR manufacturers come out with finger friendly rings with a soft-surfaced 32 pitch gear ring as the standard ring on dual purpose lenses, or at least provide an easy add-on geared ring system.
Most DSLR lenses do not offer an aperture adjustment ring. And not all cameras will communicate with all internal aperture adjustment methods. Moreover, in the rare instance where a shot requires, or at least would benefit from, changing the aperture during the shot, a lens without an aperture ring won’t allow this. Also, even when DSLR lenses include an aperture ring, it typically incorporates “clicks” meaning it only offers incremental settings, on a scale such as a third of an f:stop. Cinema lenses often offer “unclicked” rings, allowing for exactly the setting desired, even between typical settings. And the lack of “clicks” is also important to smoothly adjusting the aperture during a shot.
Cinema lenses are designed with full manual adjustment of functions; DSLR lenses often use internal, automated, methods of making adjustments that can interfere with cinema uses – especially those uses that require adjustment during the shot.
Longer Throw; Greater Precision
Cinema lenses often offer a longer throw; meaning the ring rotates farther around the lens, sometimes close to a full revolution. This might not be convenient for adjusting a DSLR lens quickly for still shooting, but allows for greater precision in focusing a cinema lens for motion work.
Lock to Lock
Many DSLR lenses continue to rotate even when they pass the optics minimum or maximum points; they have no hard-stop at the end-points. This means that adjusting past the end point invalidates any fixed points that may have been set in between. So there are no absolute locations in the ring rotation matched to a specific zoom length, focus plane, or aperture setting on the ring. Dead stops at each end on cinema lenses eliminate this issue, and allow a selected value to be returned to easily, by rotating the same amount in the reverse direction.
On DSLR lenses markings are often on the top of the lens, and oriented towards the body; this makes sense if a photographer is most likely to pivot the camera up, and look at the settings from behind the camera. However, in video rigs the camera is often fixed in place on a fairly large rig for shoulder “steady-cam” holding, or on a large tripod-based rig. In such situations, the most convenient way to view the lens settings are usually from the side and horizontally. So it’s no surprise that cinema lenses tend to be marked horizontally, from the side; instead of perpendicularly on the top. A small difference that adds up over time.
F-Stops and T-Stops
Another difference between Still and Motion lenses is that Cinema lenses are often marked in T-Stops, not F-Stops. F is for Focal, T is for Transmission. It can be thought of as the same as the equivalent F value, but normalized for whatever light the lens in question fails to transmit. So two different lenses marked with F-Stops may produce slightly brighter or darker results, if one transmits more light than the other. For T-marked lenses, any two should match, even if their transmission ratios differ. This is handy when shooting a scene with multiple cameras using different lenses.
Varifocal Versus Parfocal; Zoom Lenses Only
With zoom lenses, DSLR lenses tend to lose focus as zoom is changed, which requires refocusing (or continuous autofocus adjustment) to capture the same item in focus at differing zooms. For motion, this is a problem, as it is a common type of shot to keep a person in focus while zooming in for a closeup, or out for a context shot. Most Cinema lenses are designed to be parfocal, meaning they retain focus while zooming.
When the focus of a lens is changed, the apparent zoom changes. With DSLR lenses this effect tends to be quite noticeable, as it is not critical for still imaging. For expensive Cinema lenses, the effect is less apparent. Lower cost Cinema lenses may not improve this effect.
Most other variations are specific to one or another lens, including issues such as sharpness, speed, bokeh, and build quality, so it is not possible to generalize about them. Even price does not always lean in one direction; while there are many cinema lenses that cost more than standard DSLR lenses, it is also possible to find dedicated cinema lenses which cost less than their DSLR counterpart, but which still match many performance features, since the lens is targeted to that specific use.
The information in this article should assist you in determining if you are ready to move up to dedicated cinema lenses; or if you are best served by multipurpose lenses that also work well for your still shooting. Keep revisiting the issue (and possibly this article) as your motion work increases, to decide when, or if, you are ready to make a move to dedicated glass.