The lens of your camera is arguably one of the most important parts of the camera ; it has the job of controlling light, adjusting focus (and focal length in variable focal length lenses), controlling depth-of-field through the aperture, and adding character to the shots you have lovingly framed. (It should be noted that the sensor of a digital video camera body is also very important, in terms of sensitivity, resolution, size, and other factors, but it is out of the scope of this article.)
There are quite a few factors to consider when choosing the lens you will use for a shot, as well as the lenses you will pack for a shoot. Do you pack one or two variable focal-length lenses, or do you pack a series of strategic length prime lenses? Do you stay with your native lens mount? Do you use vintage lenses? Do you need super-fast lenses?
As of the writing of this, I’ve been known to primarily use three or four prime lenses (24mm, 35mm, 50mm, and 85mm), while packing a 105mm or 135mm with a set of extension tubes for extreme macro usage. This setup will not work for everyone, as I will explain.
There are several types of lens mounts, and depending on the type of camera body you use, one (or two) will be a “native” mount. For example, if you shoot using a Canon EOS camera (T3i, 7D, 5D mk3, C100, etc), you will most likely be using primarily EF mount lenses (and/or EF-S lenses if you aren’t shooting with a full-frame sensor). These native lenses have the advantage of having auto-focus / focus-confirmation electronics, as well as being able to mount with no additional hardware required. Auto-focus isn’t really an issue with cinematography, and focus-confirmation isn’t a huge advantage, especially if your camera has focus peaking – but these lenses were designed to work with your camera body.
Other lens mounts can be accommodated with adapter rings, which can usually be purchased for varying amounts from online retailers. I have a few M42 adapter rings for using old Pentax screw-mount lenses with the EF mount on my camera, and they work flawlessly for me. Some of the more expensive ones even have focus confirmation capabilities.
Photographers might give some pause to the idea of not having focus confirmation or auto focus, but cinematographers should be fine with it. Lens mount should only factor into your decision to use a lens by whether or not you have the appropriate adapter ring configuration to use that lens, in my opinion.
Prime or Variable Focal Length (Zoom)
A great deal of the answer to this question depends on the primary type of cinematography in which you tend to engage. A variable focal length lens is essentially a single lens which offers an “infinite number of focal lengths between its two bounds”, but there are other factors to be considered when using one. For example, many lower-cost variable focal length lenses will tend to have variable maximum apertures, depending on the target focal length.
If you’re engaged in documentary cinematography or non-planned shoots (such as many modern “web series” shoots), you may want to stick with the widest range of variable focal length lens you can accommodate. A 24-70mm lens will usually handle most shots which would be required by those mediums, and will mostly eliminate the hassle of changing lenses during critical (and possibly situationally-limited) shoot times.
A serious trade-off is that most variable focal length lenses are not “fast” (i.e. do not have a very low f-stop number for their maximum aperture size), and therefore tend to require more light. The faster lenses among that class tend to increase in cost greatly.
Prime lenses usually do one thing, and try to do it very well. They range down (and below) f/1.2, and are far more cost effective for a single focal length. If you have the time to change lenses in between shots, and tend away from smash zooms (which I tend to find are a bit over-used) and dolly/zoom combination shots, you might want to tend towards a collection of primes.
How fast is fast?
The majority of consumer-grade lenses tend to have smaller maximum aperture sizes than f/2.8, but there are a fair number of inexpensive primes which can be had with an f/2.8 maximum aperture size, and relatively inexpensive (compared to some) lenses can be had down to f/1.4 or so, depending on the relative concessions you’re willing to make regarding the lens quality, mount, manufacturer, et cetera.
As the aperture size increases, the depth of field decreases in size, but the amount of light hitting the sensor increases. Low light cinematography has historically relied on “fast” lenses rather than increased sensor sensitivity, primarily due to the increasing role that sensor “noise” plays at high ISO levels. This tradeoff means that you may have to decide whether depth of field or light sensitivity will be the primary determining factor in the maximum aperture rating of the lenses you’re using.
NOTE: Another thing to note is that lenses tend not to be their sharpest or best when fully open, so you may have to shoot slightly further shut than the maximum aperture rating.
Some cinematographers (and photographers) will swear by vintage glass. Optics from lenses like old Carl Zeiss lenses are still amazing, and some of these lenses are sold for less than the comparable modern lenses for them. It can be a potentially expensive habit, however, since cinematographers have been driving up the cost of purchasing these lenses, as their lack of focus controls is far less bothersome than it would be to photographers.
If you can purchase vintage lenses (or happen upon a cache of them), it’s something to seriously consider. They have their own character, and when used thoughtfully, can add much to your footage.
NOTE: If you’re going with variable focal length lenses exclusively, you may be able to safely skip this section. It deals mostly with the reasoning behind using certain focal length lenses.
Selection of focal length depends on a number of factors. Entire chapters, and even whole books have been written about selecting focal lengths for cinematography and photography. A great deal of it has to do with the type of shot you are working with, as well as the framing, etc. I’m going to hit some of the considerations, but I suggest further reading.
When considering focal lengths on cameras, I tend to consider them using the standard of a “full frame” sensor, since my camera has one. This means that the written focal length of a lens corresponds directly to the effective focal length of that lens. A larger “crop factor” (which is the case for smaller sensor sizes, like the Canon APS-C sensor and the Micro 4⁄3 sensors) means that a lens’s effective focal length is longer for those sensors. You can figure out the effective focal length by multiplying the stated focal length by the crop factor. For example, an APS-C crop factor is 1.5x, so a 35mm lens would have an effective focal length of 52.5mm, and a 50mm lens would have an effective focal length of 75mm.
“Wide angle” shots, which are usually used for establishing shots in cinema, generally tend to rely on very “wide” lenses, which are lenses with short focal lengths. As you move further away from 35mm effective focal length, the field of view present in your frame increases, which increases geometric distortion towards the edges of the frame. This has been referred to as a “fish eye” effect, when present in more than moderate amounts.
As an aside, I have seen cinematographers use extremely wide lenses (18mm and shorter) to shoot closeup shots of actors and actresses in tight quarters – and I must warn against it, unless you are acutely aware of the geometric distortion which you are introducing into the frame. This has very unpleasant effects on the faces of actors when used for close shots, and I know few actors who take kindly to being represented in a grossly distorted manner.
A 50mm effective focal length is essentially what your eye sees; at least, that’s the way I’ve come to think of it. It’s a very neutral lens to use for most shots. I recommend that this length be a standard part of any lens kit you’re putting together.
50mm lenses have been popular with the Canon DSLR cinematography crowd, primarily due to the inexpensive nature of the “nifty fifty”, a 50mm f/1.8 prime which clocks in at a little over 100 USD new. Its optics aren’t that fantastic, but its point of entry is so low in the cost department that many people will own one. If you do, consider buying an f/1.4 version of the same lens (or the f/1.2 L, if you’re successful, or have some sort of trust fund laying around), as the optical and build quality is far superior to the 50mm f/1.8 lens. It’s a “midway” focal length, but very usable for a variety of shots.
Greater than 50mm effective focal lengh lenses are considered “long” lenses. They tend to “compress” the space they capture, much as wide angle lenses tend to expand and distort it. One must be careful with using long lenses for handheld and steadicam work, as camera shake tends to be magnified with longer lenses.
Long lenses can also be used for closeup and extreme closeup shots by using “extension tubes” – what my brother used to refer to as “expensive air”. They increase the amount of light required, and are not as easy or compact as most macro lenses, but they’re relatively cheap, and cut down on the number of lenses you have to carry.
What the hell is a “bokeh”?
The term “bokeh” is a recent addition to the vocabulary of the photographer and cinematographer ; it simply refers to the blur produced by out of focus objects, particularly lights, by a lens. It is determined largely by the quality of the optics of the lens, as well as the number of blades in the lens’s aperture. Higher blade counts generally produce more “pleasing” bokeh, approaching the cinematic standard of almost circular light blur.
You haven’t told me which lenses!
This isn’t intended to dictate which lenses a cinematographer must carry, nor push certain choices over others, but merely to attempt to educate about sensible lens selection.
Consider buying a Pelican case, or other shock resistant case, for travelling to shoots. If you’re carrying a lot of glass, you can’t afford to deal with the downtime of a broken lens.
There are a huge number of lenses, both modern and “ancient”, and you can equip yourself with any variety of lenses, depending on your particular idiom and shooting style. Don’t fall into the trap of assuming that lens selection is unnecessary, or that everything should be shot with a single lens ; it’s just another aspect of cinematic creativity. Good luck!