I seem to be on a lens kick lately. After all, cinematography is my mistress. The difference between the cinema lens and photo lens seems to be a popular discussion in the indie film camera department.
Gear debates are easy to get wrapped up in. I believe this is because there are so many quantifiable details to cite. White papers, field tests, comparisons…a quick Internet search will yield a plethora of data on whichever favorite lens you wish. Like most anything else, any lens is simply a tool. It’s the intent behind its use that is vastly more important.
If you’re spending any time in the camera department on a movie project, at some point you will no doubt wonder what the differences between a “cinema” lens and a “photography” lens are. Check out the cinema lens primer here for a baseline that this article will build upon. Let’s take a detailed look between the two.
But more importantly, should you give a damn?
What is a lens?
A convex element that bends light. It’s that simple. It doesn’t even have to be made from glass: 3D printed lenses are just around the corner.
The technology is thousands of years old, perhaps dating back to ancient Mesopotamia. The basic light-bending principles have not changed. Remember that when sifting through marketing speak for the newest whiz-bang product.
A camera lens today can be described as a series of lens elements assembled in a body and attached to a mount:
Multiple elements correct for optical aberrations, such as distortion and color irregularities.
Notice how the term “iris” describes the mechanical feature that determines the “aperture”, or the hole that light travels through. When you adjust your lens’ exposure, you are closing/opening the iris to change the aperture size.
The diagram is simplified for quick understanding. Many lenses contain many more elements than depicted. Also not depicted are the mechanics for focusing, or adjustable focal length (commonly called zooming).
This foundational understanding of camera lenses is important because it speaks directly to what a cinema lens does that a photography lens doesn’t need to. Think about it: a photograph is a single image. Motion picture is a series of single images played rapidly to give the illusion of movement.
Consistency of moving image
In the United States, movies play back at 24 frames per second. The average edited shot length is about 2 seconds. So let’s say about 50 individual pictures per shot.
If you read reviews for photography lenses, you will undoubtedly come across tips for removing chromatic aberration via Lightroom. Usually this is a simple, straight-forward process. Sometimes a click or two automatically adjusts for the lens’ shortcoming. This is for a single image.
You can’t do this the same way to a movie clip.
If your lens is a variable focal length, some times you need to snap-zoom to get a great closeup of something. Your autofocus motor takes over because the lens isn’t parfocal. No problem, you just re-focus and take the picture.
You can’t do this mid-shot during a movie shot.
Cinema lenses cater to consistency in a way that photo lenses don’t need to worry about.
Major cinema lens and photo lens differences
- Parfocal – Variable focal length lenses are a great tool when shooting a movie. Professional cinema lenses hold focus throughout the entire focal range. This means as you zoom in and out, your focus doesn’t change, which makes the focus puller’s job easier. A photographer can just re-focus: we don’t see the blurry “frames” like we do in film.
- T Stop measured – A photo lens’ aperture comes in “f” stops, which is a theoretical transmission of light standard. Cinema lenses are calibrated in “T” stops, which is an actual transmitted light measurement at any given aperture. This means that all lenses set to T3 should expose identically. Not true for photo lenses – differences in manufacturing can cause radically different exposures, even at the same f stop. For photo, not as big an issue. But imagine shooting half a scene, changing lenses, then shooting the rest underexposed by half a stop. Hello expensive post-production.
- Geared controls and long focus throws – It is extremely common to change focus mid-shot while filming a movie. This doesn’t really happen with stills. Therefore cinema lenses have toothed focus gears to mesh with focus pulling equipment, and significantly longer focus throws for precise manual control. Photo lenses, on the other hand, often have short snappy focus throws so their internal motors can find correct focus quickly at the tap of a button.
- Controlled breathing – Lens elements are physically moved when a lens’ focus is adjusted. This small change in focal length results in the shifting of the image. A well-constructed cinema lens corrects for this in order to enable smooth focus changes mid-shot. Many photo lenses exhibit distracting “breathing” when adjusting focus.
- Professional mount – As lenses get lighter and smaller, this one may come down to personal preference at the indie level. However, the ARRI PL mount most definitely remains the cinema standard due to it’s rugged, ubiquitous nature. Photo mounts may flex under stress, causing image shift during a motion picture shot.
- Color matched – Cinema lenses are often manufactured in sets. This is to ensure each lens “matches” the rest of the set in terms of image output. Modern photo lenses from the bigger manufactures often meet this standard, but a good cinema lens set leaves no question.
Should you give a damn?
It really depends on your workflow. Remember, a lens is a tool. Some great photo lenses exist that easily be adapt into great cinema lenses. If you don’t know why you’re choosing a particular tool, focus on fundamentals first. The audience won’t know, or care, what you shot the movie on anyways. I’d rather watch a film made with a $50 plastic lens that had motivated cinematography, engaging characters, and a fun plot than something like Jupiter Ascending (2015).
When the skills outpace the technology, worry about upgrading. Until then, use what you’ve got.