Still lenses and cinema lenses, while each serves their own function, at the end of the day they are simply two sides of the same coin. Each is designed with a specific purpose in mind – to optimize the photographer or videographer’s speed and precision. You wouldn’t use a two-door Honda Accord to plow a driveway, just like you wouldn’t use a huge Ford F150 to commute 100 miles – but they’re both vehicles.
Photography vs Cinema Lenses
Frequently, still photo lenses are smaller, more durable, and more lightweight than their cinematic cousins. With the obvious exception of large telephoto lenses, they are small enough that you can hold the camera body and lens easily. Event photographers frequently have two bodies strapped to their person, each with a different lens on it. This allows for quick switching between lenses without missing any of the action! There is no way that you could do that with a cinema lens. They are too large and simply aren’t designed to be used that way.
Cinema lenses tend to be more expensive, larger, and more delicate but also have to accommodate more features. Cinema lenses need to be parfocal, with a smooth zoom, large focus throw, hard stops, and minimal breathing. All of these factors add up to a larger, more complicated (and more expensive) lens.
Main Points of a Lens
I’ll go through each main axis of a lens: focus, iris, and zoom, and describe the differences in each. All of the differences come down to usage. What is the lens designed to do? Still lenses are durable, lightweight, and have high optical quality. When shooting still photos, the photographer has the ability to stop between each frame and reset focus, zoom, aperture, etc. Cinema lenses don’t have that luxury. The next frame is stitched to the previous one, running together typically at 24 per second. Cinema lenses need to perform while the focus, iris, and zoom values are changing. This difference is the main reason why cinema lenses are designed the way they are.
Focusing with Cinema Lenses: Focus Throw and Breathing
In both still photography and video, focus is critical. It’s the one thing you can’t fix in post. It’s easy to resize, brighten or darken an image. But if the focus isn’t spot on, there isn’t much that can be done to fix it. That said, each lens approaches this crucial task in a different way. Most still lenses are optimized to work with autofocus. The physical focus ring on the lens is frequently grooved or covered with rubber to make it easy to grip with your hand. In contrast, cinema lenses are usually built to have a human find focus. Autofocus is rarely used, if at all. Many cinema cameras don’t even offer an autofocus feature.
The Term “Focus Throw”
The term focus throw describes the physical distance that the focus ring needs to travel in order to move the focal point between minimum focus and infinity. In still photo lenses, this is very short. The autofocus feature helps the lens find precise focus quickly. A larger focus throw would mean that the motors in the lens would need to move the focus ring farther to achieve focus – resulting in time lost. For still photographers, a fraction of a second can be critical! The perfect expression on a subject’s face can fade in an instant.
The focus throw is quite large with cinema lenses, allowing for the focus puller to have more room to find the precise focal distance. On a film set, the person pulling focus may not be the same person who is operating the camera. The 1st Assistant Camera has the important job of making sure that subject is in focus, frequently using a follow focus unit like the Arri FF-4 or the Bright Tangerine Revolvr Atom Cine Kit. In order for the follow focus to work, cinema lenses are built with a .8 pitched toothed gear attached to the focus ring. Follow focus units are very important, so please also check out this Follow that Focus Like a Pro article.
The 1st Assistant Camera has the important job of making sure that subject is in focus, frequently using a follow focus unit like the Arri FF-4 or the Bright Tangerine Revolvr Atom Cine Kit.
The person pulling focus needs to be able to actually see the difference on the lens between the distances of, say, 3′ and 5′ or 4′ and 4 ½’. On a still lens, the distance between these marks is almost imperceptible, making it almost impossible to pull between these marks on the fly. This also makes using a still photo lens with a follow focus much harder since the marks will be millimeters away from each other.
In order to keep the marks on the follow focus correct, cinema lenses have hard stops at each end of the focus ring. This is really just a fancy way of saying that the focus barrel will physically stop once you hit its limit. Once the lens reaches infinity, that’s it – it stops. You can’t turn anymore. On a still lens, the focus barrel will turn forever! This can be very annoying when using still photo lenses for video work since it will throw off all of your carefully arranged marks. This doesn’t matter to still photographers since they aren’t using marks to find their focus. The autofocus on the camera can compensate no matter what position the focus ring is in.
This test was conducted with two lenses, both on the Alexa Mini. The first was the PL mount Angenieux 30-76mm lens, shooting at an f/5.6 at 31mm. The second was the EF mount Canon 24-70mm f/2.8L II lens, shooting at approximately 32mm and at an f/5.6. The close end of the focus was 3′ and the far was 7′ for both lenses.
Because the focus will change within the shot, cinema lenses also need to be concerned with focus breathing. Focus breathing is best described through demonstration. As the focus distance changes, the image shifts slightly as the elements move within the barrel of the lens. This is incredibly hard and expensive to correct. Only the most expensive and high-end cinema lenses have completely corrected this issue. In the example below, keep your eye on the small terra cotta pot in the bottom right corner. As the lens changes focus, watch the location of the pot within the frame. In the first part of the example, the pot will move slightly as the Canon 24-70mm L Series lens changes focus. In the second part, the pot barely moves at all as the Angenieux Optimo changes focus.
I used the same two lenses in this test again. The Canon lens was zoomed all the way in to 70mm, still shooting at an f/5.6. The Angenieux was zoomed-in to 76mm, still at a f/5.6. Apologies for the slightly mismatched framing!
Iris Smoothness in Cinema Lenses and F-Stop vs T-Stop
Next stop – iris (terrible camera pun intended)! The aperture of a modern still photo lens is frequently controlled within the camera, normally in 1/3 of a stop increments. The change between stops is clunky and noticeable. They frequently don’t have an external iris gear at all. Again, no one will see that change happen, so this is fine for photographers.
Cinema lenses have a separate ring for the iris, which allows for manual control. The iris ring spins smoothly. It does not have any predetermined increments. It is possible to smoothly transition from a T-2.8 all the way to a T-16. In addition to focus, there is another toothed gear attached to the iris.
Unlike with the focus gear, you wouldn’t ever use a follow focus unit on the iris gear. If the camera is not easily accessible, a wireless follow focus with multiple channels, like the Freefly Pilot, can be used to control the iris as well. These systems are most frequently used when the camera is on a Steadicam, gimbal stabilizer, jib, or crane. It also allows for “iris pulls.” If the subject walks out of a building into the sunlight, the camera cannot adjust automatically to the new lighting conditions like our eyes can. It is possible to change the iris within the shot and to adjust for the new lighting conditions. Done correctly, the audience won’t notice a change!
In both tests, I started the lenses at f/5.6. Then I opened up to the widest aperture, an f/2.8 for both lenses. Then I closed back down to an f/5.6, continuing to close the iris until it was at an f/22. For the Canon 24-70, I set the Alexa Mini to change the iris in full stop increments to illustrate the change quickly and clearly. It can also be set to ¼ stop increments.
T-Stops vs F-Stops
The aperture of cinema lenses is also measured in T-Stops, not F-Stops. F-Stops are determined based on a mathematical calculation of the light throughput of a lens. Each manufacturer may use a different calculation, resulting in a minute difference between brands. T-Stops are an actual measurement of the light throughput of the lens since a small amount of light is lost as it passes through the glass elements. Put another way, F-Stop measuring relies on the size of the opening at the front of the lens whereas T-Stop is measuring the light that actually hits the sensor (the lens’ transmission). This measurement is standardized across manufacturers and does not vary from lens to lens. Don’t freak out! The difference between the T-Stop and F-Stop of the exact same lens is very small, at most 1/3 of a stop. It’s not a huge deal, but it is worth pointing out.
Parfocal Lenses and Controlling Focus During Zoom
As with focus and iris, the major difference between still and cinema lenses comes from the fact that you will be able to see the action of the zoom in the shot. There are similarities between the two: still photo lenses frequently have a rubber grip or grooves on the zoom ring to help with manual zooming. Cinema lenses have the same toothed gear attached to the zoom ring which allows for motors to be easily attached to the lens.
However, cinema lenses need to be parfocal. A lens that is parfocal will hold focus throughout the zoom range. When you zoom in and out, the focus will be kept at the distance that you set it to. It would be horrible to have a camera zoom all the way in for an actor’s closeup, only to get to the end and have the person’s face be out of focus! A quick and easy way to check focus on a cinema lens is to zoom all the way in, focus on your subject, and then zoom out to the desired shot. This does not work well with most still lenses. This is a frequent mistake of videographers using still lenses, like the Canon L Series glass. The difference in focus may be slight, but it’s enough to mess up the shot.
Parfocal vs Varifocal
Still zoom lenses are not typically parfocal, they are often varifocal (focus changes – however slightly – as focal length and magnification changes). But photographers don’t really need their lenses to be parfocal. For a still image, you zoom to find the shot, depress the shutter button halfway, and the autofocus takes over. You take the shot and move on to the next one. Again, photographers will never see the zoom changing inside a still image. But seeing this zoom change during recording while also staying in correct focus is essential for filmmakers.
When we went to shoot the example for this part of the article, I was impressed with how well the still lenses did hold their focus. As we zoomed out, the focal point did change, but the depth of field became larger as the lens became wider. The original point of focus was still included within the “acceptable” range of the lens. It actually ended up being the most difficult concept to demonstrate! As multimedia trends blend these two mediums more and more, quality and ability of the gear start to merge as well.
This test was by far the most difficult to illustrate! I used a different lens here, the Canon 24-105mm, opened all the way to an f/2.8 with an ND.6. I started at about a 32mm and zoomed-in to 105mm. The peaking focus tool on the camera was used to find the most precise focus, instead of my eye. With the Angenieux, I was using the full range of the zoom, shooting at an f/5.6 with no ND.
Mount Types for Cinema Lenses
With still lenses, the manufacturer of the lens typically determines the mount. Canon makes EF mount glass, Nikon makes F mount, Sony makes E (or FE mount to use the a7/a9 series full frame E mount parlance), and so on. The lenses are designed to be used with that company’s cameras. They do not need to be concerned with making sure the lens can work on any camera out there.
To mount the PL lens, simply place the notch over the small pin and tighten the friction mount on the camera. This style of lens mount is very sturdy and can support the increased weight and size of cinema lenses.
PL Mount and Other Options
Almost all high-end cinema lenses are PL mount, or “positive-lock” mount. At the end of the lens, there are four flanges with a notch in each flange. On the lens mount of the camera body, there is a small pin. To mount the PL lens, simply place the notch over the small pin and tighten the friction mount on the camera. This style of lens mount is very sturdy and can support the increased weight and size of cinema lenses. Due to the increased crossover between still and video lenses, many cinema cameras are now offering Canon EF mount options, including RED, ARRI, and Blackmagic. Sony has also made a dent in the cinema market with the FS7 and the a7S cameras. There are many third-party adapters that will allow you to use the EF glass you own on new Sony cameras, like the Metabones Canon EF Lens to Sony E Mount Camera T Smart Adapter. Sony’s increased presence has prompted some cinema lenses to be made with a native E mount, like the Fuji MK 18-55mm and Fuji MK 50-135mm. This removes the need for a bulky adapter.
The best lens to use is the one most suited for the purpose of your specific shoot. Sometimes it is necessary to use a lightweight still photo lens on a more traditional cinema camera.
Some lens manufacturers are blurring the lines between traditional still and cinema lens categories in an effort to make cinema-quality lenses more affordable. One of the best examples of this is the Canon CN-E KAS S Compact-Servo 18-80mm. This lens is parfocal, has .8 pitched gears on the focus ring (to allow the use of a follow focus unit), and an external iris ring. However, it does not have hard stops on the focus ring.
All in all, the best lens to use is the one most suited for the purpose of your specific shoot. Sometimes it is necessary to use a lightweight still photo lens on a more traditional cinema camera. If you need to move quickly, you’ll want a lens that is small and lightweight – especially if you are running-and-gunning all day! Alternatively, you may be shooting video on your DSLR. If you’ll be zooming in the shot or racking focusing, you may require some of the qualities of a cinema lens. At the end of the day, a lens is an important tool in your creative arsenal. Use the best tool for the job!Tags: filmmaking, videography Last modified: May 20, 2020