Behind the Lens

Creating Lenses for Large Format Sensors

Creating Lenses for Large Format Sensors

We spoke with Seth Emmons, Director of Communications of Leitz Cine about what he expects to see at this year’s NAB Show. Visit them at Booth C3643.

Q: With all the major camera companies introducing larger sensor cameras, what is the artistic benefit to filmmakers?

A: That’s such an important topic right now because most filmmakers and cinematographers don’t have experience with full format filmmaking. We’re getting these questions a lot. Why should I shoot in full format? What effect does it have on my image?

The biggest change is the new vocabulary of image style and composition that is opened up through a physically larger sensor. Cinematographers are used to telling the AC to throw on a 35mm lens and open up to T2.8. The DP knows what that is going to look like in regard to angle of view for framing and depth of field for composition. No matter what brand lens he or she puts on their Alexa or RED, that 35mm is going to have these same features of AoV and DoF. But, with larger sensors, those touch points shift. Now you can experiment with relative angle of view and relative depth of field for increased creative options.

Q: What do you mean by relative angle of view and relative depth of field?

A: Here’s an example. Shots featuring greater “magnification”, meaning that the background feels closer to the foreground, can give an intimate and dramatic feeling to a scene. Longer focal length lenses have more magnification than wider lenses, that’s just a factor of lens physics. Let’s say a DP wants that magnification factor in an intimate, two-person scene. They need to use a telephoto lens to achieve this feeling, but telephotos have very narrow angles of view. To get two people in the shot you have to pull way back from the actors, and you don’t get to see much of the background because of the narrow angle of view.

What’s different with a larger sensor is that your telephoto lens gets an wider angle of view, you’re literally seeing more on the sides, so you can keep the same focal length characteristics (magnification and depth of field), but the lens is shooting wider. Now you can push the camera in closer for the same framing or stay back and get more of the background into the shot while still maintaining that intimate and dramatic feeling.

With a larger sensor the camera can push in closer to the characters in a way that feels more natural to the viewer but still keep that great feeling of magnification. And, the wide angle close ups that are popular right now will take on a whole new feeling as well.

Q: Walk us through how exactly the angle of view changes?

A: Sure. For ease of calculation I’ll use the Leica Thalia 35mm T2.6 lens. The Thalia lenses cover every sensor format including ARRI Alexa 65, so we can calculate for the whole range of larger sensors with this lens. But to start, imagine the 35mm focal length lens set to T 2.6 on a Super35 digital sensor or film camera. Picture it in your mind. Every DP knows what a 35mm looks like.

Let’s put some numbers to that. That horizontal angle of view is approximately 37.9°. Even if a lens is designed to cover larger sensors, on a Super35 sensor that’s always going to be the angle of view. Angle of view is a factor of focal length and sensor size only. If the sensor size changes, the angle of view changes.

Now let’s change sensors to the new ARRI Alexa LF (or RED Monstro, or SONY Venice, or Canon 700 FF, they’re all within a few millimeters of each other). It has a larger sensor (1.5x larger horizontally than Super35). Our 35mm Thalia lens still covers the whole sensor, but the larger the sensor gets, the wider the image appears. Now the horizontal angle of view of that 35mm lens is 55.3°. This lens now looks much wider than you’re used to with a 35mm. In fact, the lens that has approximately a 55.3° angle of view on S35 is a 23mm lens. So, this 35mm lens on Alexa LF will have the angle of view like a 23mm lens. (The image below illustrates larger sensors and increased angle of view.)

Interview Image

As you can see, this lens now looks much wider than you’re used to with a 35mm. In fact, the
lens that has approximately a 55.3° angle of view on S35 is a 23mm lens. So, this 35mm lens on
Alexa LF will have the angle of view like a 23mm lens.

Q: So if the lens looks like a 23mm on a full format sensor, why not just label the lens a 23mm?

A: Great question. That gets to another characteristic of lenses that we mentioned earlier, depth of field. Depth of field is a factor of the lens focal length and never changes when sensor sizes change. Even though the angle would feel right, the DoF and magnification, which is also tied to focal length, would be off. But rather than see this as a point of confusion, I see this change in relative depth of field as another area for cinematographers to play with this new image-making vocabulary.

Q: If the depth of field doesn’t change when using larger sensors, what do you mean by relative depth of field?

A: This is about a change in perception from what we are expecting. We know that longer lenses have a shallower depth of field than wider angle lenses. So, when you can take a longer lens and give it a wider angle of view you are carrying that shallower depth of field into the wide shot, which might have been more difficult to achieve optically on Super35.

For example, our 35mm Thalia at T2.6 has a 1’9” depth of field at 6’. On the Alexa LF it’s relative angle of view makes it look like a 23mm lens. The relative question is at what aperture would a 23mm lens have a 1’9” depth of field at 6’? The answer is approximately T1.7. You could replicate the angle of view and depth of field of the shot on Super35 with a 23mm lens at T1.7.

Q: So, if the same angle and depth of field can be achieved on Super35, what’s the benefit of shooting full format?

A: Magnification. You can’t replicate the magnification on Super35 because you’ll be doing the shot with a 23mm lens. That feeling of bringing the background closer to the subject can’t be faked with a different focal length. Creatively, that’s probably the biggest change in the look of an image that cinematographers are going to be pulled toward. It’s hard to put into words but you feel it immediately.

The other main benefit of shooting full format over Super35 is practical. You can achieve the look of a super speed lens at a slower stop. Lenses in the T1.3/T1.4 class are extremely expensive, more difficult to manufacture, and often rather large. In full format you can get a similar shallow depth of field look from a less expensive and smaller lens. The cost difference is going to allow owner/operators and more modestly budgeted projects to achieve something that was once out of their price range.

When we were shooting the Thalia demo reels there was a lot of looking at the monitor, then looking at the lens, then back at the monitor, because when you’re used to a certain format it feels so uniquely different yet familiar to see content from a larger sensor. It will take people some time and testing to learn the new vocabulary of large format lensing and how it can be used, but I for one can’t wait to see it.

Interview courtesy of Production Hub

Author
Leitz Cine