A Quick Primer on Using Zeiss CP.2 Cinema Lenses

Producing our 48 Hour Film Project had a series of “firsts” for me. One of those firsts I mentioned was the first time for me shooting with a Zeiss Compact Prime CP.2 cinema lens (pdf link) (specifically the 35mm T2.1). There’s a lot of talk among DSLR filmmakers about the joy and benefits of using Zeiss glass vs. a traditional Canon or Nikon lens. Using Zeiss glass for filmmaking is supposedly even better than using the “Luxury” L-series lenses that Canon offers. As promised, I wanted to briefly touch on my experience using the lens, as well as help you understand what that heck that “T” stands for.

A Lens Designed for Filmmaking

First and foremost, these lenses are specifically designed for filmmaking. They’re manufactured in a way to make adjusting focus and aperture silky smooth. That means at wider apertures like F1.8 to 2.8, not only is it easier pulling and adjusting focus (especially if you’re using a dedicated focus puller), but you’ll be able to keep and hold focus easier. This is something we definitely noticed using the 35mm CP.2. We didn’t even use a follow focus, just our hands, and it was great. There’s a shot in the film where the camera pushes in on the main character, deep in thought and looking concerned. We used a camera slider for that shot, and marked focus points at the beginning and end of the shot. Our DP Bryce then just turned the aperture ring evenly with his hand throughout the shot and it worked perfectly. FYI: I didn’t get a follow focus for two main reasons. Most importantly, given our tight schedule, every second counted. I didn’t want to have to fuss with putting together and connecting a follow focus. The nice thing though is that follow focus gears are built in, so if you do use one, you don’t need to fuss with adding gears. Second, I don’t own one and I was already a little over my wife-approved budget for this project that was not generating any income. 🙂 So when it came to which equipment to rent, I put my money towards the lens instead.)

The iris on the lens has 14 blades allowing for greater sharpness and control at wider apertures (most traditional lenses have significantly fewer blades, as little as half). Having that many blades makes the opening perfectly rounded as you go through aperture ranges. A good analogy is pixel depth in a photo. The higher the dpi, the smoother the rounded edges are on an image. Have you ever zoomed in on a low resolution image, you’ll notice it looks very jaggedy. The more pixels there are, the smoother the edges. It’s kind of the same thing with having more iris blades. The more blades, the smoother the circle.

Another nice thing I like about the lens was that in addition to focus marks, there are distance marks as well. If you’re going through all the motions to really dial in your focus, these are great. (You ever noticed in behind the scenes videos on DVDs when there’s a guy using a tape measure to measure the lens to the subject? That’s why. To dial in focus based on aperture, shutter speed, etc.) Having the distance marks also makes it easy to know which direction to turn the ring when pushing in or out as you adjust focus. I sometimes forget. 🙂 These marks are traditional focus marks you might set, and the lens is perfectly grooved for using with a follow focus rig.

The CP.2 lenses are specifically designed for DSLRs and 4/3″ cameras and there are five different mounts available: PL, EF, F, Micro 4/3″ and E. That gives you a lot of flexibility with regards to cameras you can use it on. We used the 7D, but could have also used the T2i. These are crop-sensor cameras with EF mounts. What’s nice about these lenses is that if you use them on a full-sensor camera like the 5D Mark II, you don’t get any vignetting around the edges which is common with wider angle lenses. (Here’s a demo video on how to change mounts.)

One last thing. The casing on this thing was huge. I was used to shooting with Canon’s 35mm F1.4L. So I was expecting something that size. When I opened the shipping box from BorrowLenses.com, and saw this relatively big pelican-style case, I was surprised. I then opened it and was worried if they had sent me the wrong lens. Apparently, they are all designed to be that size, regardless of the glass, so as to make then uniformly able to fit in cinema matte boxes.

T- vs. F Stops

The other thing about this lens which is different than traditional DSLR lenses is that it’s rated on T-stops vs. F-stops. It’s kind of confusing explaining the difference. The T-stands for transmission, as in how light is transmitted through the lens. A traditional lens has aspects of it that will effect the amount of light that can get through it, depending on how it’s manufactured. For instance, there’s a lot more parts to a zoom lens vs. a prime lens (e.g. a 24-70 vs. a 35). Therefore, less light can actually be transmitted through it at any given focal length compared to a prime lens. Cinema lenses are calibrated in T-stops, which is essentially the equivalent F-stop of an ideal lens assuming 100% of the light can get through at that point. So in practice, the T-number of an aperture will be greater than the F-number of that aperture (i.e. an F1.8 lens may have a T-number of 2.x). Consequently, the depth of field of such a lens will be shallower than a lens whose F-number is the same value (e.g. a T2.1 lens has a shallower DoF than an F2.1 lens). As long as you remember that, when picking your cinema lenses, you’ll know what to look out for.

Go For It

In the end, I loved using this lens and it was worth the extra money it cost to rent. The images were sharp, working it was smooth, and the results were terrific. About 90% of our film was shot with just the 35mm. If you have the budget to rent one, and the project is worth giving it the best possible look, I say go for it.

Here’s a goo video by Cinema5D about the compact primes.

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