Since the advent of DSLRs, photographic lenses are more and more present on film sets. Not only on SLR cameras but also on cinema cameras, from the most affordable (like DZOFILM Vespid Prime) to the most high-end (like the Red Dragon-X or the Arri Alexa Mini).
So, since they are much cheaper than their cinema counterparts, either to buy or to rent, why not use only photo lenses on a shoot?
In this "cinema vs photo lenses", we will decipher the main differences between these two ranges and see in which cases to use one or the other.
The construction of the lenses
The difference is obvious when you have in front of you a model of each category (including when the formula of the lenses is identical, like those of Zeiss Contax), the cinema lens is more imposing.
The first observation is the difference in weight and size (which is a determining factor when using a DJI Ronin or a MOVI).
The reason for the construction of the body of the cinema lens lies in the need to be able to adjust the point with precision during a shot. This is the job of the first assistant operator (also called pointer or focus puller in English). In order for him to be precise in his task, the diameter of the camber is larger. Thus the stroke of the pointing ring is longer with more graduations that serve as markers. In general, the front diameter of a photo lens is between 42mm and 82mm. In cinema, it varies between 80mm and 162mm.
Many photographers work alone, setting up their camera, defining their frame and setting up the body and lens for their photography. Generally speaking, they will need to find the point very quickly to capture the immediacy of an action; or they will take the time to wait for the light or the defining element of their scene to trigger, so they will have time to choose their focus distance.
On the other hand, on a set or in a documentary, the notion of tracking the focus, when a character moves, or the camera moves, implies being able to change the distance several times, without always being able to foresee where the focus should be.
The main reason, which explains the differences between these two classes, is the specific use of each craft.
The automatism and electronics of cinema lenses vs. photo lenses
Here again a difference related to the trade. The automatism is very much used in photography. The performance of the collimators allows a fast and precise automatic focus in photography (at least enough so that at a given print the slightest deviation in focus is not visible). A collimator able to react continuously on 24 or 25 FPS is more delicate to design and control. Canon seems to be the manufacturer in advance on the development of this process, which is already well developed on its C100 and C300 mark II models. But in practice it is only rarely used, because the point tracking is precious to cinematographers, directors and producers. To take the risk of placing it in the hands of the machine is not possible (at least to this day) and the dexterity of the human remains privileged (moreover, it allows to play in an artistic way with the blur, sensitivity that the machine does not have).
Nevertheless, cinema lenses also have electronics to display (as in photography) the focal length, the iris opening and the focusing distance. DZO pictor zoom, with its parfocal design, goes even further by displaying the depth of field distance between the foreground and the background.
Optical formulas and lenses
Once again, each profession has its own needs. In cinema, images are projected on a large screen. In photography, the prints, with some exceptions, are intended for the web or magazines. The camera lenses are therefore more precise (or sharpened) to compensate for the display surface. In addition, each model is worked to "erase" some of the micro-details. This specific treatment of the lenses is largely what gives the "cinema look" to the image.
The treatments are also more advanced to avoid defects such as: chromatic aberration, pumping, flare or distortion. It is always the notion of continuous images that makes these defects appear in video. Finally the iris is often composed of more blades, so that the bokeh is round.
To ensure continuity between all the shots of a film, a series of optics is balanced to the maximum between each focal length. The contrast, colorimetry and aberrations vary little. Sometimes the body and weight are also the same within the same series of lenses, which optimizes the focal length changes on the shoot.
The most telling example is that of the steadicam cameraman who must take the time to rebalance his sled if the lenses do not have the same characteristics.
It is all this work on the lenses, on the research of the style and the construction of the whole series (sometimes up to 16 pieces), which creates a big difference in price between the two categories of lenses.
The other differences between cinema lenses and photo lenses
The aperture marking is noted as "f:" on photo lenses and "T" in cinema. The " f: " corresponds to the geometric aperture whose formula is f/O, or the focal length on the entrance pupil of the lens. This formula is used in the calculation of depth of field. But for what is the illumination received by the sensor, it does not take into account the absorption of the lenses that do not let 100% of the light through them. The photometric aperture noted "T" takes into account this concept and allows to know the amount of light that passes through all the lenses.
The mounts are very varied among photo lenses depending on the manufacturer of the lens or camera. In cinema, most cameras have a PL mount, although the Canon EF mount is becoming more popular, bridging the gap between the two ranges of lenses.
In the end, each discipline has its needs and the big winners of the rapprochement between photo and cinema lenses will undoubtedly be documentary filmmakers and institutional film operators. They are looking for realistic images, automation and low costs. In the past, the broadcast zoom range was theirs, but photo lenses should become established among these operators with the evolution of cameras with autofocus, stabilization, lightness and compactness increasingly developed.
Photographers and filmmakers, who each have their own constraints, will almost systematically choose lenses that meet the needs of their jobs. But each work being different, nothing prevents from using such or such material.
And for those who are looking for a cinema look at the price of photo lenses, there are filters from DZOFILM or Schneider Optics that help modify the texture of the image. In addition, there are cheaper cinema models such as Canon's CN-E, Samyang's Xeen or the recent Sigma Ciné Art to meet the needs of low-budget fictions.