The DSLR Filmmaker's Handbook. Andersson Barry

Figure 1-4: Field of view comparison between full-frame sensor (blue) and crop sensor (red)

      If you are using a crop sensor, be aware of how this affects your lenses. When you’re shooting with lenses from traditional 35 mm film cameras, the field of view will not match up with the given focal length on the lens. This is due to the fact that the sensor is smaller than the area the lens would normally be filling when shooting with 35mm film or a full-frame sensor camera.

Some people say that the focal length will be changed when used on a crop-sensor camera, but that is not accurate. Standard still lenses were designed so that the field of view would cover the full frame of the 35 mm film (Figure 1-4). A crop sensor is smaller than a standard 35 mm film frame, and when a standard lens is used, the field of view is greater than what is captured on the sensor (Figure 1-5). This creates a magnification effect. For example, your 50 mm lens will have a narrower field of view. This does not in any way change the actual focal length of the lens, just how much of the area of view is captured (Figure 1-6).

Figure 1-5: Full-frame sensor captured with an 85 mm Zeiss lens

Figure 1-6: APS-C sensor in the same camera position with the same lens. Notice the magnification effect as compared to the full-frame image in the previous figure.

      The various sizes of crop sensors have their own multiplication factor specific to that size of sensor; these are referred to as either the crop factor or the focal length multiplier. Specific crop factors range between 1.3 and 2 depending on the size of the sensor. The way the crop factor is determined is a simple division of the size of the sensor by a full frame. For example, a full-frame sensor is 36×24 mm, and a Canon APS-C sensor is 22.3×14.9 mm. Dividing 36 by 22.3, we get 1.614, which we round to 1.6. If you are using a standard 24 mm wide-angle lens on a 1.6 crop sensor, your field of view is more like what you get with a 38 mm lens than with a 24 mm lens. This can hurt you if you are shooting in a really tight location, because you may not be able to achieve a wide enough angle.

      The APS-C crop sensor is almost identical in size to the standard 35 mm film that Hollywood uses. So, don’t get worried if you have a crop-sensor camera. Before you decide which camera you should buy, look at some footage from the cameras you are looking to shoot with and choose the one that best aesthetically matches the movie you want to make. Decide the speed of film (ISO on your camera) and the grain tolerance (sensor size), and choose as you would between standard film stock, Kodak Vision stock, and so on.

      Full-frame sensors are, for a variety of reasons, the most desirable, and the Canon 5D Mark III and the Sony A7s are the two leading cameras in the DSLR space with full-frame sensors. The great part of the full-frame sensor is that traditional 35 mm film lenses retain their true focal length. If you have your trusty 35 mm or 50 mm lens (or any lens, for that matter), then there is no learning curve for what image you will get. It will look the same as when shooting still images.

A good thing to note when comparing a full-frame digital sensor to 35 mm still or motion-picture film is that a full-frame digital sensor is in fact larger than 35 mm film. In reality, a full-frame sensor is almost equivalent to a VistaVision frame (Figure 1-7).

Figure 1-7: VistaVision film frame (left) vs. 35 mm film frame (right)

      VistaVision

      VistaVision was created in 1954 at Paramount Pictures; 35 mm motion film stock is 24×36 mm, whereas the full-frame digital sensor is 36×24 mm.

      In VistaVision, instead of recording an image horizontally from edge to edge of 35 mm motion-picture film, the image is recorded vertically, allowing a much larger area of the film stock to be used for each frame. The main benefit is a much higher-resolution image and the possibility of a much greater depth of field.

      Because of the lack of speed of the film stock circa 1954, usually productions blasted the scenes with light to create a large depth of field and usually didn’t take advantage of the ability to have a narrow or shallow depth of field. Thus, if you watch VistaVision movies like Alfred Hitchcock’s North by Northwest, you won’t see a shallow depth of field because they lit everything with mega Hollywood lights. Because DSLR cameras are so sensitive, now for the first time filmmakers are able to shoot at narrow depths of field previously not seen on a mass scale.

Table 1-1 lists the dimensions of the most common DSLR sensors; Figure 1-8 compares those dimensions visually. Figure 1-9 compares various physical film sizes.

Table 1-1: Sensor dimensions

Figure 1-8: Comparisons of sensor size

      The major benefits of using a camera with a full-frame sensor are that it is more light-sensitive, creates less noise in your image, and offers the ability for a narrow depth of field.

      More Light Sensitivity The reason that a camera with a full-frame sensor has more light sensitivity is simple – there’s more space for light to hit the sensor and bigger pixels collect more light (photons). The full-frame sensor has more than double the area of the APS-C crop sensor. The bigger (fatter) pixels catch more of the light than the smaller sensors.

      Less Noise By having the larger pixels to catch the light, the camera doesn’t have to amplify them in order to match the same ISO from a smaller sensor. Think of it as blowing up your image. The larger the image you begin with, the less noise in your final print. The larger the sensor you start with, the less noise in your final footage.

      Depth of Field Most filmmakers were never happy with the look of video. When HD came into existence, it was touted for its clear and sharp image. Many filmmakers didn’t like the look because it didn’t look cinematic. That all changed with the release of the first DSLR cameras. The ability to have a shallow depth of field and the more natural color rendering of flesh tones made HD video desirable to many filmmakers who previously disliked the look of HD video.

Figure 1-9: Various motion-picture film sizes

      Depth of field is what we unconsciously think of when we want something to look cinematic. Look at your favorite movies to see how much you see of the background in any given shot. You will see that many scenes have a shallow depth of field where the background is more or less out of focus. With a traditional home video camera, you always have a deep depth of field, and when you view your footage, you will find that most things are in focus almost as far back as you can see. This is because sensors in home camcorders are small and the lenses are not fast so they have a bigger aperture than a DSLR camera.

      The larger the sensor, the more shallow the possible depth of field; the smaller the sensor, the deeper the depth of field will be. Also, shooting at lower f-stops will cause a shallow depth of field vs. a higher f-stop on any sensor size.

      With DSLR cameras, you can now create films just like Hollywood does. As a matter of fact, DSLR cameras have now been used to shoot major Hollywood film theatrical releases, many leading TV shows, and even many images you see when watching sports. You can choose a lens and paint with light just as filmmakers have since the dawn of the movie industry. And that is why shooting on a DSLR camera is revolutionary.