Digital Video - January 2009 - (Page 28)

DV 101 BY JAY HOLBEN THE FUZZINESS OF DEPTH OF FIELD SELECTIVE-FOCUS LENS TOOLS OFFER CINEMATIC STYLE. T IN DEPTH: The same subject photographed with (from left) an here’s no doubt that smaller-chip DV, HDV and HD cameras 18mm lens from 1' at f/5.6, a 36mm from 2' at f/5.6 and a 72mm have put more high-quality, inexpensive cameras into more from 4' at f/5.6. Note that the change in field of view limits the users’ hands than ever before, but the cheaper, smaller chips background seen, but the depth of field remains consistent. come with a few compromises. In last month’s column, I discussed the problems of achieving a wide-angle field of view with a smallare rendered sharp enough to the eye to appear in focus. The further chip camera, and how to incorporate lens adapters to compensate. away your focus point is from your focal plane (the camera’s chip), This month, I’ll discuss a different kind of lens adapter, the “film lens” the more depth of field you will have. With the camera focused at 2', you might only have 1-2" of depth of field, but focused at 50', you or “35mm” adapters such as the P+S Technik Mini35, Redrock Micro might have 20' or more of depth of field. M2 and Letus35 Mini, which are designed to work with with a Aperture size is one aspect of depth of small-chip cameras with fixed lenses. My Canon XL2 fitted adapter and field that you have the most control over. The primary advantage to using one of Letus Ultimate lens Lens Baby unit. As you tighten your iris/aperture, the depth these adapters is to create more “film-like” of field grows. As you open the iris up, depth of field. With these adapters, it isn’t the depth of field decreases. 35mm lenses that give you the shallow depth Lens adapters such as the Redrock of field; it’s the larger size of the target (secM2, Letus35 Mini and P+S Technik Mini35 ondary ground glass) that creates this result. allow the user to incorporate largerDepth of field is an optical phenomenon format lenses from still or motion picture whereby a range of space within an image is cameras and artificially create a larger target size by incorporating a rendered into acceptable focus through a comsecondary ground glass inside the adapter, upon which the image bination of target size, lens focus distance and aperture size. from the larger lens is projected and then re-photographed by the Notice that I didn’t include focal length in any of the factors smaller-chip camera’s fixed lens. above. As I’ll discuss later, everything being equal, focal length does This process of re-photographing the image allows the adapter to NOT affect depth of field. I’ll let that sink in a bit and address the focal take advantage of the larger-format target size, generally that of a length misnomer a little later. 35mm film frame, and therefore adopt the depth of field properties Why is shallow DOF so coveted? Not only does it provide a more of the larger format. A ground glass is a piece of optical glass that “film-like” image, it provides the visual storyteller with an essential has been ground down on one side to give it a rough texture so that tool for focusing the audience’s attention on a specific portion of the an image projected on it can be seen rather than just pass through frame. It communicates to the audience that this space is what is the glass. As the camera’s fixed lens is focusing on the glass itself, it important in this scene. is also focused on the texture of the ground glass, which will end up Breaking down the components that define depth of field, I’ll in the final picture. To avoid this, all of the adapters mentioned above start with the focus point. This is the distance that you set your lens incorporate a vibration, oscillation or rotation of the ground glass so to, generally at the position of your main subject. Technically speakthat the texture of the glass itself is rendered invisible. ing, there is only one plane in any photographic image that is perfectIt is, of course, important to note that when you incorporate mully in focus. The rest of a particular range of depth of field may fall into tiple lens elements, in addition to the camera’s lens, you’re going to “acceptable” focus — that is, the subjects within that defined space dv january 2009 www.dv.com 28 http://www.dv.com

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Digital Video - January 2009 Contents First Look: D90 Camera Sonicfire Pro 5 You Pod Instant Expert Muse 2.0 FXFactory Pro 2.0.5 Motype Fxpack DV Product Directory All Powered Up Creating Your Own Sun DV101 Production Diary

Digital Video - January 2009

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