Digital Video - December 2008 - (Page 38)

DV 101 This makes wide-angle shots on small-chip cameras very challenging. ENTER THE ADAPTER This is where lens adapters come into play. I’m not talking about adapters that allow film lenses to be used on digital cameras; I’m talking about optical adapters that attach to the camera’s lens to decrease the focal length, which, in turn, increases the angle of view. Adding the additional optical elements, especially aspherical elements, allows you to cheat the maximum angle of view to achieve wider shots. There are limits to how wide you can go with any adapter before you begin to distort the image, of course. Rectilinear wide lenses (those in which real-world straight lines are represented as straight lines in the image) are difficult to manufacture. The wider the angle of view, the more likely it is to distort the image. Fisheye lenses, the antithesis of rectilinear, provide extreme wide angles of view but also extreme image distortion. Lens adapters are calibrated by their conversion factor. A 0.7x will mean you simply multiply your focal length by that conversion factor to see how wide your converted focal length will be. 16x9 Inc. is one company that manufactures high-quality lens adapters for smallchip cameras. For my Canon XL2, a 1⁄3" SD camera that has a 20x lens with a 72mm lens thread diameter, 16x9 Inc. offers two rectilinear wide-angle adapters: a 0.7x and a 0.75x. The XL2’s lens has a 5.4mm to 108mm focal range, and the 5.4mm has a field of view of 54.8 degrees. With the 0.7x adapter, that converts the lens to the equivalent of a 3.78mm, which increases the field of view to 73 degrees. That’s an increase of 25 percent! And it gives the same field of view, roughly, of an 18mm lens on a 35mm motion picture camera. Beyond that, you start to get into image distortion and fisheye lenses. 16x9 also makes two fisheye attachments, with a lens conversion factor of 0.45x and 0.4x. The wider, the 0.4x, will turn the Canon’s 5.4mm lens into a 2.2mm! This gives you an angle of view of 103.6, but with significant distortion. TO AFOCAL OR NOT TO AFOCAL The 16x9 adapters that I mentioned above are afocal adapters, meaning that they create no specific focal point themselves, but merely resize the image by optically altering the lens’ focal length. A non-afocal adapter, such as the Red Eye adapters, create a new focal point for a given lens. The Red Eye does this by projecting the image in front of the lens, requiring a macro focus lens to work. By doing this, the Red Eye creates a wide angle of view with a single lens in a very lightweight package. The disadvantage to a non-afocal adapter is that it will only work if the lens (continued on page 41) You’ll find an extended version of this story on our site. Visit DV online. ADVERTISEMENT PRODUCT SPOTLIGHT Audio-Technica AT8022 X/Y Stereo Microphone Designed & equipped for use with either consumer or professional gear, Audio-Technica’s new AT8022 stereo microphone offers a compact housing and the pristine sound quality of a live sound field. CONTACT: www.audio-technica.com mediaproduction@atus.com 330-686-2600 http://www.dv.com http://www.audio-technica.com

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Digital Video - December 2008 Contents DV Expo Gallery First Look: Ultimate 35MM Lens Adapter Vidock GFX Pro Videostudio Pro X2 Instant Expert The Making of Roman Close-up: Dave Ruddick Crypto Camerawork Click To Play DV101 Production Diary

Digital Video - December 2008

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