Digital Video - January 2009 - (Page 32)

DV 101 lose light transmission through the additional elements. In most cases this is desirable, as you’re looking to shoot with a wide aperture to achieve shallow depth of field, but it is important to note that these devices generally require up to four times the amount of lighting you would need with the small-chip camera alone. The depth of field is then defined by the iris set on the largerformat lens and the focal distance to the subject. Exposure is controlled with the camera’s iris. As the larger-format lens projects its image onto the adapter’s ground glass, it is — by the nature of optics — upside down. This means the camera is recording an image that needs to be flipped in post. It also means that the image in your viewfinder is upside down. Some cameras, such as the JVC GY-HD250U, have a built-in image flip so that the display is right-side up. Some users incorporate an external LCD monitor mounted upside down onto the camera to view a corrected image. (The Letus35 adapter incorporates an internal prism that corrects this problem.) Note that as I broke down the various aspects of depth of field, I did not mention focal length in this equation. Although it is optically correct that a longer focal length creates larger circles of confusion and, therefore, less depth of field, where this becomes a misnomer is in the idea that if you want less depth of field, you can achieve the effects with a longer lens. This is, in fact, incorrect. It’s important to understand that I’m comparing apples to apples here. Meaning that for a given composition and subject size in the frame, the focal length of the lens you choose is irrelevant to your depth of field. As I mentioned above, the focal position plays a significant role in depth of field. This optical factor is what cancels out the larger circles of confusion for longer focal length lenses. For example, let’s say you’ve lined up a shot of your subject with a 50mm lens and the subject is 5' from the camera. This gives you a depth of field from 4' 10" to 5' 3", equaling a total of 5" of DOF (according to the ASC Manual, 9th edition). You decide you want less depth of field, so you switch to a 100mm lens. However, in order to keep the same composition and framing of your subject, you now need to move the camera further away. Suddenly you’re on a 100mm lens at 10' from your subject and your depth of field is now , 9' 10" to 10' 3" or a total of 5" — exactly the same as when you were on a 50mm lens only 5' from your subject. The fact that you moved the camera further away, thereby requiring you to adjust your focal position to a greater distance, you will have the same depth of field as your previous composition with the 50mm lens at 5'. Now, by moving to a longer lens from further way, you will have compressed the background elements and this can sometimes result in a perceived more shallow depth of field, but, really, what you’re seeing less of is the overall background area and you’re compressing the background closer to the subject, not reducing the actual area of the frame that is rendered in acceptable focus. All in all, these lens adapters, when correctly utilized, can help to refine the image created by small-chip cameras and present the filmmaker with another powerful tool in their storytelling arsenal. DV ADVERTISEMENT PRODUCT SPOTLIGHT AUDIO-TECHNICA BP4025 X/Y STEREO FIELD RECORDING MICROPHONE Audio-Technica’s new stereo condenser introduces a space-saving capsule design. In a compact, elegant housing, BP4025 offers the pristine sound quality & spatial impact of a live sound field. CONTACT: www.audio-technica.com mediaproduction@atus.com 330-686-2600 http://www.audio-technica.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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