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Old May 14th, 2004, 01:15 PM   #1
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Depth of Field Trick

This may be a widely known trick but I have never seen it referred to in print or on the net. I learned it from another shooter and am passing it along just in case you haven't discovered it for yourself.

Anyone shooting with a camera with 1/3" chips knows what a pain getting shallow depth of field can be. (I think shallow depth of field is often over-rated, but in many cases it is worth the trouble.)

Recently I shot an event with various speakers speaking from a microphone. The traditional thing to do would be to zoom in tight on the microphone, focus, then zoom back out again. The depth of field is, of course 1/3 in front of the focal point and 2/3 behind the focal point.

Before the event started I had an assistant stand roughly 10 ft in front of the microphone (in between the microphone and the camera). I zoomed in on him and focussed. When he moved away I checked to make sure that the microphone remained in focus with the shot framed the way I wanted. When the event began and I shot the speakers, the background was nicely out of focus.

The trick is to create the appearance of a shallow depth of field by moving the person being shot some distance behind the camera's focal point. Doesn't work in all settings and is pretty crude, but when it works it works well.

Rick
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Old May 14th, 2004, 04:40 PM   #2
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Well done, Rick. I actually use this trick quite frequently on the "George Lopez Show," which is my regular gig. I operate the "X" camera, and shoot a lot of "overs," or cross two-shots. Normally, you would zoom into the person facing the camera to set focus, but I don't like the way the foreground drops off so quickly, while the background remains in focus forever. (we shoot high def with the Panavision/Sony cameras) So, I direct my camera assistant to set the focus more toward the foreground to bring that person more in focus, while maintaining sharp focus and the background person. I can't say anyone notices the improvement but me, but I think its worth the trouble.

Wayne Orr, SOC
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Old May 14th, 2004, 04:47 PM   #3
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Thanks, Rick and Wayne. Since this handy tip isn't camera-specific, this thread might benefit from a move to the General DV forum where more are sure to see it.
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Old May 14th, 2004, 05:12 PM   #4
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I've mentioned this in several posts in the past, and I'm glad you have brought it to everyones attention again. However, you should be aware that DOF does not always maintain the 1/3, 2/3 ratio. In many cases it is 1/2 and 1/2. I use a DOF program for my Palm to calculate all the relevant distances and adjust the focus accordingly.
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Old May 14th, 2004, 05:38 PM   #5
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Jeff-
My wife just got a Palm, and it has been relatively safe, as I had found no use for it. If you could recommend any video/film apps that might be handy, I may just commandeer the thing!
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Old May 14th, 2004, 05:49 PM   #6
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pCam and pCine are the goodies.

My preference with video is to judge the focus splits off the monitor rather than mathematically--the format can have quite a deal to do with determining what is "sharp enough". For instance, critical focus with HD as Wayne is dealing with it is much more critical than the same shot on DV, not just because of the difference in imager, but also because of the inherent resolution.
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Old May 14th, 2004, 07:02 PM   #7
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Thanks Charles! I'll "appropriate" the PDA and try these.

On a tangent, I have heard you mention "focus splits", and have never heard that term. Could you explain it to me? S-l-o-w-l-y?
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Old May 15th, 2004, 02:09 AM   #8
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Well OK;

Think of the depth of focus as being the range of a shot that is considered to be in focus (which is regulated by the focal length, distance of the subjects from the camera, f-stop setting and focus setting). Now consider the example that Rick gave earlier and Wayne expounded upon, wherein they were able to maintain focus on the foreground element while throwing the background further out of focus. Pictorially, if one imagines the depth of focus as being represented from above as a shaded area: when the subject is 5 feet away and the lens is set on 5 feet, the shaded area will extend in front of and behind the subject (the percentages of each also discussed in this thread). Now place an actor 10 feet away, out of the shaded area. Roll the focus away until the leading edge of that shaded area remains on the guy 5 feet away, and (hopefully) the far edge is on the guy 10 feet away. You are probably focused around 7 feet, and you have thus split focus between two actors. This is the opposite effect of Rick and Wayne's technique, using the same principles.

Where this often comes up on set is when two characters are slightly staggered, both facing the camera (or a character alongside camera). Given 35mm optics and interior light levels, the camera assistant will tape out the two actors, consider the factors listed above and sometimes announce "we can't hold both of them", even by working a split (in other words, the distance between the actors is greater than that shaded zone which represents the depth of focus). A consultation will occur with the DP on whether it is desirable to rack focus between the characters; if that is not a satisfactory solution from a visual standpoint, various techniques may be used to avoid a rack. They include adjusting the position of the actors; beefing up the shooting stop by pulling ND if in use, or raising the light level, allowing for a fatter stop; or adjusting the focal length or distance of the camera. All of these techniques will increase the depth of field/depth of focus.

Hope that made sense (as usual, I wish I could make diagrams!)
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Old May 15th, 2004, 06:22 AM   #9
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That was perfect Charles, I understood every word! I didn't even giggle when you said "rack"- he he he...
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