Waldemar
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Feb 18, 2005, 8:53 PM
Post #2 of 7
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Re: [jerry] how to make srue focus is perfect......
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I just started a project where we have 2 cameras. One is on a tripod for wide shots and the other is handheld for cu. I've noticed that some of the wide footage goes in and out of focus during an interview. I've been using autofocus and I believe that when the subject talks with his hand, the camera focus shifts, causing the face to slightly blur. I've been told the way to fix this is to manually focus on the face and then tape down the focus ring and shoot at a high f-stop. Will this help? I've found that it's pretty hard to get a perfect focus on the face manually, judging from the lcd? Is there a trick to getting sharp focus on a wide shot in manual mode? Which F-stop would you suggest? Say there is not a lot of light and 2.8 is the only f-stop to use at 1/60, should I adjust the gain and stop down? Additonally, is 1/60 a good enough shutter speed to shoot a person talking? Thanks for your help.
-jerry You are absolutely right, the auto focus is tryng to deal with objecti in motion in front of your subject's face. In manual focus, which is the only reliable way to go, wherever you choose to focus on will be the ONLY plane which will be in sharp focus. By choosing a smaller fstop, i.e., larger number, there will be an illusion of "apparent focus" through a "depth of field", front to back, which will appear to be in focus. The smaller the f-stop number, the greater the depth of field. In general terms, the depth of field is about 1/3 in front of the focus plane and 2/3 behind the focus plane (relative to the f-stop you have chosen to use).
So, you focus upon the eyes in an interview and choose an f-stop of f8.0 or greater, and you should be all right.
Note, though, that your overall exposure will change. Correct exposure is a balance of shutter speed and f-stop. Having chosen an f-stop of f8.0, for example, you will need to assign an appropriate shutter speed to bring the image of your subject into a balance that looks natural. If that means selecting a shutter speed of less than 1/60 second (in interlace/normal mode for a video camera), you are going to have to deal with the issue of blurred hand movements. Shooting in frame/progressive mode won't necessarily change the blurring hand movement issue, because, in the final analysis, the image has to be translated into 1/60 shutter speed terms to be displayed (because that is how video is displayed in the US.). At this point the only option is to increase the amount of light with additional lighting to bring the overall light level up to that which allows a normal exposure.
Adjusting gain will only serve to increase grain in the image. Try to keep gain at -3. I feel adjusting down to 1/30 might work for a close up of a person's face, but you will need to make your own decision. Shooting at f2.8 and having to increase gain is an utter waste of time if your want quality video. Insist upon a good lighting environment.
G5 1.8. Final Cut/QT Pro/iMovie/Still Life. GL1. XL1-s
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