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Controlling Depth of Field on a PTZ camera in vMix
Rank: Newbie
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Joined: 9/26/2020(UTC) Posts: 1 Location: Maryland
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I'm trying to find a way to change the depth of field on a PTZ Optics 30x SDI camera so that I can create a specific vMix preset that will use a shortened depth of field, while all other presets using that camera will allow a more "standard" depth of field.
Here's the problem: We're live streaming a church service and use 3 of the PTZOptics 30x cameras. Everything is working well but there are 2 shots where we are having problems keeping the cameras focused on the subject. The first shot is a medium close view of the priest at the pulpit. Much of the time the shot is in focus, but occasionally the camera focuses on someone/something in the background and the priest goes slightly blurry in the foreground. The second shot (different camera) is another medium close shot and occasionally the camera will focus on the background and not the speaker in the foreground.
In both shots the light is good. In both cases the most obvious thing that causes a refocus is one of our choristers in their white robes moving in the background. This catches the camera's "eye" and the focus shifts. Occasionally the focus shifts to pick up a mic in the background.
What I would like to do is go into PTZOptics controls for the camera and open the aperture to reduce the depth of field. Save that to a preset in the PTZO controls. Then go into vMix and call up that PTZO preset to build a vMix preset that will have the shorter depth of field. I don't want the depth of field shortened across all shots on the camera.
Is what I'm suggesting possible or is there another way to get a shot with a shorter depth of field in vMix?
Thanks for any suggestions.
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Rank: Advanced Member
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Joined: 3/20/2014(UTC) Posts: 2,721 Location: Bordeaux, France Thanks: 243 times Was thanked: 794 time(s) in 589 post(s)
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First PTZ Optics cameras are well known to suck at focus tracking. Second reducing the DOF will emphasize your issue not reduce it (again because these cameras are not good for auto focus)
Your problem is not DOF related. Your problem is your camera auto focus is set to focus on the nearest thing that moves in the frame which is a stupid default setting and can't be changed. What you need is a way to "track" a subject so that auto focus keeps it in focus no matter what happens in the frame.
FYI, a wider aperture will not solve your issue, it will emphasize it. The best you can do is the opposite : work at f/11 or f/16 to increase the DOF so that it is less visible when the camera focuses on the wrong subject. But it won't be perfect anyway.
If you really care about focus accuracy with PTZ Optics cams : - only use wide shots where everything is in focus AND very tight shots when only the subject is in the frame (so that the auto focus can miss it) OR : - use better cameras
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Controlling Depth of Field on a PTZ camera in vMix
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