Naked Science Forum
General Science => General Science => Topic started by: Nicolas Berger on 14/12/2010 11:30:04
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Nicolas Berger asked the Naked Scientists:
I was wondering if you face a mirror from few metres away (let's say 5 metres), and try to take a picture of yourself in the mirror, does the autofocus on the camera set itself on the glass of the mirror (5 metres), or on the image reflected by the mirror (the double, i.e. 10 metres)?
What do you think?
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A clean mirror will produce an image that will be observed by the camera's optical censor whether it is a film camera or an electronic digital camera.
The camera might be in the view blocking some part of the reflective image, if not manipulated otherwise.
If the mirror is small and the background overwhelms the viewfinder then the camera will auto focus on the background.
Mirrors used in camera shots are used allot in trick photography, it's limit is your imagination
Remember the saying "Smoke and Mirrors"? It can apply.
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Apparently there are two different kinds of rangefinders.infrared reflection mirrorinfrared reflection mirror
Older cameras would have ultrasonic which would not be reflected by the mirror, and your distance would be half what you would expect.
Newer cameras often have infrared.
Infrared should be reflected by the mirror, although it may not be reflected well by the mirror. I did some tests with a TV remote and could turn the TV on and off using a small mirror and the remote (obviously different from a camera IR, but similar concept.
5 meters (16 feet) is pretty close to the "infinite" focus setting on many cameras, so the test might not be representative at that distance, and you may get a sharp image whether or not the distance is perfectly accurate.
It would be a far more representative test at 1m or 2m.
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What is the focal distance for the reflected image? At the mirror? or at the "original"? or does it make a difference?
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Nicolas Berger asked the Naked Scientists:
I was wondering if you face a mirror from few metres away (let's say 5 metres), and try to take a picture of yourself in the mirror, does the autofocus on the camera set itself on the glass of the mirror (5 metres), or on the image reflected by the mirror (the double, i.e. 10 metres)?
Most modern cameras use various forms of autofocus based upon optical imaging, therefore as long as the mirror is fairly clean, and it more-than fills the part of the picture that the camera uses for focussing, it will normally focus on the reflection and not on the mirror itself.
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Of course, Yes if it is a qualitative camera [;)]