Why does a 4mm lens have a wider angle of view than an 8mm lens ?
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In the current state of the question is very hard to understand. Can you try to rephrase it and be very clear and specific of what you're asking about? It will be easier to help you then. – Hugo Jun 30 '14 at 17:10
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The answers to What is "angle of view" in photography? should clear this up for you. – mattdm Jun 30 '14 at 17:24
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When lens are specified in mm, that is the measure of focal-length. It works as you observed, a longer focal-length shows a smaller angle-of-view, assuming the senor or film is the same.
You can make a simple experiment to understand why. Find two tubes of different lengths, say the one inside a roll of paper-towel and one inside a toilet-paper. Close one eye and look with the other through each tube. With the longer tube, you see a smaller angle of view.
The principal is geometric. If you make a cone at the base of the tube and point on the other end, you get a certain angle at the tip. If you only make the length of the tube longer, then the angle at the tip is reduced.
Itai
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