Article View: sci.image.processing
Article #157Re: Buying a lens
From: The Land of Confusion
Date: Thu, 23 Jul 1992 13:58
Date: Thu, 23 Jul 1992 13:58
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1494 bytes
In article <5435@m1.cs.man.ac.uk>, mark-r@spec0.ee.man.ac.uk (Mark Robinson (JO PhD)) writes:
> Hi.
>
> Quick question about lenses. I want to buy a fixed focus lens
> (fixed focus == less glass == lower distortion ?). I would
> like an object about 15mm diameter to fill an image with the
> object - camera distance somewhere between 40 and 70cm.
>
> How do I calculate the focal length of the lens?
>
> Cheers
> Mark
> mark-r@snow_white.ee.man.ac.uk
You need to know the active dimensions of the camera sensor array
(assuming you're using a solid state video camera). Then it's a matter
of simple proportion between the image-height:object-height and
focal-length:object-distance ratios.
--
graham a stephen ``The only key to your riddle is
(e-mail: graham@sees.bangor.ac.uk) to accept the absence of a key.''
-- Laibach, 1992
Aposiopesis is not really all that it
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Newsgroups: sci.image.processing Path: arc1-ca.pugleaf.net!sparky!uunet!usc!sol.ctr.columbia.edu!sees.bangor.ac.uk!graham From: graham@sees.bangor.ac.uk (The Land of Confusion) Subject: Re: Buying a lens Organization: University College of N Wales, Bangor References: <5435@m1.cs.man.ac.uk> Message-ID: <1992Jul23.145842@sees.bangor.ac.uk> Sender: graham@sees.bangor.ac.uk (The Land of Confusion) Date: Thu, 23 Jul 1992 13:58:42 GMT X-Posted-From: sol.sees.bangor.ac.uk X-Posted-Through: sol.ctr.columbia.edu Lines: 25