Crop Factors

Started Sep 20, 2008 | Discussions thread
hbx2004
Veteran MemberPosts: 3,162
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Re: No such thing...
In reply to Sean Nelson, Sep 21, 2008

Let's take Canon G9 as example, which has focal length of 7.4-44.4mm. For average buyer, this number doesn't tell much about reach/coverage of the lens (except it's 6x-zoom).

People are comfortable with 35mm equivalent terminology, so manufacturers also give 35mm equiv. specification (35-210mm in this case). Now, from our experience (comparing with FF lens, actually), we can imagine what angle of view this lens covers at given focal lengths: about 63°(wide)-12°(tele).

Important is, 44mm lens on G6 covers the same area as 200mm lens on FF camera -there's nothing cropped (compared to anything) as both sensors will capture whole area projected by particular lens (at comparable focal length). That is: when printed at the same size, images from both camera will have the same content -nothing was cutted/cropped from what each lens projected.

This isn't the case when we talk about APS-C sensor cameras. Because APS-C sensor covers smaller (cropped) portion of projected image, angle of view is smaller. Thus, optically, 200mm lens on APS-C (1.6-crop) camera delivers the same result as 320mm lens on FF camera.

The point is:
AP-S cameras do crop (by factor), thus we can apply "focal length multiplier".

P&S cameras don't crop -we use focal length (35mm) equivalence for easier understanding only.

Greetings,
Bogdan
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My pictures are my memories
http://freeweb.siol.net/hrastni3/

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