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Old Nov 10, 2008, 10:21 PM   #1
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Okay I was wondering how the classification for a lens works. For example the "Olympus SP-570UZ has a f/2.8-4.5 4.6-92mm zoom lens with a range of 26 to 520mm in 35mm format." Now I understand the latter part of the description were it alludes to the 35mm format but every before that baffle's me (f/2.8-4.5 4.6-92mm). For example if I were to look at an dSLR lens sometimes they don't include the 35mm format comparison. So I have not the faintest idea how far this lence will actually zoom. Can anyone enlighten me?
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Old Nov 10, 2008, 11:31 PM   #2
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Hi, well your asking about two different sets of numbers.

The first one is the camera aperture number (f stop) which describes how much light the lens is going to let into the camera. The smaller the number the more light is let in, and usually the better the lens. If you have a range (f2.8-4.5) the minimum aperture varies from the low focal range of the lens, f2.8 at 4.6mm, to the upper end - f4.5 at 92mm. More information is available at http://en.wikipedia.org/wiki/F_stop

The next set of numbers is the focal range of the lens. Its a zoom lens because it zooms from 4.6mm to 92mm. 4.6mm is wide angle and 92mm is telescopic. Now this is related to the size of the sensor in the camera. When you compare it to the 35mm format, the ratio is called the crop factor. With the 4.6mm focal length with your camera's sensor is equivalent to 26mm in 35mm format, for a crop factor of 5.6 (4.6 * 5.6 = 26mm). The larger (or closer to the 35mm format) that the sensor is the smaller the format. For more information see http://en.wikipedia.org/wiki/Crop_factor

In dSLR cameras the sensor is larger, so the crop factors are usually 1.5. 1.6 or 2.0.

Hope that helps...
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Old Nov 11, 2008, 9:22 AM   #3
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Yup that helped a lot. I was able to get what each crop factor is relative to the brand of camera.
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