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Old Apr 30, 2010, 8:47 PM   #1
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Default zoom calculation

If I have 2 lens that has 10x zoom and put them end to end, all at 10x zoom, how much total zoom do I get?
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Old Apr 30, 2010, 9:33 PM   #2
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I don't think you can do what it is you're talking about.

When a manufacturer quotes a 10X zoom, that is the ratio of the smallest focal length to the longest. That is, the lens has a focal length of, for instance, 5mm at the wide end and 50mm at the tele end. ( 50mm / 5mm =10 ) You can't stack those types of lenses. They are attached to the camera and can't be removed.

If you're talking about a 2X teleconverter, for instance, mounted on a camera's lens, it would double the focal length of that lens, but at both ends. That is, instead of being a 5mm-50mm lens, it would be a 10mm-100mm lens, which would still be a 10X zoom. ( 100mm / 10mm =10 )
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Last edited by TCav; Apr 30, 2010 at 9:47 PM.
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Old May 3, 2010, 9:14 AM   #3
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TCav has it right.

I don't want to think about what that kind of stacking would do the the effective f/stop. Could be forced to do using something like ISO 1600 to be able to get a shutter speed much faster than a quarter second in bright sunlight. Even if the magnified distortions didn't stop you from using it, that would.
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Old May 9, 2010, 9:29 PM   #4
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For better answers, we'd need to know: what camera, what lenses?

Usually when you see a zoom described as 10x or 20x or whatever, it's attached to a P&S (point-and-shoot) camera, and it's difficult to stack another superzoom atop it. A zoom for a dSLR will carry numbers like 18-250 or 50-500, and while it may be *possible* to stack another zoom atop it, the results won't be pretty.

With a dSLR, you can stretch a tele or zoom by adding a TC (teleconverter) behind the lens, but those beyond 1.4x generally suck. With a point-and-shoot, you can add a tele adapter in front, but these ALWAYS suck. Stacking zoom-upon-zoom will REALLY suck. The optics just aren't made for this abuse.

If you need tremendous reach with a dSLR, mount it on a telescope. If you need great reach with a P&S... well, too bad. Get a dSLR.
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