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-   -   Telephoto Lenses (https://forums.steves-digicams.com/general-discussion/127013-telephoto-lenses.html)

AJ DRAGON Aug 6, 2007 1:05 AM


Hi

I know this may sound stupid but I am going to ask anyway, because I don't know the answer. How does a Telephoto lens work? Take for instance the 3X Telephoto lens you can get for the Canon S5 IS. Is the 3X power added to the exiting 12X power to bring the camera up to 15X power or is it like 3 X 12 = 36?

TCav Aug 6, 2007 10:33 AM

AJ DRAGON wrote:
Quote:

How does a Telephoto lens work? Take for instance the 3X Telephoto lens you can get for the Canon S5 IS. Is the 3X power added to the exiting 12X power to bring the camera up to 15X power or is it like 3 X 12 = 36?

Unfortunately, the terminology used by camera manufacters is inexact and leads to this type of confusion.

The Canon S5 IS has a zoom lens whose maximum focal length is 72mm and minimum focal length is 6mm, so the ratio of the longest to the shortest focal length is 12 to 1, or 12X.

The 3X lens you're talking about will triple the focal length ofthe lens it's attached to. Sowhen you mount the 3X lens onto the S5 IS,its lensnow has a focal length of 18mm to 216mm. The ratio of the longest focal length (216mm) to the shortest focal length (18mm) is still 12 to 1, or 12X. It's just that the focal lengths are three times what they were without the 3X lens.

So it is neither 15X nor 36X.

But the ratio of the longest focal length WITH the 3X lens attached (216mm) to the shortest focal length WITHOUT the 3X lens attached (6mm), is 36 to 1, or 36X.


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