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Old Dec 11, 2009, 12:44 PM   #1
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Default SLR Zoom lens vs Point and Shoot zoom

I am a novice who bought an SLR recently and still learning about it. I would like to know about the difference in the nature of zoom obtained from a telephoto zoom lens like EF-S 55-250mm f/4-5.6 IS and that obtained by a normal point and shoot camera advertising 12x zoom. How to compare these? I thought of getting a feel of how much zoom will I get before buying the telephoto zoom lens. I'm so used to the point and shoot zoom config like 5x, 10x etc..

P.S I know this is a lame question, but I'd like to understand the difference.
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Old Dec 11, 2009, 1:36 PM   #2
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DSLR lenses are identified with the actual focal length of a lens, whereas P&S camera lenses are identified with the zoom ratio. This is because dSLRs have interchangeable lenses, and P&S cameras don't. For a dSLR the Canon 55-250 lens you mentioned would be a 5X zoom, but so would the Canon 28-135, even though the two lenses have very different angles of view.

So the zoom ratios you're familiar with from your experience with P&S digicams don't translate to dSLRs.
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Old Dec 13, 2009, 1:50 PM   #3
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TCav is right. Since you're not sure how much zoom you'd like, I suggest you walk into a local camera shop and walk around with a few of their lenses to see about how much magnification you're looking for and get a better idea of what you want. Of course, it would be nice to support the local shop instead of going home and ordering from B&H too.
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Old Dec 13, 2009, 2:46 PM   #4
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Another way to figure out how long a lens you want is to take a photo with the lens you've got, at its maximum focal length. Your Canon T1i has a 15MP image sensor that produces images with a maximum resolution of 4752 x 3168 pixels. Your Canon EF-S 18-55mm f/3.5-5.6 IS, at a focal length of 55mm, has an angle of view of about 28.

If, to get the composition you want, you would crop an image to 2376 x 1584 pixels (half it's original size), you want a lens with half the angle of view (14) which would have twice the focal length (110mm.)

If you would crop the image to 1188 x 792 pixels (1/4 it's original size), you want a lens with 1/4 the angle of view (7) which would be four times the focal length (220mm.)

So with a little experimentation using the gear you've already got, and some simple math, you can figure out your requirements for a telephoto zoom lens.
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Last edited by TCav; Dec 14, 2009 at 10:06 AM.
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