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Old Jan 3, 2007, 4:52 AM   #1
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Hi, i'm pretty new to the photography world, so be excuse my incompotence.


i would like to know what the numbers on the lens mean? i've done some research on the camera, Canon PowerShot SD700 IS (Digital IXUS 800 IS).. i found that the zoom wide is 35 mm and zoom tele is 140mm .. But on the camera it says 5.8-23.2mm 1:2.8-5.5

Can someone please kindly explain?

thank you
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Old Jan 3, 2007, 6:18 AM   #2
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jappy88 wrote:
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Hi, i'm pretty new to the photography world, so be excuse my incompotence.


i would like to know what the numbers on the lens mean? i've done some research on the camera, Canon PowerShot SD700 IS (Digital IXUS 800 IS).. i found that the zoom wide is 35 mm and zoom tele is 140mm .. But on the camera it says 5.8-23.2mm 1:2.8-5.5
The actual focal length of the zoom lens ranges from 5.8 to 23.2 mm. But since so many different sensor sizes are used on different cameras, almost all manufacturers also advertise numbers that are the equivalent focal lengths in a 35mm film camera (since most people are still familiar with the focal lengths on the old 35mm film).

So your Canon's lens has a real focal length range of 5.8 to 23.2 mm, but since the sensor is a tiny 1/2.5" size, when you look through the viewfinder and consider the field of view produced on that tiny sensor, it's comparable to what you would see if you looked through a 35mm film camera 's viewfinder with a 35 to 140 mm zoom lens attached.

So basically, for any of this to make sense you have to have some familiarity with the field of view produced by various lenses on a 35mm film camera.


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Old Jan 3, 2007, 7:51 AM   #3
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Yep, everything Norm said is in order.

The only thing I didn't see was an explanation of 1:2.8-5.5

Those are the aperture values. Most digicams (and many slr zoom lenses) cannot maintain a constant maximum aperture as you zoom. What these numbers mean is that when you are at 35mm the camera has a max aperture of 2.8. But by the time you zoom out, the max aperture becomes 5.5.
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Old Jan 3, 2007, 8:17 AM   #4
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JohnG wrote:
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The only thing I didn't see was an explanation of 1:2.8-5.5
Oops, left that out. Thanks.

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Old Jan 3, 2007, 11:10 AM   #5
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And as a touch more info, the human eye is roughly the equivilent to a 50mm lens. What this means is that the sizes of things in the image will generally match with what you see with your eyes.

So a 35-140mm zoom is a bit of a wide angle at 35mm. And the 140mm is about 3 times more powerful than your eyes.

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Old Jan 3, 2007, 5:31 PM   #6
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JohnG wrote:
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Yep, everything Norm said is in order.

The only thing I didn't see was an explanation of 1:2.8-5.5

Those are the aperture values. Most digicams (and many slr zoom lenses) cannot maintain a constant maximum aperture as you zoom. What these numbers mean is that when you are at 35mm the camera has a max aperture of 2.8. But by the time you zoom out, the max aperture becomes 5.5.
another little tidbit of info, the f2.8 is the equivalent of about f/11 on a 35mm camera which accounts for the huge depth of field on most p&s cameras. This is why is is so difficult to get the nice blurred background you see in some portraits. But also a big advantage when you do want everything in focus.
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Old Jan 4, 2007, 12:56 AM   #7
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thank you so much of the explanation guys. It is more apparently me now =)

Just one more question.

What lens ranges are consider "good"? for example comparing with a lens that has
35-140mm zoom and 38-114mm zoom.. which one is better?

thank you again
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Old Jan 4, 2007, 1:25 AM   #8
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Quote:
35-140mm zoom and 38-114mm zoom.. which one is better?
The first is wider and has a longer reach so many would prefer that for a general use carry all the time lens/camera.

Howeverthere is no "best" range for anything.

Choose whats best for your needs, they will not necessarily be best for everyone.

35-140 would be good for the casual snapper, its a good rangefor a smaller compact.

I use an H1 with 36-432mm reach because I like telephoto.

Others would prefer a wider camera for landscapes, say starting at 24mm or so.

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Old Jan 6, 2007, 6:48 AM   #9
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ok.. great.. thank you so much for your reply

=)
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Old Jan 7, 2007, 8:27 PM   #10
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Since we are discussing lenses, is there a formula to convert mm to magnification? I know what 8x binocsprovide but I cannot relate magnification to a 200 mm lens for example.




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