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Old Aug 7, 2006, 9:29 AM   #1
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i understand to find the zoom factor of a lens you divide one number by the other
( eg a lens of 28mm - 200 mm spec gives zoom factor of 7.1 or so).

what i dont understand is why some zoom lenses start at 28, while some start at 40 or other figures.

what is the difference of a lens starting at 28 to that of a lens that starts at 40mm?

also, whats the difference between a lense of 28-200 or 11- 22? does the one that starts at 11 mm allow you to get a wider angle of view??
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Old Aug 7, 2006, 10:31 AM   #2
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The zoom factor is fairly meaningless marketing hype.
Roughly 40-50mm gives the magnification that the unaided eye has - things look around the same size through the viewfinder as they do when you take the camera away from your eye (for an slr - lenses are all described as if they are being used on 35mm film).
Less than 40mm is a wide angle. Stuff looks smaller but you get more of it. More than 50 is a telephoto. 11mm is a very wide angle and 200mm is a medium-to-long telephoto.
The 28-200 covers a wide angle to telephoto range and so is a general purpose type lens. It probably isn't the best though as lenses that cover large ranges are hard to make and compromises are usually required in their design. The 11-22 is a very wide angle zoom and is a specialty lens unsuitable for most use.
Lenses with high 'zoom factors' are rarely any good. Very few first-rate lenses have a zoom factor of more than 3.
The actual field of view of a lens on your camera depends on the size of the cmaera sensor. Most dslrs have smaller sensors than 35mm film and so lenses appear longer (multiply the length by 1.6 for canon 20/30/300/350 for example). In this case a 'standard' lens is around 30mm which is why most dslr ship with a 18-60 or thereabouts lens.
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Old Aug 7, 2006, 11:29 AM   #3
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i have a lot of misconceptions on lenses so. if zoom factor is a relatively meaningless number, how do you figure out, without actually using a lens, if it has the magnification you require. also if a zoom factor of 3 is generally all you get thats useable, will a lens that starts at 11 have less magnification than a lens that starts at 28, even if both lens'es have a zoom factor of 3? sorry if my questions seem simple, but i genuinely dont know this stuff and want to learn
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Old Aug 7, 2006, 12:11 PM   #4
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You think you're confused now, wait until you hear about how sensor sizes affect the angle of view and implied magnification.:-)

First to answer your question, a lens set at 11mm will have less magnification than a lens set at a focal length of 28mm. So 11mm is wider.

This is why zoom factors used to market cameras are really pointless. You need to know the exact focal range of a camera to know if it's something that fits your needs. A 28-200 is 7x zoom, but so is 18-125mm, but the 18-125 is wider since it covers down to 18mm, while the 28-200 has more reach since it extends to 200mm.

This is assuming the size of sensors are the same. On a smaller sensor, the image will appear more magnified. This is why 35mm format is considered a base, and everything is described relative to it. The 35mm was popular during the film days.

This is why a lot of DSLRs today have a multiplier, since they use smaller sensors. My Nikon D50, for example uses a 1.5x crop factor. Meaning, an 18-200mm lens actually gives me an angle of view of 27-300mm. This is why a 10-20mm was not very useful for 35mm cameras, but for DSLRs it's a great wide angle lens.


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Old Aug 7, 2006, 12:49 PM   #5
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oh my, ive really jumped in here over my head!!! right, so lets say my super zoom , has 12X zoom, a lens of 36 - 432 . but it only has a tiny sensor ( 1/4 inch i think , but not sure at all). how would you look at this in realtion to the standard ( 35mm)?

also, when you say:

This is why a lot of DSLRs today have a multiplier, since they use smaller sensors. My Nikon D50, for example uses a 1.5x crop factor. Meaning, an 18-200mm lens actually gives me an angle of view of 27-300mm. This is why a 10-20mm was not very useful for 35mm cameras, but for DSLRs it's a great wide angle lens.

does this mean that if you use a lens from a 35mm on a digital camera like your D50( lets imagine the lens fits perfectly) , you will only get half the image,and the rest will be cropped?

also can you explain what you mean about a 10-20 mm being useless on a 35mm but a great wide angle on a digicam? sorrry about all the questions

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Old Aug 7, 2006, 1:47 PM   #6
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Quote:
oh my, ive really jumped in here over my head!!! right, so lets say my super zoom , has 12X zoom, a lens of 36 - 432 . but it only has a tiny sensor ( 1/4 inch i think , but not sure at all). how would you look at this in realtion to the standard ( 35mm)?
My guess is the 36-432 is already the 35mm equivalent. So nothing to worry about.



Quote:
does this mean that if you use a lens from a 35mm on a digital camera like your D50( lets imagine the lens fits perfectly) , you will only get half the image,and the rest will be cropped?
Yes. "Even with the same lens, a smaller sensor will cover a smaller picture area, resulting in a telescopic effect." So in effect, I'm seeing a magnified image.
http://www.canon.co.jp/Imaging/enjoydslr/p_2_017.html



Quote:
also can you explain what you mean about a 10-20 mm being useless on a 35mm but a great wide angle on a digicam? sorrry about all the questions
Maybe I shouldn't have said "useless". For 35mm camera, a 10mm focal lens is usually a fish-eye, but for DSLRs with 1.5 crop factor, a 10-20 is more like 15-30mm.


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Old Aug 7, 2006, 2:35 PM   #7
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did you learn all this through expirience, or can you point me to any sites that break this down for beginners like myself? i dont have a dslr as of yet to lear all this . the reason im asking is im most likely getting a dslr ( looking at the D50) and want to know before i jump in. thanks for your help all
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Old Aug 7, 2006, 2:59 PM   #8
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I'm fairly new to photography, most of the stuff I know I learned in this site from posting questions, and reading others' questions, and answers shared by others here.

I suggest you start with the Canon DSLR site:
http://www.canon.co.jp/Imaging/enjoydslr/index.html

Also, it's probably a good idea to browse through old threads in the "General Q&A" and "Newbie Help" forum. A lot of these questions come up often.


Good Luck!
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