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Old Feb 18, 2005, 6:06 PM   #1
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For someone who is not a professional nor advanced user (more of a novice photographer) who wants to get into a dSLR, what's the difference between the following two Sigma lenses (besides the focal length)?

Sigma 70-200mm F2.8 EX HSM

Sigma 100-300mm F4.0 EX HSM

This is for use on the Nikon D70. Which would be the better lens (image quality)? Also, what do people mean when they talk about a "fast lens"?

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Old Feb 18, 2005, 7:12 PM   #2
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The lower the f number the wider the lens opens (faster) thus allowing more light to enter given the shutter speed. Faster lenses (lower f number and wider opening) cost more due to the optics etc.

Normally, the longer focal length ie: 200mm vs 300mm, the "slower" (larger f number) the lens will be and thus, not perform as well in low light situations. Zoom lenses normally have a variable f number ie: 4.5-5.6 meaning at the nearest focal length the lens opens wider while at the longer focal length it does not. To get a zoom with a fixed opening, costs lots of $$$$.

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Old Feb 19, 2005, 10:12 AM   #3
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Another issue is physical size... faster lenses are usually larger than ones with smaller maximum apatures. Take a look at the Canon 70-200 series. The f-4 ($550) is very manageable and relatively compact. The f-2.8 costs several hundred more and is twice the size of the f-4 and the 2.8 stabilized version is in the $1200 range and a load to carry around.

Both the Sigma lenses mentioned above have been favorably reviewed, but aren't compact by any standard.
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Old Feb 19, 2005, 12:57 PM   #4
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Since you didn't tell us what type of photography you do, its hard to recommend a lens. Of course, you didn't ask "which would be the best lens for me" you asked which will lead to better image quality.

The 70-200 is a very good len. I've heard good things about the 100-300, but not as many as with the 70-200.

The description of a "Fast lens" is is correct. Cameras with smaller f-stops or larger apertures allow more light than other lenses and therefor allow for the use of faster shutter speeds. So they are refered to as "Fast."

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