Lenses


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Mar 18, 2007
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#1
Can someone explain something to me?

For example, saw this lens on the Sigma website

Sigma 135-400mm F4.5-5.6 DG

What does the F4.5-5.6 mean? I know normally it is the maximum aperture, but i'm sure this does not mean the MINIMUM aperture is 5.6 right? Is there a way to see the MINIMUM aperture?
 

Melee

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Mar 31, 2007
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#2
Can someone explain something to me?

For example, saw this lens on the Sigma website

Sigma 135-400mm F4.5-5.6 DG

What does the F4.5-5.6 mean? I know normally it is the maximum aperture, but i'm sure this does not mean the MINIMUM aperture is 5.6 right? Is there a way to see the MINIMUM aperture?
"135-400mm f4.5-5.6" means that the maximum aperture is f4.5 at 135mm, and gradually reduces as you zoom further, down to a maximum aperture of f5.6 at 400mm. This is what's referred to as a "variable aperture zoom lens", as opposed to a "constant aperture zoom" or "fixed aperture zoom" (e.g. 70-200 f2.8 means the zoom has a maximum aperture of f2.8 throughout the entire zoom range). Variable aperture zooms are cheaper and lighter; constant aperture zooms are faster lenses and usually produce better image quality ('cos they're usually professional-quality lenses).

The minimum aperture varies from lens to lens; in the case of the Sigma 135-400 f4.5-5.6, it's f32. The minimum aperture is usually found in the lens specifications, e.g.:
http://www.sigmaphoto.com/lenses/lenses_all_details.asp?id=3275&navigator=3

Hope this helps. :)
 

Mar 18, 2007
178
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Singapore
#3
do that means that the more i zoom in, the amount of light i can take in, with shutter speed and ISO constant, decreases? So in other words, the maximum amount of light i can take in drops?
 

#4
That is correct. If you were to shoot say a white wall at 135mm at f/4.5 with the right exposure, then as you zoom in to 400mm with ISO and the shutter speed constant, you should have your white wall now underexposed by about 2/3 stop since 4-5.6 is one stop.
 

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