Originally posted by slowpez OK, I'm beginning to understand but now of course I have another question. Does the faster lens mean you have to give up DOF? Seems like if I have to opt for f1.4 vs. f5.6 I'm going to have a narrower DOF.
Thanks again for all the help. Susan
susan,
"a fast lens" refers to a lens that has a large maximum aperture.
any lens that has an aperture of 2.8 or less (smaller number) is considered to be "a fast lens"
that is all.
fast lens = large maximum aperture
fast lens = big hole
done.
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part 2
depth of field.
how you USE your lens is up to you
if you shoot your FA50 F1.4 at F1.4 then yes, your depth of field will be shallow, but allow you to increase shutter speed, assuming ISO is unchanged
if you shoot your FA50 F1.4 at F5.6 then your depth of field will not be shallow, but your shutter speed will decrease, assuming ISO is unchanged
however if you take a 50 F2.0, a 50F1.4 and a 50 F4.0 lens and shoot all 3 at F5.6, they will all yield the same depth of field, at the same shutter speeds, assuming ISO is identical.
so, how you USE your lens is entirely up to you.
no one is forcing you to shoot at wide apertures, wider aperture means less depth of field, it is there for artistic purposes.
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part 3
"fast lens and low light"
people often say that a fast lens is good for low light,
true, but that is not why its there
lenses shot wide open suffer from reduced sharpness, people who shoot wide open in low light conditions trying to attain a shot that would benefit from large depth of field are sacrificing
they would rather have a fuzzy, well exposed shot with high shutter speed rather than a blurry shot