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04/01/2005 03:56:15 PM · #1 |
Now iam not tryign to be funny or anything iam jus wondering what a fast lens is? and why i need one for portraits?
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04/01/2005 03:59:22 PM · #2 |
| Fast lens = large aperature which will allow for very shallow DOF for one thing. |
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04/01/2005 03:59:27 PM · #3 |
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04/01/2005 03:59:33 PM · #4 |
"Fast" refers to a large aperture. If you use a large aperture and let more light in, you can use a higher shutter speed.
The other efect of a large aperture is very small DoF. For portraits it is many times desirable to throw the background completely out of focus. A larger aperture helps in this regard.
Fro example, with a 50mm f/1.4 lens, you can take a picture of someone's face and have their eyes in focus and their ears out of focus.
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04/01/2005 04:03:57 PM · #5 |
| I heard Ed Pierce, talking for Canon. He said that you need f2.8 or faster to get a real good sharp autofocus lock. |
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04/01/2005 04:25:38 PM · #6 |
Originally posted by gwphoto:
I heard Ed Pierce, talking for Canon. He said that you need f2.8 or faster to get a real good sharp autofocus lock. |
what do you mean by that? the lenses that i use take pictures that are in focus ?
Message edited by author 2005-04-01 16:31:34.
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04/01/2005 04:43:47 PM · #7 |
Originally posted by LEONJR:
Originally posted by gwphoto:
I heard Ed Pierce, talking for Canon. He said that you need f2.8 or faster to get a real good sharp autofocus lock. |
what do you mean by that? the lenses that i use take pictures that are in focus ? |
I think what Ed meant was thatwith slower lenses, ie; f3.5 and slower, that whenyou are focusing, the lens is wide open and thhere may not be enough light hitting the autofocus sensors in some light contidions to get a real sharp focus. I know form doing weddings in low light, it is very dificult getting a focus on a black tux. When I think about it it makes sense to me. Give the sensor all the light possible and you can get a sreal sharp focus. I guess in bright sunlight it may not matter that much, but in low light, from what I understand about what Ed said was the if you sensor doesn't get enough light your focus might not be tack sharp. |
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