 Darren Deans |
Canon f2.8L or f4L? Hello, I have been searching this site and the net but can not see the answer to my question so I hope you can help me. I am looking at the Canon lenses for the EOS 5D EF 24-105mm f/4 L IS USM LENS EF 17-40mm F4 L LENS Two of them are F4 and two of them F2.8 (ignoring the IS feature for the moment and the cost!) What is the advantage of the F2.8 over the F4? If I took both zoom lens and set them 24mm at F4 or the wide angle lens and set them to 17mm and F4 would I have a different shutter speed, or different quality image? Thank you!
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Andrew Laverghetta |
f/2.8 lets in more light so you'll have a faster shutter speed which will let you hand hold in dimmer lighting situations. f/2.8 will also give you a smaller depth of field in case you want to seperate the subject from the background more than with f/4. As for the image quality, I'm guessing that the 2.8 won't be quite the same quality as 4 but I don't think that should matter because you could just close down the 2.8 to 4 and then it'd probably be the same or better. Though, with the 17-40 f/4L, when you get to a wider lens, the shutter speed doesn't need to be as high as longer lenses so you might not always need the larger aperture. I think the biggest factor would be what you use it for. Unless it's something that has a lot of motion like sports or photojournalism with low light, you could just use a tripod, especially because I wouldn't consider the 5D a snapshot camera. That's why I assume you'd have a tripod you could use. Anyway, what will you be using it for?
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Jon Close |
Additionally, f/2.8 gives a brighter viewfinder for focusing/composition than does f/4. The center focus sensor of the 20D will work in high precision AF with f/2.8 and larger aperture lenses, with marginally faster and more accurate AF than with f/4 or f/5.6 lenses. On the other hand, the f/4 zooms are smaller and lighter, with greater zoom ranges, and generally less expensive.
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Jon Close |
Oops. ;-) The 5D. The 5D also has 3 central AF sensors that work in high precision AF with f/2.8 and larger lenses.
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Andrew Laverghetta |
oops! yep, missed that. :)
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Darren Deans |
So, If I took both zoom lens and set them 24mm at F4 or the wide angle lens and set them to 17mm and F4 would I have a different shutter speed, or different quality image? Darren
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anonymous A. |
NO to shutter speed, PROBABLY to image quality. The exposure at any ISO is determined by the aperture and sutter speed. Halve the sutter speed and you have to increase the aperture by 1 f stop to get the same exposure, no matter what your focal length or zoom range is. Lenses are designed to produce the best results in the middle of their aperture ranges. You would be hard pressed to tell the difference without optical tests and benchmarks, but the the f2,8 lens stopped down to f4 should produce a crisper image to the f4 wide open. Hope that helps.
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