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Old May 23, 2007, 4:36 PM   #1
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What is the bad and good about a varable aperture lenes.
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Old May 23, 2007, 4:52 PM   #2
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the good is, you usually get a fairlylarge maximum aperture. the bad is, you don't get it at the "long" end of the zoom. there's no particular penalty in image quality as a result of variable aperture, but it can limit youin terms of exposure options. at the wide end, with the larger apertures, you can shoot in lower light, and also use aperture to control DOF. at the other end of the zoom range, with the smaller maximum aperture, you need better light, and have less control over DOF.

the benefit of variable aperture lenses lies mainly in cost. a fixed-aperture zoom lens is generally more expensive, because it maintains its largest aperture even atits maximumfocal length, and that takes more engineering and manufacturing effort to accomplish.
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Old May 23, 2007, 8:35 PM   #3
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This could be a big deal for anyone who shoots in manual...
(i.e. the aperture is variable throughout the aperture range and not just at wide open)

For example in a gym with fixed lighting changing the zoom setting will automatically change the exposure which could be a real pain in studio shoots as well...

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Old May 23, 2007, 8:50 PM   #4
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NHL wrote:
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This could be a big deal for anyone who shoots in manual...
(i.e. the aperture is variable throughout the aperture range and not just at wide open)

For example in a gym with fixed lighting changing the zoom setting will automatically change the exposure which could be a real pain in studio shoots as well...
It's not that big of a deal you just have to remember to adjust when you zoom.
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Old May 24, 2007, 5:49 AM   #5
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tjsnaps wrote:
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It's not that big of a deal you just have to remember to adjust when you zoom.
How?

The focal lenght does not show in the viewfinder... so you have to move the camera away and down to look at the focal lenght in the mean time the subject has moved or change position while you're composing using the various zoom settings.

Unless you limit yourself to the zoom two extremes (and know exactly how many stops to compensate for), but in the middle range it's a total guess - Correct?

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Old May 24, 2007, 8:17 AM   #6
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seems to me this is only an issue if you're shooting wide open. if you stop down even on stop, the lens will stay where you put it. and in most cases, that's enough to deal with the problem, since most variable lenses only change by one stop between wide and telephoto. some vary more, like my Tamron 24-135, which is a 3.5-5.6; but still, stop down to the maximum zoomed aperture, and you shouldn't have to worry about it changing on you if you change the zoom settings.


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Old May 24, 2007, 9:49 AM   #7
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NHL wrote:
Quote:
tjsnaps wrote:
Quote:
It's not that big of a deal you just have to remember to adjust when you zoom.
How?

The focal lenght does not show in the viewfinder... so you have to move the camera away and down to look at the focal lenght in the mean time the subject has moved or change position while you're composing using the various zoom settings.

Unless you limit yourself to the zoom two extremes (and know exactly how many stops to compensate for), but in the middle range it's a total guess - Correct?
Oh come on!! you mean you don't know your own lenses better than that? To start with their is usualy ony a one stop veriance from one end to the other
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Old May 24, 2007, 9:56 AM   #8
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squirl033 wrote:
Quote:
seems to me this is only an issue if you're shooting wide open. if you stop down even on stop, the lens will stay where you put it. and in most cases, that's enough to deal with the problem, since most variable lenses only change by one stop between wide and telephoto. some vary more, like my Tamron 24-135, which is a 3.5-5.6; but still, stop down to the maximum zoomed aperture, and you shouldn't have to worry about it changing on you if you change the zoom settings.

Actually that's not how it works. The F stop is determined by the aperture size in relation to the focal length. That's why these lenses are cheaper. Their is no mechanism to change the aperture size as you zoom. Therefore the marked f stop on the lens is only accurate at the widest setting.

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Old May 24, 2007, 11:28 AM   #9
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tjsnaps wrote:
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Oh come on!! you mean you don't know your own lenses better than that? To start with their is usualy ony a one stop veriance from one end to the other
As you already know from your explanation the f-stop is a ratio so the larger the focal lenght span the larger this aperture variance will be - A Sigma 18-200 for example has more than a 1-stop variance
-> f/3.5 to f/6.3

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Old May 24, 2007, 12:12 PM   #10
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NHL wrote:
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As you already know from your explanation the f-stop is a ratio so the larger the focal lenght span the larger this aperture variance will be - A Sigma 18-200 for example has more than a 1-stop variance
-> f/3.5 to f/6.3
And to Squirrel's point. If you're using manual and set aperture value to 6.3 you can zoom in/out and exposure will remain unchanged.
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