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Old Jan 17, 2010, 11:33 AM   #1
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Default f stop confused

ok guys i got the lens kit with xsi 18-55mm lens f/3.5-5.6.....why is it i cant go under the 3,5 f stop setting but i can over the 5.6 setting ..isnt the lens limited to thoughs settings ??very confused here...
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Old Jan 17, 2010, 11:50 AM   #2
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The apertures in the specs for your lens are a maximum aperture of f/3.5 at a focal length of 18mm, and a maximum aperture of f/5.6 at a focal length of 55mm. You can get smaller apertures, but not larger ones, and the largest changes depending on the focal length.

The maximum aperture of Canon's 18-55 IS kit lens is f/3.5 at 18mm, f/4.0 at 24mm, f4.5 at 35mm, and finally, f/5.6 at 55mm.
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Old Jan 17, 2010, 1:57 PM   #3
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In case TCav's post seems to be backwards, the smaller the number, the more light the lens can let in. F numbers indicate how much light a lens can let in, and so they always quote the most it is capable of (being a very important indicator of a lens's capability). It's actually a ratio with the "F" standing in for focal length. It's very difficult to keep the same ratio on a zoom lens, so they are often stated as the range the lens is capable of - which is what TCav stated.
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Old Jan 17, 2010, 5:22 PM   #4
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One more post on the subject found with a quick search:

http://forums.steves-digicams.com/ne...tml#post803221
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Old Jan 17, 2010, 5:37 PM   #5
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ok guys i think ive got it...i think i was thinkin backwards on this ...any aperture can close all the way but limited on the opening right???? like Tcav said .at 55mm biggest it will go is 5.6 ...ok i got it ..lol...thanks alot guys im sure ill have lots more for ya later on...
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Old Jan 17, 2010, 7:32 PM   #6
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Quote:
Originally Posted by mtngal View Post
In case TCav's post seems to be backwards, the smaller the number, the more light the lens can let in. F numbers indicate how much light a lens can let in, and so they always quote the most it is capable of (being a very important indicator of a lens's capability). It's actually a ratio with the "F" standing in for focal length. It's very difficult to keep the same ratio on a zoom lens, so they are often stated as the range the lens is capable of - which is what TCav stated.
Sheesh! You would think at this late date we could rename this stuff so that's its intuitive. More of the arcane BS that every trade has, and should be trashed...

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Old Jan 17, 2010, 7:35 PM   #7
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Chato,

It is to ingrain in the craft, it will never change.
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Old Jan 17, 2010, 8:14 PM   #8
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Technical jargon is the reason for participating in a technical endeavor. Why else would we do this if not for all the fancy words that the unwashed masses don't understand?
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Old Jan 17, 2010, 8:25 PM   #9
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Quote:
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Technical jargon is the reason for participating in a technical endeavor. Why else would we do this if not for all the fancy words that the unwashed masses don't understand?
I dunno? Maybe beginners would understand this stuff immediately?

And another thing that annoys me is that, what's "order" of f-stops? You would think that f2 would be half the light of f1, which it ain't. Sort of like the Richeter(?) scale in earthquakes, where each increase in numbers is DOUBLE the previous one, so that you never know what the hell their talking about.

If more people cursed and insulted the people who keep using these kinds of technalise (which, come on, have NO PURPOSE AT ALL) maybe we would all be better off.

(This rant is NOT directed at you... )

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Old Jan 17, 2010, 8:26 PM   #10
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Quote:
Originally Posted by TCav View Post
Technical jargon is the reason for participating in a technical endeavor. Why else would we do this if not for all the fancy words that the unwashed masses don't understand?
Shucks, I do it for the fame, fortune and government grants.

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