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03-26-2010, 06:31 AM   #1
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Question about ebay lens descriptions

I see a lot of lenses with a designation like 1:2 or 1:2.8

These are Manual and NOT zoom lenses.

I'm sure it has something to do with f stop, but since they're not zooms I don't know why there would be different f-stops at the low end?



03-26-2010, 06:34 AM   #2
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Lenses come with different maximum apertures (yes F stops), the widest you can open them, but still have the same focal lens (50mm, etc.)

Be careful and look at the photos of the item to confirm, because a 1:2 is a lot different than 1:1.2

And the seller doesn't always type it correctly.

The 1:2 has a maximum aperture of F2, which isn't a big deal.

A 1:1.2 has a maximum aperture of F1.2, and that IS a big deal.
03-26-2010, 08:32 AM   #3
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F-stop is a ratio. One way of expressing ratios is x:y. So 1:2 is the same as f/2, and 1:2.8 is the same as f/2.8.

They're just replacing "f/" (where f=focal length) with 1 and using the : notation.
03-26-2010, 09:33 AM   #4
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Yup, f-stops are ratios, the ratio of the diameter of the aperture opening to the focal length of the lens. So at f/2, the opening is half the focal length, at f/4 it's a quarter the focal length, etc. When a lens is described as being of a certain f-stop, that means it's the LARGEST opening available on that lens -- it's wide-open. The larger the opening (the smaller the f-stop number), the better, USUALLY. A smaller f-stop number means the lens is faster, can shoot in less light, and that is prized. But some lenses are real dogs when wide-open. That's when you see complaints here about a lens being soft, not crisp and sharp. But many of the ~50mm manual primes are quite sharp when closed down just one f-stop.

And as mentioned above, anything at f/1.2 is prized, and expensive. But some sellers are, shall we say, sloppy in their descriptions. Be sure you can see a picture of the lens front, where you can read the lensmaker's inscription. If it says 1:2, that means f/2, and that ain't special. If it says 1:1.2, that IS special.


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