I see these on lenses
1:2.8, 1:4.5, 1:3-5.6 e.t.c

what do they mean?

That is the maximum aperture of the lens. How much light it lets in, or more accurately how much the light is reduced by the optical elements in the lens. The lower the number the better quality the lens.

It has quite a few different features...

The lower the number:

-the brighter the viewfinder as more light reaches it.
-the more pictures you can take in low ambient lighting, like indoors or in the evening.
-the easier/faster the camera will autofocus (probably meters faster too).
-the shallower the depth of field can be.
-the more expensive the lens.

Anything F2.8 (1:2.8) or lower is considered professional. Canon has been the only company to produce a 1:1 lens, a 50mm. It cost several thousands of dollars where you can get a Canon 50mm 1.8 lens for less than $100.

hope that helps.

:)

hmm....
ok, from my understanding,

the ratio is actually the minimum aperture setting of the lens.
e.g, if lowest aperture is 2.8, then ratio will be 1:2.8 e.t.c

thx

p.s a 1:1, yeh, just met someone who told me we can't get those lens below f(2)locally....
too few people actually buy those. :p

Just so you know f/2.8 would be the highest aperture.
And, let's say f/4, would be lowest ... see how it's all nice and backwards :)

oh, yeh.....
thx nemesis..........

Actually most of the lenses under F2 aren't "that" expensive.

The 50mm F1.8 is under $100
The 50mm F1.4 is around $400
The 85mm F1.8 is around $300

Generally the wider or longer you go from 50mm the more expensive the lens is. So a 20mm F2.8 and a 200mm F2.8 could be the same price (in the thousands).

:)