Sigma 24-70mm f /2.8 on D7000

[Dirk]

Originally Posted by Freezframe_2

What is meant by constant aperture is that the range is 2.8 only compared to some other lenses having a range of 5.6,4.0,2.8!

Brady

+2
indeed that is what i meant . because when a lens is f 2.8 constant the lens glass it self and the internal lenses will have to be cut more precisely than with a lens of variable aperature like 3.5-6.4

[KikiD]

I still don't get it. The term constant seems very strange to me and have never heard it used before. A 2.8 lens is just faster than a 5.6 or slower than 1.4 not constant well thats my persovnal opinion, would love to hear others chime in with their opinion ... Thanks!

[KikiD]

Oh i think i get it now, sorry i'm a bit slower ... Your strictly speaking of "zooms" where the apeture is variable on the one end .. Sorry my bad ....

[Dirk]

Originally Posted by KikiD

Oh i think i get it now, sorry i'm a bit slower ... Your strictly speaking of "zooms" where the apeture is variable on the one end .. Sorry my bad ....

yes that's right and the lens we are talking about here is a zoomlens , not a prime !

[Steven G Webb]

Originally Posted by Freezframe_2

What is meant by constant aperture is that the range is 2.8 only compared to some other lenses having a range of 5.6,4.0,2.8!

Brady

And the reason a constant aperture lens is preferable is the widest aperture is available through the full range of focal lengths. Not only is that a plus for exposures in low light, and in keeping a shallow depth-of-field but it aides in focusing in low light. A lens focuses at its most open aperture, when a variable aperture lens is zoomed, that aperture stops down reducing the amount of light passing through for focusing.

[KikiD]

Originally Posted by Dirk

yes that's right and the lens we are talking about here is a zoomlens , not a prime !

Yes I understand I said it was my bad - I misinterpreted "constant"

[KikiD]

Originally Posted by Songman45

And the reason a constant aperture lens is preferable is the widest aperture is available through the full range of focal lengths. Not only is that a plus for exposures in low light, and in keeping a shallow depth-of-field but it aides in focusing in low light. A lens focuses at its most open aperture, when a variable aperture lens is zoomed, that aperture stops down reducing the amount of light passing through for focusing.

Yes I understand I said it was my bad - I misinterpreted "constant"

[raghunath]

I can only speak for the Nikkor 24-85mm f/2.8-4 on my D7000. I bought this lens after much research and agonizing over alternatives. I am thoroughly happy with its sharpness, very low CA and a really beautiful buttery bokeh specially at focal lengths over 50mm.

I would have loved a constant f/2.8 but can't afford it!