Aperture Setting

[frjeff]

A real newb here,.............trying to get away from AUTO on my new Rebel XT.

One of the lenses I am using is a Canon 28-135 f/3.5-5.6 IS.

If I want to use the Av mode setting (aperature priority), can I select a stop outside the range of 3.5-5.6? I really feel dumb and dumber here, but none of my books really explain those f/ markings on lenses.

What do they mean exactly?

Is there a "sweet spot" aperature on this and all other lenses? Somewhere in that range?

Your help is gratefully received.

Fr. Jeff

[Jim G]

Those markings you see are the widest f/stops you can set. At 28mm focal length you can set it between, say, 3.5 and f/22 (not sure about the top number, might be 32) and at 135mm you can set it between f/5.6 and f/22 (again, maybe f/32).

Edit: Oh, and the sweet stop is often a stop or two down from maximum aperture.. someone who's used that lens can comment on that though :)

[Naturalist]

One of the lenses I am using is a Canon 28-135 f/3.5-5.6 IS.

The 3.5-5.6 tells you what the maximum aperture values are at each end of your focal range.

At 28mm, the largest you can open up to is f/3.5.
At 135mm, the largest you can open up to is f/5.6.

When set at the aperture priority you can select any aperture you desire BUT will not be able to go any larger that what you lens was designed for.

As for the "sweet spot" I am not familiar with this lens.

[JeffreyG]

Usually lenses perform best when they are 1-2 stops down from their wide open position. So your lens is wide open at f/4 at 50mm. The lens will probably sharpen up a lot by f/5.6 and maybe a little more by f/8. I doubt f/11 would gain much and there is usually no light level where f/11 does not like a tripod in any case.

[frjeff]

Usually lenses perform best when they are 1-2 stops down from their wide open position. So your lens is wide open at f/4 at 50mm. The lens will probably sharpen up a lot by f/5.6 and maybe a little more by f/8. I doubt f/11 would gain much and there is usually no light level where f/11 does not like a tripod in any case.

JeffreyG - so, how do you determine the best performing f/stop at various focal lengths of any zoom lens?
Is there a graph/chart of some sort for each, or do I guess initially?

Thanks to all for the great feedback. I feel a bit more equipped to make somewhat more intelligent settings!

[Liveengineer]

Here is some info u might like in relation to your lens
http://www.photozone.de/8Reviews/lenses/canon_28135_3556_is/index.htm

[Jon, The Elder]

Fr. Jeff....

Use this site to get the info you want. It comes in real handy for situations like yours.

http://www.dofmaster.com/dofjs.html

My wife and I still use our 28-135's for walk around lenses. A very much underappreciated piece of glass. Wide open and at the extreme ends, it may not be as sharp.