Lense F stop confusion

[sbp]

using lense 24-105/F4.0 If I shoot F10 Does it really Shoot F10? or something else goes with it?

Thanks

[Holly]

If you are in Manual or AV mode and set the f-stop to 10....then it will shoot it at 10. The lense capability of 4.0 just indicates that it is able to go down to an f-stop of 4.0.

It can always go higher than what the lense indicates, never lower.

[Shane]

If I understand your questions correctly . . .

Yes, if you set your camera to F10, it means it will shoot F10.

The F 4.0 in your lens name is the lowest it will go, not what it shoots all the time.

[Shane]

Arghhhhhhh... Holly beat me by a few seconds! ;-)

[Holly]

Gotta be faster than that Shane. :)

[JohnT]

Also, the f/4 indicates that it is a "constant" f/4, meaning that you can shoot at f/4 within the entire zoom range of the lens. You probably already knew that.

[sbp]

yes john that is why I got question. I read that it is constant F4.0 for full range, then I thought then how would I shoot higher F stop.
Now it make sense that I can go higher but not lower.

Thanks all.

[Gordon]

The constant F4.0 means that it is an F4 or slower at 24mm and F4 or slower at 105mm (and anything in between)


Often cheaper lenses would be F4 at 24mm and F5.6 at 105mm (i.e., when you zoom in, you can't use as fast an aperture.

The confusing reason for that, is that the constant F stop lenses actually have a variable aperture as you zoom (which is trickier and more expensive to make)
The cheaper lenses, with a variable F stop, actually have a fixed opening, that stays the same size as you zoom.

This is because F stop is related to focal length - so the actual hole has to change as the focal length changes, to keep a constant F stop.

[CaptainTom]

Originally Posted by Gordon

The constant F4.0 means that it is an F4 or slower at 24mm and F4 or slower at 105mm (and anything in between)


Often cheaper lenses would be F4 at 24mm and F5.6 at 105mm (i.e., when you zoom in, you can't use as fast an aperture.

The confusing reason for that, is that the constant F stop lenses actually have a variable aperture as you zoom (which is trickier and more expensive to make)
The cheaper lenses, with a variable F stop, actually have a fixed opening, that stays the same size as you zoom.

This is because F stop is related to focal length - so the actual hole has to change as the focal length changes, to keep a constant F stop.

Good explanation of variable f-stop zooms. But, I am uncomfortable with reference to "slow/fast" when discussing aperture......

[sbug_adam]

pretty easy.. the higher the F-stop (lower number F5.6, F4, F2.8 etc..) the faster your shutter speed

the lower the F-stop (higher number F11, F22, F64, etc..) the slower the shutter speed.

which is why a 70-200mm 2.8L is a boat load more money than a 70-200 F3.5-F5.6

adam

[CaptainTom]

Light does not act like a water hose. The more you close the opening on a water hose , the faster the water comes out. Close the aperture on a camera and the light does not go in "faster". The shutter is what would be "slow or fast".
I understand what you are saying, but it is my opinion that it is incorrect to use fast and slow when discussing aperture. Hence, a 1.4 lens should not (although it is widely used)be referred to as a "fast" lens. I guess it's kind of like saying nucular when the word is nuclear. If it's used incorrectly enough it becomes correct......... but you will never here me say nucular.

[Collins]

Point taken, and I agree; it seems just seems to be a convention that stuck for whatever reason. It's also possibly easier/cooler/more convenient to say "fast lens" versus "large aperture lens"

[sbug_adam]

i dont see how its wrong.. smaller the number the FASTER shutter speeds you can use..

adam

[RandySmith]

I had my f2.8 lens mounted, this shot was taken last night at f11, for 30-SECONDS ! ! Of course it was just about dark thirty though (I couldn't resist the light and shadows on the silo's and barns).... but I suppose I could have opened the aperture for a shallower DOF to "speed" up the lens to a 2 second exposure ...... heh, heh .... I tend to think of lenses in more of what will be my minimum or maximum DOF, depending on what I want to do. The only time it becomescritical for me is when I'm shooting sports at nighttime and I need to have the aperture wide open, with a shutter speed that will allow for minimal bluring due to camera shake.

Randy

[Gordon]

Originally Posted by sbug_adam

i dont see how its wrong.. smaller the number the FASTER shutter speeds you can use..

adam

Exactly. Similarly, fast film is used to describe high ISO film, that again lets a faster shutter speed be used than if a slower film was used.

A fast lens allows faster shutter speeds to be used in the same available light, than with a slower lens. This is due to the max aperture size, so a larger aperture is a faster lens - reciprocity rules ;)