Seeking clarification on Aperture Values on Rebel

[csondagar]

If a lens is marked 18mm-55mm f3.5-f5.6, and the Rebel Aperture Value range is f1.0-f91 then does it mean that with 18mm I can use AV from f3.5 to f91? And with 55mm (zoomed) I can use AV from f5.6 to f91?

[CyberDyneSystems]

... Well yes and no..

It turns out that "aperture value" is a different number entirely from the "f/stop" which are the numbers we are familiar with.. like f/3.4 - f/5.6... I doubt that there is a lens that will stop down to "f/91"

You will get the lenses full f/stop range though.. starting at the widest f/3.5-f/5.6... you would need to look up the lens info to see how far you can stop it down..

Hope this helps.

[Calis]

I've got mine in my hand now and the EF-S 18-55 will stop down to f/29

[arumdevil]

... Well yes and no..

It turns out that "aperture value" is a different number entirely from the "f/stop" which are the numbers we are familiar with.

This is something I was not aware of before, but I noticed this in the exif data:

Exposure time: 1/4000 sec
F-Stop: 3.5

then farther down there is

Shutter Speed: 1/4000
Aperture Value: 3.6

So why are there two? and which one is the settings I made on the camera?

cheers,

[arumdevil]

Oh, and bye the way - the EFS 18-55 will stop down to 22 @ 18mm and 36 @ 55mm

[Calis]

Which would make sense, as I didn't think to check at different focal lengths and the f29 I got was at around 35mm.