Can somebody please explain these lens numbers?

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Hiekel Essterol

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I know its a really stupid question, but Im really stupid.

I have a Canon EF-S 18-55mm f/3.5-5.6 IS lens.

I know that the IS means it has image stabilization.
I know that the 18-55mm is the length range of the lens.
Its the f/3.5-5.6 bit Im confused by. Im thought this would refer to F Stop, but why are there 2 numbers? It can't be the range as it goes from F5.6 to F36.

Can someone shed some light please?
 
At 18mm the max aperture will be f/3.5 and at 55mm the max aperture will be f/5.6
 
Hiekel Essterol said:
I know its a really stupid question, but Im really stupid.

I have a Canon EF-S 18-55mm f/3.5-5.6 IS lens.

I know that the IS means it has image stabilization.
I know that the 18-55mm is the length range of the lens.
Its the f/3.5-5.6 bit Im confused by. Im thought this would refer to F Stop, but why are there 2 numbers? It can't be the range as it goes from F5.6 to F36.

Can someone shed some light please?
Click to expand...

Maximum aperture at 18mm is f 3.5 & maximum aperture at 55mm is f5.6
 
It's the maximum aperture for the lens range i.e.

at 18mm the aperture can be set to a maximum of f/3.5

at 55mm the aperture can be set to a maximum of f/5.6

Does that help?

.DAVID.
 
3 answers in less than a minute - now that's impressive lol

.DAVID.
 
Very much appreciated all of you. Thanks a lot for helping explain it. Makes sense now. Told you it was a stupid question :-D
 
Perhaps not the best link but was the first I came across and it explains better than I possibly can:

http://www.curvygirlguide.com/tech/what-do-the-numbers-on-the-lens-mean/

Quote from the above link:

"The numbers represented by a ratio indicate the widest aperture available for the lens. An aperture range of 1:3.5–5.6 means that the lens can stop down to 3.5 at the widest end of the lens’ focal length—18 mm in this example and f/5.6 at the longest end of the lens’ focal length—55 mm"
 
Aperture numbers are a ratio of focal length/aperture diameter. So 1:3.5 will give you the aperture diameter as a ratio of the focal length.

That's why bigger numbers equal smaller holes and vice versa.
 
Hiekel Essterol said:
I know its a really stupid question, but Im really stupid.

I have a Canon EF-S 18-55mm f/3.5-5.6 IS lens.

I know that the IS means it has image stabilization.
I know that the 18-55mm is the length range of the lens.
Its the f/3.5-5.6 bit Im confused by. Im thought this would refer to F Stop, but why are there 2 numbers? It can't be the range as it goes from F5.6 to F36.

Can someone shed some light please?
Click to expand...

Further to the other answers, if you put the camera in Av mode, and with the lens at 18mm, set the aperture to f3.5. If you zoom into 55mm, you will see the aperture setting on the camera change. Assuming you have the camera set to 1/3 stop increments, it will display f3.5, then f4.0, f4.5, f5.0 and finally f5.6
 
Some lenses (like most canon L lenses) are able to retain the same aperture throughout the entire focal length range too - for example Canon 24-70 f/2.8L
 
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