08-15-2015 06:18 AM - edited 08-15-2015 06:18 AM
I'm having a strange issue if anyone has any input. I am using the EF-S 18-55mm 3.5-5.6 IS STM lens on a Rebel SL1, and it doesn't seem to allow me to go wider than 4.5. I took the lens off and put it back on, and managed to get it to 3.5 for a few seconds before it went back to 4.5 as the widest. Is the lens broken, or is there something I'm missing?
I tried some of my other lenses on the camera and didn't have this problem.
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08-16-2015 12:55 AM
The name on the lens always lists the lenses lowest possible aperture. But for many zoom lenses, the lowest possible aperture varies depending on the focal length you selected and that's why your lens (the EF-S 18-55mm f/3.5-5.6 IS STM) has the "lowest possible aperture" listed as a range instead of a single value.
The lowest value you see in that range is only attainable at the widest possible focal length (the 18mm end). As soon as you zoom in -- even a tiny bit -- it'll drop to f/4 and will keep increasing. When you are about halfway through the zoom range, it'll eventually make it to f/5.6.
There are zoom lenses that are able to provide a constant focal ratio (they do not vary as you zoom in) but these tend to be fairly expensive lenses. For example, the Canon EF-S 17-55mm f/2.8 IS USM can provdie a focal ratio of f/2.8 at any focal length in its range.