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lens f stops


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Those numbers (4.5 and 5.6) are just maximum apertures at the respective focal lenghts 80

and 200mm. It doesn't mean that the apertures can't be made smaller. <p>It's up to you to

dial in whatever aperture you need (up to the maximum available) to make the picture look

how you like it.

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Alice,

 

Your zoom is what is known as a "variable aperture" zoom. As others have noted, the widest aperture varies with focal length. This means that as you zoom, either you or the camera has to adjust exposure. If you use automatic exposure modes, the camera does it for you.

 

I recommend picking up a copy John Shaw's Closeups in Nature; his explanation of apertures and exposure in general is the best I've seen to date. I re-read it periodically. Even if nature photography isn't your cup of tea it still goes over the basics very well.

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I always think in terms of my 50mm 1.8 lens.

 

1.8 is the most open the lens can be - 22 is the most closed.

 

Most lenses close down to either 22 or 32. If this relationship doesn't make sense, think in terms of slicing pie. If you slice pie 1.8 times you get a lot of pie, slice 22 times and you don't get very much.

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Something I like to add that i did not see posted.

 

Yes it is f/4.5 at 80mm and its f/5.6 at 200mm however it dose not jump to f/5.6 right at 200mm. It slowly progresses as you zoom . Like for example it can go from f/4.5 at 80m, then at 100mm be f/5.0, then 120mm to 200mm be f/5.6. I don't know the specs of your lens you mentioned. But could be likely.

 

JT

 

If you know into photography and sick of reading plain text explanations, try <A HREF="http://www.canon.co.jp/Imaging/enjoydslr/">Canon's SLR introductory site</A>. They have good information for the beginner and its not all diagrams. (It may be Canon but it all carries accost the brands)

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