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my sigma 50-500mm DG lens has range of f 4.5 - f 6.3, but in my Canon 70D camera I can still set fstop to 22 in manual mode. 1)How these two correlate? 2)Would a f22 setting in camera will have no impact when is lens at 50mm?
3)Can going upto f22 spoil the camera or the lens? or both?

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f/4.5 - f/6.3 is only the wide open aperture. It varies from f/4.5 at 50mm to f/6.3 at 500mm.

You can select f/8 or f/11 or f/22 anytime you want at any focal length. At 50mm you can select f/4.5 but if you zoom to 500mm, the aperture will automatically jump to f/6.3

No you can't hurt the lens by selecting f/22. It is designed to operate that way.

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  • Hi, thank you for the prompt reply. Yes I know the aperture varioes from when lens is set at 50mm to 500mm But if the lens is only built to have an aperture range from f/4.5 to f/6.3, how does setting aperture to f/22 help on the camera help? or does it help at all? – James Apr 28 '15 at 12:03
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    @James You'll find the answer to your question here. – Hugo Apr 28 '15 at 12:15
  • Generally all lenses get sharper as you "stop down" from the wide open f/stop. This rule gets over ridden by the fact that "diffraction" increases as you stop down and can cause some softness. This starts to become noticeable at about f/11 on crop cameras and f/16 on Full frame cameras. – Mike Sowsun Apr 28 '15 at 12:15
  • Ok. Thank you Mike. Hugo and DHall, I shall do a bit of reading on the links provided and try to do some field work and get back. – James Apr 28 '15 at 12:30
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The lens does have not an aperture range from f/4.5 to f/6.3. when apertures are quoted for lenses, it's just the widest/maximum that they can go, as this has a big impact on the performance of the lens. There's no restriction (within reason) as to how small they can go (f/22, f/32 etc).

With zoom lenses, it's normal that their maximum aperture will change depending on whether or not the lens is zoomed in or not, so f/4.5 to f/6.3 means max aperture of f/4.5 when zoomed out and a max of f/6.3 when zoomed in.

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