Lens aperture values

Discussion in 'Photography Beginners' Forum' started by hightower, Feb 27, 2010.

  1. hightower

    hightower TPF Noob!

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    Hi, I am having a hard time understanding a concept even after doing searches on here and on the internet. So my kit lens is f/3.5-5.6 and at certain focal lengths I can get it opened up to f/3.5. However I am curious as to why I can stop it all the way down to f/22 or greater even though the lens indicates 3.5-5.6. Does that range only refer to how much you can open it up at its respective focal lengths (18-55mm)? In other words is that range just indicating the lowest (biggest aperture) end of things and not the upper? If that is true, is it safe then to assume that all lenses can stop down to the greater numbers like f/22 or greater? Does the camera body play into any of this? Thank you!
     
  2. hower610

    hower610 TPF Noob!

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    f3.5 is the largest aperture at 18mm and 5.6 is the largest aperture at 55mm.
     
  3. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    Yes you have it right - the aperture values listed on the lens are the maximum apertures (smallest f numbers) that the lens can achive. Your zoom lens has two because of the variable max aperture as it zooms - there are zooms which have a single aperture and thus can keep that from their short through to their long end.
    I belive if you experiment with your lens the minimum aperture also changes depending on the focal length

    The minimum aperture (biggest f number) is the sort of thing you have to look for on the lens makers website or other spec sheet refrences. Mostly this is a less limiting side provided the lens can make it down to around f22 and most lenses that I know of in modern production can make it to f22. Some can go far further though I have to say honestly that I've never shot below f16. This is because of an effect called diffraction which starts to take effect around f16 (it varies depending on the lens and camera body used) and which causes the image to be softer. On the net its pretty hard to notice, but printing and fullsized its far more noticable.
     
  4. djacobox372

    djacobox372 No longer a newbie, moving up!

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    You're correct... although some lenses will only stop down to f16, and some will stop down all the way up to f64.

    What's important to most people when purchasing the lens is how wide it will open up--it's assumed that it will be able to be stopped down so that part is not typically part of the lens labeling.
     
  5. hightower

    hightower TPF Noob!

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    Thank you for all the input, just typing up the original post helped me think it through a little, thanks for the confirmation :mrgreen:
     

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