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Thread: apeture and its effect on sharpness

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    Member mickeymoo21's Avatar
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    apeture and its effect on sharpness

    I just got shown this very interesting artical by Ken Rockwell about the use of apeture and its effect on sharpness, where a smaller apeture produces a sharper image and that an apeture of f8 or wider should be used for maximum sharpness unless depth of field is absolutely necessary.
    I don't know if other people know about this already (I may just be lacking in knowledge ) but thought I'd share and see what peoples thoughts were.

    Here is the artical:
    http://kenrockwell.com/tech/unsharp.htm

    And here is another artical from someone else:
    http://www.cambridgeincolour.com/tutori ... graphy.htm

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    I went to the first link, had a brief read then at the bottom in the summary section he said this

    4.) Did you shoot at f/8 or larger? Shoot at f/16 or smaller and you're guaranteed a softer image.
    Now, does f/8 or larger mean; f/9 f/10 f/11 etc. Or is it reversed? f/7 f/6..
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    Have a look at his sample pictures. F8 was much sharper then F32.

    But that being said, this guy is the worse pixel peeper I have ever read about....I'm not sure what to take from that article

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    Administrator ricktas's Avatar
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    I am not a big fan of Ken, but i have found that for some lenses this is true. Shooting wide-angle, i will generally use F11-F14 as i have found that with MY lens its sharper at those apertures than at F22.

    Personally i think its a characteristic of each Lens. It is well known that certain lenses are sharpest at certain apertures, and i think Ken has just used that to create an article that extends the idea.

    Spose as long as people read his articles and go out and test the ideas he presents, and use them to get better results, its all good, but really he hasnt come up with something new here, just re-hashed something thats been known for a damn long time.
    "It is one thing to make a picture of what a person looks like, it is another thing to make a portrait of who they are" - Paul Caponigro

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    Yes, I think you have nailed that on the head Rick. Each lens has a sweet spot, I suppose its determining what that is is the challange

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    I must say these days I tend to view Ken Rockwells comments with some reservations.

    And as has been said already it depends on the lens or lens/camera combination, my Tokina 17mm ultra wide is best at around f18 or more, it seems to be a characteristic of this particular lens only, whereas for example my Nikon 80-200 is pretty much equally sharp at both ends of the scale.

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    The sweet spots take a while to find cause every lens is different but once you have found em its well......sweet.
    If at first you dont Succeed........Then Skydiving is not for you.



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    Member cwphoto's Avatar
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    Depends on the lens. Most lenses get soft from about f/11 onwards on common DSLRs due to diffraction.

    At the other end of the scale lenses are usually relatively soft at or near the maximum aperture too.

    A general rule of thumb is 2-3 stops from wide-open is the sweet spot.

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    Member TheAlfheim's Avatar
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    Quote Originally Posted by cwphoto View Post
    Depends on the lens. Most lenses get soft from about f/11 onwards on common DSLRs due to diffraction.

    At the other end of the scale lenses are usually relatively soft at or near the maximum aperture too.

    A general rule of thumb is 2-3 stops from wide-open is the sweet spot.
    Very well said.

    Stopping down further and further does not yield sharper and sharper images. There becomes a point where sharpness loss due to diffraction is unacceptable.

    Generally speaking, f/8 is a good spot for most lenses. Few benefit from stopping down beyond this point (but they dont lose quality until diffraction becomes a problem, either).

    And for those interested: The difference between standard and high quality (Canon's L) lenses is that the high quality lenses retain sharpness away from this f/8 mark - sometimes even including wide open.

    -Andrew

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    HERE'S a nice easy to understand site on the diffraction limitating effects of your aperture.

    About 2/3rds of the way down he has and easy to see/use roll over image of the effects of apertures between f/8-f/22.
    Of course each lens seems to have varying abilities at the same aperture, and as a rule a macro is usually better at say f/16 than a non macro lens will be(check out the general outcome of most lenses on Photozone to see what I mean!)

    As a rule, if I'm focusing at a distance I'll use f5.6-8, if I'm focusing closer, say 2 meters or so, I'll try up to f/11... Sometimes I'll focus at 30cm or so, and want lots of DOF, so there is no option other than f/22 or so.

    Remember that OOF areas are a relative concept. While the image may be affected by diffraction at smaller apertures, it's still going to be 'sharper(overall)' than it otherwise would be with a larger aperture.

    ps. if diffraction is your main concern, and ultimate resolution is your number one priority, then a view camera is your only solution!
    The larger the format, the less the amount diffraction you'll get at smaller apertures
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  11. #11
    avian
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    Quote Originally Posted by mickeymoo21 View Post
    I just got shown this very interesting artical by Ken Rockwell about
    This gump is one of the biggest tossers in cyberspace.

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