Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,963   Posts: 1,558,371   Online: 799
      
Page 1 of 4 1234 LastLast
Results 1 to 10 of 39
  1. #1
    EASmithV's Avatar
    Join Date
    Aug 2008
    Location
    Maryland
    Shooter
    Multi Format
    Posts
    1,877
    Blog Entries
    4
    Images
    123

    Determining optimum aperture?

    How do I do it? I want to get the optimum aperature at infinity of a fujinon-w 300mm f5.6, a nikkor-s 50mm f1.4, and an ektar 152mm f4.5
    www.EASmithV.com

    "The camera is an instrument that teaches people how to see without a camera."— Dorothea Lange
    http://www.flickr.com/easmithv/
    RIP Kodachrome

  2. #2
    Dan Henderson's Avatar
    Join Date
    Feb 2005
    Location
    Blue Ridge, Virginia, USA
    Shooter
    4x5 Format
    Posts
    1,891
    Images
    241
    my understanding is that most lenses are optimum at 2 to 3 stops down from wide open. Several years ago I did a test of photographing a highly detailed subject at all apertures of my favorite lens, the 150 mm lens of my Hasselblad kit. Wide open (f/4) was markedly worse, improving as I stopped down until f/22, when sharpness began to degrade again. So, at least for me with this lens, f/8, f/11, and f/16 give great sharpness and I try very hard to use one of those apertures. Above and below that things are not as good. Wide open and fully closed are inferior.


    web site: Dan Henderson, Photographer.com

    blog: https://danhendersonphotographer.wordpress.com/

    I am not anti-digital. I am pro-film.

  3. #3
    BetterSense's Avatar
    Join Date
    Aug 2008
    Location
    North Carolina
    Shooter
    35mm
    Posts
    2,878
    I always just use the smallest one. Since you get more depth of field, overall sharpness is improved greatly over larger apertures.
    f/22 and be there.

  4. #4
    keithwms's Avatar
    Join Date
    Oct 2006
    Location
    Charlottesville, Virginia
    Shooter
    Multi Format
    Posts
    6,079
    Blog Entries
    20
    Images
    129
    It's not an easy question to answer because lens resolution certainly isn't constant across the frame- not even close. So stopping down affects the resolution in different ways across the frame... smaller apertures tend to lift edge resolution up to its maximum (basically, by making use of the best-corrected, centralmost portion of the lens), while also bringing center resolution down via diffraction softening. This effect is seen quite nicely in the lens test applets at dpreview (disclaimer: it's a site catering to digital gear... but they do an exceptional job in presenting their lens test data and it makes my point in a tidy visual way). Compare the center and corner performance at f/8, f/11 and f/16 in the link.

    With view cameras, the matter is further complicated because we use tilts and shifts, so that the central portion of the lens doesn't necessarily correspond to the central portion of the film. Furthermore, we sometimes stop way down in LF just to maximize the coverage. Actually, that is usually my biggest concern when using ultrawide lenses in LF... actual resolution figures are hardly a consideration when you're worrying about image circle!

    Anyway, best resolution with LF lenses ... on average, across the frame ... is usually had at f/11 or so. What do you do with this information? Well, what I often do is focus wide open, do my movements, refocus, get a sense of the DOF required by the scene, and stop down only as just much as I need... or maybe a stop further. In other words I simply let the scene determine how I stop down, while also keeping f/11 in the back of my head.

    If I feel like I want the most consistent level of resolution across the frame (e.g. for some macro subjects or for reproduction) then I will tend to stop down further.... going to f/45 or f/64 is fine if that's what you're after, and of course the other major issue is how much you will enlarge the negative. If you are dealing with an LF negative that will be contact printed or barely enlarged then you can stop down with virtual impunity. It's a very different story with 35mm, of course, for which the enlargement factors are typically much larger.

    But I think the bottom line is to let artistic vision guide your aperture decisions, not a chart
    "Only dead fish follow the stream"

    [APUG Portfolio] [APUG Blog] [Website]

  5. #5

    Join Date
    Apr 2008
    Location
    Los Angeles, CA
    Shooter
    Multi Format
    Posts
    8,021
    Images
    4
    I like this explanation: http://www.kenrockwell.com/tech/focus.htm. In short, it is different for each image. It depends on the image depth. Once you know the image depth, you throw it into this formula: f/optimum = square root of (375 x image depth in mm).
    Last edited by 2F/2F; 08-11-2009 at 10:03 PM. Click to view previous post history.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

    - Rob Tyner (1944 - 1991)

  6. #6

    Join Date
    Aug 2008
    Location
    North Carolina
    Shooter
    Multi Format
    Posts
    513
    Quote Originally Posted by BetterSense View Post
    I always just use the smallest one. Since you get more depth of field, overall sharpness is improved greatly over larger apertures.
    That's not necessarily true. You'll actually lose sharpness at higher apertures due to diffraction.

    You DO get more DOF, but overall sharpness is not higher.

    The way to get the most DOF is to stop down to say f/16 or f/11, and use your distance scale to put the markers between infinity and the lowest number. I believe it's called hyperfocal distance.

  7. #7
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,297
    For most pictoral photograpy, optiumum aperture depends on just two things, (1)your acceptable circle of confusion size, and (2) the focal spead between the near and far points that need to be sharp in the resultant picture. There is a lot of math involed but a simple chart will show you the aperture based on focal spread. http://www.largeformatphotography.info/fstop.html (Same thing that 2F/2F mentioned)

    If you are taking pictures of flat objects, then you will be using larger apertures (to minimize diffraction) and lens abberations that limit edge sharpness will come into play. To determine the optimum aperture under these conditions you need to look at the MTF (modular transfer function) chart or a lens resolution chart for your lens. http://www.schneiderkreuznach.com/fo...R44907_2AE.pdf
    Last edited by ic-racer; 08-11-2009 at 09:46 PM. Click to view previous post history.

  8. #8
    BetterSense's Avatar
    Join Date
    Aug 2008
    Location
    North Carolina
    Shooter
    35mm
    Posts
    2,878
    You DO get more DOF, but overall sharpness is not higher.
    I was making the point that although absolute focus in the focal plane itself may be optimal at some moderate aperture, the greater DOF of smaller apertures can result in a sharper final images because more of the image will be in focus. That's my philosophy anyway...F/22 and be there.
    f/22 and be there.

  9. #9

    Join Date
    Apr 2008
    Location
    Los Angeles, CA
    Shooter
    Multi Format
    Posts
    8,021
    Images
    4
    Quote Originally Posted by BetterSense View Post
    I was making the point that although absolute focus in the focal plane itself may be optimal at some moderate aperture, the greater DOF of smaller apertures can result in a sharper final images because more of the image will be in focus. That's my philosophy anyway...F/22 and be there.
    You get more depth of field (meaning more on either side of the plane of critical focus that appears just as acceptably sharp as the plane itself), but the plane of critical focus is not as sharp as it could be.

    Practically speaking, f/22 is not a problem, except perhaps in super wide lenses. However, f/45, f/64, etc. are not worth the extra depth of field they bring when using a view camera, unless your camera does not allow any tilt or swing, and you are making tiny prints (meaning contact prints, basically). You can just use your optimum aperture, and tilt and/or swing to get what you want sharp.

    If you like the effects of diffraction, which you very well may, by all means, use them...but at least understand that they are there.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

    - Rob Tyner (1944 - 1991)

  10. #10

    Join Date
    Jul 2007
    Location
    Netherlands
    Shooter
    Medium Format
    Posts
    5,686
    I think the inclusion of DOF as a thing that bears considering is not very helpful.
    DOF is acceptable unsharpness, and is hardly a measure for optimum lens performance.

    What also should not be forgotten is that diffraction always reduces what a lens can do, even at larger apertures.
    Many lenses are limited by residual aberrations wide open, and the beneficial effect of stopping down will be greater than the limiting effect of diffraction. When you find the point that both aberrations and diffraction are equally bad, you have found the optimum aperture.

    You have to run tests to find it. Each lens design is different, and graphs only show so much. So test.


    Now if you think it worth, practically speaking, to stop a lens down to its optimum aperture, you should also not want to stop it down any further.
    So forget about DOF.

    Stopping down to f/22 (or whatever the smallest aperture is) is a way that is guaranteed to not get the best out of your lens, ever.
    The effect of diffraction is quite large: possible resolution is halved (!) about every two stops the lens is stopped down.
    DOF calculators are all wrong. One big fault they have is that they do not take this overall image degradation that stopping down causes into account, which makes the difference between 'sharp' and not sharp much smaller, hence DOF much larger, than the formulae suggest.
    So you do get huge DOF. But never "sharper final images". Never that what you paid for when you bought the lens, never what it is capable of.

    f/22, and miss out.

Page 1 of 4 1234 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin