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12-40 what f-stop?

Discussion in 'Native Lenses' started by mesmerized, Aug 23, 2016.

  1. mesmerized

    mesmerized Mu-43 Veteran

    344
    Jun 18, 2012
    Dear Users,

    I've been travelling in Japan lately and trying to take photos of this wonderful country. Most of the time I choose f/4 for landscapes as I've heard from another user on this forum that on a crop sensor it's enough for keeping the distant objects in focus. Usually, I see people go for f/8 or even f/11 for the sharpest result... What would be your advice?

    Thanks
     
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  2. yendikeno

    yendikeno Mu-43 Regular

    128
    Sep 5, 2015
    I have and use the 12-40 f2.8 lens. For landscapes I much prefer using f8 for most shots I take, and typically focus into the frame about one-third of the way. For me, this pretty much insures that all elements I want in focus will be in focus.
     
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  3. king_solom0n

    king_solom0n Mu-43 Regular

    60
    Jun 9, 2015
    I use anywhere from f4 to f8 depending on the situation. From my understanding, the sweet spot for a lot of micro four thirds lenses is f4 and diffraction kicks in around f11.
     
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  4. Clint

    Clint Mu-43 All-Pro

    Apr 22, 2013
    San Diego area, CA
    Clint
    I'll typically use f/5.6 up to about 30mm and then as the zoom progresses to 40mm start opening up to f/4.0, but then that all depends on what I want in sharp focus.

    I have used f/13 when at 17mm needing the extra depth of field to get something about 4' away in focus as well as 200' away.
     
  5. pwol

    pwol Mu-43 Regular

    66
    Apr 21, 2015
    CT
    According to Olympus M.ZUIKO Digital 12-40mm f/2.8 Pro Review - Sharpness 1 | PhotographyBLOG ...

    12mm: Centre sharpness is commendably high even wide open at f/2.8, with peak performance achieved at f/5.6. Diffraction kicks in at f/16 and gets worse at f/22. The corners are also very sharp at f/2.8, with the best performance again at f/5.6.

    18mm: Centre sharpness is commendably high even wide open at f/2.8, with peak performance achieved at f/5.6. Diffraction kicks in at f/16 and gets worse at f/22. The corners are also sharp at f/2.8, with the best performance again at f/5.6.

    25mm: Centre sharpness is commendably high even wide open at f/2.8, with peak performance achieved at f/5.6. Diffraction kicks in at f/16 and gets worse at f/22. The corners are a little soft at f/2.8, with the best performance achieved at f/5.6.

    40mm: Centre sharpness is OK wide open at f/2.8, but peak performance is achieved until f/8. Diffraction kicks in at f/16 and gets worse at f/22. The corners are soft at f/2.8-f/5.6, with the best performance achieved at f/8.
     
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  6. vm666

    vm666 Mu-43 Regular

    132
    Jan 19, 2013
    Paris
    This is a rule of thumb for full frame lenses. For MFT, you have to divide by two.
    You mileage may vary with the lens. It appears that the 12-40 is optimal at f/4-f5.6, but diffraction is never a big problem: Olympus 12-40mm f/2.8 Pro M.Zuiko Digital ED Review
     
  7. Replytoken

    Replytoken Mu-43 Hall of Famer

    May 7, 2012
    Puget Sound
    Ken
    In addition to the above advice, I would recommend spending some time here: Depth of Field Table . If you want to keep distant objects in focus, it helps to understand the DOF you have available to you.

    --Ken
     
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  8. oldracer

    oldracer Mu-43 All-Pro

    Oct 1, 2010
    USA
    I never heard that one.

    The issue is balancing two things: (1) As the physical aperture gets smaller and smaller, the image gets sharper. An infinitely small pinhole will in theory be the sharpest from a ray-tracing point of view. (2) As the physical aperture gets smaller and smaller, diffraction effects begin to deteriorate the image. So you are looking for a "sweet spot" where the reduced aperture improves the image but diffraction effects have not become serious enough to begin messing things up.

    The reason M43 sweet spots occur at larger f-stop openings/larger apertures numerically than for equivalent larger camera lenses is that the equivalent larger lens has a larger physical aperture at a given f-stop. For example at f11, a 25mm M43 lens (50mm equivalent) will have a smaller aperture than a 50mm FF lens (theoretically, half). So diffraction effects begin setting in sooner for M43. I have no idea whether using a 50% multiplier is the right number or not, but it's not completely out of the question.

    To the OP, the easiest thing is to do some testing. With the camera on a tripod put a resolution test target a reasonable distance away and see what you get at identical exposures using different f-stop settings. One of these: 1951 USAF resolution test chart - Wikipedia, the free encyclopedia printed on a good laser printer is probably good enough. Or you can go nuts: Resolution Test Targets - Resolution Test Target

    And, as @Clint@Clint points out, there are things like DOF and subject motion that drive aperture selection beyond just the optimum resolution question.
     
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  9. astrostl

    astrostl Mu-43 Veteran

    360
    Oct 4, 2014
    St. Louis, MO
    Justin Honold
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  10. dalto

    dalto Mu-43 Regular

    186
    Jul 6, 2016
    Texas
    +1 to this advice. Before you spend too much time thinking about diffraction and critical sharpness make sure you have a good grasp of DOF. Since DOF varies greatly with the distances involved there is not a single answer here for getting everything in focus.
     
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  11. vm666

    vm666 Mu-43 Regular

    132
    Jan 19, 2013
    Paris
    The F-stop value is the focal length divided by the diameter of the diaphragm.

    This explains why MFT lenses see diffraction at f/8 - f/11 instead of f/16 - f/22 for FF lenses.

    Why they are optimum at f/4 instead of f/8 is probably another story.
     
  12. Carbonman

    Carbonman Mu-43 All-Pro

    Jul 10, 2014
    Vancouver BC
    Graham
    I think the F-stop value is the focal length divided by the apparent diameter of the diaphragm when viewed from the front of the lens. It's been a long time since I've even thought about this stuff.
     
  13. EarthQuake

    EarthQuake Mu-43 Top Veteran

    834
    Sep 30, 2013
    Assuming your DOF is wide enough, F4-5.6 is the sweet spot. The corners sharpen up vs 2.8 at most focal lengths stoping down a stop or two. F8 will be less sharp, F11 and F16 especially significantly less sharp due to diffraction. F11-16 should only be used to ensure you have wide enough focus when you have a near subject and a distance background. Fstops smaller than F8 can also be useful when trying to force a slow shutter speed for certain types of photography, like waterfalls, however, an ND filter is generally preferable.

    The reason you divide the fstop by two vs 35mm is that diffraction typically soften images past F16, and similar effects are seen past F8 on M43. From what I understand, diffraction is caused by projecting an image through a very small physical opening, like looking through a screen door. 12/2.8 means half the physical aperture opening of 24/2.8, but the same physical opening as 24/5.6, so for the purposes of diffraction (and DOF/total light too), 12/8 on M43 is roughly equivalent to 24/16 on 35mm.

    It's worth noting that at most focal lengths the 12-40/2.8 is such a good performer, even wide open in the corners, that there is often little reason not to shoot wide open, other than DOF. Though the long end tends to show the most improvement stopped down a stop or two.
     
    Last edited: Sep 5, 2016
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  14. astrostl

    astrostl Mu-43 Veteran

    360
    Oct 4, 2014
    St. Louis, MO
    Justin Honold
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  15. mesmerized

    mesmerized Mu-43 Veteran

    344
    Jun 18, 2012
    Thank you all!