Depth of Field ~ distances and zoom lenses

Discussion in 'Photography Beginners' Forum' started by PJcam, Jan 26, 2018.

  1. PJcam

    PJcam No longer a newbie, moving up!

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    I have read Understanding Exposure by Bryan Peterson, a very good book, highly recommended

    I have now purchased another of his books, Exposure Solutions, but I read something I am now sure about so ask you guys if you can confirm for me please.

    [The books I purchase are Kindle ebooks, excellent and a fraction of the cost]

    First it talks about single-focal length lenses, they have Depth of Field Scale that makes it easy to preset focus for a given scene. So far so good.

    Then it says, most people go for wide angle lenses (I have), then he states that they don;t have the DoF scale, I agree. But he goes on the say they do however, have distance settings, which, similar to DoF scales, allow you to preset the DoF before taking the shot.

    Are these the mm focal distance measurement?

    He then continues and says... you'll find these numbers above the distance setting mark on the lens. He then says... set aperture to f/22 and then align a specific distance - 3 feet (1 meter) or 6 feet (2 meters) depending on the focal length you are using.

    Can someone explain this please? I am aware of the lenses mm settings but not sure how this relates to the 1 or 2 meters he is stating.

    Thanks in advance, I am very grateful.

    All questions are easy... if you know the answer.


     
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  2. Dave442

    Dave442 No longer a newbie, moving up!

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    These settings were common on manual focus lenses. Many of my newer lenses have done away with these scales (if you in auto-focus mode it really throws the usefulness out the window).

    If you have a lens with the numbers noted, then all you do is set your f-stop on the lens and then set your closest focus distance to that number and check that the farthest focus distance covers the required in-focus distance of the scene. If you need more in focus then stop down another stop and check again.

    So he is saying to put the 3 feet under the 22 on the one side and you are probably past the Infinity mark at the 22 on the other side if using a wide-angle lens. I would not go to f/22 for difraction, but that is another issue. On some lenses the f-stop numbers are colored and then there are just notched lines that have a corresponding color where you would line up the distance scale.

    The problem is that many of these lenses used a DOF scale based on a certain size of "Circles of Confusion" that with todays digital cameras is not adequate, so just be a bit more conservative.
     
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  3. Designer

    Designer Been spending a lot of time on here!

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    No, the distance scale is in feet or meters, and sometimes both on the same scale. It is the distance to focus, from which you can figure the DOF. Get hold of a DOF app for your phone so you can check the DOF any time.
     
  4. PJcam

    PJcam No longer a newbie, moving up!

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    Thank you Dave442, all my lenses are brand new so your reply makes sense as to why I cannot see the details he is stating.
     
  5. Designer

    Designer Been spending a lot of time on here!

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    Single-focal-length lenses (also called "prime") have a simple calculation for DOF, which is easier for most people to read. Some zooms also have a DOF scale, but you have to remember to note your aperture in order to read it correctly.

    The reason wide angle lenses don't have the DOF scale on them is because the DOF scale would be so compressed that it would be hard to tell one number from the next. The DOF, in other words, is quite deep, and therefore is almost irrelevant.
     
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  6. PJcam

    PJcam No longer a newbie, moving up!

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    Thanks designer, I have just downloaded two Apps, DOF Calculator Aimen RG and DOF Jonathan Sachs they both look good in their own ways, I will play with them more later. Thanks.
     
  7. PJcam

    PJcam No longer a newbie, moving up!

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    I guess this leads to the next question.
    With a modern AF lenses that I have are these items relevant?

    The camera and lens will work it out depending which lens I am using and what aperture I have set.
     
  8. Dave442

    Dave442 No longer a newbie, moving up!

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    You still need to consider the DOF. If you need to have focus from 6 feet to Infinity then check the numbers in a DOF Calculator that would give that range and then just auto-focus on something around the distance required, recompose and take the shot. With most DOF Calculators you may need to try some different distances as the focus point and different Apertures to find the combination that gives the near and far distances desired. Also check out Hyperfocal Distance if you want to have the far point of acceptable focus at Infinity with the maximum amount of the scene within acceptable focus.
     
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  9. PJcam

    PJcam No longer a newbie, moving up!

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    The author suggests focusing on something near, 3' or 6' when using a wide angle lens as he states everything from there to infinity would be in focus (with this lens type). He also states of you focus on the middle, the items in the foreground will be out of focus as it sets from focus point to infinity.

    That's sounds reasonable to me and something I will test out, I then wonder about the other information, is it really needed. I will check the two Apps and learn more.

    Thanks for your comments.
     
  10. ac12

    ac12 No longer a newbie, moving up!

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    A DoF scale would work on a Push/Pull zoom, but NOT on a 2-ring zoom where you zoom by turning the zoom ring.
    This is because the DoF changes with the zoom position.
    On a P/P lens, you have curved lines for the DoF scale, so you can see the DoF changing as you zoom.
    Can't do that with a 2-ring zoom. The DoF would be correct at only ONE zoom setting, and wrong for everything else.

    This is one thing that I miss on the old Nikon manual focus zooms.
     
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  11. petrochemist

    petrochemist TPF junkie!

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    It sounds like this book isn't a patch on Bryan's 'Understanding Exposure', but that is a high standard to match.

    Many lenses today don't have distance scales or aperture rings, but even when these where the norm then how DOF information was displayed could vary significantly from lens to lens.

    If you focus on something at 6' with a wide angle then you might get everything from there to infinity focused acceptably, but there are far too many variables to assume so on any camera. A better approach may be to focus at the hyper focal distance for your lens/aperture. Then by definition everything from half that to infinity is focused. You may never need to refocus at all. There are actually a few lenses where focusing is based on this - such as the Olympus 9mm fisheye body cap which is fixed at f8.
     
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  12. KmH

    KmH Helping photographers learn to fish Supporting Member

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    At this link:
    Understanding Depth of Field in Photography
    scroll down to where they have a chart that shows lens focal length and focus distance to maintain about the same DoF.
    Note that the focus distance increases with lens focal length.
    If the focal length doubles, so does the focus distance - to maintain the same DoF.

    Right below that is a chart that shows how lens focal length also affects the distribution of DoF in front of and behind the point-of-focus (PoF).

    The shorter the focal length of a lens, the deeper and less adjustable the DoF.
     
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