Hyperfocal distance AF

Discussion in 'Digital Photography' started by kallisti, Oct 2, 2018.

  1. kallisti, Oct 2, 2018
    Last edited: Oct 2, 2018

    kallisti macrumors 65816

    kallisti

    Joined:
    Apr 22, 2003
    #1
    There is a focus point for any lens at a given aperture that maximizes sharpness from near to infinity, resulting in the largest possible DOF with "acceptable" sharpness. This is commonly referred to as the hyperfocal distance.

    For many subjects, setting focus at the hyperfocal distance can be desirable (usually landscapes with something of interest in both the foreground and background, but true for many subjects).

    The hyperfocal distance is related to the focal length of the lens, the aperture, and the circle of confusion (which relates to both the lens and sensor as I understand it, but may really apply more to the sensor in common usage).

    "Acceptable" sharpness is somewhat subjective.

    On a practical level, there are subjects that you want to be sharp near to infinity. If you set focus at infinity, the DOF will be narrower (making near objects blurry) compared to if you set focus closer than infinity which would still keep infinity "acceptably" sharp but bring nearer elements into focus.

    The usual solution is to stop down the lens, extending the DOF.

    But for any lens at any aperture, there is an optimal focus point that will create the maximal DOF near to infinity with acceptable focus along the spectrum.

    Finding this focus point can be a bitch. Focus peaking (only available with an EVF or using LV) is often not accurate. Using rule-of-thumb approximations (especially with AF) are often not accurate. On a tripod using LV and manual focus you can check focus across the frame and find the sweet spot. Time consuming and not really viable with hand held shooting.

    Zeiss Batis lenses for Sony offer a digital DOF scale based on the lens and the aperture selected. I've used them with some success to nail the hyperfocal distance (often erring on the side of moving the focus more towards infinity to make sure distant elements are sharp at the expense of a loss of near DOF).

    Why can't AF cameras offer a "hyperfocal AF" option? Meaning, the camera automatically sets focus to the hyperfocal distance based on the attached lens and the aperture for the body being used. Possibly including an option to adjust the distance based on user preference (i.e. tweaked to nearer focus to allow for a nearer DOF or tweaked to infinity focus to ensure sharp infinity at the expense of loss of near sharpness).

    There are lens issues that wouldn't guarantee across the frame sharpness (i.e. field curvature), but the ability to automatically set the focus of the lens to the hyperfocal distance at a given aperture would seem to be useful for many subjects. One of the things I liked about using a Leica rangefinder was the ability to "zone focus"--i.e. setting focus manually at the hyperfocal distance and then compose without having to think about focus.

    Possibly I'm missing something and feel free to point out issues. But I've run across this problem for many landscape shots (especially hand held) where I end up crossing my fingers that the focus I chose with AF was close to the hyperfocal distance. Why can't this be an option on any camera with AF to do this automatically (perhaps using lens profiles for interchangeable lens cameras)?
     
  2. anotherscotsman, Oct 2, 2018
    Last edited: Oct 2, 2018

    anotherscotsman macrumors 68000

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    UK
    #2
    I’d agree with you on how useful this would be under a lot of circumstances but especially landscape. I tend to use relatively wide angle lens for which the HD is usually only a couple of feet at f8 or f11 and set focus manually or AF on a relatively close object.

    The calculations required to estimate the HD are not complex and so should be easily done in camera. In defence of the manufacturers (not that they need or necessarily deserve defence) the current fashion for many photographers is for shallow DoF and major bokeh.

    What would be even more useful is a focal length display on the lens or in camera - many lenses don’t even have a focal length indicator!
     
  3. dwig, Oct 3, 2018
    Last edited: Oct 4, 2018

    dwig macrumors 6502a

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    Key West FL
    #3
    Not quite correct.

    The hyperfocal distance as nothing to do with getting "the largest possible DOF". It is, instead, a special DOF calculation that places infinity at the far limit of whatever DOF the lens, at the chosen aperture, delivers. It matters not whether that DOF is wide or narrow.

    Shooting at the hyperfocal distance is a technique that keeps subjects at infinity "reasonably" sharp while not wasting any of the DOF at distances beyond infinity and thus getting as much of the closer distance subjects possible, at the given aperture, reasonably sharp. It is of advantage in typical landscape/cityscape shots when sharpness at infinity is valuable. It is of little use otherwise.
     
  4. Darmok N Jalad macrumors 68000

    Darmok N Jalad

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    Sep 26, 2017
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    Tanagra
    #4
    I am aware of hyperfocal values, but have never really applied them. I suppose I thought that was what the “landscape” mode on the camera dial tried to do? I figured it was probably not perfect, but it at least helped in that regard.
     
  5. simonsi macrumors 601

    simonsi

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    Location:
    Auckland
    #5
    Did the Leica indicate the hyperfocal distance to use? There seems to be two aspects to your request, having built-in DoF tables in the camera for it to use, and the ability to drive the lens to the given hyperfocal distance.

    TBH that would be fairly easy for a camera manufacturer to do - but it is not the only use case for DoF and hyperfocal calculations. The other is to compute the DoF required to keep two objects at different distances sharp and calculate the aperture and hyperfocal distance to focus at. THAT requires an understanding of the image components that no camera can fully have.

    Which is why I suspect the manufacturers have left it to tables/apps and MF for those that need to do this.
     
  6. kallisti thread starter macrumors 65816

    kallisti

    Joined:
    Apr 22, 2003
    #6
    From Wiki:
    "In optics and photography, hyperfocal distance is a distance beyond which all objects can be brought into an "acceptable" focus. As the hyperfocal distance is the focus distance giving the maximum depth of field, it is the most desirable distance to set the focus of a fixed-focus camera.[1] The hyperfocal distance is entirely dependent upon what level of sharpness is considered to be acceptable."

    The Leica had a usable DOF scale on the lens barrel and the hyperfocal distance could be approximated by setting the infinity focus marker over the "distant" DOF marker for a given aperture. Using Batis lenses on a Sony one can manually set focus to where the digital DOF display on the lens barrel displays infinity at the far end. The digital DOF scale display on these lenses changes with changes in aperture.

    I am opining that having this ability as an autofocus option would be useful for some types of photography (i.e. landscapes or cityscapes) especially hand held (though it might serve as a good starting point even for manual focus on a tripod where there are foreground or mid ground elements that might not be in the DOF for a given aperture if focus is set to infinity).

    The key drawback is the definition of "acceptable" focus. But I'm not saying it should be the only focus method, it just might be useful as an option for some situations.
    --- Post Merged, Oct 4, 2018 ---
    You are correct and I was perhaps a little loose in my definition of the hyperfocal distance. Thanks for the clarification/correction :)
     
  7. simonsi macrumors 601

    simonsi

    Joined:
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    Auckland
    #7
    First two sentences contradict ;-)

    The first implies it is the closest distance beyond which all objects are in focus. The trouble with this is the lens needs to be set approx 1/3rd of the way into the DoF range as objects infant of the focus plane are in focus as well as beyond it.

    The second sentences uses a "focal distance" term which is what you need in terms of setting the camera, apps will give you the distance at which to <focus> to give the required DoF in front of, and behind, the focal plane in order to keep the depth range what you need for your image.
     
  8. kallisti, Oct 4, 2018
    Last edited: Oct 4, 2018

    kallisti thread starter macrumors 65816

    kallisti

    Joined:
    Apr 22, 2003
    #8
    I think we are somewhat arguing semantics. @dwig above gave a better definition. To paraphrase, the hyperfocal distance is that distance where the DOF for a given scene shot with a specific focal length and aperture is maximal while including elements at infinity.

    The size of the DOF for any focal length and aperture is a constant determined by math (with a caveat, discussed below), creating a zone of sharpness. But the placement of that zone of DOF sharpness within an image is dictated by the point of focus at the time of capture. If focus is set at infinity, part of the zone of DOF sharpness is "wasted" by extending beyond infinity to the detriment of near or mid range elements. Using the hyperfocal distance as the point of focus, the "far" element of the zone of DOF sharpness is set to objects at infinity, allowing the near portion of the zone of DOF sharpness to hit nearer elements in the composition, effectively increasing the DOF across the image.

    The actual DOF doesn't change, but you are in effect shifting the zone of acceptable sharpness forward to include nearer elements in the composition, hopefully without affecting sharpness of elements at infinity.

    It's actually a bit more complicated as the DOF also changes by focus distance. The closer the focus distance, the shallower the DOF independent of focal length or aperture (the bane of macro photographers).

    The beauty of the hyperfocal distance is that it ensures the maximal size of the zone of DOF (i.e. sharpness) for a scene extending to infinity at a given focal length and aperture--by recovering the "lost" DOF that is "wasted" extending beyond infinity when focus is set at infinity; it shifts the plane of focus (and by extension the zone of DOF sharpness) forward to include more mid and foreground elements without losing sharpness at infinity. Or at least too much sharpness at infinity ;)
     
  9. tizeye macrumors 6502

    tizeye

    Joined:
    Jul 17, 2013
    Location:
    Orlando, FL
    #9
    While I typically use a 16-35 for landscape and architectural, at f8 and beyond DOF is 3' to infinity. It also makes a great walk around lens which I keep on the camera rather than a 24-70. In fact, in the 24-70, I am about to sell it and get a 24 which will complete the full prime set for that range.

    In terms of hyperfocal, one area not discussed is focus stacking as you need to expand the DOF. Only good for static subjects as need to take multiple exposures with different focal points to stack.
     

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8 October 2, 2018