Hyperfocusing vs infinity focusing

Discussion in 'Minox' started by mtc photography, Dec 20, 1998.

  1. Discussion of merits of hyperfocusing and infinity focusing
    Harold Merklinger's object field depth of field concept and its application to Minox photography
     
  2. Many photographers, no matter what format they use, 8x11, 35mm, or medium format, when taking landscape photographs like to set camera lens on hyperfocal distance, to maximize depth of field.
    But many photographers are not happy with the lack of sharpness of distant objects in their pictures; they feel these distant objects look too blurry in their pictures. Some try to stop down (for 35mm camera ), or double up the hyperfocal distance.
    Harold Merklinger, in his book "THE INs and OUTs OF FOCUS"
    [​IMG]
    presented an alternative depth of field theory, and provides a good alternative solution.
    H.Merlinkger's analysis was based on object field instead of image field. His argument was that instead of looking at circle of confusion on the image plane, why not ask the question "what is the smallest resolvable object in the object plane "
    In landscape or street photograph, accordingly to Merklinger, if you focus at hyperfocal point, the circle of confusion of distant object remains within preset limit, but the DISK OF CONFUSION grows rapidly without bound.
    That explains why distant objects are fuzzy in the picture.
    On the other hand, if the lens is focused at infinity, the disk of confusion is always equals to the diameter of lens opening, which is DOC= focal_length/ fstop.
    For example for 35mm lens, DOC= 4.4mm at F8, DOC= 3.2 mm
    Disk of Confusion is the smallest diameter the lens can resolve at a selected aperture.
    One can choose how small the detail necessary in picture by simply looking at the size of opening of the lens, and turning the aperture ring to dial in the proper size.
    For example if the thinnest tree twig has a diameter about 5 mm then you pick F11 for your Minoxar lens, with DOC = 3.2 mm, then the tree twig will be resolved in your picture. ( Up to 100 M, beyond that the actual DOC will grow without limit again, due to diffraction)
    Same for Minox 8x11 camera, which has a DOC = 15mm/3.5=4.3 mm. When focus Minox 8x11 at infinity, any feature greater then 4.3 meter will be resolved up to 30 meter (due to diffraction, which is a different topic ).
    In 35mm photography and Medium format circles, Merklinger has many followers (myself included ).
    I apply his method to Minox ultramiature photography as well. During travel, I simply set my Minox at infinty and shoot.
    I don't remember this topic ever came out at subminiature list discussions.
    There are some discussion of Merklinger DOF theory at USENET GROUP
    and Leica list
    Is small lens opening-- large f stop better ?
    If disk of confusion governs the resolution of objects, then it seems the smaller the lens openning the higher the resolution.
    It is not-- because of diffraction.
    The effect of diffraction on DISK OF CONFUSION and what is the optimum aperture at certain distance is a topic for another technical article
     
  3. Disk of Confusion for Minox 35

    For 35mm camera, (Minox GTE/GTX/GTS, GL, EL,MDC etc etc ), to apply Harold Merklinger's depth of field theory for landscape photography is quite simple: take a look at the opening of you Minoxar/Minotar lens. For instance if you select F8, then the diameter of your len's opening is 35mm/8 = 4.4 mm.That 4.4 mm is the smallest DISK OF CONFUSION for a Minox 35mm camera set at F8. In other words object smaller than 4.4 mm will not be resolved.
    Choosing aperture becomes very simple, DOF becomes very simple: Set lens at infinity, set aperture to match the smallest size you want to resolve, that is all.
    Disk of Cofusion for Minox 8x11, focusing at Infinity

    when focus Minox A/B/C/LX/TLX at infinity , the DISK OF CONFUSION is 15mm/3.5 = 4.3mm regardless of distance. In another world, 4.3 mm is the smallest distant object you ever expect to resolve with Minox 8x11 camera.
    Of course, diffraction effect put a limit on how far out this 4.3 mm holds true.
     
  4. Disk of Confusion of 8x11 when hyperfocusing

    When COMPLAN/MINOX lens is focus at hyperfocal distance H the DOC ( DISK OF CONFUSION ) =0;and object at half of H has a DOC = 4.3mm/2 = 2.2 mm; at twice of H, the DOC = 4.3 mm, beyound this, DOC increases linearly with distance, wihout bound ! For example, if Minox 8x11 camera is focused at its hyperfocal distance 4 meter, then at 2 meter point, DOC = 2.2; at 8 meter point DOC = 4.3 mm; at 12 meter, DOC = 8.6 mm, at 16 meter, DOC = 13mm, at 50 meter, DOC = 49 mm.
    That is why, if you only look image plane, when a lens is focused at hyperfocal point, even though circle of confusion still within 1/60mm limit, and objects from 2 meter to infinity are supposed to be "sharp", but as a matter of fact the Disk of confusion grow geometrically, keep getting bigger and bigger. That is why far object becomes quite blurry.
     
  5. What happens to disk of confusion when you focus you Minox( be it 8x11 or 35mm ) ?
    When you focus your Minox at infinity, the light rays are parallel to optical axis, forming a cylinder of with diamter of cross section equals to the lens aperture opening. In other words, when you focus Minox 8x11 camera at infinity, the DOC is always 15/3.5= 4.3 mm; for Minox 35 camera, DOC =35MM/fstop, for example when fstop =f8, DOC for Minox GT-E = 35/8= 4.4 mm.
    When focus at infinity, from geometrical optics point of view, Disk of Confusion, ie the smallest object which can be resolved, never increase, in contrast to focusing at hyperfocal distance H, DOC increases without bound beyond 2*H.
    Hence, for landscape pictures, where distant mountaitns, cathedrals, street scences are your main object of interest, you should focus at infinity instead of at hyerfocal distance H; On the other hand, if your near object is more important in your composition, but you want to retain distant background to play secondary roles, then focus at hyperfocal distance.
     

  6. Why Focusing at Infinity Makes Sharper Landscape Picture

    In landscape pictures, main subjects of interest are located 10 meters and stretch to infinity.
    In the following two tables illustrate the difference in sharpness between focusing at hyperfocal point and focusing at infinity for objects 10 meters and beyond.
    • Lens: Minox 35 camera Minoxar 35mm lens
    • Aperture : f8
    • Hyperfocal distance : 4.6 M
    • Lens opening = 35mm/8= 0.44 CM
    • TABLE 1

      • At 2x 4.6 m, the disk of confusion = lens opening =4.4 mm;

      • Beyond that, disk of confusion increases without bound.

      • For example at 100 meter, the disk of confusion is 9 CM, meaning feature smaller than 9 cm will not be resolved.

      • For instance, you will not be able to see people's eyes (about 2 cm) or mouth ( 5 to 6 cm ).

      • Objects bigger 9 cm for example a hat will still be resolved at 100 M

      • Circle of confusion INCREASES with distance, although still stays within the limit of 0.033 mm.
      TABLE 1: FOCUS AT HYPERFOCAL
      Distance M ​
      Circle of confusion mm ​
      Disk of confusion cm
      0.9 ​
      0.1500 ​
      0.36
      1 ​
      0.1200 ​
      0.34
      2.3 ​
      0.0300 ​
      0.22
      3 ​
      0.0200 ​
      0.16
      3.8 ​
      0.0070 ​
      0.08
      4 ​
      0.0050 ​
      0.06
      4.5 ​
      0.0010 ​
      0.01
      4.6 ​
      0.0000 ​
      0
      5 ​
      0.0020 ​
      0.04
      6 ​
      0.0080 ​
      0.13
      10 ​
      0.0180 ​
      0.51
      20 ​
      0.0260 ​
      1.45
      30 ​
      0.0280 ​
      2.4
      40 ​
      0.0290 ​
      3.34
      50 ​
      0.0300 ​
      4.29
      100 ​
      0.0320 ​
      9.01 ​
      TABLE 2
      The disk of confusion remains at 0.44 cm from 10 meter to infinity.
      By focusing at infinity, you will be able to resolve feature greater than 0.44 cm-- you can see people's eyes, camera straps etc 100 M away, not just hats.

      • At 5 meter, , that is the near limit of depth of field, the circle of confusion is 0.03mm

      • From 5 M and beyond, the circle of confusion DECREASES with distance, at 10 M coc= 0.015 mm, at 50 M coc= 0.003 mm at 100 M coc=0.0015 mm. You can see that these numbers are much smaller than the corresponding numbers of table 1

      • Although the actual circle of confusion when focusing a lens at infinity is not as small as these numbers, due to diffraction effect but are still as small as the resolution of the lens permits.
      TABLE 2 FOCUS AT INFINITY
      Distance M ​
      Circle of confusion mm ​
      Disk of confusion cm
      1 ​
      0.16 ​
      0.44
      2 ​
      0.08 ​
      0.44
      5 ​
      0.03 ​
      0.44
      10 ​
      0.02 ​
      0.44
      20 ​
      0.008 ​
      0.44
      30 ​
      0.005 ​
      0.44
      50 ​
      0.003 ​
      0.44
      100 ​
      0.0015 ​
      0.44 ​
      Most photographic lenses are were optimized at infinity, hence sharpest at infinity
      Leitz Elmar 50/3.5 invented Infinity lock on lens Focus at infinity is the only Isodisk case.
      Focus at infinity packs the maxium amount of information into negatives, independent of limitation of human eye, with no constrain on viewing distance, no constrain of enlargement factor.
      On film resolution is determined by the size of disk of confusion not by circle of confusion.
     

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