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Discussion in 'Pentax Chat' started by Dave_Cox, Dec 12, 2007.

  1. Dave_Cox

    Dave_Cox Well-Known Member

    OK, first couple of pics using the Zenitar:



    I still have a bit to learn about using this lens. Two things that I have already got:
    1) It needs 1-1.5 stops over exposure to get detail in the ground for a landscape, you can't even handhold a cokin ND grad in front of this as the field of view is so wide
    2) You can't rely on hyperfocal focussing - for some reason that I don't understand this doesn't seem to work with the DSLR and any lens. You have to actually focus on infinity and work backwards from there using the aperture to control DOF.
  2. johnriley1uk

    johnriley1uk Well-Known Member

    I don't understand what you mean by this. Focusing on the hyperfocal distance has to maximise your DOF, there's no way it can't, it simply being an optical fact of life.

    Can you explain more fully what problem you are experiencing?
  3. Dave_Cox

    Dave_Cox Well-Known Member

    Not just with this lens, but a couple of other non-A coupled lenses. Set the aperture at f11 (for instance) and set the infinity mark on the focussing ring at the f11 mark on the aperture ring - the picture will be out of focus. Actually focus on an object at infinity (the infinity mark is actually set at the focusing line on the lens ring) and the picture is in focus, with good DOF. A bit long winded but that's what happens.
  4. OleTj

    OleTj Member

    "Hyperfocal marks" on lenses for 35mm film won't give the expected results on smaller digital sensors:

    The DOF is calculated for a given CoC (Circle of Confusion), which is determined by the limit of visibility in the finished print. If you want a greater enlargement, you would choose a smaller CoC. I can't remember what the definition of "finished print size" is for 35mm, but since the sensor is smaller the picture must similarly be enlarged more - so you need a smaller CoC, and the hyperfocal technique doesn't work if you go by the markings.

    Add to this the common practice of "pixel-peeping" which enlarges all faults and softnesses way out of proportion: How often do you make 36" wide prints? That's how big the print would be from a 3000x2000 pixel image, viewed at 1000 pixels wide on my 12" wide laptop screen.

    So in conclusion: Yes, the DOF marks on older lenses don't work. Personally I think they don't work on 35mm film either, so I prefer Harold Merklinger's "reverse focus" (Google him).
  5. johnriley1uk

    johnriley1uk Well-Known Member

    The "hyperfocal distance" is a concept that works with all lenses and all formats. The circle of confusion may well be different but then so is the amount of enlargement needed for a given print size. The smaller the format, the smaller the CoC needs to be, the higher the resolution of the lens needs to be and the more DOF there is.

    The simple thing is to set a small aperture, such as f11 or f16, and focus one third of the way into a scene. This will be the hyperfocal distance as near as makes no difference and will maximise DOF.

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