Why are the hyperfocals off?

Discussion in '35mm Cameras and Accessories' started by thuggins, Sep 23, 2012.

  1. thuggins

    thuggins Member

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    I was getting ready to take out my Kodak Retina 1b and Voightlander Vito II, and was playing with the hyperfocal scales. On both cameras the scales are one stop off. So for f8 the hyperfocal distance should be about 34 feet. But on both cameras this distance is shown for f5.8. Checking an OM 50mm showed the correct hyperfocal, about 34 ft at f8.

    Why would both the Kodak and the Voightlander be off by one stop? Was it one stop of insurance to make sure everything was in focus?
     
  2. BMbikerider

    BMbikerider Member

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    I would think that either both manufacturers were playing safe or possibly your calculations are out. It is odd that BOTH cameras should be wrong.
     
  3. ath

    ath Member

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    DOF and consequently hyperfocal scales are based on an acceptable circle of confusion. What is acceptable depends on the user, or in this case on the maker of the scale. They simply had different standards how small a CoC had to be to deliver a "sharp" image..
     
  4. Peltigera

    Peltigera Member

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    I am pretty sure that through out the hyperfocal distance the circles of confusion are circles of least confusion - that is to say the same size. The concept of acceptable does not apply if all are the same size. I suspect both Kodak and Voigtlander were playing safe.
     
  5. ath

    ath Member

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    It starts with the question "which size is acceptable". There is no standard; some companies used the same values, other companies other values. And your personal acceptance limit is another thing and most probably depends on the size of the print as well.
    DoF calculators often use the most used value or even allow you to set your own CoC.

    If you look at say 50mm lenses from different manufacturers you will find a variety of DoF scales.

    DoF is mainly subjective. "playing safe" implies an objectivity which is simply not there.
     
  6. Ian C

    Ian C Member

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    The current circle of confusion diameter used by most camera and lens makers is c = 1/1500 the diagonal of the image rectangle on film. The circle of confusion for the 35mm format is generally taken as 0.029mm.

    Using circle of confusion diameter 0.029mm, the hyperfocal distance for a 50mm lens at f/8 on the 35mm format is 10.8 meters = 35.5 feet.

    A 50mm lens on the 35mm format at f/5.8 would achieve hyperfocal focus at 34 feet with a circle of confusion diameter of 0.042mm.

    In particular, if the maker had chosen a circle of confusion diameter of 0.042mm as “good enough”, then the markings make sense.


    On page 17 of the Kodak Retina 1b manual (First version PDF), the last example gives a 22-foot hyperfocal distance at f/8. You have to read it carefully to see that this is the actual focusing distance being used (“The depth of field then extends from 11 feet to infinity.”)

    This leads to a circle of confusion diameter of 0.047mm.

    http://www.cameramanuals.org/kodak_pdf/kodak_retina_ib.pdf
     
    Last edited by a moderator: Sep 23, 2012
  7. thuggins

    thuggins Member

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    Yep! Those are the values that the DOF field scale shows. So it is apparent that manufacturers were using a larger CoC back then, compared to the modern "standard" of .03mm. I would assume this was related to the grain size and sharpness of the film that was available at the time.

    This appears to have been the standard back then. I've checked a couple of my Oly 35's from the 1950's, and they show the same scales as the Kodak and Voightlander.

    Thanks for the input, guys!
     
  8. Ian C

    Ian C Member

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    It might also be due to the intended use of the camera. This was thought of as a nice consumer-grade camera with decent lens whose main use was typically small snapshots for a family photo album or 35mm slides for projection at modest size.

    With that in mind, a circle of confusion diameter of 0.047mm was likely viewed as “good enough for its intended purpose.”
     
  9. ath

    ath Member

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    Back in 1938 Windisch stated that for the leica lenses a circle of confusion of 1/30mm has been defined. So it seems not to be a matter of changing times.
    Marketing wise the lenses with bigger dof seem to be "better" unless one cares to understand the resaon behind this.
    I'm leaning towards a mixture of intended use (which includes print size or the popular slide projection) and company standard.
     
  10. ic-racer

    ic-racer Member

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    One stop 'off' from what? There is no 'gold standard' for CoC size. You can calculate the hyperfocal distance based on any CoC size you want. My rule-of-thumb is to use the marker that is two stops smaller than what is marked on most 35mm camera lenses.
     
  11. Prof_Pixel

    Prof_Pixel Member

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    The Kodak Professional Photoguide, 1st Edition, 1975 says "Technically, the circle-of-confusion size used to calculate the depth of fields for each situation is about 1/1000 of the focal length of the normal lens for each format". So your 0.047mm figure is about what I'd expect Kodak to recommend.
     
  12. wiltw

    wiltw Subscriber

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    To add to the confusion about DOF, if one assumes the vision standard of 20/20 vision, even the manufacturer standard for CofC leads to overly generous DOF zone sizes, and a person with 20/20 vision would really NOT consider all of the out-of-focus zone to be 'acceptably sharp'. That is why many of us long ago had adopted the practice of looking at the DOF scale corresponding to an aperture value which was ONE LARGER than what was selected on the lens, for the DOF scale references....i.e. use f/5.6 marks on DOF scale when the lens aperture was f/8