1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

something of an Error in "AskAP" this week

Discussion in 'AP Magazine Feedback & Suggestions' started by Terrywoodenpic, Jul 8, 2012.

  1. pilliwinks

    pilliwinks Well-Known Member

    That's correct when you're focused on the hyperfocal distance; as you get closer, the depth of field arrangement alters, and by 1:1 it's 50/50 on each side of the plane of focus.

    If you can gain access to a copy of Sydney Ray's "The Photographic Lens" there is actually a diagram in it showing how the depth of field vaires with focal length and focused distance, showing how the "fore and aft" values change. The diagram is stated to be derived from tables prepared by ARthur Cox.

    If you recall the simplification for depth of field based on focusing on fractions of the hyperfocal distance, you'll see how it's working in practice.
     
    Last edited: Jul 9, 2012
  2. 0lybacker

    0lybacker In the Stop Bath

    Cor! I'm glad I had an offline day, yesterday. Think I'll try and have another one tomorrow!

    Daft biker was just being daft and as for ... no comment.

    I thought it was common knowledge that AP incorporates at least one mistake (inadvertant) on the Queries page at the start of the 'silly-season' just to keep the Letters page going ... ;) ...

    :)
     
  3. Terrywoodenpic

    Terrywoodenpic Well-Known Member

    Sensible cameras like the Rolleiflex had the scale shown automatically....
    Your 1/3 to 2/3 is a useful rule of thumb.

    However there is no cut off point. There is only one exact point of focus, every thing else is progressively less in focus.
    Depth of field could be called depth of increasing fuzziness.
     
  4. AlexMonro

    AlexMonro Old Grand Part Deux

    Having now read the piece in question, I don't think it's wrong as such. but could perhaps have been clearer if the implied "Telephoto lenses... compressing perspective for the subject to be the same size in the frame by shooting from further away" had been explicitly stated (and possibly better expressed than my attempt! :) )
     
  5. daft_biker

    daft_biker Action Man!

    It'll work sometimes but in practice it ranges from half and half when using wide apertures at high magnifications to being almost all behind the point of focus when using small apertures at low magnifications.
     
  6. Bob Maddison

    Bob Maddison Well-Known Member

    When focused at the hyperfocal distance, everything should be in acceptable focus from half the hyperfocal distance to infinity. As the lens to subject distance is reduced, the front / rear distance approach equality. At 1:1 magnification (on the sensor), the lens to subject distance is equal to the lens to sensor distance (measured from the front and rear nodal points, hens the front / rear DoF are equal. Closer than 1:1 and the front DoF becomes progressively less than the rear DoF. Thus, whilst hyperfocal diatnce is a useful concept, it isn't easy to apply under all circumstances and a good VF may be more helpful.
     
  7. Bob Maddison

    Bob Maddison Well-Known Member

    Just another bit of useless / helpful information depending on your perspective: As we can see in the examples published, DoF is greater when the image is enlarged AFTER being taken than before. Thus cropping a WA photo will give you more DoF than using a longer lens from the same position (note the words). Whether or not the loss of definition in the cropped image is acceptable is another matter.

    Another bit of information: For maximum DoF without cropping the image, work as far from the subject as your lenses will allow. Thus for maximum DoF in macro work, the longer the focal length the more the DoF. However, too much DoF can mean sacrificing differential focus that is so important in some macro work.
     
  8. P_Stoddart

    P_Stoddart Well-Known Member

    Are you refering to me by any chance? :p

    If so you can just send me a PM if you wish to keep it a secret. :D
     
  9. RogerMac

    RogerMac Well-Known Member

    Just a note to point out that the enlargement on the crop I showed is equivalent (on the monitor I am using to view it) to approximately a 40 inch print, or something larger than A1. In fact I was surprised by how good the crop IQ was at this magnification, but if I was taking that image for pictorial reasons I would NEVER have cropped like that - in fact I would have widened the aperture to deliberately get less DOF



    Roger
     
    Last edited: Jul 9, 2012

Share This Page