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Thread: Phase One KB 1221, Use of Non-retro focus lenses

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    Phase One KB 1221, Use of Non-retro focus lenses

    http://www.phaseone.com/en/search/ar...1&languageid=1

    Dates from August 2009, but specifically states:
    "Furthermore the P 65+ is not recommended with extreme wide non-retro focus lenses like the Schneider Kreuznach 35mm XL and even the Schneider Kreuznack 47 mm XL
    Even though these lenses has more than 70 mm image circle, they are producing a very steep angle incoming light along the edges, occasionally causing thin lines to show up in the image. Note that this can also occur with the P 40+". <<see attached image>>

    I mention this not to raise a red flag, but to say that I never have experienced this phenomenon. Using a 24mm SK XL and 35mm SK XL with my Cambo RS I have never had the lines show up with moderate rise or shift. Can't remember any of you mentioning this, but wanted to throw it out there. Anyone experienced this?

    George
    Last edited by ggriswold; 21st July 2013 at 08:36.

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    Re: Phase One KB 1221, Use of Non-retro focus lenses

    Yes, I see it occasionally. I shoot P65+ on Horseman SW-D with Rodenstock 35mm Apo-Sironar Digital and Schneider 24mm Apo Digitar XL.
    It is sometimes visible, usually in areas with lighter tones. It's an artefact caused by light striking the sensor at a very steep angle.
    The new Rodenstocks which I think are a semi-retrofocus design are better performers in this regard.
    Cheers,
    Siebel
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    Re: Phase One KB 1221, Use of Non-retro focus lenses

    Quote Originally Posted by siebel View Post
    Yes, I see it occasionally. I shoot P65+ on Horseman SW-D with Rodenstock 35mm Apo-Sironar Digital and Schneider 24mm Apo Digitar XL.
    It is sometimes visible, usually in areas with lighter tones. It's an artefact caused by light striking the sensor at a very steep angle.
    The new Rodenstocks which I think are a semi-retrofocus design are better performers in this regard.
    Cheers,
    That directly matches our experience with various clients.

    24mm XL with the 65+ is the is the worst offender, followed by the 35mm XL with moderate movements in areas of continuos light tone.

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    Re: Phase One KB 1221, Use of Non-retro focus lenses

    Will a LLC in C1 correct this optical aberration? Is it worse when the lens is tilted or the back shifted to the edge of the image circle?

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    Re: Phase One KB 1221, Use of Non-retro focus lenses

    LCC can fix the light fall off but I'm pretty certain that the lines are beyond it's ability.

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    Re: Phase One KB 1221, Use of Non-retro focus lenses

    This problem is not unique to Phase One.

    Hasselblad recommends against using their digital back with the SuperWide body and its 38mm Zeiss Biogon lens, for the same reason. The incident angle of the light toward the edges of the sensor is too acute for proper detection, resulting in color fringing or other optical anomalies.

    This problem cannot be corrected by using a lens with a different optical design, since by definition the distance from the rear node to the film when focused at infinity must equal the focal length. Thus the angle of incidence of the light rays at any point on the film plane will be the same for all lenses of a given focal length.

    - Leigh

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    Re: Phase One KB 1221, Use of Non-retro focus lenses

    Quote Originally Posted by Leigh View Post
    This problem cannot be corrected by using a lens with a different optical design, since by definition the distance from the rear node to the film when focused at infinity must equal the focal length. Thus the angle of incidence of the light rays at any point on the film plane will be the same for all lenses of a given focal length.
    - Leigh
    Retrofocal design means that the exit pupil sits farther away from the film (sensor) plane and thus reduces the angle in which the light hits the sensor

    You'll be hard pressed to see any colour shift effects with e.g. the Mamiya/ Phase One 28mm lens on a 645 body

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    Exclamation Re: Phase One KB 1221, Use of Non-retro focus lenses

    Quote Originally Posted by yaya View Post
    Retrofocal design means that the exit pupil sits farther away from the film (sensor) plane and thus reduces the angle in which the light hits the sensor
    Nope... sorry

    The retrofocal design places the rear principle plane behind (toward the film) the rear physical lens element. This allows the glass to be moved forward far enough to clear an SLR mirror movement or similar internal obstructions.

    The definition of focal length, i.e. the distance from the rear principle plane (exit pupil) to the film plane has not changed.

    - Leigh

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    Re: Phase One KB 1221, Use of Non-retro focus lenses

    Quote Originally Posted by Leigh View Post
    Nope... sorry

    The definition of focal length, i.e. the distance from the rear principle plane (exit pupil) to the film plane has not changed.

    - Leigh
    To correct things further, the rear principal plane and the exit pupil are NOT the same things... Exit pupil is basically just the "virtual aperture" of the lens.
    Jack
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    Re: Phase One KB 1221, Use of Non-retro focus lenses

    An old document that gives a good primer to the wide-angle colour casts matter, including the basics of retro/ non-retrofocal designs:
    Cast effects in wide angle photography
    Yair Shahar | Product Manager | Phase One | Mamiya Leaf
    e: [email protected] | m: +44(0)77 8992 8199 | yaya's blog

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    Re: Phase One KB 1221, Use of Non-retro focus lenses

    Interesting article, thank you Yair.
    Using a Cambo RS with a P40+ would it work to create and save LCC corrections for each lens and say +/- lens rise and fall (steps of 5)?
    35mm 0
    35mm +5
    35mm +10
    35mm -5
    35mm -10 and so on.

    I have been doing the LCC on each shoot and correction file pulldown is filling up with lots of LCCs. Maybe for critical work do new ones, but for more general work you could access the "library".
    The other reason I haven't done standard LCCs if there is some bad surprise with lots of dust (say a lens change and no laptop to check sensor) you are covered with the dust removal in Capture One.
    What do you think?

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    Thumbs up Re: Phase One KB 1221, Use of Non-retro focus lenses

    Quote Originally Posted by Jack Flesher View Post
    To correct things further, the rear principal plane and the exit pupil are NOT the same things...
    Yep, you're right.

    I never work with exit pupils, so I wasn't thinking straight. Lens design programs only work with principle planes and nodes.

    Thanks.

    - Leigh

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