Difference between Minoxar lens and Minoctar lens on 35mm models

Discussion in 'Minox' started by mtc photography, Mar 7, 2004.

  1. Minoxar and Minoctar probably has the same optical formulation
    (ie, glass types, power and bending of elements, airspace thickness
    etc ). The main difference probably MC-Minoxar is multicoated,(hence
    MC), Color-Minoctar is not multcoated.

    There are other subtle differences;

    (GT-E, MDC) MC-Minoxar 2.8/35 Germany
    Color-Minoctar 2.8/35 ; no Germany

    Depth of field ring:

    GT-E MC-Minoxar: full circle red color ring with
    white lettering and white index mark and two
    left and right white dots as DOF bracket.
    ML Color-Minoctar: black ring white lettering with
    red index bracket
    Aperture control ring:

    MDC MC-Minoxar: click stop
    GT-E MC-Minoxar: no click stop,
    Index mark on aperture ring
    aperture number 2.8..16 on camera body
    ML Color Minoctar: no click stop
    index mark on body
    aperture number 2.8 to 16 on aperture

    Focusing ring:

    MDC MC-Minoxar: focus from 90 cm to infinity
    GT-E MC-Minoxar : focus from 70 cm to infinity
    ML Color-Minoctar: focus from 90 cm to infinity

    Exposure meter window on lens
    GT-E MC-Minoxar ; 180 degree semicircle arc
    ML Color Minoctar 120 degree arc

    Screws on focusing ring
    GT-E MC-Minoxar one screw hole at far left of 0.7m mark,
    second screw hole between 1.2m and 1.5m
    ML Color-Minoctar one screw at left of 3ft mark ( about
    0.8m position), second screw between 10 and 20 feet (3ft to 6 ft)
  2. It is very odd that the designers of the MDC would include a lens, Minoxar, that has been in production on the GT-E for some years yet restrict it's use to the same range as the lens on the ML and GT, the Minoctar.

    The GT-E foucs down to 70cm as do the GT-X, GT-S and GT-E II.

    The MDC has a minimium focus of 90cm, the same as the ML and GT.

    Although the name has changed on the lens the MDC still has not taken the full advantage that it apparently offers over the ML.
  3. The same Minoxar lens was allow to close focus on GT-E to 70cm, one
    MDC close focus only to 90 cm.

    I believe the designer of MDC wanted to control the lens abberations
    to tighter specification than on GT-E

    I use a model four element three group Tessar lens
    with Schott glasses, SK16, LLF6 and O_S_TIL27 to see the effect of change of first airspace to Seidel abberations.
    The front element of this model Tessar is made of SK16(index 1.62041 ) radius 16.392mm, thickness 3.035616mm. The focal length of this element alone is about 25mm, ie, twice as strong as the whole lens.(That is why changing first airspace is an effective means of
    changing focus length of lens to focus.

    The first airspace is made variable for front element focusing,
    all the other parameters are left unchanged, ie only the first air
    space is allow to change.

    when air space is 2.779178mm,
    the focal length of the lens is 50.792358 mm focus at about about 1 M the lens has 9% spherical abberation ( SA3 =-0.090105 ) and less then 2% distortion (DIST3 =-0.014181 )

    Whan front element extends out to increase airspace to 3.679178mm, the focal length =49.530873 mm, lens focus at 0.67M

    spherical abberation double to 19% (SA3 =-0.188079) distortion increases to 23% (dist3= 0.231360)

    Other Seidel abberations such as chromatic abberation, astigmatism,
    and field curvature etc are not
    as sensitive to change of first airspace thickness.

    In terms of sensitivety of first airspace variation in Tessar,
    apparently distortion is most sensitive, followed
    by spherical abberation.

    Hence limit the close focus distance of MC-Minoxar lens on MDC to 1M
    is good idea, in order to keep overall performance standard high.

    I am not saying that Minoxar close focus to 70cm has 23% distortion
    because my model Tessar is not Minoxar, which I have no lens formulation data.

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