Difference between Minoxar lens and Minoctar lens on 35mm models

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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;

Marking:

(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

ring

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)

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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.

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The same Minoxar lens was allow to close focus on GT-E to 70cm, one

MDC close focus only to 90 cm. <p>

I believe the designer of MDC wanted to control the lens abberations

to tighter specification than on GT-E<p>

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.

Note:

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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