Optical variants of the four element 90/4 Elmar?

I Have an interesting observation about that most pedestrian of Leica lenses, the long-lived 4 element 90/4 Elmar. Other than coating, does anyone know of changes in the optical configuration to this lens (prior to release of three element version)?

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I ask this question because I believe there was. Yesterday I was examining three examples, two postwar coated A36 SM lenses (636,xxx and 874,xxx) and a later M mount lens (1713,xxx). The SM lenses appear optically identical, but the M lens is different. Specifically, when a SM lens is mounted on a Leitz 90mm SM to M adapter, and placed on a table next to the M lens, with both set at infinity focus, lens units screwed on firmly,the M lens is longer. I'm not referring to the lens mount, but rather the front of the convex front element is several millimeters higher in the M. This is hard to measure, but easy to see.

The front element in the M is less convex (flatter) and when I look directly into the lenses' front elements my reflection appears upside down in the M, right side up in the SM.

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Thoughts?

I have not looked into the reflections, but I have noted that the

lens head is thicker and considerably heavier for the M mounted

Elmar. Perhaps someone out there has a list of which lenses were

tweaked or recomputed for M mounts in the 1950's. I suspect the

Summaron 3.5/35 and the Summarit 1.5/50.

According to Dennis Laney's "Leica Collector's Guide", the 90mm Elmar

went through the following design changes:

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1931-1932: Fat Elmar. Optically a four element triplet (last two

elements cemented).

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1933-1951: Thin Elmar. Optically the same, but with slimmer lens

tube.

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1951-1963: New style mount. Optically the same, but use of satin

chrome rather than black, as well as the more universal aperture

numbers. This lens is also available in both LTM and M mount (from

1954).

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1954-1968: Collapsible Elmar. This lens uses the same 4 element

triplet design, and interestingly it retains this design through the

life of the lens, even though the rigid mount switches to a three

element design in mid-production of the collapsible.

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1964-1968: New optical design. This is where the optics switch from

the heretofore four element triplet design to the straight triplet

with three elements. Justification was stated as advances in glass

properties which allowed one less corrective element.

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So, based on this information as well as the illustrated cross

section of each lens design in the book, the four element Elmar did

in fact use the same optics for the duration of its long life. The

external cosmetics did change quite a bit, but the glass

configuration was the same until 1964, when one element was dropped.

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This could be wrong I guess, but there is only one optical design

represented (pictured in cross-section diagram) for all of the four

element lenses.

Al-

It appears so. Leitz never officially announced the optical design

change from the collapsible 5cm Summicron to the first rigid, and

showed the same cross section. Yet it is obvious to anyone who puts

the two lenses next to each other that they are NOT the same.

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The 9cm/90mm Elmar is an exceedingly common lens. There must be at

least a dozen readers of this forum who own both LTM and M versions.

Hopefully they will contribute there observations soon.

I hadn't noticed these discrepancies. But as you are aware, Leica

made small changes in the optical specs of lenses in the past without

acknowledging them publicly, so what ou say is possible. Sometimes,

these changes were made to facilitate production or because a

particular type of glass used in the lens is no longer available. So

far as I know, the major improvements in actual performance of the

90/4 Elmar were only two: 1) addition of optical coatings after the

war; and 2) the three-element Elmar of 1963-1968 was a better

performer.

Adam,

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I cross referenced my information from above with another book, Paul-

Henrey Van Hasbroeck's "LEICA, A HISTORY ILLUSTRATING EVERY MODEL AND

ACCESSORY" and have found a conflict with the Laney book on this

subject.

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There are variations listed. From serial number 592, 451 the lenses

were coated. And more to your question... from serial number 116,

050, the front element was "flatter". So I would say there is a

strong possibility that what you see it truly a different element

shape, albeit with the same basic formula of four elements in a

triplet formation.

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Having more than one Leica collectors books is like having two

watches with different times displayed. Which one do you believe?

Van Hoesbroeck-

Even though he is at odds with all the rest on this subject, the

directly observable facts support him.

I have LTM Elmar No.808948 of 1950 & M mount Elmar No. 1827276 of

1961, supposedly the same lens. The front of front element to back of

back element distances are respectively 22mm and 28mm, not to mention

a doubling in lens head weight, obviously largely brass mount weight.

It may be the same design, but it ain't the same lens