Archived posting to the Leica Users Group, 1997/06/02

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Subject: Lenstests.
From: captyng@vtx.ch (Gerard Captijn)
Date: Mon, 02 Jun 1997 13:51:23 +0200

Certain LUG members, including  me, have questioned the seriousness of
certain elements of lens tests. I found a quite illustrative example today.

One of the best lenses in todays range of M glass is the Tele-Elmarit-M
90mm/f2,8. The french photo monthly Chasseur d'Images published in 1996 an
excellent test, awarding 5 stars (their highest rating is 5 stars and they
give 5 star rating to only to a few lenses).

The Elmarit-R 90mm/f2,8 is optically identical to the Tele-Elmarit-M (same
glass mounted in different metal). Chasseur d'Images rated this month the
Elmarit-R 4 stars. If one compares the definition diagrams, the corners come
out approximately the same but the center of the Elmarit-R shows clearly
better definition than the center of the identical Tele-Elmarit-M. Given the
extremely small tolerances under which Leica produces glass, normal
production variances cannot explain these differences. It must be the
testing methods used. QED.

Despite obvious flaws in lens testing however, I think that lens tests are
useful for those in the market for a new lens. The best aperture of both -M
and -R versions was f 5,6.   
 
Gerard Captijn
Geneva, Switzerland
Email: captyng@vtx.ch
Telephone/fax: +41 22 700 39 28