Archived posting to the Leica Users Group, 1998/05/04

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Subject: [Leica] Apocromats & Zoom Lenses & Leica philosophy
From: Erwin Puts <>
Date: Mon, 4 May 1998 20:08:47 +0200

"If apocromats are lenses which have been corrected so that the three primary
"colors are in focus on the same plane, then why are there no short focal
"length apocromats, e.g. under 100mm in 35mm format?

Long focus lenses enlarge the object to be photographed, relative to the
'standard' or wide angle lenses. Optical aberrations, being nasty fellows,
also enlarge the chromatic aberrations when the focal length is larger,
Therefore with a wide angle lens these chromatic aberrations are well
within manageable proportions and grow out of hand when in telephoto
livery. Chomatic corrections are quite difficult to manage and then APO is
an answer.

"Do Leica apocromats have an improved color rendition over lenses in which
"only two of the primary colors are in focus on the same plane?

Definitely yes. Leica lenses are even superior to APO designated lenses
from other manufacturers, as the designation APO is not defined. If some
lens had apochromatic-style corrections at f/8, but worse performance at
full aperture it still can have the sticker 'APO", even if it is of very
limited value.

"There is a newer 35-70 f4.0 zoom which appears to be cheaper than the older
"f3.5.  Who designed and who manufactured this lens?

German design, Kyocera build it

"I have heard rumours that different lens families of Leica lenses (i.e. =
"Elmarits or Summicrons, etc.) reflect differing aesthetic preferences =
"(sharpness, colour saturation, contrast). Is this true? If it is, what =
"is the exact philosophy behind this (what are those families purported =
"characteristics)? Is there any documentation from Leica about this?=20
"I know that there are differences; from experience I have learned that I =
"like Elmarits better than others, I'm just not sure why.....

Personal likeness is not debatable. The families of Summicron and Elmarit
just reflect maximum aperture, and no aesthetic design differences. That
said, it is true that a 2,8 design and a 2,0 design will have different
types of aberration correction at full aperture, vanishing when approaching
5,6. In colour saturation and contrast (which is the same as sharpness)
there are no different design  goals.

"The two aspheric elements
"probably play a big part in teh better image quality and lower cost (fewer
"lens elements needed to make corrections if there are aspheric elements).

Be careful here, broad sweeping generalisations can only confuse. The
1,4/35 with one aspherical has the same number of elements than the 1,4/35
with 2 asph elements. And the ASPH Summicron has the same number of
elements than the non-asph version. The Vario 4.0 has the same number of
elements than the vario 3,5. BTW the Vario 4 has only ONE aspherical
surface and not TWO. It is the Tri-Elmar that has TWO aspherical surfaces.