[Leica] Tri-Elmar and zoom and Thank you Erwin!!

["Kotsinadelis, Peter (Peter)" <peterk@lucent.com>]

Thank you Erwin.  At least now I understand why the T-E v. a zoom.
This is what I was looking to understand when I posed the question 
about what LUGgites thought of a the G Zoom. And later asked if Leica
would be able to have a zoom on an M body.  

Peter K

- -----Original Message-----
From: Erwin Puts [mailto:imxputs@knoware.nl]
Sent: Saturday, December 18, 1999 2:37 AM
To: leica-users@mejac.palo-alto.ca.us
Cc: leica@topica.com
Subject: [Leica] [Leica} Tri-Elmar and zoom


Why did Leica design a three focal length lens and not a zoom? First 
of all the Tri-Elmar is optically a zoomlens, just as all other 
zoomlenses. The design uses the familiar fixed main optical cell, the 
front cell for focusing  and the moving lens groups as compensator 
for back focal distance and variator for change of focal length. The 
Leica M happens to use a mechanical linkage to bring in the correct 
frame masks when changing lenses. So the "zoomlens" must have a 
mechanical linkage too in order to activate the correct frames when 
changing focal length.  Had the M body a zoom viewfinder like the 
Contax G, then the tri-elmar would be called a vario-elmar-m 4/28-50 
asph and would function like any zoomlens.
Because the Tri-Elmar has been designed to be used on all M bodies 
(backward compatibility!), the mechanical engineering needed to 
consider the demands of all M bodies, including the M3, was quite 
daunting. Not well known is the fact that any zoomlens when changing 
focal length also changes focus a bit. The Tri-ELmar is so accurately 
engineered and mounted that no change of focus is detectable when 
changing focal length. Can the intermediate positions be used? In 
theory yes, but when you use any intermediate position the several 
lens groups are located "somewhere" in the mount and so the actual 
plane of focus is also located "somewhere" in space. You will get a 
sharp picture but you do not know where you are focusing at, whatever 
the rangefinder says.
Some comments on the maximum aperture. We now speak with some disdain 
about an f/4 aperture. Do we remember that from 1925 till 1960 the 
workhorse lens was the Elmar 3.5/50? And that with film sensibility 
around 10 to 50 ASA. Many HCB pictures are made with apertures around 
5.6. In my view the demand for f/2 lenses and wider, even in the 
classical M picture environment is a bit exaggerated. Of course there 
are situations where a 1.4 and a filmspeed of 1600 will save the day. 
But in many situations an f/4 will do very fine. Optically the 
Tri-Elmar is equal to the current 28, 35 and 50 lenses at relevant 
apertures. A few years ago Canon did a very extensive study on the 
use of apertures and examined thousands of pictures. Result? 
Apertures wider than 2.8 are very scarce in practical use. There is 
hardly any professional zoomlens with an aperture wider than 2.8. 
That fills the need of many users.
I use the silver chrome version quite extensively myself and find it 
a jewel to use.Its weight and smoothness and the clear M-finder let 
me use shutterspeeds of 1/15 and lower and with 400ISO XP2 Super I 
get very fine grained images, even in very dark surroundings. When 
shooting at around 2 to 3 meters my favorite subjects ( cats and 
models) the additional depth of field (when compared to using a 
Summicron wide open) gives more depth to the body (literally and 
figuratively). There are always two sides on any coin.
The argument that you do not have to consider a Tri-Elmar when you 
already have a 35 or a 50 is not fully valid. I had a pre asph 2/35 
and when considering a move to the 2/35 asph I also looked at the 
T-E. I even sold my 2/50 Summicron. For low light I can use the 
Summilux 1.4/75 and for superior image quality at f/2 I have the best 
of all: the apo-summicron 2/90.
The additional freedom and flexibility you gain when using the T-E at 
close distances in dynamic situations more than compensates the f/4. 
You even get new perspectives as you are forced to limit yourself to 
this aperture. There is no need for stopping down given the excellent 
image quality.

Erwin