Archived posting to the Leica Users Group, 1998/09/21

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Subject: [Leica] Lens wt vs finish->Now question about titanium
From: Frank Dernie <FrankDernie@compuserve.com>
Date: Mon, 21 Sep 1998 15:26:19 -0400

Dan Cardish wrote

"I have been told that titanium is no more coslty than steel, and not any=

more difficult to machine."

Sorry Don you have been told wrong. =

 Loads of "high tech" materials are used in consumer goods for marketing =
or
fashion  reasons only. (They are often used inappropriately by engineers =
as
well!)
Titanium is more difficult to machine than aluminium and much more
difficult than brass. It is true that there are some difficult to machine=

steels, none are appropriate for a lens barrel.
Even the cheapest titanium alloys are expensive.  For manufacturing small=

quantities however the material cost is usually small compared with
manufacturing costs. In fact most engineering plastics are many times moo=
re
expensive than metals but when parts can be injection moulded in vast
quantity work out quite inexpensive compared to the same thing in metal.
This is the problem for Leica. They do not make a mass market camera so
their production volumes are small. They can never be cheap.

Titanium would be inappropriate for the barrel of a lens. Whilst the
turning would be easy the engravings would be difficult. To achieve an
attractive surface finish is expensive. The coefficient of friction is hi=
gh
and the surfce is prone to galling unless specially coated (expensive and=

inconsistent colour from batch to batch) so the feel would be either
horrible or inconsistent and would change with temperature due to
differential thermal expansion with the brass parts aligning the optical
elements. A titanium lens would be between the black and chrome ones in
weight.

The anodised aluminium Leica M lenses are wonderfully light but prone for=

the high spots to show marks quite easily due to the softness of the ally=

under the surface. The chrome plated lenses are harder and seem more
robust. I think they look great too, but I resent their weight. Pure
titanium would be in between the two in robustness and weight so what wou=
ld
be the point? (Many people frget that Ti is heavier than Ally) I am sure
the coating on the brass of the "titanium" lenses is not pure titanium (i=
f
it were it would be less robust than chrome not more so as the literature=

claims) and choosing it is a matter for cosmetic taste only.

Alexey Merz wrote
"high tensile strength, excellent corrosion resistance,and superior
resistance to fatigue-related failure".
Titanium is certainly excellent at corrosion resistance but the 6Al4V
normal alloy is not especially strong and all Ti alloys are extremely not=
ch
sensitive and prone to cracking. Also because of its low Youngs modulus
Titanium parts are not very stiff. Still its a good material for a very
limited number of applications. It is specified far to often for
fashionable rather than technically sound reasons!

Ti does not make a very good choice for a lens barrel in my view.

Cheers Frank