[Leica] Contax N1 + Photokina hopes now hopelessly OT

[Frank Dernie <FrankDernie@compuserve.com>]

Chris Lee wrote
<snip>
The 645's outer plastics are very different from those used on the Aria.
The
goal is to achieve the lowest weight and maximum protection. A mixture of
carbonfibre and plastic was used. The former gives the camera its impact
resistance and lightweight (carbonfiber is actually stronger than steel in
impact absorption), and the latter allows the body to be formed into a more
complex shape. (Very costly do to with carbonfiber if no plastic is added.)

Especially in the low quantities of the Contax 645 produced, the
carbonfiber+plastic can actually be a lot more expensive than steel. It was
certainly not a cost issue.



Chris
As a person who has been using composite materials (mainly carbon/epoxy) in
high performance structures for 20 years I feel an urge to correct, with
respect, a couple of your comments above which are commonly held
misconceptions probably due to marketing use of the buzz word carbon fibre.
Carbon fibre itself is very long fine fibres and is sold as "rope" and
cloth, without a plastic matrix holding the cloth together it is like a
dish towel. It cannot be used structurally apart from as a composite matrix
of plastic reinforced by these fibres. The things that differ between the
high tech and cheap and cheerful versions include the plastic used for the
composite matrix, the ratio of matrix to fibre, the fibre length and its
orientation.

In a high tech carbon structure the matrix is usually a thermoset plastic
such as epoxy and between 50% and 55% carbon fibre. The cloth or
unidirectinal strands of carbon are continuous from one end of the
structure to the other and oriented to give the stiffness required in the
directions necessary. The mechanical properties of the structure are
dominated by the carbon, the plastic is just there to glue the fibres
together.

In the type of "carbon fibre" used in most commercial products the matrix
is a thermoplastic which can be injection moulded. The fibres are little
bits of chopped strands a couple of mm long, any longer and they clog up
the injection moulding machine. The orientation of the fibres is "whichever
direction when the plastic set". The mechanical properties of the part are
dominated by the plastic though there is a worthwhile improvement in
stiffness and particularly temperature stability.

Carbon fibre is actually not particularly strong but it is stiff. Its
resilience is dominated by the type of plastic matrix it is reinforcing. It
is not particularly expensive nowadays, although the manufacturing process
for the high tech structures is.

The thermal stability added to polycarbonates by the chopped carbon strands
is probably the most attractive property for use in lenses (faintly OT)

Carbon Fibre (and titanium) are actually used more for marketing reasons in
consumer products then any real engineering property despite the BS.
cheers Frank