Mako2011 wrote:

Sensei Rob wrote:

Mako2011 wrote:

Polycarbonate can withstand forces nearly 200 times stronger than steel. 2DPA-1 and Hemp Plastics are also much stronger than steel

This is a bit of a weird one. You'll often hear things like "spider silk is stronger than steel", or in this case, various plastics are stronger than steel, but the figures never really hold up.

For example, if you look at the young's modulus (the point at which a material elastically deforms), you get these figures:

I don't think your numbers tell the practical story

Polycarbonate can withstand blasts of over 900 psi and is about 200 times stronger than steel by weight, and is also more flexible than steel. Polycarbonate typically has a tensile strength of between 55–75 MPa (advantage steel) but has an advantage over metal in strength-to-stiffness Ratio. Many PC have an impact rating in the IK10 range...same as stainless steel.

We also see the use of Polycarbonate with stainless steel fiber. Pros and cons to that one.

Bottom line...the advantages of "plastics" in lens design really do exceed the use of metal by large margin now. Same basic durability for much less cost and weight with additional design advantages/flexibility

The problem is that plastics is often used for making a product lighter and at lower cost.

From my experience it is plastic parts that most often break, The last three cameras that has broken for me has been because of broken plastic parts. Plastic part just do not seem to last as long as metal parts can.

The last three failures I have had on cameras was because of failure on a plastic part.

- Broken plastic gear in a mirror mechanism

- Broken plastic battery cover

- Crack in plastic body

At least for movable parts, metal seems to be superior to plastics as plastics do not seem to have same life length and wear out faster.

Plastic may work better for fly-by-wire lenses, compared to fully mechanical focus and zoom on DSLR.

I have had numerous of plastic lenses with worn plastic focus and zoom mechanism after a few years leading to increased play and to low friction in the mechanism. Where all metal lenses work fine after 40-50 years.

Plastic can work fine if designed carefully, but it seems that in most cases it seems that low cost is prioritized above life length.