Often cheap polymer thermoplastics,in other cases advanced carbon composites and semi-crystalline Polycarbonates and in other cases Metals such as Aluminium, Brass and Magnesium alloys. Lens barrels are seldom made of a singular material, they are frequently a mixed combination of materials.
Originally posted by pschlute All lens elements are glass.
Optical glass which is a silicon dioxide based amorphous solid*, is easily manufactured, formed and polished. However its optical properties and physical properties can be modified through the addition of various metal oxides and non-metals such as: Boron, Lead**, Copper, Cobalt, Tantalum, Cadmium**, Phosphorus**, Calcium, Vanadium, Magnesium, Sulfur and Arsenic**. These elements are added in trace amounts to alter mechanical properties as well as optical refractive index (and also to change colour transmittance of the lens itself). Older lenses can have radioactive elements such as, Thorium (mildly radioactive) Strontium (very radioactive) Lanthanum isotopes (strongly radioactive), as these elements decay radioactively the energy given off causes the lens element to eventually turn Yellow / Deep amber - The precise manner in which this yellowing occurs is a matter of ongoing debate: One hypothesis suggests it is the formation of colour centers created through highly energetic radioactive decay within the structure of the glass itself that cause the discoloration; another hypothesis is that the micrometer thin metallic coatings on the surface of the lens element ( there can be up to 13 different coatings of various metallic compositions on a single lens element) are affected by the radioactive decay and are (reversibly) transformed into an altered chemical state by it.
Originally posted by i_trax Mine is STABILIZED , good for milkshakes.
Wouldn't having a gyroscopically stabilized container suppress any external force and lead to a disappointing milkshake?
Originally posted by 35mmfilmfan in fond memory (or is that mammary ?) of Marie Antoinette
If those glasses were made these days they would look
VERY different.
Originally posted by BigMackCam Except the ones that aren't For example, the hybrid aspherical elements in various models, including the DA15...
These are at least
partially made of glass with a polycartbonate aspheric element bonded to it. I'd imagine it would be quite a nuisance to get the refractive indexes of the materials to match.
*Natural glass does exist, any natural process where high temperatures and a suitable silicate material is present can produce glass, lightning strikes on the beach (Fulgerites) Volcanic glass ( Obsidian). Also naturally grown crystals can be used for lenses, though they have pretty abysmal optical transmittance compared to synthetically lab grown ones.
** Thankfully the inclusion of these elements has been greatly reduced over the decades since RoHS and similar environmental safety and waste management measures have been put in place.