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Imagemaster wrote: Well I guess structural engineers don't have a clue what they are doing when they use rubber as a seismic isolation material in buildings.
You may guess they are clueless, but I know they have a clue, certainly. Let me provide it to you:
Rubber damping for seismic purposes is completely different from the situation of a rubber lens hood.
The seismic damping material is already in contact with the grounded elements and the structural elements. It does not receive an impact. The rubber absorbs the energy but retransmits it on the other side. The ground delivers a very sharp shock to the rubber: a high G force, since as you know, G stands for gravitational acceleration. The ground delivers a very high acceleration (second derivative) to the rubber and that also includes higher order derivatives (the third derivative is known as "lurch"). When the rubber transmits the energy, it does so more slowly than it received it. So the acceleration (dv/dt) is reduced because of the longer time involved. Thus the building does not experience the sharp shock.
The absorption and retransmission of energy is the principle by which a rubber ball bounces.
The situation with rubber lens hoods is very different, as will be obvious to most of our readers. A lens hood that receives an impact is not in contact with the impacting object until the moment of impact. But more importantly, the material is very different. Collapsible rubber lens hoods are not resilient. They collapse on impact, moving out of the way of the impactor and absorbing no energy. The energy of the impacting object is not impeded until it hits the hard metal ring that tightly connects the hood to the lens. The small dimension of the ring does not permit energy absorption in any significant amount and the energy is transmitted into the interior of the lens, where it can dislodge elements and disturb IS and AF mechanisms. Without a metal or plastic hood in the way, the impactor may also reach the front glass element.
Collapsible rubber screw in lens hoods can also impede the use of filters due to vignetting when stacked.