On 03.6.7 11:52 PM, "Alan Chan" <[EMAIL PROTECTED]> wrote: > Could it be some sort of super rigid aluminum alloy? I > don't think so, but I have no answer.
Alan, you gave me an opportunity to look into the construction of the metal barrel lenses ! :-). I am an engineer but certain knowledge is rusty and I am not even consulting with any URL's ;-). So, please don't jump on anything I say here off the top of my head. As far as I remember (regardless of what Bruce said ;-), aluminum alloys has been classified by 4 digit numbers depending on the alloy contents. It starts with 1000 series and up to 7000 series etc, 1000 series being almost pure aluminum (i.e., very soft). In fact, aircraft grade aluminum should be 7000 series (7075 or something lime that).. I really do not know if the different aluminum alloys are used in the different parts of the lens (I seriously doubt it). If certain parts are under a lot of stress, they could be using high strength aluminum but I fail to see why they bother to change the alloy material for the lens construction which I believe is a low stress construction, but I obviously am not a lens designer so I won't go any further. But I am personally interested in what you are reporting and will see if I can find someone who can answer these questions. I am almost certain that you are not seeing steel (but I could be wrong). As Tom (Rittenhouse) said, the corrosion is an additional factor. Aluminum severely corrodes but the anodizing cures it. I just cannot imagine that a lens uses so many different kinds of the same material, but if they do, it would be very interesting to know why. Your observation on thread in the other post is very interesting too. It sounds almost like a "galling' but it does not happen on aluminum. Cheers, Ken
