@paulbrogden10 wrote:
just a quick question does it get dust in it easily seen some for sale with dust in it? makes you think why as I thought the sport was sealed.
I don't think it is practical, nor physically possible, to make a lens that is absolutely sealed against a vacuum, not unless the lens had absolutely no moving parts, whatsoever. In order for a lens to internally move lens elements back and forth inside of the lens, an exchange of air, or a volume of air, must be displaced from one side of the lens element to the other.
Similarly, any lens that changes its' physical length must somehow accomodate this air displacement when internal elements move back and forth to focus the lens. If not, the lens will either suck air in, more and more as it is used, until it reaches a critical pressure differential and BAD happens. Or, more and more air can be pushed out of the lens body, until it reachess a critical pressure differnetial until EVEN WORSE happens.
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"Fooling computers since 1972."
