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Tom K. wrote:
Why would it need a zoom lock switch? The 24-70 version 1 didn't need it.
I can think of a few reasons:
- This lens will extend significantly, since it uses an optical layout ("positive-lead" type) that requires that.
- Since it uses positive-lead type optics, the front group of elements is very large and heavy, and therefore acted upon more strongly by gravity.
- The new design translates a small movement of the zoom ring into a large change in length at the wide end of the range (that's why the focal lengths are tightly bunched up at the wide end); said another way, gravity has a large mechanical advantage in extending the zoom at the wide end. This means it will likely flop out to say, 35 mm, with relatively little force (especially after a few years of use!).
- When extended, the total length with hood will increase, whereas the old lens was shrouded in a fixed hood so didn't increase in overall length; it's therefore more important that this new lens doesn't extend by itself.
- The new construction may use more plastic (maybe even the extending barrel?) to reduce weight and cost, which may take its toll on snugness.