|Drop your lens and you're
lucky to get away without mechanical damage. Somewhat less common
is broken glass - apart from the occasional smashed filter.
This lens had been knocked and tiny glass shards were falling out the
front so I decided it would be best to go in, clean up the crack and
Typically, the optical performance of these lenses far outdoes their
mechanical performance. This lens here received a knock so hard
that it cracked the front element... or did it?
|The Nikon Nikkor 24-120 auto-focusing zoom
lens has a great selection of focal lengths and is one of the more
popular choices for Nikon enthusiasts.
|A ring and a
few screws later and the element is out on the table. I immediately
noticed that the crack was less a fracture and more a tearing away of a
section of glass.
Closer examination revealed that the glass was broken off exactly in the
pattern of a smear of cement that had been applied in three places
around the element in order to hold it more securely in place (something
the plastic retaining ring was probably not capable of doing on its own!).
|So what happened
This could start an entire debate on the merits of using reinforced
plastic lens barrels. First, the barrel does not dent on impact...
nice.. next, it is too weak to held the heavy glass elements in with its
very loose-fitting plastic thread. Therefore, the glass is secured in place
with cement. On impact, the cement holds onto the glass so tightly that
it literally tears a chunk of the element off as the barrel flexes. So
does anyone or anything benefit from this design decision?
Beware of rant:
No, in fact it isn't even a design decision at all... it's a marketing
and economics decision. Certain political persuasions would even
have you believe that it was your own decision seeing as you are the
consumer... so it's your own fault after all! :))
These particular 24-120 Nikkors are a common patient of mine, usually
turning up with stripped AF teeth or completely bent out of whack from a
fall. In any case, whilst the focal length range is attractive,
this lens is otherwise not worth the high cost unless you insure it
against such damage.