Ooooh I can agree with that statement, the zoom mechanism of the EF 16-35mm F4 isn't sealed. Mine fell head over (the tripod fell down) into the beach sand... costly repair to get sand because through the zoom mechanism it got to "everywhere" inside the lens although it was really deep down in the sand. Just enough to reach the zoom mechanism...
Fortuneatly, it was at the very end of my trip to New Zealand (night 30 of 31). It just ruined my shots from one night
That sucks. Truly. I feel bad for you. Hopefully better days of shooting since!
It also sounds like you didn't have a protective filter in front of your lense. Yes? If so, why?
I know some people get freaked out about filters in front of their lens due to concerns about color neutrality, light transmission, etc. (This might not be you, Exploreshootshare — but for others.) It is possible to get high quality filters for non-bulbous lenses, to such a point that any effect on your image is probably no worse than your human inability to 100% dial in white points, etc. or the reality that you'll probably adjust balances, hues, and tones in post anyhow. If you're an out and about person, it's much more satisfying (and part of the adventure) to toss $50+ filters that are cracked, scratched, etc. than it is to take your lens to Canon for repair — assuming you even have that option for older or grey market lenses. Heck, glue a spider-cracked filter to a printed photo from your adventure as a conversation starter.
And yes, it's possible to have an accident that shatters your filter and scratches your lens — but seriously, your front element would probably have been junked in the crash anyhow. So you might as well protect against general scenarios. And salt spray. And dust grit. And... the chance to use your sleeve for a quick wipe.
But for the true purists with the chutzpah and grit (pun intended), your lens will get an extra .02% of light and a .01% color fidelity by going full commando with your front element. Sealed or not.
Here's a fun article by Roger Cicala at Lens Rentals on the topic of filter quality. It finalized my opinion on the topic, and since then I always slap a very good filter on my lenses. When I have to toss one, I feel no worse than using up tires on my truck after a good set of adventure years.
Well, I've written (with some misgivings because it has a tendency to create rioting in the streets) several articles about protective filters. Articles that say sometimes you shouldn't use protective filters, and others that say sometimes you do need to use protective filters, and most...
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