Weather Proof Lenses

[bohaiboy]

A poster in another forum subject suggested that the Canon 100-400 isn't weatherproof. 

I have a few questions regarding that statement as he did not reply to it:

Does your comment on the 100-400 lens reflect on the L series as well?
Why would they not make an L Series weather proof? 
And one more ?  How can you tell if you have water damage inside?

[neuroanatomist]

So...here's the deal.  Only some L-series lenses are 'weather and dust resistant' - mostly the newer ones.  The way to tell is that sealed lenses have a rubber gasket at the mount ring. Older L lenses lack sealing because Canon hadn't yet included it as a feature. Most newer L lenses are sealed, with some exceptions (e.g. 85L II).

The 100-400mm, and other per-1999 white lenses, are actually partially sealed. They have moderate sealing at the switches and focus/zoom rings, but lack the mount gasket.  Note that this info isn't in spec sheets, it came from an email exchange I personally had with Chuck Westfall (Canon's tech guru). 

As for water damage, if you see moisture inside, or you know it's been exposed to water and electronic systems stop working, water damage may be the cause.

[bohaiboy]

Thx neuro, I have a 100-400 4.5-5.6L IS USM and a 24-105 1:4L IS USM.  I do not see any seal on the mounting areas of either, so I guess I should assume they are not weatherproof.  Guess I will be more careful in the elements.  I wonder if there is a way to put some type of thin O-Ring on the base to help.

One would think that Canon would have made the connection that 100-400 is MOST LIKELY going to be used in an outside environment.

[neuroanatomist]

The 24-105 L is sealed, and has the gasket.

It's worth noting that a sealed lens is only useful if the body is also sealed (1-series >> 7D = 5DIII > 5DII = 50/60D, nothing lower or older is sealed).

Here's where the gasket is: