[Guest]

At least for canon lenses I can vouch that I never had rain problems. I have been shooting with canon for over 10 years and dragged my equipment from the dusty Australian and Indian deserts up to the mountains of the Himalaya without any problems. No dust in the lenses and no water damage.

With Nikon I know that they equip some of their pro-sumer lenses with rubber seals at the lens mount. I am not sure what the point of this is because the rest of the barrel of pro-sumer lenses isnt sealed. Of course most modern nikon professional lenses are fully sealed. Canon L lenses are almost all weather sealed including mount seals (the exception being old L lenses like the 70-200 f/4 non-IS).

Sigma and Tamron lenses are not sealed per se but I never had any weather related problems with them ( Used Sigma 70-200 2.8 and Tamron 17-50 2.8). With regards to weather sealing they are as good as canon or nikon consumer lenses.

However with sigma I had miserable Af experince and the build quality was just crap. Of course while new their lenses feel nice and solid. But my 70-200 lost lots of its EX-paint over the time and the HSM motor started making squeaking noises. In addition Af could not be calibrated beccause it backfokused at one focal length and front-focused at others. Their was also a focus shift when stopping down. USelss piece of crap.

Tamron was a very good lens. extremly sharp and precise fokus. I just hated the loud motor which was a nuisance in quiet places so I got rid of the lens. Taking about third party lenses, Tokina's lens are very nicely build and their wideangle lenses are just great. In general I would howver strongly adivise to buy only original lenses. Unless of course you need somthing canon or nikon dont make such as an 8-16mm lens or an 11-16 f/ 2.8 or a 50-150mm.