I’m sometimes asked how/if Sigma’s Art, Contemporary and Sports lenses are protected against the elements. Hopefully this post will shed some light on this topic!
The following excerpt from an interview with Sigma should drive the point home:
Q: Several readers wanted to know: “Is the 35mm weather sealed on Canon weather sealed bodies?”
A: No, the only lenses that are weather-sealed are in the Sports category.
Things are clear for Sports lenses – they are fully weather proofed (the 120-300mm f/2.8 S has the same level of sealing as the 150-600mm f/5-6.3 S). The others are not.
However, a somewhat contradictory information came from a Sigma rep regarding Art lenses in particular:
The rubber gasket on the Nikon lens mount does not weather seal the lens. It in fact it traps moisture that can enter through other areas. In order for a lens to be truly sealed for moisture it would require an air check valve which no other manufacturer uses. We seal the lens with special bandings that allow the barrels to move and air to flow throughout the lens. It is very important for moisture that is in humid air to be able to escape the lens. The seals we use will keep dirt and moisture out of the lens but if you get hit by a wave or caught in a prolonged downpour our lens will suffer the same fate as the Nikon lens you falsely trust with its rubber gasket.
This was posted on the DPReview forum.
Art (and Contemporary?) lenses are designed not to let moisture build up inside them, when they’re subject to temperature contrasts, and more generally, used in a humid atmosphere.
But it’s unclear how the lenses keep “dirt” out if they are made to let air flow in and out. From the rep’s explanation, it sounds like they could actually be less sealed for very small particles, compared to lenses with no “air check valve”. Hard to tell without proper tests though.
Oddly enough, this feature is absent from Sigma’s marketing claims, so I suppose it must not be such a strong asset. In any case, I wouldn’t call this “weather sealing”. So don’t assume that your Sigma 35mm f/1.4 Art lens can handle rainy or dusty conditions like Sports lenses can.
Also, the 150-600mm f/5-6.3 Contemporary boasts a rubber gasket at the mount, but this is primarily to prevent water and dust from entering the camera. Unlike its Sports sibling (see image), the lens has no seals throughout the barrel.