If you're shooting in a difficult environment, where there's inconsistent weather or potentially people bumping into your lenses, it's nice to know you've got a filter protecting your expensive investment.
While many people do use filters, often they're haze filters that have an effect on the image even when you don't want one. Sigma has brand new ceramic lens filters that they claim have no effect on the image and transmit nearly 100% of the light. Essentially these should be stronger than most glass filters, and are also scratch and shock resistant, water repellant, and prevent static electricity from attracting dust. The coating also minimizes ghosting and flares. Here's more on the filters and the technology involved:
And here are the specs on these filters:
- Clear Protection Filter
- Prevents Damage to Lens
- 1x Filter Factor, +0 Stop
- 99.76% Transmittance
- No Effect on Image
- Clear Glass Ceramic Construction
- Scratch- and Shock-Resistant
- Water-Repellent Coating
- 67, 72, 77, 82, 86, 95, and 105mm
- Availability: January 2016
- From $93 to $315
These could be great for people who shoot lots of sporting events outdoors where the weather can be unpredictable, and where it's entirely possible for something to knock into the front of your lens. Every piece of glass is going to affect your image in some way, but the idea with these is that things should be nearly identical — just with an extra protective layer.
The Sigma filters aren't cheap though. The least expensive filter is the 67mm at $93, and the 72mm and 77mm are a little over $100 (and they go up exponentially from there as they get bigger). If you know you're putting your expensive lenses in harm's way and you want a protective filter, these are worth a look.
They aren't shipping just yet, but expect them sometime in January.