Many sources are telling people that welder’s filters are safe for viewing today’s transit of Venus across the sun, an event that won’t occur again until the year 2017. This advice is both true and dangerously incomplete!
If you buy a welder’s filter it must be shade number 14 and either:
Green Glass (which is fragile and increasing difficult to obtain, now becoming a special order item at welding stores)
Polycarbonate with gold coating (polycarbonate alone provides glare protection for the visible light spectrum but is nearly transparent to infared)
Many #14 welder’s filters lack the gold coating and so many people are suffering eye damage that experts are considering dropping the welder’s filter recommendation altogether.
See Doctor (of astronomy) Ralph Chou’s presentation of ways to view the Venus transit on YouTube at http://youtu.be/4RGr9FcBrSM.