genius. will have to try - -4 to -14 seems like a really useful range too. the only draw back I can see is knowing exactly how much light is being blocked for metering purposes - not a problem if you've TTL but if not, if could mean either calibrating the filter or removing it each time to meter through it ... mind you, you'd probably need to take it off to compose anyway ... unless you're using a TLR or RF.