Thanks a lot. Is it worth getting a 10 stop ND filter for my 10-20mm lens? Also, I am sure that I read somewhere that ND filters can be used to 'eliminate' people etc from a picture. I really cannot get my head around that. Why do they 'disappear'?
Thanks
Brian
Technically speaking they don't. What you read could have been a couple different things but most likely what they were saying is with a long enough exposure, say, 1 minute in duration, something like a person casually walking through the frame would not be in the frame
long enough to be visible in the final shot. Now if a person were to verrry slowly walk through your frame during that one-minute exposure, maybe stopping and freezing in place for a few seconds while they did so, you could get some "ghosting" of the person in the final shot which could be used for creative effect.
You might have come across another technique, called Median Stacking, that's commonly used to remove crowds of people from places like landmarks and what not, but that requires multiple exposures in lieu of a ND filter; though I guess you could use them in conjunction with one another.