dinsdale wanted in on the action. >> he got a sequence of film. >> on his fourth day at the lake, timwhat thousands before and since have tried and failed to film. >> he described it as for all well being like the back of an african buffalo. same color tone. quite an enormous -- quite a large object. it was seven feet wide, seven feet out of the water with a sort of reddish-brown hide. and as he watched this thing, it suddenly took off. then he realized -- remembered why he was there. then he started filming. >> is this the elusive loch ness monster finally caught on camera? >> well, that's the perennial question, isn't it? that's the $64,000 question. he really didn't know what it was he'd filmed. >> for 50 years, this grainy, 62-second film has captivated the world. >> it was analyzed by the royal air force in 1965. and they measured the object you can see in the film. and they say it's six feet wide across, five feet high out of the water. it moves up to ten miles per hour. as it's moving, it gets lower in the water. and their assessment is it's not a boat, can't be a submarine. so