The Blue tit is smaller and has blue and yellow in its colouring while the great tit is more blacks and greens and is much bigger - a much more agressive bird than the blue. You can also get coal tits, long tailed tits, marsh tits and willow tits. ....as you can see, I know a lot about tits, I lived a very sheltered life when I was a kid. You should speak with EOS man - (Andy) he went over to the scilly isles photographing puffins with Andy Rouse the wildlife photographer - he probably has a few tips too. (uses a canon though so he is not a real photographer)