A Sigma 150-500 zoom... and Park cameras didn't have any filters in stock big enough! Its 86mm! I was wary about its size and balance for hand holding, but its fine, beautifully balanced with my Sony A77, was taking pics inside the shop whilst trying it, no problem. Now, where have all those birdies got to? Next stop, mission "get a picture of a hare", now that'll be a challenge.