I've been using my Nikon D5100 with the Sigma DG 70-300mm (borrowed from a friend) for field hockey pics and have been very pleased. Also use my Nikor 55-200mm with great results.
Below are some action pics, none of them are staged, all taken during game action. Actual pics of the girls are equally good (IMO), but I don't want post them publicly.
Field Hockey 4 by Jason Weller, on Flickr
Field Hockey 3 by Jason Weller, on Flickr
Field Hockey 2 by Jason Weller, on Flickr
Field Hockey 1 by Jason Weller, on Flickr
13 (1 of 1) by Jason Weller, on Flickr
20 (1 of 1) by Jason Weller, on Flickr
Below are some action pics, none of them are staged, all taken during game action. Actual pics of the girls are equally good (IMO), but I don't want post them publicly.





