Think I have a sick apple tree

Hi all, im new here. We have moved to my in laws house which has 4 well established apple trees, the varieties I don't know. The trees are at least 40 - 50 years old. My husband has come in this evening with this leaf, a lot of leaves have also fallen, (we were going to blame the children!) the tree seems to have a good covering of blossom.  Is this a rust disease? Fungal? If so Any thoughts what can we do?  

We did prune some branches earlier in the year, the trees haven't had a lot done to them over the last few years. A reasonable  number of apples seemed to be marked last year, although a good amount were edible. 

Any thoughts much appreciated.