Back button focus

At tonight's camera club we had the opportunity to ask about specific camera related issues, and this included filter lenses and back button focus.  

Here is our Chairman nonpcplod, showing someone how to do the settings step by step.  This sort of one-to-one help is invaluable to those of us less knowledgeable and a reason why I find the group so supportive.

I was in the kitchen and supposed to be serving the tea and biscuits.