I'm building a home studio to record Math classes: I have a blackboard (1,90m width by 1,20m height) and the distance from the camera to the blackboard would be around 1,80m (on a tripod, 1,70m from the ground).
How can I calculate the lens I should buy to record the full width and height of the blackboard?
I'm planning on buying a Canon 70D for the studio.
Thank you.