Friday 28 September 2018

Concave mirror on Blackpool Pier

I loved the mirrors on Central Pier in Blackpool. This was the concave one. When you are reflected, the top of the mirror sends the rays from your head downwards. The bottom of the mirror sends the rays from your feet upwards. If you stand a long way off, the two rays cross over and the rays from your feet end up on top. You look upside down.
Closer in, the rays have not had a chance to cross over so you are still the right way up. What is more, given that your brain thinks the image is as far behind the mirror as you are in front, it computes where the rays that are converging must have been behind the mirror, working out that they must have been further apart back there. So your brain gives you an image that is bigger than the original.