Originally posted by yeatzee And vice versa
I don't know the science behind it, I just know that I would have had to take a picture of the spiders abdomen in focus to get the reflection spider's eyes in focus
it's actually quite simple really, when you are focusing on a mirror you are actually focusing in a virtual image, as i'm sure you know a mirror reflects light, but what most people don't know is that the light reflected from the mirror is travelling twice the distance that the subject is standing on it.
I'll give you a practical example: if you stand in front of a mirror and focus on the physical plane of the mirror, your reflection will be out of focus. But if you focus on your reflection you will be focusing on an image that is optically twice the distance you are standing from the mirror.
I hope this helps.