What causes the blur when my fingers are almost touching?

Question

I can see this with my bare eyes

Answer 1

You are essentially observing an interference effect. This is equivalent to what you would see in a single slit experiment.

The fringes are caused as the light rays that passes between your fingers are travelling slightly different distance to reach you eye. This causes their phases to be somewhat different. As a result the light rays partially cancel, causing the blur.