Razor-cut?

I was doing some measurements on my Raynox 250 closeup lens to compare measured and calculated minimum focus distances (when the camera is at its minimum focus distance). This is a shot of a sewing-pin pushed through a piece of cardboard at the maximum focus distance (camera focus at infinity). The shadow to the left of the pin is a blurred image of another pin 10.0 mm closer, which comes into focus if the focus of my SX30 is changed to its minimum value of 1.4 m at full optical zoom. So much for the technical stuff.

Near the bottom of the picture there is a blurred widening of the black region. This is below the plane of the cardboard and we are seeing the out-of-focus image of the cardboard that was poked aside as the pin made the hole.

What looks like a horizontal cut across the whole top surface of the cardboard is not a cut at all. Looking at the cardboard by eye, there is no cut or crease. The sharp "cut" is actually shallow depth-of-field - just the portion of the cardboard's surface that is in focus. It is a DOF slightly larger than 0.1 mm, viewed from a shallow angle. From all the turmoil along the "cut", one would think that the cardboard must be quite rough but it is actually the smooth outer surface of cereal-box cardboard.

My wife thinks I'm a little child who can be captivated by poking pins through cardboard and then pestering complete strangers to come and see.

Stephen Barrett wrote:

My wife thinks I'm a little child who can be captivated by poking pins through cardboard and then pestering complete strangers to come and see.

Stephen,

As a dedicated member of the child/technician brigade, I totally understand. Some things are just too cool and it's fun to make discoveries by seeing what makes things tick, even if it be only the way things appear when seen by a childlike yet practiced eye. And who knows what inspiration your findings may present to others who may get ideas for something different and interesting. I do look forward to your posts.

Ed

Stephen, you must apply for a master's degree or doctorate in microscopic photography

Really I'm Very interesting to read your Lessons

Thanks for the comments Ed and Hossam.