Bob Steadman asked me to make a lens system to show the POV of a monster that had very poor vision and was looking for a victim to devour. The monster only saw a small spot in focus. That is how we actually see. What I ended up with is a plastic negative diopter eyeglass lens with a hole in the middle. What this does is shift focus "beyond infinity" and therefor out of focus. What is seen through the hole is in focus at what ever the lens is focused on. The negative diopter can be moved around to simulate scanning the scene.

Getting an eyeglass lens dispenser to sell you blank lenses can be a struggle. Some want a prescription. Call around and tell them what you are doing and you will find an understanding person. Tell them that you are not making glasses, but camera filters.

The hole can be drilled with a Plexiglas drill on a lathe (6 jaw outside chuck best) and enlarged with a small sharp boring bar. Taper the hole slightly aimed at the center of the lens to minimize the blend of the diopter and the rest of the scene. You will have to do some experimenting. Try a still lens and camera for testing.
I held the diopter in a Cokin still filter holder. Cokin Professional (P series) has adapter for almost all smaller lenses. Don't overlook the Cokin filters. They will even work with zooms at longer focal lengths. You can attach them to a lens cap or make a matte box rod holder.

You have to use quite wide apertures and mid range focal lengths to soften the blend line.

This method will allow selective focus that is now in vogue. Cutting the diopters smoothly is a trick. A belt sander with very fine grit will do okay. You have to carefully hold the plastic diopter to not scratch it.

Another trick is having a 50 to 100 mm cylindrical lens cut in half-length wise. It will give the same effect as the Cokin "Action Maker Filter" but with more control. Want to give a blur behind a car? The cylindrical lenses are available from Mels Griot. Have them cut them. You might find plastic cylindrical reading magnifiers that could be cut and polished with a sander.

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