Optical Experiment

This post will explain how to easily make a room sized camera obscura by placing a lens on a window and having the outside view projected onto the opposite wall, as seen below:



Carboni's "The sky in a room" site explains this experiment and how to mount the lens on shutters. His plans look like they would work great, but if you don't want to spend very much money or if you would like to see it first before permanently attaching shutters, there is a less expensive option.

What I did was cover the entire window with poster board to block all light from entering the room, cut a 1" diameter hole in the poster board, and then taped the lens over the hole.

A blank lens can be purchased from an optician at a store that sells eye glasses. Depending on the size of your room, you may need to have it ground to the appropriate size, as described on Carboni's site.

Miscellaneous notes:

Before asking the optician to grind the lens, try it on the window first, the one that I bought worked great without modification.

It will look better if you use white poster board with white duct tape, or black poster board with black duct tape.

Keep in mind that the landscape will be upside down as seen projected on the wall.

The effect works well on sunny days, and not very well when it's cloudy.

The best use for this is probably if your window faces the east, so you can see the sunrise on your wall when you wake up.

The room needs to be totally dark except for the light entering through the lens.

In the afternoon, it will look a little better after your eyes have had a few minutes to adjust.

Also it's best if the window faces a view with some activity, it can be entertaining to see cars moving and people jogging upside down across your wall.

If the image doesn't seem bright enough, it will help to mount a small box over the lens. The box should be open at the top and have a hole in the bottom sized to allow light to fall on the entire opposite wall, but to block light from falling on the other two walls, the floor, and the ceiling. This will limit the amount of light in the room and make the image appear brighter. Or instead of a box, you could taped some folded pieces of paper next to the lens to block the light.

Probably a good idea to clean the window inside and out to be sure that you get the maximum amount of light possible.

Viewed from up close, the image on my wall is not perfectly in focus, but as you can see in the photo, if you step back it looks decent.

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