Picture taken with camera obscura on scanner bed
Scanners have found their way into many households. I rarely get any use from my scanner at home, but as these devices are piggy backing on printers now days it would be silly not to get a machine with the both combined. I’ve come across a way of using the scanner to take pictures. I don’t mean scanning photographs (silly!), but more akin to a camera, capturing an image of the world in front of it.
This type of scanner photography, sometimes referred to as as scanography encompasses a whole range of techniques of acquiring images of things that are not just your standard sheet of paper. Most of scanography is taken up by imaging various objects on the glass plate of the scanner, but the part I’m really interested in is taking a photograph of the scene in front of the scanner. This can be achieved by focusing the image from a camera obscura onto the plate which the scanner scans its image. Looking around I found a little video on Make magazines website of a camera obscura you could attach to a flatbed scanner but as we now have these clunkier printer scanner all in one machines, turning the whole thing on its front seems like a daft thing to do if you wanted your machine to continue working. I knew there was a solution and that it would involve a mirror.
I could use a mirror at 45 degrees to reflect the rays travelling horizontally toward the camera obscura, down toward the scanning face of the scanner. I decided to put the mirror inside the box rather than on the top, as it would allow me to keep the opening for the light on the front face. After a quick test with a pinhole I realised that I would need to gather more light, which could be done by enlarging the hole and using a magnifying glass. Its important to choose a lens with a suitable focal distance. To measure the distance, grab your lens and a ruler and try to project the light from your tv (or other similar bright object) onto a piece of paper. When you are doing this make sure the distance from the TV to the lens is about the same distance your subject is likely to be in front of the scanner. Measuring the distance from your lens to the paper (showing a clear image of the tv) and jot it down somewhere. It’s hard to tell what a suitable lens is but my one had a diameter of about 8cm, and a focal distance about 25cm. Having a lens that is just bigger than the diameter of a roll of tape is useful as I found I could use this to hold the lens and slide it back and forth to adjust the focus. You need to match your lens with your box and find an arrangement that would allow the distance from the base to the mirror and the distance from the mirror to the lens sum up to the focal length you found earlier.
Camera Obscura on scanner
I used black paper inside the box to stop stray light from inside the scanner overwhelming the light coming from the source. A used roll of tape made a good holder for my hand lens, which I secured with tape to the box after cutting a hole slightly smaller than the lens into the box. Other things that could work is using black paint inside the box and I can imagine a tin can or half a Pringle tube to help hold the lens.
I used a small glass mirror and attached it to a piece of cardboard I had cut off the flaps. In hindsight a lighter plastic mirror would have been lighter and less likely to drop. Conveniently as the box used to hold reams of paper, the flap on the long side could fit inside at a 45 degree angle as its length is root 2 times the width. To reinforce the card I took the two edges of the cut card and folded them at 90 degrees so it was less likely to buckle, cutting the corners at 45 degrees allowed it to fit inside the box.
I little doodle of making the mirror holding card
There’s a few tweaks which I found useful when trying to get a more practical box. Some scanners don’t have covers which are detachable and open to a wide enough angle to fit the entire box. For this I had to reshape the back half of the box so that it would. The tape lens holder was replaced with a thicker one (like used for parcel or duct tape) so more control of the focus could be achieved. The further the lens from the bed, the close the focal distance. Having a box that is a bit larger than the bed is a good idea as the light from the scanner will not reflect off the edge of the box. I haven’t had much success when using this on photocopier machines, maybe because of its auto-leveling function which drowns out the light coming through the lens with the excess being reflected by the box edges. It may be possible to get it to work on them by making sure the rest of the glass is covered with a material that reflects very little light (black cloth?).
Funny thing about taking scans is that although you take colour one the resulting image is appears greyscale. I hypothesised that this is a by-product of the way some modern scanners acquire colour information. Instead of having three sensors that can sense red, green and blue light, and combining this to form coloured images, this scanner shone in a sequence red light, blue light and green light and measure the input with a sensor that is sensitive to all light across the visible spectrum (hmm… I wonder if it reacts to infra-red also?). Follow me on my experiments with trying to trick it into giving me colours in my next post.
Scan taken from further away