slit scan at last

Today I finally got round to experimenting with an analogue slit-scan setup. I’ve started toying with this idea just over a year ago, tinkered with it in Processing, and have been actively preparing for this analogue version for the last few days.

I printed a large abstract image found on the web onto an A4 size transparent sheet, placed it on an A1 size light table, then covered it with a large sheet of dark paper into which I’d cut a narrow slit, just narrower than the width of the image.

I placed all of these under an old photographic enlarger that is securely bolted to the wall in the darkroom at work. I cut a hole in the base of a plastic box for the camera lens to poke through, then used gaffer tape to hold the box against the lens mounting on the enlarger.

Testing the rig proved rather laborious. When the enlarger head was high, I had to stand on a chair to review the test image on the camera’s LCD screen, so a live feed to a laptop would have been useful. In the end, I had the aperture set at f16, started the movement at 50cm above the base of the enlarger and stopped when the enlarger head couldn’t go any lower. Even then, I had to raise the light table on boxes so that the enlarger head finished close enough to the image.

My Heath Robinson rig did what it had to do, but it was far from perfect. The widest part of the lens was too wide to fit through the hole, so I had to take the lens off the camera body when I inserted the camera into the box, then reattach the lens through the hole. This was made even more awkward by having to feed the shutter release cable in between the strips of gaffer tape. As a result, I had to switch off the Auto Power Off setting on the camera as it was too awkward to keep re-waking the camera before each test shot. Furthermore, there no way of fixing the camera in place so that it would slot into exactly the same orientation in the hole in the bottom of the box.

Still, these were merely nuisances rather than serious flaws. I could, if I were going to be using this kit often enough to make it worthwhile, arrange things better and in such a way that the various parts could be locked down to avoid undesired movement.

Even so, there are still too many variables with this approach. One or two might have given it an acceptable hand-made appearance rather than a sterile digital look, but even the few frames I captured differed too much.

As you’d expect, there was no motor to raise or lower the enlarger head, so I had to do it manually. Not only was it difficult to maintain a constant speed of camera movement during each photograph (which led to horizontal bands of brighter and darker patches), but it proved impossible to maintain constant overall exposure for each frame. My hands soon got tired and I slowed down, so the later frames were exposed for longer and were therefore brighter.

There is a more fundamental problem with this whole approach, however. I’m not convinced that this is really how the original slit scans were created, but I’ll leave discussion of that to another blog post. In the meantime, I’ll go away and compile a brief clip of my first attempt.

Tags: slit scan