Saturday, 12 January 2008

Photographing a large paper sheet

Once in a while you get landed with the job of photographing something which would be better off scanned, but due to the size of it, or design of it, photographing it is far more practical. In this case, it was a rather large A1 plan. While I can't show you the actual plan due to the contents not being mine to pass on, I can show you how it was done.

So what do we need for a shot of the plan? Well, there are some fold marks on it, so the most important thing is to get these as flat as possible. Having done this, all you need is very flat, low contrast, non-directional light. Any directional light will show up as highlights or shadows at the creases.

I set up two diffusers to the top and bottom of the plan. You'll notice if you look at the following image that they are angled away from the plan. If they were angled over the plan, there'd be more chance of getting worse highlights on the creases. The diffuser in this case the white diffuser from a Portaflash 5 in 1 Reflector set, supported by a Portaflash 5 in 1 Reflector Support which attaches to any light stand. Because I like them, and they're inexpensive, I used a Portaflash Light Stand

A couple of flashes were then positioned on the outside of the diffusers. I guessed at 1/4 power on the 550EX (equivalent to Canon 580EX II) flashes, and was spot on for ISO 400 f/5.6. Because the plan was sitting vertically, I was using a relatively wide angle lens, and didn't really need too much depth of field. I stood to one side and leaned out over the image. The flash is exposing the image, so I wasn't too worried about shaking the camera provided I got a reasonably good framing.

The light wasn't just the diffusers either. Because of the positioning of the flashes, I was getting a lot of fill light from the ceiling, with the exception of the area blocked by me and the camera.

Having got the shot, I brought it into PS and did a slight adjustment to square up the plan in the frame, and that was the job done. The result was just about as good as a scan, except the resolution wasn't too hot. A1 paper is pretty large to photograph with a 10 megapixel dslr (I use a Canon EOS 40D). Given a dslr with 16-25 megapixel, this image would have been every bit the match of a scanner. Still, everything was readable with a 10 megapixel shot, so it did the job.

The other option for improvement would be to pin the plan up, light it the same way, but everything set relative to the plan hanging on the wall and use a longer lens. This would help reduce the slight distortion I saw with the wide angle lens. Not only that, but with a long lens, you could take two or three shots across the plan, and then join them as a panorama style image. This isn't great done with a wide angle as the distortion makes a mess of the joins.

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