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Digital Photography of Documents

John and Rosie Wells

Digital cameras are ideal for copying  documents, especially faded manuscripts. The conventional techniques that we apply to our ground-based and kite aerial archaeological photographs are equally applicable to documents.

Working outside the visible spectrum (Ultra-violet / infra-red) is made more easy, as filters are not needed to block visible light, if the document is lit only by the light of interest. Care should always be taken and appropriate eye protection worn when using UV light.

Professional systems are much more refined (and are coming down in price) but the modern digital camera and (often free) photographic software make basic aspects of these techniques available to everyone.

Colour Channels and Filters

1422 Conveyance to John Bompas by John Tuttebury, son and heir of Henry Tuttebury  

Original colour Colour removed
Red Channel and colour then removed Blue channel then colour removed

Although the differences between the above images is minimal, with some documents, they can be quite pronounced, especially if the document is multi-coloured.  There are other very effective software based techniques. Such approaches can minimise the need for potentially harmful methodologies, using say, ultra-violet light , as pointed out by others.

However, there are few problems nowadays with recording UV images, especially if work is limited to UV-A (320-400 nm). Cameras can be modified to increase their sensitivity to UV light, but many are sufficiently sensitive to work without modification.
 

Fuji S5600 camera converted for full spectrum use plus B+W 403 filter. Illumination: Cheap, hand-held, 41 UV LED flashlight in normal room lighting (400 ISO, f3.2, 1/4sec.)

 

Fuji F30 compact camera (unmodified), 41 UV LED flashlight in darkened room, no filter. (400 ISO, f2.8, 1/15th sec.)

 

As an experiment, we took apart a £20 Premier fixed focus camera, removed the lens (held by two screws) and crudely prised out the hot mirror filter (primarily used to reduce IR transmission but also reduces UV) and then re-assembled the camera. In a darkened room, we illuminated the manuscript with the same UV LED flashlight as above and took the photo below. No filters were used. This illustrates how effective UV images can be produced with equipment (camera plus lighting) costing less than £30. The modified camera can only focus on nearby objects as no plane glass insert was used.

Premier DS-3090S camera (3MP-9CA) (100 ISO, f2.8, 1/8th sec.)

We find that UV LEDs produce crisper images than 365nm UV fluorescent tubes. The light from the LEDs also has a much more prominent visible violet component than from the tubes and will therefore contribute to the above image.

 

Shorter UV wavelengths can be used to control the growth of moulds and other micro-organisms but they can also cause fading of the image / text and damage the substrate.

 

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