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How to digitise slides. Recommendations and working lists for the reproduction of a very special artefact

The advantages and disadvantages of scanners:

As stated in the section “Technical processes” every reproduction method has its positive and negative sides. There is no “best” device for the reproduction of all objects, compromises are inevitable. Thus it is necessary to take into account what is “won or lost” with a particular apparatus.

1. advantages of scanners:
– a scanner will reproduce the object in its real size;
– a carefully calibrated scanner programmed for homogeneous series of slides assures a homogeneous reproduction as the scanning conditions stay identical
– a scanner is suited for mass production;
– a high-end scanner with its high-resolution sensor and its high colour depth may be able to capture more information from the original than a still-camera.

2. disadvantages of scanners:
– only flat objects can be captured;
– only slides up to a certain size can be scanned;
– the scanning can be relatively slow, depending on the scanner’s speed;
– slightly deformed slides (with curved glass, warped frames) may not be scanned properly as they can’t lie flat on the scanner glass (focus problem);
– mechanical ones with a crank can only be scanned from the flat side;
– scans of frame (reflected light) and image (transmitted light) in a consecutive order is time-consuming as it needs changes in the handling of the scanner (reprogramming, proper configuration of the cover for transmitted light);
– slides with the emulsion on one side of the glass and hand-colouring on the other, or moving slides with two glass plates combined may not be accurately reproduced (focus problem);
– scanner lenses may produce distortion at the scan’s edges what can happen also with still-camera lenses.

3. risks of scanning:
– risks of Newton’s rings are likely to form on the surface when the glass of the slide is in direct contact with the scanner glass; therefore, an accessory (anti-Newton’s ring glass) is needed;
– slides with printed dots or an offset-grid may produce unwanted textures or moiré patterns in the duplicate.

Just for the curious readers: interestingly, a special type of camera uses the scanner principle. According to Eib Eibelshäuser (2005, p. 222, 236) a professional still-camera has a scanning back with a one-dimensional sensor; its row is between 5 and 7cm long and can contain up to 8.500 light sensitive units. When they move, they can cover a surface up to 10cm long (thus 50 to 70cm²) and produce files up to 150MB / scan which can be used for to print images in DIN A2 (see also Langford 2008, p. 113-114).