Focus on Pictures


Photography of shiny objects


Digital or conventional photography ?

The photographer (not the camera) takes the picture. The camera merely records and testifies to your skills as a photographer.

This is not the place for a detailed discussion of either digital or conventional photography. If you want to know more about these do by all means pay a visit to e.g. 'The image' or to 'Making the transition from film to digital'.

In principle it is irrelevant whether you use a digital or a film camera, as it is not the camera but the photographer who takes the picture. Photography is the art of seeing, of optimally depicting a scene by writing with light, where the camera acts as an instrument that offers a limited or a wide range of technical facilities. In practice. however, depending on what you are willing to pay for the photographic equipment, there are important differences, each type of equipment having pros and cons.

What will you use the picture for:

This is not the end of the story. After all, we need to know the colour of each pixel: colour resolution. There are several systems to represent colours in the colour spectrum. In the RGB system the primary colours Red, Green and Blue Colours can be used in any combination to produce all the colours of the spectrum, including white (see colour temperature Kleurtemperatuur). In digital parlance each primary colour is represented by a number of bits. You should regard a bit as something that can represent two states, such as on/off, yes/no, black/white. One bit can therefore have two states, 2 bits 4 states (2²). An 8 bit resolution can therefore represent 2 raised to the 8th power = 256 colour shades, similarly 16 bit resolution maximally 216 = 65536, and 24 bits (also called ‘true color’) 16.777.216 colour shades. If red, green and blue are each represented with 8 bit resolution (each 256 states), then the combination is said to be 3x8 = 24 bit. This is the resolution that one commonly sees on computer screens. Although 24 bit resolution therefore seems satisfactory, it leaves something to be desired. This is because by far the most information is contained in the lightest parts of the picture, leaving little resolution in the darker areas. If you use software to adjust the tonality of the picture (via Levels, Brightness, Contrast) you are shifting bit levels. If these levels are limited to 8 bit, then shifting easily creates gaps, and this is most noticeable in shadow areas, which loose detail. Therefore, preferably record you digital pictures in RAW format (not JPEG, which is 3x8 = 24 bit), which allows you to read and store the picture at 3x16 = 48 bit resolution. Doing all your adjustments at 48 bit resolution best preserves detail in the darkest tones. Do read more about this in 'Maximizing image information without blowing it' in Making the transition from film to digital.

Reproduction via flat bed scanner

Violet: enamel on copperViolet: enamel on copperViolet: enamel on copper

This enamel panel is 25x25 cm, which is too wide to be scanned in one go by an A4 scanner. The panel was therefore scanned in two stages. A heavy metal ruler was aligned against the lower border and the first scan performed. The panel was then allowed to slide along the ruler (which was carefully kept in place), and a second scan performed. Using Photoshop® the two scans were carefully superimposed, leading to the picture on the right.
You are likely to find that there are differences in colour levels at the edge of the scan, which show up when you superimpose them. I therefore recommend that the scans overlap widely. You can then discard an edge portion and obtain a transitionless picture. Perform any software manipulation of the image after you have flattened the superimposed images.

Brooch, émail cloisonné

Champlevé silver brooch covered by white or black paper while scanned in a flat bed scanner.

Brooch, émail cloisonné

Silver and gold cannot be satisfactorily reproduced by a flat bed scanner, the metal appearing quite dull. This is because the metal reflects the dull interior of the scanner. There is little you can do about this: replacing the colour of the scanner lid by white or black paper does not improve things (see picture on the left); in either case the silver looks like zinc. Also note the undesirable shadows.
The picture on the right was reproduced from a slide. While taking the photograph care was taken to surrond the brooch with white reflection screens. As the silver now reflects a white environment, the metal looks like silver, as it should.

Depth of field

The number of pixels in an image is just one technical criterion. For artistical presentation of the object it is usually best to isolate it from its surroundings: keep the main subject in focus and the surroundings out of focus (control the depth of field), so that attention is automatically focussed on the object of interest. If you own a camera body with a range of lenses, then control of the depth of field can be easily achieved by choosing an appropriate lens and lens aperture.

Most film camera's record a scene on a 24x36 mm film surface area, the larger format view cameras used by professionals on a much larger surface area. The same scene recorded at the same lens aperture on a large surface area has less depth of field, i.e. a smaller difference in the distance with which objects are sharply reproduced that are close to and further away from the camera. The depth of field is the area in front of and behind a focused subject in which the photographed image appears sharp; it extends from one third in front of the point focused on to two-thirds behind it. The smaller the lens aperture, the larger the depth of field. For any given lens aperture (f-stop) depth of field decreases as you increase the lens-to-subject distance. If you keep the image size the same by adjusting the distance between camera and subject as you use lenses of different focal length, depth of field is the same; however, if you maintain the same distance from the subject, for the same f-stop the depth of field decreases progressively from wide-angle to telephoto lens. Low-end digital cameras generally depict the entire scene in focus, the layman's delight. This is because the Charge Coupled Device (CCD) in such cameras tends to be very small. They therefore need a lens with a very small focal length, in the order of 15 mm. Such low-end cameras are also limited in the maximum lens aperture. Thus their depth of field extends from less than a meter to infinity. On that account such low-end point-and-shoot cameras do not allow to manipulate the depth of field and are unsuitable for our purposes.

Conclusion: the choice is up to you. If you want to take photographs for presentation on the computer screen, the internet, or you are not after large format prints, then there is ample choice of analog and digital cameras. Many amateurs have already gone digital, but similarly there are those who want to produce work of the highest quality and have decided to wait and see until this can be matched or improved upon by digital camera bodies, and until prices have fallen.

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