Photography of shiny objects
Digital or conventional photography ?
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.
- Conventional photography has gone through considerable development and standardisation, and has reached a high level of perfection in the past 1½ centuries.
- Digital photography has developed very rapidly so that the gap with film photography has been closed and the possibilities in some respects exceed that of film photography; cheaper cameras do not yet have the same level of sophistication. There have been rapid developments notably in the field of detail (resolution, reproduction of contrast and colour) with which pictures are recorded, so that the quality of 24x36 mm film photography is being matched. When does a digital picture match the one recorded on film? This depends on a number of factors, including light sensitivity. If you prefer to work with 100 ASA films or greater film speed, then a 6 megapixel camera suffises; if you prefer to work with finer grain films (such as Kodachrome 64 or Fuji Velvia), then you should as of now work with 10-16 megapixel cameras to obtain results comparable to that of a film camera (see e.g. or ). The predominant factor is not so much the number of megapixels, but also how noise free they record the scene: by increasing the number of pixels on the same small surface the amount of cross-talk tends to increase, a phenomenon that occurs especially at the higher 'film' speeds. For some years the results obtained with larger format negatives or slides are likely to remain superior to what digital 'slide' cameras can offer. However, people who do not need to produce the very largest format prints will find that a digital camera has a lot going for it. One should never forget that a high quality lens is of greater importance for a good picture than a camera body.
- Only the more expensive (digital) camera bodies offer a range of lenses and facilities to manipulate the exposure settings so as to obtain a correctly exposed picture; as of now the digital camera bodies are more expensive than the conventional ones, and used conventional bodies can now be bought at bargain prices.
- A tremendous advantage of digital photography is that one can change the light sensitivity on the fly between usually 100-1600 ASA without changing film, the independence of film that needs to be developed, and the possibility to immediately check whether the picture meets your expectations; if the picture can be inspected on screen on site one can also pay attention to details. Digital photography also obviates the need to scan a negative or slide. Finally, new developments in the field of photography are nowadays limited to digital photography. Also the facilities for post-processing digital pictures as of now incorporates all the tricks and techniques developed during the era of film photography, and goes even beyond that such as in stitching images together to create a panorama, or High Dynamic Range (HDR) photography.
- When it comes to storing film, the costs are negligible, whereas those for digital storage are still high and storage media inherently less secure. In the case of digital material the format in which it is stored (RAW, TIFF, PSD or JPG format) determines whether, and if so how much, information is irretrievably lost; also storage formats have not yet been definitively standardised. It remains to be seen whether what works satisfactorily now can still be used in say 5-10 years from now, judged also against the background of continuous changes in software and digital storage systems.
What will you use the picture for:
- If you want to make very large enlargements then at this stage a conventional film camera is not only considerably cheaper, but film will also produce superior results. This can be explained as follows. In films the picture is stored in three layers of microscopic colour-sensitive grains, tightly packed in the films emulsion.
Using an appropriate 24x36 mm film a picture can easily be enlarged to A3 (29,7x42 cm) or double that format without producing a noisy, grainy image.
Maybe you want to reproduce a picture on a colour printer via your computer? Affordable film scanners offer a resolution of 4000 dots (dots, pixels) per inch = 2.441.046 pixels per cm². Scanning a standard image (24x36 mm = 8,64 cm²) thus yields 21.090.637 pixels. This implies considerable overkill allowing you to make a flawless print on A4-format, or larger if you have an appropriate printer. This also considerably exceeds the number of pixels produced by the available best 5 to 8 megapixel cameras. However the 16,7 megapixels are certainly on a par with 24x36 mm film cameras.
- Does the picture need to be reproduced in print? In that case you should consider which resolution is required. Let us assume that the printer requires 300 dpi (dots per inch, also called ppi = pixels per inch), hence 90,000 points per inch². If you used a digital camera that produced 2,000,000 pixels per picture, then it can be enlarged to 2,000,000/90,000 = 22.22 inch². Starting from an image in which the width is 1½ times its height (height = x inch, width = 1½ inch, surface area= 1½ x² = 22.22 inch², so that x = 3.85 inch), then the maximum format to which it can be reproduced is 14.78 x 9.86 cm. If it should be blown up beyond this size this entails computer software to generate new pixels by interpolating between adjacent pixels, appropriately matching the colour and luminosity of these pixels. Whilst such software is available, the quality of the picture is always adversely affected by the interpolation procedure.
- Is the picture required solely for reproduction on a computer screen, then the minimum requirements are easily met. The resolution of a computer screen is 72 or 96 dpi. If your screen displays 1024 x 768 pixels, this implies 786,432 pixels for the full screen. If your digital photo camera produces as few as 1,000,000 pixels then ¼ of the picture falls outside the boundaries of your screen. For most purposes a 500x380 (190,000) pixel picture on screen is sufficiently large; to that end your 1 megapixel image should be downsized by a factor 5¼.
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 ). 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
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.
Champlevé silver brooch covered by white or black paper while scanned in a flat bed scanner.
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.