Simply put: numismatic photography is the process of photographing money. Coins are a large collectors' market, and creating professional images of collectibles is a necessity for both catalog and online auctioning. Paper money -- although just as collectible -- falls under federal imaging restrictions which limit the practicality of digital reproduction.
Coins come in various shapes, sizes, colors, and textures, and over time, they show wear and tarnish. Different coins may require different methods of photography to produce a satisfactory image, especially considering the subjective nature of collectibles. Some collectors like to see a coin's provenance in its wear and toning, while others only want to appreciate the artistry or spectacle. Various lighting and photographic techniques can be used, depending on the desired result.
A simple axial-lighting setup.
In my basic axial-lighting setup, I use a single e640 monolight as the lightsource. I don't mount any modifiers aside from an 8.5-inch reflector, since I want to be able to vary the diffusion amount; by changing the distance between the light and any diffuser, I can fine-tune the contrast. For the reflecting medium, I use a simple pane of glass mounted in a reflector-holder which allows me to adjust the glass' height, tilt, and swing. The camera is mounted on a lateral arm which can be raised, rotated, and swung to find the ideal position. I typically place a lens shade around the coin, in order to prevent any direct lighting, as well as to add shadow detail. I occasionally use a sheet of black velvet behind the camera-side of the reflecting glass, to prevent light from reflecting back at the glass, which would cause glare.
The issue with photographing a reflective coin head-on (axially) is that little light will directly illuminate the flat surface of the coin, since the space directly in front of the coin is occupied by the camera. Enter a little trickery: by placing a simple piece of glass or transparent acrylic above the coin, and at a 45-degree angle, light projected parallel to the coin's surface will reflect at a 90-degree angle -- right at the coin.
Because of its flat nature, axial lighting is often reserved for cases where the coin can't be properly illuminated by other means. However, with modifications, this method can be useful with any type of coin. Using various light modifiers, and varying the position and angle of the glass will produce an array of effects. With proof coins, a frosted relief with a polished field is supposed to have a floating effect. By tilting the reflecting glass to reposition the light, depth can be added to the image.
While axial lighting can provide even illumination, it can reduce the appearance of texture. More-concentrated, off-axis lighting can add texture and luster to the image.
As the name suggests, with dark-field lighting, the coin's field remains dark while the relief is illuminated. This effect is achieved by illuminating the coin from an obtuse angle, and eliminating any direct, axial lighting. Without the axial light to reflect, the field remains dark, while the more diffuse surface of the relief is able to reflect some light towards the camera. Although it offers little detail for appraisals, dark-field lighting is often desired by collectors who simply want to appreciate the relief.
This James K Polk dollar was photographed using the same lighting arrangement as the axial setup, minus the angled glass. A reflector was used to redirect some light, taking into account the appropriate angle for shadow detail. Any imperfections in the field would show up as faint streaks, which can be subdued or eliminated through the shifting of the image's shadow-level. Cross-lighting techniques
Holograms are a lot of fun, and great examples of light-mechanics. They can be tricky to photograph, however, because of the specific angles at which parts of a hologram can be seen. Two-dimensional holograms like this Larry Johnson card from Upper Deck present a color-shift as the perspective is changed. When light is projected at the card from a specific angle, the appropriate colors will be displayed.
Holograms on currency can be more complicated, like the multi-channel hologram on this British 10-pound note. As the perspective changes, the hologram will reveal an image of Britannia or the number 10. As well, not all of the Britannia components are illuminated from the same angle, requiring a composited image.
Modern proof coins are a distinct category of coins, typically featuring a highly-polished, mirror-like field, and sharp detailing in the relief.
As someone who likes to travel, I also like to hold on to money from different countries. The coins I collect are usually well-circulated, so they have plenty of "character." I don't collect anything for its intrinsic value, but rather its artistic merit, or even simple sentiment.