Black Model D viewers are generally considered the best to
use, as some users say that the brown Model D suffers slightly from a halo of light that
forms in the viewing lenses, although it is hardly noticable and wouldn't worry most viewers.
The Model D is probably the most
popular viewer to use for most people due to it's high optical quality,
large magnification and ability to focus.
Some people replace the original
tungsten bulb with a modern, brighter halogen alternative. The original
bulb gives a warm light, whereas the newer halogen bulb give a bright,