The AO-370 can use common light bulbs of up to 100w that is, it accepts bulbs with the standard screw type base used in most table lamps. This allows one to avoid the common problem of expensive bulbs found in many microscope illuminators. A 100w Mazda bulb was the original bulb specified for this unit but common bulbs work fine for many applications. There is an on/off switch in the cord.
This AO illuminator has a condenser lens with a 2.5 inch diameter, truly a massive piece of glass.
The lamp can be focused via the slide mount provided for the bulb socket, then locked in position using the knurled screw provided. The height of the bulb can be adjusted by loosening the screw which retains the bulb socket, then sliding the socket up or down and re-tightening the screw.
The diaphragm works smoothly over its range of 10mm to 60mm. Kohler illumination is achieved by proper use of the focus and iris controls. A filter, color or ND, can be installed in the slot in front of the iris.
When I purchased this unit the brass iris control lever was missing, a common problem with this model illuminator. I replaced the large brass lever with a steel pin; this projects only 3/16 inch so it is unlikely to be damaged (unlike the original large brass lever). The iris has little friction so this pin adjusts the iris easily and smoothly.
The stand allows adjusting the tilt and height of the illuminator to easily accommodate the needs of microscopes utilizing mirrors. The base seems to be cast iron and is surprisingly heavy and consequently very stable.