A simple and easy-to-use miniphotometer has been designed; the expense involved amounts to only a fraction of that required for large commercially available microphotometers.

The instrument can be employed for routine investigations and for teaching reflected light microscopy in conjunction with standard reflected light microscopes.

The reflectance of grains down to 50 µm size can be measured in white and monochromatic light employing continuous band and line interference filters. The systematic error does not exceed 1·5 % of the values measured. The only aspect that distinguishes the miniphotometer from larger instruments is the limitation of spot size. A comprehensive test programme including comparative sets of measurements on a Zeiss MPM spectral microphotometer has shown that the results obtained by both instruments coincide well.