A special kind of enlarger head that has three colored filters (cyan, magenta and yellow - the principal colors used to alter an image) that move into and out of the enlarger's beam of light in calibrated stages. This changes the color balance of the enlarging light.

A dichroic head is a staple of printing color photography, without one it is nearly impossible to have control over color correction in your final output. Often overlooked though is the usefulness of a dichroic head in black and white printing. Not only is a dichroic head capable of producing the same filtration that one normally uses contrast filters for, it can create inbetween levels of contrast as well.

Approximate equivalents:

Filter:      Dichroic equivalent:
  #1            40 yellow       
 #1.5           10 yellow
  #2          No Dichroic Filter
 #2.5           40 magenta
  #3            60 magenta
 #3.5           100 magenta
  #4            200 magenta