You are in luck, gone are the days of your only choice being a 19mm Optical Density (OD) probe. Today, you have no fewer than three (3) from which to choose. The Optek comes in either a 5 or 10mm optical path length (OPL) while the Sartorius offering comes in a 10mm OPL. The Mettler Toledo solution uses backscattering in place of absorbance so no OPL. The one best for you will really depend on the specifics of your application.

Sartorius

Hamilton

Optek

Mettler Toledo