We developed a cryostat for optical observations at ultralow temperatures a
nd in strong magnetic fields. The optical system consisted of a LED, a ligh
t transmission path and a CCD chip, with till components installed inside t
he inner vacuum can of the cryostat. We have been able to cool a He-3 sampl
e to a temperature of 0.6 mK in zero magnetic field and to 2 mK in 9 Tesla,
while looking at the crystallization and melting of the solid He-3. The CC
D chip gives a heat leak of only 200 pW to the He-3 in our Pomeranchuk cell
. The performance of the nuclear demagnetization cryostat as well as the op
tical system are described.