We report the development of very fine collimator slit patterns for ga
mma ray imaging. Astronomical objects emitting gamma rays cannot be im
aged in a classical way. However, it is possible to measure Fourier co
mponents of the images by observing gamma ray sources through pairs of
patterns of fine slits placed at a mutual distance of several meters.
The finest pattern should have slits 50 mum wide at a pitch of 100 mu
m. To achieve high contrast images, the slit geometry must meet high p
recision goals. The absolute slit position accuracy must be on the ord
er of a few micrometers within an area of 130 mm x 130 mm. The slit pa
tterns have been realized by stacking long thin blades separated by sm
all spacers. The application of flexible spacers and precision referen
ce frames results in a high pitch accuracy. The spacer design was opti
mized using finite-element analysis. The spacers were made via a multi
step precision etching technique. Measurements on the full-size slit p
atterns show low slit position errors.