There are two sets of flat field lamps that can be used with 90Prime.

In the black computer rack by the KVM computer there is a box labeled “Platform lamps”.

You have to turn this box on, then choose halogens or U-Band lamps. If you use the U-Band lamps, wait a few minutes to allow the lamps to warm up.

If you stow the dome, and then tip the telescope to 40 Elevation/180 Azimuth you will be lined up with the flat field screen.