Cleaning the optical path

The dewar window and filters can pick up dirt and dead insects over time. Potentially the shutter may need cleaning too, although this has proven less likely.

To clear loose particles off of the filters, try to blow them with a canister of compressed air if they are small. Somewhat large bits of lint or insects may be lifted off of the filters using a piece of lens tissue. If an object is really stuck to the filter, another procedure may need to be used (to be developed). Both sides of the filters can be accessed while in the filter wheels without detaching them from the telescope. Pull the filter wheels out from the guiderbox as per instructions on the access panel or the instructions given in section 3.7. The filter wheels can be moved by hand. There are empty filter slots which you can move into place to access each filter. The top sides of the filters will tend to require the most attention.

If you have opened the guider box, you can look down on the top of the shutter. Try to keep the shutter leaves clean.

Cleaning the dewar window is a somewhat involved process. It is necessary to remove the camera from the telescope to access the dewar window. Currently we have no cart to hold the camera while it is not on the telescope. With two people, the camera can be detached: one person to hold the camera while the other works on it or moves the observing platform, etc. We have rigged a "camera cart" out of the tall set of stairs and foam pads (see image below). To remove the camera this way:

1. Turn off the camera power.
2. Detach the electronics cable, shutter cable, and optic data cables from the camera. The cryogen lines can/should remain attached.
3. Gather together several foam blocks that will be able support the dewar and the electronics box while resting on the top of the movable stairs.
4. With one person holding the foam blocks in place, the other can slowly raise the platform bit by bit to raise the foam blocks in place underneath the dewar.
5. One person hold the camera steady while the other uses the hex wrench (an English size) to unbolt the dewar from the filter assembly. It is best to start with the bolt nearest the electronics box because this is a difficult one to access. When all 7 bolts are removed, the camera weight should be supported on the foam blocks.
6. Lower the observing platform a short ways (e.g., 20 cm) to access the dewar window.
7. Try blowing compressed air on the dewar window to remove loose particles.
8. To clean the dewar window more thoroughly, create a mixture of 100 parts distilled water and 1 part detergent soap (about 1 drop soap in 1 cup water). Dip cotton balls into the mixture and wipe them across the dewar window, using a fresh cotton ball frequently to avoid building up dirt which could scratch the window. Rinse the detergent away using cotton balls with plain distilled water. You can dry the window with additional cotton balls.
9. To reattach the camera to the telescope, raise the platform to move the camera close to its attachment.
10. One person should hold the camera while the other bolts it into place.
11. Reattach the cables and power on the camera.

Figure 8.2: The camera dewar and electronics box lowered onto foam blocks on top of the movable stairs. The cryogen lines remain attached to the dewar. The top of the dewar (and dewar window) are now accessible.

Figure 8.3: Cleaning the Dewar Window