Here are instructions for changing pixel scale in the SONIC.  The
same procedure is used for installing or removing the shipping cover. 

Parts that need to be changed include: lens extension, internal light
baffle, and thermal link between dewar and lens assembly.  Parts for
each pixel scale are labeled and are listed on top of the dewar.
Briefly, they are as follows:

0.8 arcsec: long lens tube extension, long light baffle (gold
plated), long thermal link, attachment on front of Lyot stop.

1.6 arcsec: medium lens tube extension, medium light baffle (gold
plated), medium thermal link, attachment on front of Lyot stop.

3.5 arcsec: no lens tube extension, very short light baffle (plain
aluminum, about 1/4 inch thick, short thermal link, attachment on
back of Lyot stop.  The attachment bar on the front of the Lyot stop
must be removed.

Shipping: no lens, no light baffle or very short one, no thermal
link, plain cover over lens opening.

The "back" of the Lyot stop is towards the lenses; the "front" is
towards the dewar.

Finally, the spacers between the dewar and Kron camera flange change.
We always use the Kron camera flange and the 1.5 inch plain aluminum
spacer.  The 1.6 arcsec optics use only those.  For 0.8 arcsec, add
the 2-inch anodized spacer.  For 3.5 arcsec, initially try the 2-inch
spacer, but the 1-inch spacer may have to be added as well.  (The 3.5
configuration is untested.)

Procedure:

1. Find a clean place to work, and make sure the vacuum pump is ready
to be used.  Get the plastic box of SONIC parts.  

2. Gather the following tools: allen drivers 5/64, 3/32, and 9/64,
long nose pliers, small screwdriver, Kimwipes, vacuum grease.

3. If the Kron camera flange is attached, remove it so as to gain
access to the SONIC lens.  It's probably easiest to remove the seven
allen bolts connecting the flange to the dewar.

4. Make sure the detector is at ambient temperature and is above
freezing.  You can use the heater to warm up the detector, but make
sure the temperature change does not exceed 1 degree C per minute.

5. Slowly open the dewar valve to let air into the dewar.

6. Remove the round access plate on top of the dewar by loosening
three captive screws (3/32 driver).

7. Loosen two captive screws connecting thermal link to dewar (3/32
driver again).

8. Loosen six captive screws connecting lens assembly to dewar (9/64
driver).  These are the screws closest to dewar.

9. Remove lens assembly from dewar.  You may need to use the long
nose pliers to release the two screws on the thermal link.

10. If removing 0.8 or 1.6 arcsec lens, loosen three captive screws
(5/64 driver) holding light baffle in place in the dewar, and remove
the light baffle.

or
 
If removing 3.5 arcsec lens, remove the short light baffle by
removing three screws.  These are NOT captive.  (?)

11. Install correct light baffle for new configuration.

12. Remove extension tube (if any) from lens assembly by loosening
the six captive screws (9/64 driver) on the OUTSIDE of the lens
assembly barrel.  NEVER loosen the six screws counterbored around the
very front of the lens assembly.

13. Disconnect the thermal link from the Lyot stop by loosening two
captive screws (3/32 driver).  If going to the 3.5 arcsec
configuration, remove the bar on the front (dewar side) of the Lyot
stop.  (Caution: screws NOT captive.)  Do not loosen the three screws
holding the Lyot stop to the fiberglass posts.

14. Connect the new thermal link to the Lyot stop.  If you are going
from 3.5 arcsec, you will first have to attach the bar to the front
of the Lyot stop.  (You may have to reverse the thermal link end for
end to get it to fit properly.)

15. Connect the correct extension tube to the lens assembly.  Clean
and regrease both o-rings if needed.

16. Put the lens assembly on the dewar, rotating as necessary so the
thermal link fits properly.  If you have installed the thermal link
wrong way round, go back to step 14.  Tighten six screws, being
careful not to get metal shavings under the o-ring.

17. Tighten two screws holding thermal link to dewar.

18. Replace access plate on dewar top, cleaning and regreasing o-ring
if necessary.

19. Pump vacuum in dewar as soon as possible.