Focus Values
Blanco 4m Telescope
This is a summary of focus information taken from the white board in the
console room and from night assistants's books.
Prime Focus:
TCS focus value is in microns of motion of the focal plane, but is
for no PF corrector. The actual motion of the focal plane when using the
ADC corrector is 1.076 times greater. Larger values correspond to moving
the focal plane upwards (away from M1).
Approximate focus values (at 10 deg C) for Mosaic:
| Filter |
UCTIO |
BCTIO |
VCTIO |
RCTIO |
ICTIO |
| Focus |
? |
14402 |
14487 |
14372 |
14397 |
Change with temperature: decrease focus
setting by 110 units (microns) per 1 deg C increase in temperature.
Focus offsets between Mosaic filters:
| Filter: |
UCTIO |
BCTIO |
VCTIO |
ICTIO |
| Offset: |
RCTIO+? |
RCTIO+30 |
RCTIO+115 |
RCTIO+25 |
f/8:
TCS focus value is in microns of motion of the focal plane. Larger
values correspond to moving the focal plane upwards (towards M1).
Actual motion of secondary mirror is 10 times less.
Approximate focus values (at 10 deg C):
| RC Spectrograph |
177000 |
| Echelle Spectrograph |
182000 |
| CFCCD, R filter |
??? |
| Hydra |
143000 |
| CIRIM |
175700 |
Change with temperature: decrease focus setting
by 780 units (microns) per 1 deg C increase in temperature.
Actual motion of secondary mirror is 10 times less (i.e.
-78 microns/deg)
Focus offsets between filters (CFCCD):
| Filter |
U |
B |
V |
I |
| Offset |
R+900 |
R+0 |
R+0 |
R+600 |
f/14:
TCS focus value is in microns of motion of the focal plane. Larger
values correspond to moving the focal plane upwards (towards M1).
Actual motion of secondary mirror is 31.5 times less.
Approximate focus values (at 10 deg C):
Change with temperature: decrease focus setting
by 2930 units (microns) per 1 deg C increase in temperature.
Actual motion of secondary mirror is 31.5 times less
(i.e. -93 microns/deg)
f/30:
TCS focus value is in microns of motion at the secondary mirror.
Larger values correspond to moving the focal plane upwards (towards
M1). Actual motion of focal plane is 146 times larger.
Approximate focus values (at 10 deg C):
Change with temperature: decrease focus setting
by 104 units (microns) per 1 deg C increase in temperature.
Actual motion of focal plane is 146 times larger (i.e.
-15155 microns/deg)
M.Boccas, J.Baldwin (8 January 1999)