Red Side
Collimator |
Gratings |
Filter Wheel |
X-Y Stage |
Direct Imaging
Collimator
A typical focus value is presently about 20000. The range is 4700 to
45000. The focus does not appear to be affected by removing or
inserting the dichroic. The off-axis paraboloid is silvered and
overcoated.
Gratings
Blue is left in the displayed spectra. The total range for the tilt
is 5400-35400. A flat mirror may be inserted into the grating tray
for direct imaging on the red side. The tilt to use for access to the
grating tray is 5400.
Access to the grating tray is via a long black door just above the red
side dewar. It is held closed by two captive screws, and it's hinged
at the bottom. Each grating is clearly labeled on the end facing the
door, so it's easy to see which ones are there without the necessity
of taking them out. Be particularly careful of the fragile ion pump.
The grating positons in the tray are numbered 0, 1, 2, from left to
right. A reinforcing plate blocks the position in the middle of the
access door, so you may need to change the grating tray position (with
the spectrograph controller) in order to check all three gratings.
Select position 1 to see the two outside gratings (positions 0 and 2),
and either end position to see the center grating.
There is a "Current Setup" card in the control room where you may
record which gratings are in which tray positions. We suggest that
you always look for yourself (or ask a telescope technician) to verify
that the gratings you requested are where you think they are.
It is strongly preferred that observers do not change their own
gratings. The entire community depends on their good condition, and
the replacement cost is thousands of dollars each, not to mention the
time involved. If you must do it yourself, do not under any
circumstances do so without being explicitly checked out on the
procedure. The tilt to use for loading the grating tray is again
5400, and you will need to move hte tray in order to gain access to
all three tray positions, as previously described. Never place a
grating anywhere except in the spectrograph or in the grating
file. Again, we prefer that the technicians make any changes required.
| grating | grooves/blaze | A/pix | range | tilt* | useful range (approx.) |
|---|
| 1 | 600/5000 | 2.35 | 2820 | 2.21(c)+5631 | 3800-10000 |
| 2 | 600/7500 | 2.32 | 2780 | 2.29(c)+4980 | 3800-10000 |
| 3** | 830/8460 | 1.70 | 2040 | 3.15(c)+5097 | 3800-10000 |
| 4 | 1200/5000 | 1.17 | 1404 | 4.72(c)+4178 | 3800-7310 |
| 5*** | 300/4230 | 4.59 | 5508 | 1.10(c)+5716 | 3800-11000 |
| 6*** | 300/7500 | 4.60 | 5520 | 1.09(c)+5742 | 3800-11000 |
* c is the desired central wavelength, in Angstroms
** 830/8460 grating in second order yields 0.85 A/pix, range is 1020 A,
and the second order central wavelength is give by 6.51(c)+4260. The
max tilt of 35,400 restricts lambda < 5293 in 2nd order.
*** Note that the 300/7500 is more efficient than the 300/4230 for all
lambda greater than ~5400 A.
|
Filter Wheel
There is provision for four round filters up to 5.5 inches in
diameter, plus an open position. Notice that small filters here in
the collimated beam will drastically reduce the effective aperture of
the telescope.
| Position | Name | Contents | Step number |
|---|
| 0 | open | empty | 23900 |
| 1 | GG455 | GG 455 (3mm) | 4700 |
| 2 | GG495 | GG 495 (3mm) | 9500 |
| 3 | OG550 | OG 550 (3mm) | 14300 |
| 4 | NS | Spinrad NS | 19100 |
X-Y Stage
We assume that you have read the general description of the stages
given in the section Blue Side - X-Y Stage,
so we won't repeat that here.
Please be clear on the fact that the observer should not find it
necessary to move the x-y stage on the red side. The two dials are
labeled x and y, and the convention adopted is that x moves along the
dispersion, and y moves perpendicular to it. The nominal y position
is so that the spectrum falls near the top of the chip for most
efficient readout. The red side x position is set to the middle of
the range of good camera imaging. It should never be advisable to
move this, since you can get the same effect by moving the grating
tilt, and the grating tilt equations are derived for this particular
setting.
For the red side, higher numbers in x move to longer central
wavelength, and higher numbers in y move the spectrum higher on the
chip; that is, to lower row numbers.
To summarize the red side x-y stage motions (scale 37 pixels/turn):
| red side |
|---|
| nominal | + moves to |
| x | 10.00 | higher wavelength |
| y | 10.00 | lower row number |
Direct Imaging
A good window for red side direct imaging using no splitter and the
tilted mirror in the grating tray (tilt = 19000) is: number rows =
200, number of columns = 200, start row = 25, start column = 450.
Check it with the top lights, not the TUB lights.