User's Guide to the Hamilton Spectrograph

Table of Contents

Quick Reference
CCD Characteristics
Grating Tilt & Dewar Height
Filter Wheel & Shutter
Calibration Sources
Photon Integrator
Image Rotator
Iodine Cell & Slit Room Controller
Guide Camera & Filter Wheel
Data Taking System
Hamilton Motor Controller
Hamilton Focus
More Info:
Spectral Format
Navigating the Spectrum
Table of Orders
Setup Procedures
Observing Hints

Data Archive
Mt. Hamilton Homepage

Readying the Spectrograph

The Coudé Camera Room

The Coudé Camera Room contains the spectrograph optics and detector. Observers enter the camera room to open or close the covers of the spectrograph optics, and to fill the CCD's LN2 dewar. To minimize dust and dirt in the camera room, observers are asked to clean their shoes in the machine pictured at right, located just outside the door to the anteroom (see next section). Visits to the camera room should be kept to a minimum to protect the delicate optics. Covers are usually opened at the beginning of a run, as described below, and left open until run's end.

Note that the echelle grating, located just to the left of the door into the camera room, is particularly delicate. Once damaged, it cannot be repaired. Please take very special care when near the grating.

The Anteroom: CCD Controllers & Stickymats

An anteroom separates the camera room from the basement. A disposable stickymat on the anteroom floor further protects the camera room from dirt. Step several times on the mat before proceeding to the camera room. If it does not feel sticky, please peel up present mat to expose a fresh one underneath (we suggest grounding yourself to the anteroom's metal wall when doing so to avoid a possible nasty static shock). If the worn our mat is the last one, please notify a staff member.

NB: As of 4 Dec 2008, there is a single CCD power supply and controller for both dewar 6 and 8. The below info is out of date.

At the time of this writing, both CCD controllers are located on a shelf in the anteroom (plans are underway to move at least one to the camera room, nearer the CCD). In the picture at left, the lefthand controller is for dewar #6, the right for #8. Observers don't usually need to do anything with the controllers, but should note the CCD temperature displayed on the front panel of the one they are using, and check that the temperature is constant to within a few degrees on subsequent visits to the camer room.

Opening the Spectrograph Optics

The Hamilton optics are suspended from the large I-beam on the east side of the camera room (left when looking down into the room). Three of them must be opened: the collimator, the cross-dispersing prisms, and the echelle grating. They are presented below in the order in which they should be opened. The grating is the most susceptible to permanent damage. To afford it maximum protection, it should always be the last optic opened and first closed.

1. The Collimator

Three collimating mirrors are suspended from the right side of the I-beam. Only one is used with the Hamilton, but observers occasionally confuse it with one further up the I-beam. The Hamilton collimator is the middle one of the three, and is located adjacent to the wooden platform about two-thirds of the way down the camera-room steps.

The collimator cover is hinged along its lower edge, and is opened by pulling on a small handle along its upper edge. The latch is magnetic and requires a fairly firm pull to release. When fully open, the collimator cover hangs from its hinged edge.

Some observers use a mask on the collimator, slightly smaller than the telescope pupil, in order eliminate any systematic effects that might arise from the slight shift of the pupil's position on the collimator as a function of telescope hour angle. Using the mask does result in minor light loss. The collimator is pictured above with and without the mask installed. Note that without the mask, the telescope pupil underfills the collimator.

2. The Cross-dispersing Prisms

The cross-dispersing prisms hang from the I-beam a few feet above, and to the left of the collimator. They are opeed in two stages, illustrated below.

First, open the hinged flap on the west (right) side of the cross-disperser housing, latching it in place with the wire hook attached to the I-beam. Don't forget this step! Observers sometimes inadvertanly neglect to do so. The spectrograph will work, but the flap will occult at least a third of the beam.

Second, slide the metal cover on the front side of the cross-disperser towards you, remmoving it completely from the housing. Stow it by leaning against the step below the cross-disperser, in such a way that it will not cause a tripping hazard.

3. The Echelle Grating

As has already been noted, because of its vulnerability to damage (not to mention its very high replacement cost!) the grating should always be the last optic opened, and the first closed, and should be treated with an extra measure of caution. Never try to open or close the grating without adequate light to see what you are doing.

The grating is located immediately one's left on entering the camera room. It is tempting to take a shortcut to the dewar on the way in, or to the camera-room door on the way out, by slipping between the grating and the nearby wall. Don't.

The grating cover is hinged along its lower edge, and held closed by a latch at the center of its upper edge (the latch is circled in the top illustration at left). You may stand either in front of or behind the grating to open the cover, but remember not to pass by the grating surface once it is open. To realease the latch, lift its back end then bring the the whole latch forward and up. Hold the cover closed while unlatching so that it does not fall open.

With one hand placed on the still-closed cover, carefully lower it until it comes to rest on the grating mount.