Before you can decide how to set up the spectrograph you need to decide on one of two options.

  1. You need a particular wavelength resolution deltalambda. In which case you will have to accept a limited spectral range. range = (256 * deltalambda)
  2. You need a particular spectral range. Then you will have to accept a resolution deltalambda = range / 256.
This is because the CCD has 512 elements and the resolution is set by 2 pixels each of which is 24 microns.

You should then calculate the necessary reciprocal dispersion you need ie nm of wavelength for each mm of detector, noting that the detector is 12.5 mm in extent.

Armed with the dispersion you need, you should consult figure 6 of the spectrograph manual to find which grating and zoom lens setting will give the desired result.

You can then use this program to predict the grating angle, the exact dispersion, resolution and spectral range for your set of input parameters.

NB. Items marked with a star* are fixed parameters for the Wast Hills set-up.

Focal ratio*: F collimator*: mm F camera: mm
Order: Lines/mm:
Lambda low: nm Lambda high: nm
Cam/coll angle*: deg Detector length*: mm Slit width: µm