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Mask manufacturing tools

There are facilities within LEXT to help prepare the parameters for mask manufacture. These are described here, but for a discussion of their use in practice, see the LDSS-2 Observer Manual.

• PREBOX: this routine is used to transform a MASK list, which contains the specification of the mask, ie. the slits and fiducial holes, in units of mm at the mask, into a BOXES list which contains the details of where the spectra are expected to lie on the detector. This routine makes use of the internal variables which define the linear mapping from mask coordinates to detector coordinates. Also, if available, it automatically applies the field distortion, which is stored in either image or list form. In order to calculate the extent of the boxes it uses the internal variables LAMMIN, LAMMAX and LAMBLAZE.
• PREDIRECT: this routine works similarly to PREBOX except that it predicts the results of a direct (undispersed) image, storing the results in a DRCT list.
• GROW: updates the BOXES list and, if available, the MASK list, by expanding the slit lengths in the direction, up to the point where they begin to overlap. The rate of growth of each slit depends on the weighting given to the object.

  This helps make maximum use of the detector area (which is, in fact, reported as a figure of merit). Several internal parameters, such as MAXSLITLEN, MINYSEP etc., define the limits of this procedure.

  Zero-orders are also monitored and are not allowed to overlap with other objects, but are accepted if they impinge only on a sky spectrum. The position of an object within a spectrum is defined by the position of its centre and the internal variable OBJECTEXTENT.

  If the /CHECK qualifier is specified then the MASK and BOXES lists are simply checked for possible overlaps, and the results reported. The lists are not modified.

• Several PLOT options are useful for mask design. For example, /BOXES, /MASK, /FIELD and /FIDUCIAL and /DIRECT. These are dealt with in detail in section 16.3, which describes the PLOT command.
• CURSOR/EDIT: when applied to list slots of BOXES or DRCT this can be used to interactively modify the heights (ie. slit lengths) and object positions of a given entry, or to delete an entry completely. If there is a MASK list available then this will be updated simultaneously.

  The default is for this routine to delete the box in which the cursor is when depressed. However, for very crowded fields this may get complicated and the /CORNER option means that the bottom left hand corner is used instead.