Telescope Image Modelling Software Release 30   November 11, 1993
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The Telescope Image Modelling (TIM) software has been developed at the Space 
Telescope Science Institute to model the output of an imaging telescope viewing
a general object with a detector. The software is rather general, although it 
was specifically developed with the science instruments of the Hubble Space 
Telescope viewing a star field in mind. It was developed in order to satisfy 
internal needs but a has been made available to the community in general. It 
has been used for planning scientific and calibration exposures, developing 
backup plans for collimating the telescope, planning target acquisition and 
generating publicity material. It is also being used to test data reduction 
algorithms and evaluate photometric reduction accuracy as well as to 
generate theoretical point spread functions (PSFs) for deconvolution 
purposes.

The software is designed to simulate the image of a large number of point
light sources with known colours as recorded on a pixellated detector after
reimaging through an optical system of known characteristics. There are
several different effects that contribute to the resulting image:
Large scale wavefront errors caused by design, manufacturing errors and
misalignment; diffraction at the entrance pupil; scattering by dust
contamination and medium and small scale mirror figure errors; attitude
jitter during the exposure; registration with respect to the detector pixel
boundaries and integration over them; variations of the image with the 
source's colour; Poisson and readout noise; background both from the sky 
and detector dark counts; and detector defects. All of these effects are 
modelled in this version of the software, indeed we believe that all significant
known effects on the final image are included.

The Cross-Calibration software (XCAL) has been developed at the Space 
Telescope Science Institute to model the spectral response of the various
Hubble Space Telescope observing modes, both photometric and spectrophotometric,
and to provide a convenient set of standard spectral energy distributions.
The XCAL software includes both an interactive program and a library
of Fortran subroutines.  XCAL allows you to compute predicted count rates
for photometry or spectrophotometry with any of the HST instruments and
for a variety of spectral stimuli.  You can generate and plot sensitivity curves
and photometric transformation diagrams for comparisons between HST and
Ground-based photometric systems.  You can also use XCAL to fit model spectra
to photometric and/or spectrophotometric data.

The TIM and XCAL software and CDBS passband datafiles which support them
are available here in the following files:

0. README          This file
1. tim30.bck       VMS Backup saveset containing TIM directory
2. xcal29.bck      VMS Backup saveset containing XCAL directory tree
3. cdbs29.bck      VMS Backup saveset containing CDBS directory tree
4. backup.com      VMS command file to retrieve the TIM,XCAL,CDBS
                   directories from the .bck files

The TIM and XCAL directories will contain further README files
with more information on how to install and run the TIM and XCAL
programs.

How to use FTP to copy these files to your local computer :
FTP> type ascii
FTP> get README
FTP> get backup.com
FTP> mget *.log
FTP> type backup
FTP> mget *.bck