imSim starts with a lower case "i". In fact there is a different "ImSim" from a very long time ago which was a description sometimes used for the suite of many simulation programs including PhoSim etc. However as can be seen at its GitHub page:

https://github.com/LSSTDESC/imSim

The imSim program we are using now, uses lower case. Due to necessities of CamelCase the internal Python class names used for the instrument takes the form XxxxImSimYyyy.

The instruments names were copied from this convention and thus now look like

LSST-ImSim

However, with the "-", I would like to request we use the proper capitalization for the imSim instrument names.

You can see the instances of the name here:

https://github.com/lsst/obs_lsst/search?q=LSST-ImSim&unscoped_q=LSST-ImSim