Evaluation of a temperature- based HST Focus Model

A study of the history of the HST focus measurements compared to the predictions of the DiNino (2008) model was recently performed covering a time period from March 2003 to December 2010. Arising from this analysis, an improvement to the secular part of the model has been implemented and the inter-camera offsets have been revised. The model performance is good, falling within 2 microns of the measured values of the secondary mirror displacement 80% of the time. A web page with a link to the model has been supplied to display the measurement and modeling results and these are linked to a method for calculating point-spread functions using Tiny Tim. Point-spread functions can be calculated using the focus offset given by the focus model.