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About Tiny Tim HST PSF Modeling

Tiny Tim (Krist & Hook 2011) is a point spread function modeling tool developed for HST. Details of the code's operation, configurable parameters, and products are given in the Tiny Tim User's Guide (Krist & Hook 2004, version 6.3). Tiny Tim is no longer maintained or supported by STScI; a final version of the source code is hosted "as-is" on Github, for legacy purposes.

On this page we provide notes from some of the HST instrument teams regarding Tiny Tim's applicability and usefulness, in addition to historical resources and information.


HST Active Instruments

Wide Field Camera 3 (WFC3)

Presently, we do not recommend using Tiny Tim for WFC3 data as it relies on outdated optical models (WFC3 ISR 2008-14, published before WFC3 was installed). As an example, WFC3 ISR 2014-10 found significant errors in the WFC3/IR Tiny Tim model. Our team has focused recent efforts on building empirical PSFs and a database of observed PSFs

Users working with WFC3 data who wish to proceed with Tiny Tim regardless should be aware that while Tiny Tim resources are hosted by STScI, it is not currently maintained.

Space Telescope Imaging Spectrograph (STIS)

For external users, we do not encourage the use of Tiny Tim nor support the software, as it is "available but unsupported." Members of the STIS team currently do utilize Tiny Tim for specific internal purposes.

Tiny Tim may work to convolve against perfect resolution models to compare against STIS disk observations, or to match the structure of PSFs down to ~10^-8 contrast levels (if PSF is adjusted to match focus and jitter evolution). However, we do not know how STIS Tiny Tim PSFs will perform in other science situations, and caution users on that basis. 

For coronagraphic observations requiring PSF subtraction, users are advised to follow the recommendations for obtaining contemporaneous PSF calibrators in Section 12.11 of the STIS Instrument Handbook.

Advanced Camera for Surveys (ACS)

We do not support Tiny Tim. For users interested in generating PSFs for ACS, we suggest looking at the effective PSF utility described in the photutils documentation. For additional background on this utility, please see Anderson & King (2000) and WFC3 ISR 2016-12. Additionally, see ACS ISR 2017-08 for comparisons to Tiny Tim generated PSFs.


HST Legacy Instruments

FOC (Aberrated PSFs)
WF/PC-1 (Aberrated PSFs)

Tiny Tim for Legacy instruments is described in the Tiny Tim Users Guide (Krist & Hook 2004, version 6.3)

A summary of the tool's use over the first 20 years of HST science operations is described in "20 years of Hubble Space Telescope optical modeling using Tiny Tim" by Krist, Hook, & Stoehr (2011). This report compares observed and modeled PSFs for FOC, WF/PC-1, WFPC2, & ACS/HRC.

A discussion of WFPC2 photometry using Tiny Tim PSFs is available in the 1997 HST Calibration Workshop Proceedings (Rémy et al. 1997).



HST Help Desk 

Please contact the HST Help Desk with any questions.