STIS Instrument Handbook for Cycle 24 . ... Space Telescope Imaging Spectrograph Instrument Handbook for Cycle 24 > Chapter 8: Target Acquisition > 8.3 Onboard Target Acquisition Peakups (ACQ/PEAK) . ... When slits less than or equal to 0.1 arcsecond wide are used, an acquisition-peakup exposure should be performed following the acquisition exposure to center the target in the slit. ... Slit (APERTURE) . ... For acquisitions and peakups you must be sure not to saturate the CCD during your exposure. ...