Introduction

ACS/WFC images can suffer from a number of optical and scattered light anomalies. Most of the optical anomalies that effect ACS have been well characterized. Hardware, software, and optical anomalies are discussed in ISR 2008-01. This is not the case for the scattered light anomalies known as ”dragon’s breath” and edge glow. Dragon’s breath is caused by reflections being scattered back to the detector. There is a knife-edged mask in front of the CCD that scatters light back to the detector when its back side is illuminated by reflections from the CCD surface. These phenomena were discovered in early testing of ACS and were mitigated by sharpening the knife edges and coating them black. However, when point sources fall on the edge of the mask, scattering still occurs (Hartig et. al.).