This study explores the use of video vignettes as a tool for the professional development of teachers. It is postulated that teachers' professional frames prime them to view vignettes through multiple "lenses," and that teachers may not recognize exemplary practice when presented with it. Think-aloud and interview data are collected as 11 pre-service and 11 experienced teachers observe exemplary astronomy teaching video vignettes. Quantitative analyses suggest that teachers rarely recognized the exemplary qualities of practice presented to them. Furthermore, teaching experience significantly influences the type of lens through which a teacher will observe exemplary practice vignettes. There is also some evidence to suggest that priming teachers with instructions may be helpful. Implications for the design of video on the Web are discussed. (Contains 5 tables and 2 figures.)