Mark Chun (IfA) Title: OTP - five years of optical turbulence measurements at CFHT Abstract: The Optical Turbulence Project (OTP) is a collaboration between CFHT, the Institute for Astronomy, and Durham University to build a data set of optical wavefront measurements to monitor and quantify three key terms in the delivered image quality budget - atmospheric seeing, dome seeing, and telescope static aberrations. OTP consists of a Shack-Hartmann wavefront sensor mounted at the bent-Cassegrain port of CFHT that collects wavefront measurements over a portion of the telescope pupil. It is used for about 15 minutes/night on night when ESPaDOnS is being used. From OTP's data we extract the total integrated seeing as well as characterize the temporal and spatial properties of the optical aberrations. Importantly, we use the temporal characteristics of the wavefront variance as a means to separate the dome seeing from the atmospheric seeing. This separation has been shown to be valid on at least a few nights of measurements with multiple wavefront sensors (mWFS) at the CFHT prime focus. Over the past five years, OTP data was collected over 60 hours spread out over over 230 nights. In this talk I will summarize the measurements, the collected data set, and what we have extracted from the full data set. The OTP "pre-dome slit" data set will be a useful measure of the efficacy and control of the dome venting.