The IMACS-IFU is an Integral Field Unit built for the IMACS spectrograph at the Magellan-I-Telescope at Las Campanas Observatory. It consists of two rectangular fields of 5 by 7 square arec seconds, spearated by roughly one arc minute. With a total number of 2000 spatial elements it is the second largest fiber-lenslet based IFU worldwide, working in a wavelength range between 400 and 900 nm. Due to the equally sized fields classical background subtraction, beam switching and shuffling are possible observation techniques. One particular design challenge was the single, half a metre long curved slit in combination with a non telecentric output. Besides the construction some preliminary results are described.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.