Figure is a scale diagram of the top and side views of the UFOE optics.
The slit is aligned vertically and has an adjustable width in the echelle dispersion direction. In the SSAC configuration, the input fiber ferrule of the UFOE is pressed against the blades of the slit. The ferrule contains two optical fibers from the prime focus, which are aligned vertically in the center of the opening of the slit. A 100 micro m spacer has been inserted between the two fibers, which makes the vertical distance between their centers equal to 580 micro m. A third fiber is located in the ferrule beside the other two so that the three form a straight line.