The two fold mirrors are fused silica lambda/20 rectangular flats (125mmx90mm and 115mmx80mm, respectively) that re-direct the telescope beam from the field lens to the first of two filter wheels. There location is indicated in the photo below. The telescope beam passes vertically upwards from below the optical table, labelled in the photo, to the first fold mirror which bends the beam through 90 degrees to be parallel to the optical table. The second fold mirror bends the beam through 90 degrees parallel to the optical table to filter wheel #1. The fold mirrors are enclosed in aluminum housing (the black box) and are not directly visible in the photo.