2025PASP..137a5002F

Binospec is a wide-field optical (360-1000 nm) spectrograph commissioned at the MMT 6.5 m telescope in 2017. In direct imaging mode Binospec addresses twin $8^{\prime} $ (wide) by $15^{\prime} $ (slit length) fields of view. We describe an optical fiber based integral field unit (IFU) that remaps a 12″ × 16″ contiguous region onto two pseudo slits, one in each Binospec channel. The IFU, commissioned in 2023, fits into the space of a standard slit mask frame and can be deployed as desired in a mixed program of slit masks, long slits, and IFU observations. The IFU fibers are illuminated by a hexagonal lenslet array with a 0$\mathop{.}\limits^{\unicode{x02033}}$6 pitch. A separate bundle of sky fibers consists of close-packed bare fibers arranged within an 11$\mathop{.}\limits^{\unicode{x02033}}$8 circular aperture. The 640 IFU fibers and 80 sky fibers have a core diameter of 150 μm, corresponding to 0$\mathop{.}\limits^{\unicode{x02033}}$90. Three gratings are available, 270 lpm with R ∼ 2000, 600 lpm with R ∼ 5300, and 1000 lpm with R ∼ 6000.