The Faint Object Camera and Spectrograph (FOCAS) is an optical imaging and spectroscopy instrument for the Subaru Telescope. It has been a workhorse instrument since the first-light phase of the telescope. We describe an integral field unit (IFU) that has recently been installed in FOCAS. The IFU utilizes an image slicer that divides a |${13{^{\prime \prime }_{.}}5}$| × |${10{^{\prime \prime }_{.}}0}$| field of view into 23 stripes, with a width of |${0{^{\prime \prime }_{.}}435}$|⁠. A sky spectrum separated from an object by approximately |${5{^{\prime }_{.}}2}$| can be obtained at the same time as an object spectrum. Test observations confirmed that the image quality of the IFU does not degrade the |${0{^{\prime \prime }_{.}}435}$| sampling, and that slice width and length are consistent with the design. Highly reflective multilayer dielectric coatings were coated on all the mirrors in the IFU, thereby offering a high mean IFU throughput of ∼85% over the field. However, the outer part of the field showed throughput degradation, which was mainly caused by vignetting as a result of misalignment. The flat-fielding accuracy was degraded by the vignetting, with the variation depending on the direction of the telescope.

中文翻译：

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现有成像和光谱仪器FOCAS的集成现场单元

微弱物体相机和光谱仪（FOCAS）是用于斯巴鲁望远镜的光学成像和光谱仪器。自从望远镜第一次亮相以来，它一直是一种主要工具。我们描述了最近在FOCAS中安装的整体式现场设备（IFU）。IFU使用图像分割器分割| $ {13 {^ {\ prime \ prime} _ {。}} 5} $ |。× | $ {10 {^ {\ prime \ prime} _ {。}} 0} $ | 视场分为23个条纹，宽度为| $ {0 {^ {\ prime \ prime} _ {。}} 435} $ |⁠。天空光谱与物体的距离约为| $ {5 {^ {\ prime} _ {。}} 2} $ | 可以与目标光谱同时获得。测试观察结果证实，IFU的图像质量不会降低图像质量。| $ {0 {^ {\ prime \ prime} _ {。}} 435} $ | 采样，并且切片的宽度和长度与设计一致。在IFU的所有反射镜上均镀有高反射率的多层介电涂层，从而在整个现场提供了约85％的高平均IFU吞吐量。然而，该领域的外部显示出吞吐量降低，这主要是由于未对准而导致的渐晕。渐晕会降低平场精度，其变化取决于望远镜的方向。