Type IV aberration-corrected flat field and imaging gratings are designed to focus a spectrum onto a plane surface, making them ideal for use with linear or 2-D array detectors. Owing large optical numerical aperture and correction from aberrations, they provide much better light collection efficiency and signal to noise ratio than traditional Type I concave holographic gratings. They are typically recommended for design requesting high sensitivity, very low stray light, moderate resolution in compact footprint.
