A modified mirror monochromator for rotation photography of large-unit-cell crystals

A double-mirror monochromator in which one of the mirrors is considerably longer than conventionally employed has been used to collect diffraction data from crystalline tobacco mosaic virus (TMV) protein (unit cell: 224 × 228 × 174 Å). Considerable improvements in speed of data collection are observed over both customary focusing optics and pinhole collimation. Quantitative comparisons are made of the quality of data collected from TMV protein by this method and by the use of nickel-filtered radiation.