McPherson Inc. has announced that multiple-pass, double-dispersion accessory optics are available for its 0.67- to 2-m-focal-length monochromators. The devices allow the user to work with a low f number, high throughput and twice the resolution. Plane folding mirrors that multiply the monochromator’s focal length also double the resolution and dispersion. The mirrors repeat the light path inside the instruments without changing the aperture ratio. Light passes over the diffraction grating twice. The multiple-pass monochromators are suitable for experiments that require higher spectral resolution but that lack the laboratory space to accommodate a larger instrument.