This is a darkfield condenser set for our 670 series microscopes. Both dry and oil condensers are included to cover a wide range of magnifications and numerical apertures. The dry condenser, with an NA of 0.7-0.9 is best-suited for lower-magnification objectives, typically up to 40X. The oil condenser has a maximum NA of 1.36, and is necessary for higher-magnification objectives. As well, the oil condenser will produce brighter highlights. When using 100X objectives, or other lenses with NA above 1, variable-NA lenses are preferred to maintain field-darkness. The darkfield condenser uses principles of light-diffraction to suppress field-illumination, while illuminating the edges of otherwise-transparent or translucent objects. This is particularly useful for quantitative analysis of low-contrast specimens. Specifications: Condenser Mount: front-loading with flange Mounting Diameter: 37mm Compatibility: 670 series compound microscopes Numerical Aperture: 0.7-0.9 (dry), 1.25-1.36 (oil) Immersion Medium: none (dry), oil (oil)