Advances in Colloid and Interface Science Ž . 92 2001 133194 Conventional optical microscopy of colloidal suspensions Mark S. Elliot  , Wilson C.K. Poon Department of Physics and Astronomy, The Uni  ersity of Edinburgh, Edinburgh EH9 3JZ, UK Abstract Optical microscopy can resolve detail at the larger end of the colloidal length scale, and to image suspensions at an individual particle level of resolution would allow the investiga- tion of local behaviour in a way denied to the established scattering techniques. However, to achieve high-contrast single-particle resolution in dense suspensions that are thick enough to show behaviour the same as would be expected in the bulk is not a trivial exercise. We Ž . build on established advanced techniques of the conventional i.e. non-confocal light microscopy of phase objects to develop a suitable experimental protocol. Furthermore, we demonstrate the effectiveness of this protocol by means of an ‘atlas’ of the hard-sphere Ž . crystalline solid where random stacking results in many complex facets , which should serve as a compendium for future study.  2001 Elsevier Science B.V. All rights reserved. Keywords: Optical microscopy; Hard spheres; Crystallization Contents 1. Introduction ............................................... 135 2. Principles of colloid microscopy .................................. 137 2.1. Resolving colloidal length scales .............................. 137 2.1.1. Resolution-limiting factors ............................. 137 2.1.1.1. Detector segmentation ......................... 137 2.1.1.2. Imaging system aperture ........................ 137 2.1.1.3. Illumination degree of coherence ................... 141  Corresponding author. Tel. 44-131-650-6799, fax: 44-131-650-5212. Ž . E-mail address: m.s.elliot@ed.ac.uk M.S. Elliot . 0001-868601$ - see front matter  2001 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 0 1 - 8 6 8 6 00 00070-1