There is a measured c o n f o c a l spot in Appl. Phys. Lett, 64, No. 11, 1994, p. 1335-1337 (Hell, et al). The spot is measured for NA=1.4, (Zeiss 100X, oil Planapochromat) 633 nm. The lateral full-width-at-half-maximum (FWHM) was 200 nm, the axial FWHM was 520nm. The extent of the PSF scales with the wavelength. The PSF measurement was carried out for an index of refraction of the specimen matched to the oil immersion system. A mismatched refractive index of the sample enlarges the spot (especially) in axial direction. This enlargement depends on the focusing depth. For further reference you can look up the 'Handbook' or one of the recent issues of 'Bioimaging'. Cheers, Stefan. __________________________________ Stefan W. Hell, Dr. rer. nat. Tel: +358 40 500 2758 (mobile GSM) Centre for Biotechnology Medical Physics and Chemistry PO Box 123 FIN- 20521 Turku, Finland tel: +358 21 633 7070 fax: +358 21 633 8000