Norbert Vischer <[log in to unmask]> writes: > > This problem is discussed in: > > Taco D. Visser, J.L.Oud and G.J. Brakenhoff: > > Refractive Index and Distance Measurements in 3-D Microscopy, > Optik, 90, pp 17-19 (1992) Other publications point out that the formula for the focal shift given in the above paper is most likely *not* the correct one. See, e.g., Carlsson (1991) J. Micros. 163:167-178 and Hell et al. (1993) J. Micros. 169:391-405. Both these papers point out that the focal shift is much better described by NFP = n2/n1 * AFP (with NFP=nominal focus position and AFP=actual focus position) Though this formula is the low-aperture approximation of the one given in Visser et. al. it gives better agreement with experimental data when using high aperture objectives. Test measurements that I did on our confocal agree with that formula as well (I used an NA 1.25 objective). Regards, Christian Soeller -------------------------------------------------------------------- Christian Soeller mailto: [log in to unmask] St. Georges Hospital Medical School Dept. of Pharmacology Cranmer Terrace London SW17 0RE