  Remote focusing (RF) is a technique that greatly extends the aberration-free
axial scan range of an optical microscope. To maximise the diffraction limited
depth range in an RF system, the magnification of the relay lenses should be
such that the pupil planes of the objectives are accurately mapped on to each
other. In this paper we study the tolerance of the RF system to magnification
mismatch and quantify the amount of residual spherical aberration present at
different focusing depths. We observe that small deviations from ideal
magnification results in increased amounts of residual spherical aberration
terms leading to a reduction in the dynamic range. For high numerical aperture
objectives, the simulation predicts a 50% decrease in the dynamic range for 1%
magnification mismatch. The simulation has been verified against an
experimental RF system with ideal and non-ideal magnifications. Experimentally
confirmed predictions also provide a valuable empirical method of determining
when a system is close to the ideal phase matching condition, based on the sign
of the spherical aberration on either side of focus.
