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What does binning mean? (Andor Technologies)
Long Working Distance (LWD) objective lenses
Most biological objective lenses are designed to focus on specimens mounted under a standard #1.5 coverslip, which is about 170 µm thick. Most of these objectives cannot focus through the plastic in the bottom of a standard microtitre plate because their working distances are only a few hundred µm and the bottom of the plate is in the order of 1 mm thick. Long working distance objectives are designed to focus on specimens relatively far away from the front lens and can cope with the thickness of a microtitre plate.
The 20X and 40X objectives have correction collars that compensate for aberrations caused by refraction variations through different thicknesses of glass or plastic. If a collar has been adjusted for a 1 mm thickness (e.g. the bottom of a plastic dish) it will not focus correctly through a glass coverslip and you will need to adjust the collar to a setting appropriate to a 170 micron thickness.
There is no systematic way of adjusting correction collars. The best way is to set the collar to approximately the correct position before observing your sample, then to focus on the sample, and finally to make fine adjustments to the collar position if necessary. The adjacent picture shows the correction collar when adjusted for a 1 mm sample thickness. The black dot marks the position of the collar and the numbers around the objective barrel indicate the thickness for which the lens will be adjusted. The knurled ring above the dot should be used to rotate the collar. Unfortunately the Leica objectives don't have a mark for the position for a 170 micron coverslip, so the correct position can only be set approximately.
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Numerical Aperture (NA)
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