Martin Wessendorf wrote:

>Although the working distance for the new objective was listed as being
>0.11 mm and that for the old objective was 0.12 mm, there was a 30+
>micron difference in the depth to which we could focus.

This could also be because coverslips usually have a specified
thickness tolerance of 30um. You will rarely find large differences
within one batch, but between batches, they can be quite noticeable.
You can also get special standard (0.17mm) coverslips with less
tolerance, but they are only worth the expense for use with non-oil
immersion lenses.
With oil lenses it is even advantageous to use thicker coverslips,
effectively replacing immersion oil with glass, and thereby trading
working distance for optical quality (less dirt, autofluorescence,
scattering, temperature-induced RI mismatch, etc). On the other hand
you can gain working distance by using thinner coverslips. Again, all
of this applies only to oil immersion lenses.

My apologies if these matters are trivial for you, I just noticed
that a lot of microscopists are not aware of them.

Cheers,

Beat


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