Chris,

The moveable lens is essentially an optical "adapter" to adjust for both
the size of field illuminated and NA of the condenser.  Obviously, at very
low power, the diameter of the field being observed is much larger than
when you "zoom in" at high power.  To fully illuminate that large field
(especially for 5x scanning lenses; occasionally for the 10x), flip the
lens out.

NA is the second issue.  If you read your objectives, you will find that
the lower mags typically have lower NAs and the higher mags, higher
NAs.  Note: Mag and NA are two independent characteristics but often run in
parallel.  The NA of the condenser should match or exceed the NA of the
objective (you can always close it down using the aperture iris in your
condenser).  According to your discussion, the maximum NA available from
your condenser is 0.9.  To achieve that value, flip in the moveable lens.

Summary: at very low mag (5x, maybe 10x), flip the lens out; at higher mag,
higher NA, flip the lens in.

More discussions available in my book, "Optimizing Light Microscopy for
Biological and Clinical Laboratories".  See our website for details.

Best regards,
Barbara Foster
Microscopy/Microscopy Education
125 Paridon Street, Suite 102
Springfield, MA 01118
PH: 413-746-6931  FX: 413-746-9311  Web: www.MME-Microscopy.com/education

"Why didn't they teach us that sooner?"  ... probably because no one
thought to call MME about customized, on-site courses.  Offered in all
areas of microscopy, sample prep,and image analysis, they make an immediate
impact on your productivity.
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At 10:32 AM 7/4/01 -0300, Chris Kushmerick wrote:
>This is not a confocal question, but rather a basic microscope question.
>
>We have an Axioskop FS microsope rigged for epifluorescence with phase
>optics.
>
>The condensor rotates to one of several positions, labelled: "1", "2",
>"3" (I assume these are the phase settings) as well as "DIC" and
>"H/DIC".
>
>Above this rotating condencer, there is another lens that can be tilted
>into or out of the light path by moving a small lever. On this lens it
>is written "0,9".  My question is, what is this movable lens? What is
>its purpose? Should I use it for phase imaging?  When I perform Kohlar
>alignment, should it be in the light path or not?
>
>Thanks,
>
>Chris
>
>--
>Christopher Kushmerick  <[log in to unmask]>
>
>Dept. Farmacologia                              tel 55 31 3499 2707
>Inst. Ciencias Biologicas                       fax 55 31 3499 2695
>Universidade Federal Minas Gerais
>Av. Antonio Carlos 6627, Pampulha
>31270-901 Belo Horizonte, MG
>Brasil
>
>Note new telephone and fax numbers.