Re: variable phase contrast -- same as Pv?

Hi Greg,

The Leitz Pv and the Carl Zeiss Jena Phv are quite different. The Leitz
Pv objectives are meant to be used with the Leitz Heine condenser, a
variable phase condenser than optically creates a hollow cone of light
which can be adjusted to any size desired. This is different from
regular phase condensers which have a turret of annuli beneath them
which can only create as many different sized cones are there are spots
in the condensers turret. Generally each stop is specific to a certain
range of objectives based on their magnification and NA. The main
advantage of the Pv/Heine type system is that you can go from
Brightfield, to Darkfield, to any magnification of Phase with the same
condenser without rotating in various annuli.

The CZJ Phv system is more like the standard phase contrast system than
the Leitz type (Leitz also had a Phaco type phase contrast, which is
identical to the traditional Zernike type). The only difference between
the Phv type and the regular Zernike type is that the Phv phase annuli
and objectives have two concentric phase rings in the same objective and
condenser annuli. These can be used together, or the outer ring can be
masked off by the condenser's regular iris diaphragm.

The reason to do this would be that the width and positioning of the
phase ring within the objective is optimized for different types of
specimens. The regular type of Zernike phase, and the Phv type with both
rings being used (the outer ring is more dominant, so the inner ring
plays essentially no role when the outer ring is used) are optimized for
relatively small specimens with smaller details relatively close
together. A larger, specimen with less internal small details would
produce significantly prominant halos when viewed in this type of phase.

The novel feature of the Phv being able to block off the outer ring,
utilizing only the smaller inner ring, which is optimized for larger
less detailed specimens. When used this way with smaller cells, the
contrast enhancement is overdone and details are lost, but with larger
cells the halos are significantly reduced and the contrast is similar to
that of smaller cells used within regular Zernike phase contrast.


I've wrote a message concerning this before in the Yahoo Microscope
group which links to pictures (although not mine, and described in
German) that illustrates the advantages. That message can be found
here:

http://tech.groups.yahoo.com/group/Microscope/message/25219



HTH,

Kevin




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"Greg" <jmchone@xxxxxxxx> wrote in news:1175963889.106266.103340
@y80g2000hsf.googlegroups.com:

Hello, I might be off the thread, but is a Leitz Pv objective also a
variable phase contrast, or does the Pv indicate something else? Greg




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