RE: Mercedes Coverslip Tape

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From:garygill <> (by way of histonet)
To:histonet <>
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	It sounds as though you already have a Sakura machine and you're simply
price comparison shopping.  If you don't already have a Sakura tape
dispenser, however, please read my post below that was originally submitted
to Histonet 1/7:

	Cover glass acts the first lens in any microscope objective, and is so
considered by lens designers.  There are specific refractive index,
dispersion values, planoparallelism, and thickness specifications for cover
glasses that plastic cover glasses can not match.  It is not enough that a
specimen, whether cells or tissue, be covered by something thin and

	Most often No. 1-1/2 thickness cover glasses are recommended in
publications.  Such recommendations are based on the interpretation of the
thickness printed on the objective itself (e.g., 0.170 [meaning 170
micrometers thick]).  art of the cover glass.  No. 1/1-2 thickness cover
glasses are correct only when there is little or mounting medium between the
specimen and the underside of the cover glass (e.g., cells grown on a cover
glass, specimen mounted on a cover glass, spring-loaded clothes pins or
weights applied to the cover glass to squeeze out the excess mounting
medium).  Such applications are research oriented and not practiced

	In practice, the thickness of mounting medium between the specimen
and the
underside of the cover glass is often substantial and acts optically as
though it is glass.

	Many years ago some authors actually cross-cut some histo slides and
measured the thickness of the mounting medium, finding it to be substantial
relative to allowable deviation tolerances.  The upshot of all this is that
No. 1 thickness cover glasses should be used routinely.

	4X and 10x objectives are insensitive to cover glass thickness, due to
their low numerical apertures.  40X acrhromat objectives can tolerate
deviations only as small as 15 micrometers.  What happens when overly thick
mounting medium and cover glass are applied?  GLARE.   High dry image
quality loses contrast, appearing cloudy, hazy, washed out, etc.  The
greater the thickness, the worse the appearance.  The cleaner the
microscope, the closer it is set up for Kohler illumination, the higher the
quality of objective (e.g., planapochromat), the more obvious the loss of
contrast appears.  If one practices sloppy microscopy, the loss of contrast
will be less obvious.  Is the loss of contrast ruinous?  Will it prevent one
from making a diagnosis?  No, but plastic tape is a triumph of technology
over technique.

	Bottom line:  Sakura plastic tape can not equal glass cover glasses
by any man or machine.  However, if saving money is your primary goal...?
At one lab where I worked, the Sakura machine was sometimes used, sometimes
not.  The surface of the mounted tape was wavy, and often pulled up at the
edges.  High dry microscopy of cells along the edges was often impossible.
Some dotting inks used in cytology etch the plastic and can not be removed.
Also, the tape scratches rather easily, further scattering light and
introducing glare.  Cytology preparations are less forgiving than are histo

Gary Gill

-----Original Message-----
From: Hagerty, Marjorie A. []
Sent: Tuesday, January 26, 1999 12:25 PM
To: 'Histonet'
Subject: Mercedes Coverslip Tape

Hi All,

Does anyone know anything about the coverslip tape from Mercedes
Medical? They have tape for the Sakura coverslipper that costs less than
the tape from Sakura. I am interested to find out if anyone has tried it
and how they liked it.


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