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 | | From: | Rene | | Subject: | Q: old diatom test slide designations | | Date: | 23 Jan 2005 06:55:01 -0800 |
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 | It's focal distance of the lens: 1/12 (inch) something like 100x (but
depending on tubelength). There was a time they really thought it was
advantageous to go for very high objective mags (up to 1/50"),
nowadays only scopes like the Ergonom500 use that trick.
For the test diatoms, Surirella gemma, Frustulia rhomboides and
Amphipleura pellucida are much used test diatoms for the higehest
powers. Check the library of microscopy-uk
(http://www.microscopy-uk.org.uk/mag/indexmag.html) for test diatoms,
to see what you're supposed to see.
The mounts are likely to be in canada balsem, which makes details less
visible then the diatom mountants in use today.
Rene.
From: justbeats (steve_beats@hotmail.com)
Subject: Q: old diatom test slide designations
This is the only article in this thread
View: Original Format
Newsgroups: sci.techniques.microscopy
Date: 2005-01-21 02:26:32 PST
I recently acquired some more Victorian and Edwardian slides to add to
my collection. To my surprise (and delight) 30 (of 72) are diatomacea
including selected arrangements, strews from far-flung places and (the
subject of my question) 8 test slides.
These test slides all date to the 1920's and 1930's and besides
describing the species they are each labelled with "for 1/12" or
"for 1/25" (or other fractions). This must be related to the
objectives each test slide is best suited to - but how? What do the
fractional numbers mean?
Thanks
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| | From: | justbeats | | Subject: | Re: Q: old diatom test slide designations | | Date: | 24 Jan 2005 00:43:17 -0800 |
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| Thanks folks - I've already visited all the links you suggested, it was
the 1/25th (et al) on the slides that had me foxed, not info about test
diatoms. Strange way to express magnification, eh? I'll look for
references to see what "distance" equates to what magnification. Ta.
Rene: I reckon you're right about the Canada Balsam - I am using max
40x objective at the moment (waiting for immersion oil to arrive so I
can use the 100x). But at 400x, I am able to resolve lines and dots in
Amphipleura pellucida and Surirella gemma quite easily (using Nomarski
DIC), but see nothing in Amphipleura lindheimerii - not even underlying
"graininess". Since I can detect "something" with a 16x objective in
the other test diatoms (but need 40x to resolve 'em), I expected the
same at 40x in lindheimerii, but the RI of the medium must be robbing
the contrast. Tried DIC, phase contrast, dark field and even oblique
lighting, all to no avail. Fun trying though. Will be interesting to
see if 100x and oil "cracks it".
Cheers
Beats
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