Re: More on A.pellucida

Hallo,

Thank so much for for your constructive contribution and the
reference to Edmund J. Spittas work. I have looked at Google
Books and found "Photomicrography" of 1899 I downloaded
it and will look at the photos. I could not locate the other work
"Microscopy" of 1909. The existence of both was unknown to
me.

Regarding the ability of some observers to resolve A. pellucida
into dots while others were not able to do so, may have two causes.

One is that A. pellucida might occur with fine or coarse structure.
There is strong variability of the parameters for samples from the
same site. There may be even stronger variability for samples from
different locations. This aspect is something which Dr. Gaugler
will attempt to clarify in the near future by using some special
samples from Mr. K. Kemp.

The other cause may have to do with what is nowadays called the
modulation transfer function. Since modern images are taken
on 36 mm film or on CCD or CMOS sensors, the size of the
a resolved element thrown upon the film or sensor compared to
the film grain and pixel size is a most important parameter. It is
desirable to have as large as possible a magnification upon
the sensitive surface as is practical and combine this with as
small as practical a grain size on film or of a pixel. The latter
of course needs to have a certain size to achieve a good S/N
ratio.

Nowadays with 36 mm film and small CCD or CMOS sizes
there are limits. In the old days when microscopists used
very large photographic plates and large projection distances
these limits were more favorable.

These two causes may have a bearing while microscopists
of over one hundred years ago, were able to resolve A. pelluci-
da into dots.

Greetings
GR.


<cladocera56@xxxxxxxxxxxx> wrote in message
news:1169492233.891301.258700@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hi

Thanks for sharing your A. pellucida results and as you remark the
comparison of SEM and LM photos of the same material is valuable.

As an aside, I think the work of Spitta to me as a hobbyist is jaw
dropping if not humbling. His book 'Microscopy' 1909 2nd edition has
very well resolved photos of A. pellucida to 'dots' with blue light and
convincingly resolved to 'dots' with green light, all of high contrast.
These photos are presented in conjunction with his chapter devoted to
using this and other diatom species and Abbe test plate as test
objects.

His earlier book 'Photomicrography' 1899 has two text pages on
photographing A. pellucida and a beautiful photo of this diatom
resolved to striae. Although it's his photo of another test diatom P.
angulatum in 'Microscopy' that blows me away, not a tricky one to
resolve but it's a beautifully crisp photo of this diatom with internal
detail.

with regards

David



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