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Hi, Steffen

Many thanks for the correction on the date for 
Rheinberg!  Funny... I think that that came from 
some ancient literature ... I will have to search 
my files to see if there is still a copy.

One point about darkfield and NA: Actually, the 
rays emerging from the condenser are at the 
condenser's maximum NA.  The  cone in the middle 
excludes the components of smaller NAs.  For this 
reason, patch stops will only work with low NA 
objectives.  However, because only a narrow band 
of illumination is selected, the light is highly 
coherent.  Again, scattering theory rather than 
diffraction theory determines what can be detected.

Best regards
Barbara Foster, President & Chief Consultant
Microscopy/Microscopy Education*
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At 04:31 AM 2/2/2015, you wrote:
>*****
>To join, leave or search the confocal microscopy listserv, go to:
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>*****
>
>Jeff,
>
>concerning resolution, normal dark field is not any differfent from
>bright field, except maybe that Rayleigh may make more sense than Abbe,
>since you have a kind of self-luminous objects. In practical terms,
>resolution will be less since you have to cut down NA either from the
>objective or from the condenser. Concerning the smallest observable
>object, dark field is somewhat like fluorescence: Not the size is
>important, but the amount of light you can get out of it. If you want to
>dig deeper, the search term is ultramicroscopy, named so because it can
>visualize particles below the resolution limit. I estimate the term was
>en vogue from around 1900 to maybe the 1950ies.
>
>A 1902 experiment studied particles down to 4 nm, with sun light as
>light source, probably still the record for size:  H. Siedentopf, R.
>Zsigmondy: Über Sichtbarmachung und Größenbestimmung
>ultramikroskopischer Teilchen, mit besonderer Anwendung auf
>Goldrubingläser. In: Annalen der Physik. 315, 1902, S. 1­39,,
>doi:10.1002/andp.19023150102
>
>Henry Siedentopf (Zeiss company) and Richard Zsigmondy also developed
>the initial version of the Slit-Ultramicroscope (Spaltultramikroskop),
>which uses an illumination principle much like todays light sheet
>fluorescence microscopes, to study colloids.
>
>There are two Nobels associated with the technique.
>Ultramicroscopy was used in the Millikan-Experiment
>(https://en.wikipedia.org/wiki/Oil_drop_experiment)  which was rewarded
>with the physics Nobel in 1923.
>And in 1925 Zsigmondy got the Chemistry Nobel for his colloid studies.
>His Nobel Lecture is online
>(http://nobelprize.org/nobel_prizes/chemistry/laureates/1925/zsigmondy-lecture.pdf)
>
>Dark field seems to be particularly useful in visualizing living
>Spirochaete bacteria, thus the technique boomed from 1906 when the
>Syphilis bacteria where discovered.
>
>Concerning Rheinberg Illumination that Barbara mentioned, that was
>developed actually a little later than she thought: Julius Rheinberg of
>London first described it in 1896 (according to one source). In
>professional microscopy it seems to have been replaced mostly by phase
>contrast. But Hobbyists still use it to make beautiful images.
>
>If you should learn German anyway to read the Siedentopf & Zsigmondy
>paper (don't know if there is a translated version somewhere), you also
>can have a look at the German Wikipedia article on
>Dunkelfeldmikroskopie, which I think is quite good. But then, I may not
>be entirely impartial on that particular subject :-)
>
>Cheers
>Steffen
>
>
>Am 30.01.2015 um 23:44 schrieb Jeff Spector:
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > Post images on http://www.imgur.com and include the link in your posting.
> > *****
> >
> > Greetings,
> >    Can someone please point me to some references involving the theory
> > behind darkfield microscopy? I understand the basic idea, but all I can
> > find are different iterations of the basic idea that you block most of the
> > light and only image scattered light. I'd like to learn a bit more about
> > technical aspects of  darkfield, i.e. what is the smallest object you can
> > observe? What role do illumination power and camera exposure play in the
> > quality of the final image. What role does specimen thickness/size play in
> > the final image and can you discern objects of different size
> > etc...
> > Any help would be greatly appreciated. Perhaps I simply need to read up on
> > scattering theory?
> > thanks..
> > -jeff
> >
> >
> > --
> > ------------------------------------------------------------
> > Steffen Dietzel, PD Dr. rer. nat
> > Ludwig-Maximilians-Universität München
> > Walter-Brendel-Zentrum für experimentelle Medizin (WBex)
> > Head of light microscopy
> >
> > Marchioninistr. 27
> > D-81377 München
> > Germany