Talk:Dark-field microscopy

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Electron Microscopy Section

This is basically awful. I just used it in the final exam in transmission electron microscopy so the students could find all the errors. It really needs to be rewritten from scratch. — Preceding unsigned comment added by 165.124.144.215 (talk) 19:20, 22 March 2018 (UTC)[reply]

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Explanation

I found the explanation to be vague. And the diagram not of much help. This is not a criticism. I just think there are a lot of dopes out there like me who just don't understand things. Maybe somebody could look it over.Longinus876 (talk) 21:30, 14 June 2010 (UTC)[reply]

I second this, especially the 3D'ness of the diagram makes things a good bit confusing. A simple 2D sideview like for example http://www.jic.ac.uk/microscopy/more/T5_2.htm makes things more clearer. -- 89.245.88.200 (talk) 12:03, 15 August 2010 (UTC)[reply]
done, tell me if you want to change something in the image...R0oland (talk) 12:45, 18 December 2012 (UTC)[reply]
That illustration, http://upload.wikimedia.org/wikipedia/commons/thumb/b/be/Dark_Field_Microscope_%40D..svg/180px-Dark_Field_Microscope_%40D..svg.png, lacks clarity. Only after seeing http://www.jic.ac.uk/microscopy/more/images/5_1.gif, did I understand how a dark field microscope works. The major problem with the current illustration is that it's upside down. But even if it were rightside up, the www.jic.ac.uk image is far superior. Also, the text mentions "patch stop (see figure)", but the illustration has no such label or feature. Also, the text mentions "direct illumination block (see figure)", but the illustration has no such label or feature. MarkFilipak (talk) 00:57, 15 July 2014 (UTC)[reply]


I don't edit wiki articles directly, however if someone else would like to (and if they agree with me):

Bright-field:

  • Typically, light is focused through a sample (thing to be imaged) by a condenser lens.
  • Some is blocked by opaque parts of the sample.
  • The remainder passes through the objective lens, to be viewed.
  • This produces a white image, with sample details appearing darker than the surroundings (as the sample absorbed some light).

Dark-field

  • A blocking disc is put between the light source and condenser, blocking out the middle part of the beam (resulting in a "polo" of light).
  • The condenser focuses the beam onto the sample, as in bright-field.
  • In the focal plane, the entire sample is illuminated, despite the donut-shape of the beam before being focused. This is due to diffraction (see Fourier optics). Beyond the focal plane, the beam regains its "donut shape".
  • Without a sample, this donut has a hole just large enough so that none of the light can enter the microscope objective - the blocking disc effectively casts a shadow onto the objective.
  • With a sample, some light from the beam is scattered (reflected in lots of directions) - some is scattered towards the objective
  • Only the scattered light enters the objective (as the blocking disc prevents unscattered light from entering the objective).
  • This produces a dark image, with sample details appearing brighter than surroundings, as light that passed unscattered through the surroundings did not enter the objective.

Hope that helps! - Mark KC - 93.97.30.204 (talk) 16:20, 11 May 2011 (UTC)[reply]

Assessment comment

The comment(s) below were originally left at Talk:Dark-field microscopy/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

Darkfield examination of blood films has no medical usefulness. It is a pity that the references point to commercial sites making spurious medical claims.

Last edited at 22:13, 5 May 2007 (UTC). Substituted at 12:50, 29 April 2016 (UTC)

Diagram

I disagree with this edit by Graham Beards. Whether the diagram is upside-down is less important than whether it clearly illustrates how dark field microscopy works. The 3D image does not do that as well as the 2D ray diagram. Srleffler (talk) 22:02, 7 September 2022 (UTC)[reply]

The image's being upside down has proven to be a problem with my students and by extension, probably our readers. I think you have to already understand the principal before the image makes sense. My preferred image is clearer for novices to interpret. Graham Beards (talk) 05:36, 8 September 2022 (UTC)[reply]
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