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Condenser for dark field

 
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Andy Davies



Joined: 09 Dec 2014
Posts: 94

PostPosted: Thu Aug 09, 2018 7:52 am    Post subject: Condenser for dark field Reply with quote

I'm looking for recommendations for a condenser lens to do macro dark field using lenses such as a nikon 60mm 1:1, Canon Macro 35mm 3-5x and a Mitty 10x.
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Pau
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Joined: 20 Jan 2010
Posts: 4381
Location: Valencia, Spain

PostPosted: Thu Aug 09, 2018 9:05 am    Post subject: Reply with quote

What kind of illumination? (reflected or transmitted)
What kind of subject? (flat, volume, transparency...)
Microscope condensers are designed for transparent or very small subjects.
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Alan Wood



Joined: 29 Dec 2010
Posts: 269
Location: Near London, U.K.

PostPosted: Thu Aug 09, 2018 11:46 am    Post subject: Reply with quote

Andy

I think it will be difficult to find a dark-ground condenser that can illuminate an area large enough for the Nikon and Canon lenses.

There are other ways to achieve dark-ground, such as an inverted ring-light with a black card centre:





You need to experiment with the height of the kitchen bowl (which is just a spacer) and the diameter of the clear circle in the black foamboard on top.

Alan Wood
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Pau
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Joined: 20 Jan 2010
Posts: 4381
Location: Valencia, Spain

PostPosted: Thu Aug 09, 2018 12:09 pm    Post subject: Reply with quote

For big subjects I use a dark field fiber optic ring just held rear the subject
http://www.photomacrography.net/forum/viewtopic.php?p=68418
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Alan Wood



Joined: 29 Dec 2010
Posts: 269
Location: Near London, U.K.

PostPosted: Thu Aug 09, 2018 2:01 pm    Post subject: Reply with quote

I had almost forgotten about fibre-optics dark-ground illuminators; this one is by Schott-Fostec:



The subject could be supported on a piece of (very clean) glass.

Alan Wood
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Andy Davies



Joined: 09 Dec 2014
Posts: 94

PostPosted: Thu Aug 09, 2018 4:31 pm    Post subject: Reply with quote

Subjects would include comb jellies that vary from a 5mm (sea gooseberries) to 10cm (beroe). I'd be using transmitted light on a horizontal macro rig.
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Pau
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Joined: 20 Jan 2010
Posts: 4381
Location: Valencia, Spain

PostPosted: Fri Aug 10, 2018 1:05 am    Post subject: Reply with quote

So you want to shot them in a mini aquarium, do you?

For the 10X a microscope condenser with a central stop would do if the total thickness is small enough. For larger subjects the discussed ring lights seems the best option, although placing a black background and illuminating the subject laterally by means of several light sources also would do.

This (poor) image was taken through a stereomicroscope eyepiece illuminating the Petri dish just with one Ikea LED lamp and placing a black card under the dish.

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enricosavazzi



Joined: 21 Nov 2009
Posts: 1024
Location: Stockholm, Sweden

PostPosted: Wed Aug 15, 2018 10:31 am    Post subject: Reply with quote

See also the paper:

Kawano et al 2013: Darkfield Adapter for Whole Slide Imaging: Adapting a Darkfield Internal Reflection Illumination System to Extend WSI Applications. Plos One 8:3, p. 1-12.

link to PDF: http://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0167774&type=printable
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