Condenser for dark field

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Andy Davies
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Condenser for dark field

Post by Andy Davies »

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.

Pau
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Post by Pau »

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

Alan Wood
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Post by Alan Wood »

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:

Image

Image

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

Pau
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Post by Pau »

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

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

Image

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

Alan Wood

Andy Davies
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Post by Andy Davies »

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.

Pau
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Post by Pau »

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.
Image
Pau

enricosavazzi
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Post by enricosavazzi »

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/articl ... =printable
--ES

Andy Davies
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Joined: Tue Dec 09, 2014 3:25 pm

Post by Andy Davies »

I have tested a slide projector condenser lens with a torch and can see a cone of light produced by the lens. This cone is in focus on the subject. Would the size of the patch stop match this cone somewhere between the lens and the subject?

Would the appropriate field of view of the camera lens then be just a bit smaller than the view blocked out by the patch stop when focused on the subject? This would be the case if dark field was set up on a microscope.

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