Daffodil pollen
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Re: Daffodil pollen
Interesting! How'd you do it? Magnification?
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Re: Daffodil pollen
Thanks. The first one is a 20X objective with a feathered darkfield stop.
The second is with a 40X objective.
Mike
The second is with a 40X objective.
Mike
Michael Reese Much FRMS EMS Bethlehem, Pennsylvania, USA
Re: Daffodil pollen
Hi,
Indeed an interesting effect. Pardon my ignorance but what is a ‘feathered darkfield stop’ (as opposed to a regular darkfield stop).
Mike
Indeed an interesting effect. Pardon my ignorance but what is a ‘feathered darkfield stop’ (as opposed to a regular darkfield stop).
Mike
Re: Daffodil pollen
I think OP is referring "reverse iris darkfield diaphragm", originaly proposed by W. R. Traviss and patented by W. Watson (London, UK) in early 1900s. It's interesting and rare device, only few times it appeared on ebay.
Last edited by Duke on Fri Apr 16, 2021 11:43 pm, edited 1 time in total.
“Thoroughly conscious ignorance is the prelude to every real advance in science.” - JCM
- rjlittlefield
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Re: Daffodil pollen
I would guess Olympusman is referring to the technique he described at https://www.photomacrography.net/forum/ ... 63#p245763 :
--RikOlympusman wrote: ↑Fri Feb 15, 2019 9:48 amIn photographic lighting, a feathered edge from a light source is attained by placing a card between the light source and the subject so that there is a diffused edge on the lit area.
In the case of a feathered darkfield stop, the spider stop is swung under the condenser so that there is a transitional zone between the bright field and the dark field. In this image you can see a darker area on one side of the spirogyra and a brighter one and on the other side a brighter side. This is also the technique I have been using for Rheinberg illumination.
The effect is almost like COL illumination in which a condenser is shifted off-center to somewhat sidelight the specimen, resulting in the three-dimensional effect.
Re: Daffodil pollen
Thanks Rik and Duke.
The W Watson device is interesting indeed. Pity it is so rare.
Mike
The W Watson device is interesting indeed. Pity it is so rare.
Mike
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Re: Daffodil pollen
In the diagram Duke shared, under "A", illustrates a Leitz condenser, which mixes DF (darkfield) and BF (brightfield), and it's capable to seamlessly switch between the two as the name implies. Obviously the BF obtained would be truly BF, but rather oblique due to the Traviss Stop. If there's an option to swing out the Traviss Stop mechanism, true BF can be achieved. Many older microscope condensers allowed components to be swung out.
Here's what the Watson condenser looks like:
More information: https://www.microscope-antiques.com/VHtraviss.html
Here's what the Watson condenser looks like:
More information: https://www.microscope-antiques.com/VHtraviss.html
- rjlittlefield
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Re: Daffodil pollen
If I understand correctly, the point of Olympusman's "feathering" approach is to produce an asymmetric cone of light, which then gives a sort of 3D appearance.
I assume the Expanding Stop would do the same thing if swung off-center, but that's because of the swing, not the expanding feature.
Please correct or clarify, if I have gotten that wrong. Thanks!
--Rik
I assume the Expanding Stop would do the same thing if swung off-center, but that's because of the swing, not the expanding feature.
Please correct or clarify, if I have gotten that wrong. Thanks!
--Rik
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Re: Daffodil pollen
Yeah you're correct Rik, there's many ways to achieve the effect. With a Traviss Stop, you'd probably have more control but the same can be achieved with cardboard and scissors, or Saul's Kit.
I only wanted to add a little information to Duke's comment since I was coincidentally doing some research on a "centred iris", something I came across before but forgot the terminology of when trying to explain an oddball darkfield condenser with the expanding aperture mechanism to a friend.
I only wanted to add a little information to Duke's comment since I was coincidentally doing some research on a "centred iris", something I came across before but forgot the terminology of when trying to explain an oddball darkfield condenser with the expanding aperture mechanism to a friend.