Technique for dark field using a Nikon EPI-D objective

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wwp347
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Technique for dark field using a Nikon EPI-D objective

Post by wwp347 »

I am considering a Nikon objective with a designation of EPI-D. I would like to know more about this type of objective. How versatile would this objective be? I want to photograph dark field with excellent dark backgrounds. Would this help create a darker background? Can this be used for bright field or other modalities?
Thanks for your time and consideration,,
BudP

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Scarodactyl
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Re: Technique for dark field using a Nikon EPI-D objective

Post by Scarodactyl »

Epi-d is not one I'm familiar with, usually their epi darkfield are marked BD.
Epi darkfield is not that much like transmitted darkfield. The objective just has an added hollow shell around it that light can pass through and acts like a ring light casting illumination inwards. This makes the objective fatter so it's harder to illuminate if the working distance is short. Aside from being fatter they're the same as their brightfield metallurgical equivalents.

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Re: Technique for dark field using a Nikon EPI-D objective

Post by enricosavazzi »

As Scarodactyl said, transmitted darkfield and epi-darkfield are two different things. In addition to one being done in transmitted illumination and the other in incident illumination, the "darkfield" in epi-darkfield is somewhat misleading. In transmitted darkfield, any portion of the FOV that does not refract/diffract/diffuse light appears automatically dark. In both epi-darkfield and epi-brightfield, the background is dark only if the subject is placed onto a light-absorbing material (e.g. some kind of velvety cloth) or a transparent sheet, and behind this sheet there is a sufficient distance to the actual background (enough to make it appear dark), or if the background reflects light in other directions than into the objective.

In addition, to achieve epi-darkfield you need the right type of epi-illuminator. To use epi-darkfield you must use a microscope epi-illuminator equipped with a darkfield cube. Many of the simpler epi-illuminators have a slider with fixed (i.e. not interchangeable) brightfield and darkfield optics. The more versatile epi-illuminators use interchangeable cubes. In most cases epi-fluorescence illuminators can also be equipped with epi-darkfield and epi-brightfield cubes, but in this case you should replace the UV lighthouse with a VIS lighthouse if you intend to do imaging in the VIS range.

Virtually all objectives, including BD ones, can be used with epi-brightfield. Only BD objectives (with a light-conducting cavity surrounding the objective optics) can be used for epi-darkfield.
--ES

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Re: Technique for dark field using a Nikon EPI-D objective

Post by rjlittlefield »

wwp347 wrote:
Fri Jan 17, 2025 6:39 am
I am considering a Nikon objective with a designation of EPI-D. I would like to know more about this type of objective. How versatile would this objective be? I want to photograph dark field with excellent dark backgrounds. Would this help create a darker background? Can this be used for bright field or other modalities?
The notation "EPI D" appears on Nikon model MUE42100. That's a 10X NA 0.30 CFI TU Plan Fluor BD, for example shown at https://www.edmundoptics.com/p/10x-obje ... r-bd/52721 .

As described by the other replies, this objective can be used in for both brightfield and darkfield, with both epi and transmitted illumination.

However, there is nothing particularly special about this objective that will "help create a darker background". It's really just a good 10X NA 0.30 with a fat hollow barrel that allows light to be pumped down around the lenses to illuminate the subject.

--Rik

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Re: Technique for dark field using a Nikon EPI-D objective

Post by Lou Jost »

Some Nikon objectives are labeled Epi because they are specially designed to avoid flare when bright light is sent through the objective's lenses to illuminate the subject. Their normal BD objectives, as everyone knows, have shrouds and mirrors to illuminate the subject with light coming from outside the lenses of the objective. These two features are not always present in the same objective. Maybe "Epi-D" refers to an objective that is specifically designed to support illumination by either of these paths, while the more common "BD" objectives expect only transmitted light ("B") and shrounds-and-mirrors light ("D"), not light shone through the objective's own lenses?

wwp347
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Re: Technique for dark field using a Nikon EPI-D objective

Post by wwp347 »

Thanks for the information everyone. This objective has a 32mm thread diameter. Even if I were to adapt it to a 25mm nosepiece, it seems likely that it would defeat the use of the perimeter light barrel. Probably not what I am looking for. I wish to have access to a good transmitted dark field setup. I plan on starting with dark field stops and see if I need to go further. Occasionally Nikon dark field condensers become available on eBay. Currently only high NA (1.4) dark field condensers are available which work with high magnification objectives. I suspect I am looking to do dark field in the 20-60x range. I assume this would require a lower NA dark field condenser and don’t know whether this would be an improvement over dark field stops.
Thanks for your time and consideration,,
BudP

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Re: Technique for dark field using a Nikon EPI-D objective

Post by Pau »

First: do you want to perform transmitted or reflected (epi) dark field? The illumination, suitable subjects and equipment are all different!
Pau

wwp347
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Re: Technique for dark field using a Nikon EPI-D objective

Post by wwp347 »

Transmitted dark field for photography . Not sure how dark field reflected light is useful, but I am always interested in exploring new techniques.
Thanks for your time and consideration,,
BudP

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Re: Technique for dark field using a Nikon EPI-D objective

Post by Lou Jost »

Pau wrote:
Sun Jan 19, 2025 10:44 am
First: do you want to perform transmitted or reflected (epi) dark field? The illumination, suitable subjects and equipment are all different!
I think it might be worth distinguishing the two kinds of reflected light darkfield: lighting through the "shroud-and mirrors" around the objective, versus lighting through the glass of the objective. These two techniques put different demands on an objective's design.

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Re: Technique for dark field using a Nikon EPI-D objective

Post by Scarodactyl »

I don't think you can do epi darkfield through the glass of the objective.

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Re: Technique for dark field using a Nikon EPI-D objective

Post by enricosavazzi »

Scarodactyl wrote:
Mon Jan 20, 2025 12:40 am
I don't think you can do epi darkfield through the glass of the objective.
Exactly, you can only do epi brightfield by illuminating the subject through the objective optics.
As far as I know, there is only one type of epi darkfield.
--ES

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Re: Technique for dark field using a Nikon EPI-D objective

Post by Lou Jost »

Scarodactyl wrote:
Mon Jan 20, 2025 12:40 am
I don't think you can do epi darkfield through the glass of the objective.
I think you can, using a distant black background. I admit I haven't tried it though, so I could be wrong.

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Re: Technique for dark field using a Nikon EPI-D objective

Post by Pau »

Lou Jost wrote:
Mon Jan 20, 2025 7:11 am
Scarodactyl wrote:
Mon Jan 20, 2025 12:40 am
I don't think you can do epi darkfield through the glass of the objective.
I think you can, using a distant black background. I admit I haven't tried it though, so I could be wrong.
Or you can put a black background with good light absorbing materials, but this is not what we call Dark Field illumination
Pau

wwp347
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Re: Technique for dark field using a Nikon EPI-D objective

Post by wwp347 »

Does anyone have experience with a EPI-D objective? It seems the 32mm thread size adapted to a 25mm nosepiece wouldn’t work. Is that size used for metallurgical microscopy?
Thanks for your time and consideration,,
BudP

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Re: Technique for dark field using a Nikon EPI-D objective

Post by Macro_Cosmos »

These special BD objectives have a wraparound shroud with reflector lenses at the very front to strategically form the cone for darkfield. BD should stand for bright/dark if I am not mistaken. BDs are fatter because of all the extra optics surrounding it.

A hallow cone is cast through the objective lens. Unless there is something in focus, it will appear dark. The shroud is acting as a condenser. This is true darkfield, so I do not think the label is misleading. Quite a few parts are needed to achieve this. It is totally fine to use a mercury burner lamp for this, make sure a uv-ir cut filter is installed. I would just swap out a halogen lamphouse though, mercury burner lamps are painful to work with.

BDs can be used for transmitted darkfield, most objectives lenses with sufficiently low NA compared to the hallow cone can do darkfield transmitted. Another easy method for lower magnifications is to simply illuminate the glass slide with a strategically placed LED torch.

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