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Serpentine

 
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Epidic



Joined: 04 Aug 2006
Posts: 137
Location: Maine

PostPosted: Tue Jul 10, 2007 11:42 am    Post subject: Serpentine Reply with quote


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rjlittlefield
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Joined: 01 Aug 2006
Posts: 19783
Location: Richland, Washington State, USA

PostPosted: Tue Jul 10, 2007 1:35 pm    Post subject: Reply with quote

Nice picture Very Happy , but I have little idea what I'm seeing. Sad

What can you tell us about the subject and/or how the picture was shot? (I'm always curious about both. Wink )

Thanks,
--Rik
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Epidic



Joined: 04 Aug 2006
Posts: 137
Location: Maine

PostPosted: Tue Jul 10, 2007 3:44 pm    Post subject: Reply with quote

This is a sample of Serpentine - a rock/mineral. This can do a better job of telling what it is than me:

http://en.wikipedia.org/wiki/Serpentine

Serpentine is more beautiful in the macro world. I have a photo of a beautiful green/red piece taken in Gros Morne National Park. I will scan the slide and post it when I get my scanner hooked up.

It was taken with a Nikon 5x objective and no photo-EP on the tube - I think the CCD is a 14mm square chip. Episcopic darkfield illumination. The image is a stack of 28 frames compliled with Helicon Focus.

I have not posted in a very long while. I have not had a scope to use until now. I just took this snap this afternoon and thought it was interesting.
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Tue Jul 10, 2007 6:07 pm    Post subject: Reply with quote

Epidic wrote:
It was taken with a Nikon 5x objective and no photo-EP on the tube - I think the CCD is a 14mm square chip. Episcopic darkfield illumination. ... I have not posted in a very long while. I have not had a scope to use until now.

Ah, but it sounds like you are well equipped again!

This sounds like a dedicated microscope camera. What make/model?

Also, I am curious about this term "episcopic darkfield". I searched the web for a description or definition, but did not find anything helpful. As I understand the terms, "episcopic" means that the light comes from above and is reflected by the specimen, and "darkfield" (with transmitted illumination) means that no light enters the objective unless it is refracted, reflected, or diffused by the subject. But by just those definitions, all episcopic illumination would be darkfield unless, say, there's a mirror in the background. So I figure that, in combination, the words "episcopic darkfield" must mean something very special. What is it?

Thanks much,
--Rik
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Epidic



Joined: 04 Aug 2006
Posts: 137
Location: Maine

PostPosted: Tue Jul 10, 2007 7:20 pm    Post subject: Reply with quote

Yes, my present postition puts me in charge of some nice research microscopes. A job perk I am just starting to enjoy. (I still have my Vanox DIC metallurgy scope I got off ebay, but my transition from Japan to Maine has not given me the chance to use it.)

The camera is a Diagnostic Instruments Flex camera. It is a 4MP chip with pixel shifting technology that can bring the resolution up to 16 MPs or 64 MPs.

You are right about episcopic illumination is also known as vertical illumination. It is "darkfield" in that the light is not coming from the objective lens, but a ligh path that is built around the objective. Very much like a condensor in transmission scopes, but above the specimen. Switching between "brightfield" and "darkfield" does have the same relative change as you see in transmission scopes, but with maybe less contrast.

Obviously, episcopic scopes have no "field" in that it has no area of undiviated light within the image like a diascopic scope. An episcope scope will still produce a diffraction pattern of a line grating behind the objective like a transmission scope - the diffraction orders are quite clear. Now a question I have never asked is if the diffraction pattern shifts between darkfield and brightfield on a transmission scope reversing the constructive and destructive orders of the diffraction pattern - I think it might. And would this happen in an episcopic scope? If that is the case, then you would have a "real" dark/brightfield difference in the reflected light paths. I don't know if the targets I have would show a conclusive result - it can be really hard to clearly separate the orders, at least with what I have.

Anyway, Nikon calls it "darkfield" and "brightfield," and if it is good enough for them... Wink
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Tue Jul 10, 2007 10:21 pm    Post subject: Reply with quote

Thanks for the explanation. I had not thought about the distinction between light coming from around the objective versus through it. The terminology makes perfect sense with that in mind. BTW, a Google search for "episcopic darkfield" (with the quotes) produces a whopping 5 hits, none offering an explanation. "episcopic brightfield" is almost equally as bad, 6 hits with no explanation. This is probably the worst failure of web search I have ever seen.

Prior to your explanation, the only discussion I had seen of reflected "brightfield" versus "darkfield" illumination was in an article by Ted Clarke. I just now reviewed that article, and it seems to me that Clarke's "brightfield" means specifically that both illumination and viewing rays are perpendicular to the focus plane, so that a planar mirror subject would be seen as bright, not dark. Related, but perhaps slightly different?

Congratulations on your new position! Having access to good equipment is indeed a nice perk. Very Happy

--Rik

Edit: corrected URL for Ted Clarke's article.


Last edited by rjlittlefield on Tue Jul 10, 2007 11:14 pm; edited 1 time in total
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discomorphella



Joined: 01 Oct 2006
Posts: 605
Location: NW USA

PostPosted: Tue Jul 10, 2007 10:55 pm    Post subject: Reply with quote

Nice shot. It's a great thing having good scopes at work and at home....I work surrounded by optical and electron microscopes, then I go home to my own...my co-workers know I am a microscope nut...but they have no leg to stand on for ribbing me....they are also microscopists...
Anyhoo....you have the same kind of conjugate planes with episcopic (reflected) illumination as you can with diascopic (transmitted) illumination. All modern epi illumination systems let you implement Koehler illumination. You can put an annular aperture in the appropriate place in an episcopic illuminator and get darkfield or a plain iris and get brightfield. Darkfield comes from blocking the zero-order peak (in the back or fourier plane) or unscattered light (object plane) , and gathering only the off-axis scattered light. You can have regular brightfield with epi or transmitted illumination, and similar partially coherent imaging theory is just as applicable as for a transmitted light scope. Hope this is not entirely confusing.

--David
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Epidic



Joined: 04 Aug 2006
Posts: 137
Location: Maine

PostPosted: Wed Jul 11, 2007 5:53 am    Post subject: Reply with quote

Rik and David, thanks.

The relation to the zeroth order is a great way to express of the difference between BF and DF. Very simple and succinct.
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