Dark field objectives as condensers for transmitted dark F

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Linden.g
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Dark field objectives as condensers for transmitted dark F

Post by Linden.g »

This may have been noted before, just in case it hasn't I thought it was interesting. I wanted to do some dark field transmitted light microscopy on my Olympus BH-2. Not having any stops or dedicated dark field condensers I decided too try using a set of Olympus Neo S Plans as condensers. I took out the sub-stage condenser and used the objectives pointing up after blocking off the central light path at the back of each lens. They seem to make good dark field condensers as long as you use one with a higher NA than the viewing objective.

Linden

ChrisR
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Post by ChrisR »

Interesting. I wonder what the NA would be for a "BD" objective used like that (under stage, light through annulus only).
High NA versions have less than 1mm of working distance, so the thickness of a normal slide would be a problem.

An alternative is a ring of LEDs, eg "Angel Eyes".
Last edited by ChrisR on Mon Jan 04, 2016 9:37 pm, edited 1 time in total.
Chris R

zzffnn
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Post by zzffnn »

Linden,

At what (viewing) objective NA did you try it that way? Up to NA 0.65, DIY darkfield stops onto regular condenser should work well.

You can also adapt other darkfield condensers onto BH2, say with Lego's/super glue or by making a condenser adapter. I am trying to do this for my Nikon Labophot 2, which seem to have a highly similar (may even be the same) dovetail as your BH2.

I asked what dedicated darkfield condensers fit onto Labophot easily with minimal modification: http://www.photomacrography.net/forum/v ... hp?t=29572
But I have not received much input.
Selling my Canon FD 200mm F/2.8 lens

Linden.g
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Post by Linden.g »

I have the universal condenser, BH2-UCD and would have to make some stops. Using the Neo-Splans is probably more of a curiosity. They seem to work in these combinations.

Neo-Splan 50 (0.80) with Splan 40 (0.7)

Neo-Splan 50 (0.80) with Splan 20 (0.46)

Neo-Splan 50 (0.80) with Splan Apo 20 (0.7)

Neo-Splan 20 (0.46) with Splan Apo 10 (0.40)

Neo-Splan 10 (0.3) with Splan Apo 4 (0.16)

Neo-Splan 5 (0.13) with Splan FL 2 (0.08)

It was easy to test. I took of the BH2-UCD and used a microscope slide as a bridge over the forks of the mount and aligned by moving the objective around to center.

I would be interested to know what people use for the Olympus Splan Apo 100 (1.4) and the Splan 100 (1.25) as they both have NA larger than what appears to be supported by the Olympus dark field condenser DCW (1.4-1.2)

zzffnn
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Post by zzffnn »

You need either a funnel stop made specifically for a specific objective or an objective with iris for stopping down aperture. Effect and image quality would be highly similar, though iris is more convenient and don't need to be removed when switching to brightfield.

At NA >= 1.25, you pretty much have to use dedicated darkfield condenser, iris objective or funnel stop.

And in case you have not read this thread:
http://www.photomacrography.net/forum/v ... 245700848f
Selling my Canon FD 200mm F/2.8 lens

Pau
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Post by Pau »

Linden, your idea about using BD objectives as DF condenser is very interesting, how do you illuminate them?
I would be interested to know what people use for the Olympus Splan Apo 100 (1.4) and the Splan 100 (1.25) as they both have NA larger than what appears to be supported by the Olympus dark field condenser DCW (1.4-1.2)
The wider dark field condensers I'm aware of are 1.2-1.4 like the Oly (and BTW oil immersed). I'm sure that it's due to a Physics limitation, you just can't do DF at this large NAs. For DF the condenser light inner cone NA (1.2) must be wider than the objective NA to avoid direct ligh enterring in the objective, if not you just can obtain circular oblique illumination.

As zzffnn says the only way is to stop down the objective to have a smaller NA (but not 1.25, it must be 1 to 1.1 max).

I have a 50 1.0 oil objective that works very nicely for DF
Pau

Charles Krebs
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Post by Charles Krebs »

I would be interested to know what people use for the Olympus Splan Apo 100 (1.4) and the Splan 100 (1.25) as they both have NA larger than what appears to be supported by the Olympus dark field condenser DCW (1.4-1.2)
The 100X S Plan Apo has an adjustable diaphragm built into it for that purpose. You close it down until it is just smaller than the lower NA of the oiled darkfield condenser,

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Post by rjlittlefield »

zzffnn wrote:And in case you have not read this thread:
http://www.photomacrography.net/forum/v ... 245700848f
I presume that URL is intended to refer to http://www.photomacrography.net/forum/v ... hp?t=10839 .

URL's that contain "view=previous" or "view=next" can be broken in an instant if somebody posts a reply that bumps one of the threads.

--Rik

Linden.g
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Post by Linden.g »

Pau

I'm using the base light as is with a LED light source instead of the standard 100 w bulb. https://www.flickr.com/photos/13084997@ ... 697012197/

Charlie, I had no idea that the S plan Apo 100 could do that! :o thank you. Seems a shame to stop down such a nice lens.

I found this internal reflection method interesting http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3592912/

Thanks for all of the help

Linden

Charles Krebs
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Post by Charles Krebs »

I found this internal reflection method interesting
Then you might find this interesting:

http://www.mvi-inc.com/products/microsc ... diography/

Pau
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Post by Pau »

Linden.g wrote:I found this internal reflection method interesting http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3592912/
Charles Krebs wrote:Then you might find this interesting:
http://www.mvi-inc.com/products/microsc ... diography/
Yes, this is an interesting method, I've tried it time ago with very little succes due to the inadequate light source. I was tempted to buy a line light fiber optic but I didn't follow the project
http://www.dolan-jenner.com/Pro/Linelights.htm

But sadly it doesn't work for higher NA than an oil DF condenser
From Darklite FAQS:
QUESTION: "With a darkfield condenser, an objective with a numerical aperture approaching or exceeding 1.0 requires an iris diaphragm which must be stopped down. Is this also true of the Darklite?"
ANSWER: Yes. Without the iris, stray light will enter the objective and destroy the darkfield effect.
However, unlike many darkfield condensers, the Darklite works exceptionally well with dry objectives with numerical apertures as high as 0.95.
The last paragraph seems inaccurate because oil DF condensers work nicely at that aperture, for sure many must refer to dry condensers

In fact it's not clear in any of both sources but I guess that oil objectives just will not work because the total internal reflection principle will be broken at the oil-glass contact surface.
Pau

Linden.g
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Post by Linden.g »

Thank you for all of the advice and links to some interesting equipment. Here are a couple of test images using Neo-Splan 50 (0.80) as condenser with Splan 40 (0.7). The first diatom is approx 50% crop. Both are from prepared test slides.


Image

Image

phil m
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Post by phil m »

Baker; the English microscope maker that became Cooke-Baker, thenCooke and eventually, Vickers, made a condenser that had an R.M.S. thread. One of the attachments, that has occasionally shown up on ebay and that fits into this is a Baker DF condenser lens section or nose, with an R.M.S. thread. I always wondered why they would have such a thread, unless there was a purpose in using objectives as condensers. I never came across any literature to explain the reason for this condenser design, or any recommended objective matching.

From the beginning of Spencer offering apochromats until AO ceased making them temporarily, at the time of converting to infinity correction in the early 60's, they offered a 1.3 N.A. achromat-aplanat and a 1.4 N.A. achromat-aplanat. Although the two condensers are completely interchangeable in the substage, the optical section is completely different on the two. The 1.3 has a similar condenser section to the Baker, with an R.M.S. thread and presumably facility to use objectives as condensers, although to my knowledge, they never made a DF condenser with an R.M.S. thread.

It seems the use of objectives

Choronzon
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Post by Choronzon »

Here's a photo I took in San Juan Puerto Rico at a TIRF install. Total Internal Reflection Fluorescence. As you can see, the total internal reflection principle works just fine with immersion objectives. In this case, a 100x 1.4 apo TIRF. As you can see, the excitation from reflected laser light is internally reflected inside the thick chroma slide (488 excitation). It's very dependent on the entrance angle of the beam to get total internal reflection. TIRF illumination such as this is capable of illuminating living neuro and cellular material not easily seen without super resolution or 2 photon and single photon microscopy.
Image
I am not young enough to know everything.

rjlittlefield
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Post by rjlittlefield »

Choronzon, this is one of the most beautiful and immediately informative images that I've ever seen, regarding how something works in a microscope. Very nice!

--Rik

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