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Some Diatoms Mounted in Realgar
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Cactusdave



Joined: 09 Jun 2009
Posts: 1631
Location: Bromley, Kent, UK

PostPosted: Wed Jan 10, 2018 12:20 pm    Post subject: Some Diatoms Mounted in Realgar Reply with quote

I recently had a couple of oil immersion lenses for testing and 'sale or return' from member Photomicro. These were a Leitz Leitz NPL FLUOTAR 50/1.00 OEL 160/- and a couple of Zeiss Planapo 40/1.00 Oel 160/- . One of these he warned me might be a lemon and he was certainly right! The other two lenses however were good and I subsequently bought them Thanks Photomicro. Smile

As a test for these lenses, I looked out a slide of 'mixed test diatoms' mounted in Realgar (arsenic sulphide) by Klaus Kemp. Realgar is an exotic, toxic and dangerous mountant, favoured by 'serious' diatomists because its high refractive index (quoted between 1.9-2.4, typically the higher figure) significantly enhances the resolvability of minute structural details in certain diatoms. I have a few Realgar slides but they have all deteriorated quite badly by crystallisation and clouding. The one I chose is the newest, least deteriorated and most usable.

There are some interesting (and hair raising Shocked details of making mounts with Realgar in this 1885 reference (full text)) https://www.jstor.org/stable/3220589 . I wonder why the much safer sounding tin chloride in glycerine and gelatine mountant described in this reference never caught on? Most modern diatom mounts are made using the synthetic resins Zrax refractive index 1.7 or the similar Naphrax. http://www.mikrohamburg.de/Tips/TE_Mountingmedia.html

To test the lenses I used genuine Zeiss immersion oil for immersion, with DIC as described in this thread http://www.photomacrography.net/forum/viewtopic.php?p=193908#193908 The X40 DIC slider was used and the condenser was equipped with the NA 1.4 aplanatic achromatic top lens. The condenser was at maximum height but not oiled to the back of the slide. I was immediately impressed with the clarity and detail of the diatoms in the mount with both these lenses. Pau has praised the Leitz NPL Fluotar X50 I think, and he is quite right, it is an excellent lens which gives very good DIC with the Zeiss components. The Zeiss X40 planapo is also very good and produces very nice DIC.

A few sample images. All this set unstacked.



Leitz X50 NPL Fluotar, 1.0.


Crop from this image.




Leitz NPL Fluotar, 1.0 again.



Crop from this.




Zeiss Planapo X40, 1.0. Stitch of 9 images.



Crop from this image.

[
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Beatsy



Joined: 05 Jul 2013
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PostPosted: Wed Jan 10, 2018 2:59 pm    Post subject: Reply with quote

Yowzers! You can really see the extra contrast in those Dave. Even if you did some levels adjustment in post, it's still very clear that way more contrast (than usual) was there to start with.

Would love to see a version with the condenser oiled too. That would resolve even more.

Just a small point - as I understand it, higher RI mountants only increase contrast, not resolution (and give greater apparent depth of field of course).
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rjlittlefield
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PostPosted: Wed Jan 10, 2018 3:46 pm    Post subject: Reply with quote

Nice images!

Beatsy wrote:
higher RI mountants only increase contrast, not resolution (and give greater apparent depth of field of course)

The greater DOF should be real, not apparent. This is because at a fixed NA for the objective, the entrance cone has a narrower angle in the high RI medium.

Independent of contrast, the resolution should be independent of RI. The shortening of wavelength in the high RI medium is exactly balanced by narrowing of the entrance cone.

For details that are otherwise low enough contrast to get lost in the noise, there may be an increase in observable resolution due to the increase in contrast.

--Rik
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zzffnn



Joined: 22 May 2014
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Location: Texas USA

PostPosted: Wed Jan 10, 2018 6:34 pm    Post subject: Reply with quote

Photo #4 (counting from top) shows some stunning "dotting" there. Thank you for sharing!
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carlos.uruguay



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PostPosted: Wed Jan 10, 2018 7:40 pm    Post subject: Reply with quote

Super!
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Cactusdave



Joined: 09 Jun 2009
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Location: Bromley, Kent, UK

PostPosted: Thu Jan 11, 2018 9:38 am    Post subject: Reply with quote

Thanks for your comments, and especially thanks to Rik for answering Beatsy's point better than I could have managed. Very Happy

For some more on Realgar diatom mounts, and pushing resolution to the utmost by manipulation of wavelength of illuminating light and polarisation, when seeking the ultimate in 'diatom dotting', this article by David Walker is worth a read.
http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artjan10/dw-slide2.html

To conclude my pictures, a couple more with the Zeiss Planapo X40, 1.0. A stack of nine images with Helicon method C.



Finally a crop from the above.


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arturoag75



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PostPosted: Thu Jan 11, 2018 1:12 pm    Post subject: Reply with quote

Impressive job.
Just a quastion: is there available somewhere a mounting media with RI higer than zrax?
Arturo
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Jacek



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PostPosted: Thu Jan 11, 2018 1:18 pm    Post subject: Reply with quote

Very nice
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Beatsy



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PostPosted: Thu Jan 11, 2018 5:10 pm    Post subject: Reply with quote

Cactusdave wrote:
Thanks for your comments, and especially thanks to Rik for answering Beatsy's point better than I could have managed. Very Happy


I have been suitably clarified, or corrected Smile

Nice image again. Seriously good detail for N.A. 1.0!
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dragonblade



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PostPosted: Thu Jan 11, 2018 10:39 pm    Post subject: Reply with quote

Stunningly detailed images.
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Cactusdave



Joined: 09 Jun 2009
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PostPosted: Wed Jan 17, 2018 9:45 am    Post subject: Reply with quote

Thanks again everyone. I must return to this slide at some point with the Zeiss X63, 1.4 planapo, oil. It should give some nice detail.
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Pau
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PostPosted: Wed Jan 17, 2018 10:01 am    Post subject: Reply with quote

Congrats, good performer objectives, and I think you got them at a bargain price.
In your opinion, how well compare the NPL Fluotar 50/1.0 with the Planapo 40/1.0? As you now I only own the Leitz and I'm not sure if is worth getting the Zeiss
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MicroBob



Joined: 29 Jan 2016
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PostPosted: Sat Jan 27, 2018 1:55 am    Post subject: Reply with quote

Hi Dave,

Thank you for posting these impressive images. The high r.i. of the realgar really shows.

Concerning the Leitz NPL Fluotar 50 1.0: I have this objective in the 160mm TL version. I think this objective is made to be used without cover slip and I found a free working distance of 0,22mm for it. I have used this objective for diatoms but there is really not much space left between front lens collar and cover slip. Is this the same with you objective? How do you like it from a practical point of view? I'm a bit afraid to damage my cover slips when revolving the objetive in place.

Bob
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Cactusdave



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PostPosted: Sat Jan 27, 2018 5:56 am    Post subject: Reply with quote

Thanks MicroBob. I also have the 160mm tube length version. The lens is marked 160/- meaning it can be used with or without a coverslip. It would be marked 160/0 if it was designed to be used only without a coverslip.

I find it a very good lens, with the extra bit of magnification over a X40 1.0, oil, useful. There is a good choice of oil immersion lenses at this magnification point. The Zeiss X40, 1.0 oil Apo and Planapo objectives are both nice if you can find non-delaminated examples. I've also heard good things about the Wild X50, 1.0 Fluotar, HI, though be aware this is a short, 37mm parfocal objective.

Quote:
I'm a bit afraid to damage my cover slips when revolving the objective in place.



Personally I would never directly revolve an oil immersion objective into place. I wouldn't trust parfocality to that extent, and I don't think it's good practice. I would always rotate an immersion lens in position with it well above the slide, carefully lower it till the front of the lens had just made proper contact with the drop of immersion fluid and then begin to slowly bring the objective closer to the coverslip with fine focus only of course, continually watching for the focal plane of the subject in the eyepieces.

David
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MicroBob



Joined: 29 Jan 2016
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PostPosted: Sat Jan 27, 2018 6:19 am    Post subject: Reply with quote

I found a list of Leitz objectives from 1985 here:

http://www.science-info.net/docs/leitz/Leitz_optics_1985.pdf

This should be 160mm era.

The 50:1 objective has a "-" for cover slip thickness like the weaker dry objectives. I'm not shure though that this has the same meaning here. 0,2mm is not much when cover slips have a slight upwards tolerance.
But the image of this objective is really nice!

I normally have my objectives on the turret so that an oil lens moves sideways parfocal into the oil drop. I probably have to adopt here.
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