Some Diatoms Mounted in Realgar

Images made through a microscope. All subject types.

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Cactusdave
Posts: 1631
Joined: Tue Jun 09, 2009 12:40 pm
Location: Bromley, Kent, UK

Post by Cactusdave »

The designation on the Leitz NPL Fluotar X50, 1.0, oil of 160/- means that it is not specifically corrected for a 0.17mm thick coverslip. The Zeiss Planapo X40, 1.0, oil, iris is similarly designated 160/-. This does not mean they cannot be used with coverslips of 0.17mm, it simply means that the lens is not specifically corrected for this thickness of glass. There might be sound marketing reasons for this. These lenses would be good for examining fixed, but not coversliped blood films in a Path. lab. This was potentially a big market.

I have successfully used both the Leitz lens and the Zeiss to look at modern high quality diatom mounts where the coverslip thickness is likely to be of the order of 0.17+/- 0.02mm with no problems of working distance. With coverslips significantly thicker than this, any oil immersion lens (and some dry Planapos,) may be unable to reach focus. I can only reiterate the advice I was given a long time ago. When working with immersion lenses, or any lenses with tiny working distance, exercise great care when finding the focal plane on any slide where you can't guarantee the thickness of the coverslip. There may not be one before you hit the coverslip! :cry:
Leitz Ortholux 1, Zeiss standard, Nikon Diaphot inverted, Canon photographic gear

Pau
Site Admin
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Joined: Wed Jan 20, 2010 8:57 am
Location: Valencia, Spain

Post by Pau »

I subscribe almost all Cactuscave says.
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.
Formerly I proceed like you and I still do in some cases but I find easier and also better to avoid air bubbles to directly revolver the objective because I have very good parfocality between Leitz objectives. This doesn't apply when I mix Zeiss and Leitz objectives like I sometimes do with the NPL Fluotar 50/1.00 and Planapo 63/1.4
Pau

jmc
Posts: 238
Joined: Fri Apr 17, 2020 3:14 am

Re: Some Diatoms Mounted in Realgar

Post by jmc »

Cactusdave wrote:
Wed Jan 10, 2018 12:20 pm
There are some interesting (and hair raising :shock: 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
Well aware that this is a bit of a thread resurrection, but I wanted to respond to the question raised in the opening post. The Tin Chloride, Glycerin, Gelatin mixture apparently only has an RI of about 1.7, so therefore doesn't really offer the extent of benefits observed for Realgar (RI >2), and is more in line with the more conventional organic based high RI mountants. I guess this was why it wasn't more widely used. The information came from p186 of "An introduction to the microscopical study of diatoms" by R.B. McLaughlin. Link here to the PDF of the book - https://www.mccrone.com/wp-content/uplo ... mbook1.pdf

Big fan of Realgar slides, and always good to see images done from them.
Jonathan Crowther

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