Zeiss Cardiodid condenser fails with high NAs - peeling paint ?

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Hobbyst46
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Re: Zeiss Cardiodid condenser fails with high NAs - peeling paint ?

#31 Post by Hobbyst46 » Thu Aug 22, 2019 4:02 pm

Update for those who find it of interest:

My old immersion cardiodid condenser failed, as reported some time ago. The main part of the cardiodid is a sealed glass optical component, that from the outside looks like a frustum on top of a cylinder. This part is blackened from the outside (the perimeter and top frustum), and is enclosed within a brass housing. The black coating on the outside was peeling off, exposing the glass and allowing a lot of light through.

As a quick remedy I covered it with pieces of the infamous black sticky electrical isolation tape. At first the results were OK, but within a couple of weeks, the immersion oil caused the tape to swell and partially separate from the glass. This in turn led the viscous layer around the main part and, upon trying to clean it very gently with light petroleum or isopropyl alcohol, the black coating was mostly wiped away. Si=o much for the electrical tape...

I then tried black paints: several brands of permanent markers (Sharpie, Artline, others), airplane model paint, oil paint, wood paint... I painted glass slides with those paints and exposed them to immersion oil. The permanent marker inks dissolved within minutes. Other paints resisted for between hours and a day, then swelled.

My next step was self-adhesive black tapes that are marketed by optical parts suppliers (Thorlabs and others). Tested them as before - stuck a small piece of each on a glass slide, and flooded it with immersion oil.

Two different tapes failed, the coating seemed to dissolev. But, one type of tape resisted immersion oil for a least 4-5 days. I covered my poor condenser with this tape, and it seems to work. Nice dark field as ever.

The thickness of the top black layer of the tape is thin - about 5um, and I see that it is snesitive to scratching, so should be wiped only very gently!! but, it is made of some inorganic substance, so should be compatible with oil.
Now I will wait and see if this coating can be declared permanent.

MicroBob
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Re: Zeiss Cardiodid condenser fails with high NAs - peeling paint ?

#32 Post by MicroBob » Thu Aug 22, 2019 5:42 pm

Hi Doron,
a two component car paint will probably be resistant to immersion oil. You can even buy it in a spray can, I bought one for ca. 23€. This is a lot of money for a spray can but the paint is absolutely great. Next to the decorative object the paint was meant for I prepared wy wooden wine bottle boxes I use for loose microscopy stuff to take the rest of the paint. The easier way would be to talk to a car body shop and come along when they have black paint mixed ready.

Bob

Hobbyst46
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Re: Zeiss Cardiodid condenser fails with high NAs - peeling paint ?

#33 Post by Hobbyst46 » Thu Aug 22, 2019 7:00 pm

Thanks Bob, if the tapes fail I might try that route.

apochronaut
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Re: Zeiss Cardiodid condenser fails with high NAs - peeling paint ?

#34 Post by apochronaut » Fri Aug 23, 2019 10:16 am

Something like rust-oleum would work or any of the paints used on the floors of auto shops or any shop that uses greases oils or industrial chemicals. Should be available in a decent hardware store in a 1/4 l. tin.

Hobbyst46
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Re: Zeiss Cardiodid condenser fails with high NAs - peeling paint ?

#35 Post by Hobbyst46 » Fri Aug 23, 2019 11:45 am

apochronaut wrote:...
MicroBob wrote:...
Thanks, folks, for the suggestions. Engine paint might work. Still, my doubt about paints is that a thick layer of paint might be needed to really block the unwanted light rays. Besides, if for some reason the result is not satisfactory, removal of the paint from the glass surface might be a difficult task. Especially if the paint is solvent-resistant.

The advantage of the special coated adhesive tape is that a layer of a few micron thickness is absolutely opaque.
Anyway, if my present coating treatment will fail, it is good to know that the engine paint option is still there.

Hoping to post a few more dark field diatom images soon...

MichaelG.
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Re: Zeiss Cardiodid condenser fails with high NAs - peeling paint ?

#36 Post by MichaelG. » Fri Aug 23, 2019 12:27 pm

Hobbyst46 wrote:Anyway, as you say, UV is not for everyone, especially for home use.

I am still thinking of blue light. ...
405nm is probably [in my estimation] the most cost-effective choice; a usefully short wavelength, with inexpensive sources and optics readily available.

*** Safety precautions will still apply ***

MichaelG.
Too many 'projects'

NinetySix
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Location: Melbourne, Australia

Re: Zeiss Cardiodid condenser fails with high NAs - peeling paint ?

#37 Post by NinetySix » Thu Jan 18, 2024 12:19 pm

Just thought I would dig up this old gem of a thread to convey the story of my success in restoring the opaque black paint on my Zeiss Ultra condenser.

The product I used was a rattle can of VHT wheel paint. I didn't buy it specifically for this purpose - I shamelessly salvaged it, full, from a roadside pile of hard waste - so there may be slightly more suitable products, but I can confidently declare that this one works well.

I suspect the key factor here is that it is a polyurethane paint, so it forms a quite tough coating, with impressive chemical resistance. I made it a point not to clean the Cargill type B oil off it after using it till the next time I used the scope, so a couple times now it's been wet with oil for a week and it's still holding up.

I used 3m purple masking tape and an x-acto knife to carefully trim around the flat top of the condenser (a steel blade will always come off second best to glass, but I would definitely avoid using a fancy carbide tipped razor blade) and then just taped over the rest of the condenser top, still in its housing, and gave it about 4 light coats on a warm day. I removed the masking tape within about 30 mins, and cleaned up the top edge very carefully with the x-acto, and the result appears to be a perfect knife-edge stop.


Cheers

Hobbyst46
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Re: Zeiss Cardiodid condenser fails with high NAs - peeling paint ?

#38 Post by Hobbyst46 » Thu Jan 18, 2024 1:42 pm

NinetySix wrote:
Thu Jan 18, 2024 12:19 pm
Just thought I would dig up this old gem of a thread to convey the story of my success in restoring the opaque black paint on my Zeiss Ultra condenser.

The product I used was a rattle can of VHT wheel paint. I didn't buy it specifically for this purpose - I shamelessly salvaged it, full, from a roadside pile of hard waste - so there may be slightly more suitable products, but I can confidently declare that this one works well.

I suspect the key factor here is that it is a polyurethane paint, so it forms a quite tough coating, with impressive chemical resistance. I made it a point not to clean the Cargill type B oil off it after using it till the next time I used the scope, so a couple times now it's been wet with oil for a week and it's still holding up.

I used 3m purple masking tape and an x-acto knife to carefully trim around the flat top of the condenser (a steel blade will always come off second best to glass, but I would definitely avoid using a fancy carbide tipped razor blade) and then just taped over the rest of the condenser top, still in its housing, and gave it about 4 light coats on a warm day. I removed the masking tape within about 30 mins, and cleaned up the top edge very carefully with the x-acto, and the result appears to be a perfect knife-edge stop.


Cheers
Great job !!

Sure Squintsalot
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Re: Zeiss Cardiodid condenser fails with high NAs - peeling paint ?

#39 Post by Sure Squintsalot » Thu Jan 18, 2024 6:41 pm

It would be interesting to compare our darkfield systems.

I've cobbled together a similar system to look at diatoms at high magnification. Using glycerin immersion above and below my slide, at 100x, I can get about 200nm resolution, but only with very specific kinds of diatoms: only the thinnest layers of frustules. The photos are a little less clear than what I see through the eyepieces:

Here's a shot of the surface sheet of a Rhizosolenia:
Screenshot 2024-01-18 113234.jpg
Screenshot 2024-01-18 113234.jpg (75.52 KiB) Viewed 672 times
Screenshot 2024-01-18 113330.jpg
Screenshot 2024-01-18 113330.jpg (116.96 KiB) Viewed 672 times
I'm assuming that my resolution isn't imaginary, but I am always open to that possibility. The literature claims resolutions down 40nm are possible, but I suspect that lighting systems, sample prep, and subject are very specialized. I just wish diatoms weren't so finicky to image at this magnification.

apochronaut
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Re: Zeiss Cardiodid condenser fails with high NAs - peeling paint ?

#40 Post by apochronaut » Fri Jan 19, 2024 8:45 am

this is reflected DF? The thing about DF is that very high resolution is reported and can be realized but but similar to fluorescence this involves the imaging and/or separation of illuminated points. The detail is in the fact that they are there, not that you can see snything about them. A similar type of resolution occurs with phase systems that reveal inclusions.
In my experience, around .2 microns is the extreme likely possibility for the perception of recognizable detail of any sort and if , you can peer through the floater field.
I particularly like DF as an imaging method for very small , very transparent aquatic organisms, most less than 5 microns. The bulk of them are almost impossible to see in BF ; you get only a sense of their presence, fleeting, an occasional glimpse of flagellum not to return, like a melting snowflake. Under DF , you can follow them and see their sub-micron structure and motility / behaviour charactrristics but it involves very careful preparation with measured , clean glass, a very good adjustable objective and a pretty high N.A. condenser free of aberration. All of that is outside the scope of the average DF set up and impossible with DF stops in an abbe condenser, or a dedicated dry DF condenser for that matter.
DF really comes into it's own as in it's earliest praised usage ; as an ultra microscope, revealing things virtually unseeable in BF.

Sure Squintsalot
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Re: Zeiss Cardiodid condenser fails with high NAs - peeling paint ?

#41 Post by Sure Squintsalot » Sat Jan 20, 2024 12:20 am

This is transmitted darkfield. The checkered scale bar is 10µm X 3µm, calculated as a fraction of the field of view, taken with a Zeiss stage micrometer.

The dark line separating the striae looks to be about 200nm-300nm. Within each striae is a honeycomb network of puntae(?), of which there appear to be 4-5 punctae per micron. You'll have to squint hard in the detailed view, but you can make out the separation between the punctae which may be close to 100nm. Racking up/down doesn't seem to change the position of the puntae, indicating, I think, an undiffracted view and thus a useful resolution pretty close to 100nm. Which, from what I've read is actually quite good (for a punter like me using an off-the-shelf LED).

Resolving the absolute limit of a system is pretty satisfying and extremely useful.

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