Bought in - Darkfield condenser, NA 1.35-1.45.

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patta
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Bought in - Darkfield condenser, NA 1.35-1.45.

#1 Post by patta » Wed Jan 26, 2022 6:47 pm

For oil immersion or TIRF; it needs to work on thin slide (0.17mm, sample between two coverslips)
Gives darkfield illumination up to objective NA 1.25.

Fits 39mm condenser sleeve;
Height 32mm from flange;
Top diameter 21mm.
(Swift & Son pol scopes)


ask 1000 NOK + shipping
almost new
no warranties apart the NA which has been tested.

Can also swap with other similar gadget
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Last edited by patta on Fri Jan 28, 2022 9:34 am, edited 3 times in total.

apochronaut
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Re: FS - Darkfield condenser, NA 1.35-1.45

#2 Post by apochronaut » Wed Jan 26, 2022 10:45 pm

What kind of condenser is this and what happens when you use a slide? I presume you printed the mount.

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Re: FS - Darkfield condenser, NA 1.35-1.45

#3 Post by zzffnn » Thu Jan 27, 2022 12:15 am

How should a microscopist move 0.34mm of cover slips at such high NA, as regular slide holder won't work with such thin mount?

For me, practical usability/ ergonomics are also important in microscopy.

Would a regular oiled cardiod darkfield condenser achieve higher inner NA, when 0.34mm mount is used?

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Re: FS - Darkfield condenser, NA 1.35-1.45

#4 Post by patta » Thu Jan 27, 2022 10:21 am

apochronaut wrote:
Wed Jan 26, 2022 10:45 pm
What kind of condenser is this and what happens when you use a slide? I presume you printed the mount.
All 3D printed, apart from one piece of glass. I've made it yesterday, it is somewhat similar to the "Cassegrain" http://cnum.cnam.fr/CGI/fpage.cgi?M9975 ... 00/119/0/0
Can easily modify the base to fit other mounts. No centering arrangement for the time being.

With a 1mm thick slide it doesn't work at all; the light is concentrated only 0.2mm above the condenser plane; above that, it spreads to a large ring.
To get longer working distance, it will need much larger top assembly; but this was the max that would fit inside a 22mm hole in the stage with also enough space to baffle out as much stray light as possible.
NA 1.45, it is a darn shallow angle.
zzffnn wrote:
Thu Jan 27, 2022 12:15 am
How should a microscopist move 0.34mm of cover slips at such high NA, as regular slide holder won't work with such thin mount?
Stage clips + move by hand, works with some care. Dummy slide coverslip holder + standard mechanical stage, works fine. Except when the 0.34mm glass cracks....
I have several two-coverslip mounts from a previous project, where the condenser was another oil objective. Work ok but are darn delicate.
zzffnn wrote:
Thu Jan 27, 2022 12:15 am
Would a regular oiled cardiod darkfield condenser achieve higher inner NA, when 0.34mm mount is used?
I don't think so. Well I've never had a regular cardioid in my hands. Maybe they do, like the Leitz Heine, or maybe they do the opposite, with NA increasing as you go away. Depends where the radial focus has been placed by the designer, before, at or after the axis. Somebody tried?
A ring light without condenser, did this trick neatly, with NA depending on the ring distance from the sample. Hmmm...

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Re: FS - Darkfield condenser, NA 1.35-1.45

#5 Post by patta » Thu Jan 27, 2022 1:03 pm

ERRATA CORRIGE

Sorry after a more careful look the specs declared didn't seem to be exact :oops: . Not sure what can be trusted: the design trigonometry, the DIY apertometers, or the NA inscribed on an objective?
Anyway, below, that's the little plastic baby against a "big" boss. :lol:
The subject is an horrible mount of diatoms with air bubbles inside.
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DF_condenser_cassegrain_ludicrous.jpg
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Last edited by patta on Thu Jan 27, 2022 2:46 pm, edited 1 time in total.

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Re: FS - Darkfield condenser, NA 1.35-1.45.

#6 Post by apochronaut » Thu Jan 27, 2022 2:29 pm

You say, one piece of glass, which is presumably a lens. A Cassegrain condenser has a DF stop with a silvered upper surface, a concentrating lens and a reflecting primary mirror. A benefit is freedom from ca, sa as well as high N.A.
I am curious about the one piece of glass and the ca and sa?

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Re: FS - Darkfield condenser, NA 1.35-1.45.

#7 Post by Chas » Thu Jan 27, 2022 9:20 pm

What a lot of fun.... and it looks like it works !!

Out of interest; what does the 'HI' stand for on the objective ...is it homogeneous immersion or just a model of objective?

You mentioned an LED ring light and I wonder if 'Colonel Woodward's' ball-type oblique illuminator mounting might somehow work well with an LED ringlight:
Woodward's second illuminator1.jpg
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Woodwards second illuminator 2.jpg
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Maybe a high refractive index ball material might add to its perfomance too (???)

(Prior to this design he designed an oblique illuminator that was a small prism on a condenser mounting. It was was oiled to the underside of the slide).

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Re: FS - Darkfield condenser, NA 1.35-1.45.

#8 Post by apochronaut » Fri Jan 28, 2022 1:13 am

HI is a standard designation for homogeneous immersion. I would presume the objective has been immersed. It looks a bit distant from the coverslip/slide.

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Re: FS - Darkfield condenser, NA 1.35-1.45.

#9 Post by patta » Fri Jan 28, 2022 9:06 am

Those illumination methods from 100 years ago, they are amazing, and can't be found today! Great inspiration for some DIY. Guilty is somebody around that keep posting about them.

I've tried this early morning "TIR", total internal reflection (without the F for fluorescence), with the sample mounted in water; the illumination, coming with NA >1.33 should bounce back at the glass-water interface, and only the cells immediately near to the glass slide should intercept some light. But didn't manage to get the effect. Either all black or chunks fully illuminated. Need cells that stick better to the bottom glass?

Yes at previous post, was really a 60x in oil immersion, with NA (nominal?) 1.40. About the working distance of this objective (without spring mount!) I'd rather not speak about...
Aberrations from the condenser, shouldn't be a big issue, but I don't actually know yet how to examine in detail the resulting illumination, because of this 1.40, all gets small and difficult to observe. Edit: found some white, cloudy grease, to visualize the ray path. will see.

Anyway, since there isn't much enthusiasm for darkfield at 1.40, I'm going to trade the excess NA for some working distance, see if can make another condenser that work over a standard glass slide 1.2mm thick, hopefully still dark at NA1.25.
The current little condenser, isn't going away anymore, will stay with its newly found friend, 60x 1.40; maybe will get an Homal eyepiece to complete this vintage row of ducks.

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Re: Bought in - Darkfield condenser, NA 1.35-1.45.

#10 Post by apochronaut » Fri Jan 28, 2022 12:32 pm

A laser will show the TIR path quite distinctly as a bounced beam, or not, if it doesn't take place.

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Re: Bought in - Darkfield condenser, NA 1.35-1.45.

#11 Post by patta » Thu Feb 03, 2022 11:09 am

Working on it, no laser yet, but 1.2mm slide seems to be feasible. And managed to observe/measure the aperture with the "prism apertometer".
After some use of the above above condenser, the main issues emerged are... Bubbles, bubbles between the condenser and the slide; so hard to get them out. And oil seeping down in the condenser inners (#!§###!!). I never had an oil Cardioid, but I'm now thinking that it has been engineered specifically to ameliorate those two issues, with its large glass flat top.

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Re: Bought in - Darkfield condenser, NA 1.35-1.45.

#12 Post by apochronaut » Thu Feb 03, 2022 12:38 pm

Darkfield condensers are certainly well sealed, top and bottom. A big reason for that is to preserve the finish on the mirrors. The older ones I have used or looked at, used a very precise press fit between the mirrored oil immersion element and the metal surround, like a wine cork in a bottle. There may be some form of sealant at the interface between them, a black paint perhaps but I have never seen any evidence of that nor have I had one apart. It would be difficult without breaking the mirrored glass. In DF condensers, black is as important as shiney.
Newer versions might have the top element mounted into a sort of black epoxy or something akin to that.
I have never had one leak. That seems more common with refracting condensers which use a thin, flat, horizontal surface as a sealing surface, whereas oil immersion DF condensers use a wider vertical surface and usually have a bevelled surround down to a moat. I don't get the moat. I have never had quantities of oil running down a condenser. Perhaps it's necessary in production DF work. A lineup of Russian soldiers or something like that........ следующий !
The modern B & L DF condensers, such as were issued for the 100 watt research Balplan have an enormous moat. You could fill it with olive oil and have some crostini while at the microscope.
.

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Re: Bought in - Darkfield condenser, NA 1.35-1.45.

#13 Post by Chas » Thu Feb 03, 2022 8:29 pm

CTS made a small brightfield RMS-mount oil condenser where the (~5mm diameter) top lens is covered over by a (~10mm diameter) 'coverslip'.
The coverslip is set into a recess machined into the top metal of the condenser, so that the whole top surface is nearly flush.
The 'coverslip' seems to be bonded both to the metal and to the top surface of the lens.
-Just an idea.

Good one ( left) and one where the coverslip has broken way (right) :
CTS glass slip on top of condenser.jpg
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Last edited by Chas on Fri Feb 04, 2022 10:08 am, edited 4 times in total.

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Re: Bought in - Darkfield condenser, NA 1.35-1.45.

#14 Post by Hobbyst46 » Thu Feb 03, 2022 9:05 pm

The Zeiss West cardiodide condenser consists of a single glass element (consisting of the mirrors and top flat surface), apparently totally sealed as Apo mentions. Oil can leak, if used excessively, in between the glass element and the metal frame. The external black paint on the glass element can be thus exposed to oil. And it DOES dissolve or swell, though very slowly, in oil. Of course that is all seen on a DF condenser that is 70+ years old, might have never happened when the condenser was a teenager...

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Re: Bought in - Darkfield condenser, NA 1.35-1.45.

#15 Post by patta » Sat Feb 05, 2022 12:12 pm

Ok I'll glue a round coverslip over it and be parsimonious with olive oil.
This project swelled from "a couple of hours" to "a couple of weekends"; hope it stops before "a couple of months".

CTS, never thought about them; weird stuff they made!
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Re: FS - Darkfield condenser, NA 1.35-1.45

#16 Post by josmann » Sat Feb 05, 2022 6:43 pm

zzffnn wrote:
Thu Jan 27, 2022 12:15 am
How should a microscopist move 0.34mm of cover slips at such high NA, as regular slide holder won't work with such thin mount?
I think my approach would be to get some 1mm sheet metal and glue a rectangular (40mm) coverslip to it. I sketched it out here quickly - as shown it may need more room around the perimeter to accommodate the condenser for a full size coverslip. Something along these lines could be really useful to have around!
coverglass holder.jpg
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Re: Bought in - Darkfield condenser, NA 1.35-1.45.

#17 Post by Chas » Sat Feb 05, 2022 7:59 pm

There are a couple of existing designs for double-coverslip mounts (which are really good for seeing or 'reaching' both sides of something like a v.small insect).
Double-coverslip mounting seems to be used by nematologists.

Cobb's aluminium holder: eg https://www.wur.nl/en/show/Cobbs-alumin ... ders-1.htm

I have just come across a mention of the 'Higgins-Shirayama slide' this looks like it could be made on a 3D printer (?)

(I have just made a Cobb's holder out of an aluminium soft drink can, fold the material around a glass slide, trim it, squish it and punch a ~3/4 inch hole in the middle -- not as nice as the real deal as the cans aluminium is thinner and stays a bit springy).

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Re: Bought in - Darkfield condenser, NA 1.35-1.45.

#18 Post by Chas » Sun Feb 06, 2022 10:31 pm

I think this might turn out better than a homemade aluminium Cobb's slide holder.
It took 3 attempts to get it to print as it kept lifting off the bed .. I guess it needs some extra bits to get it to stick down (????)
Its the same size as a 3x1 slide and takes 60mm long coverslips ...Has 3mm deep ends and the rest is 1.5mm deep the side runners are 2mm wide.... its stronger/less flexible than I imagined it would be.
3 x1 inch holder for 60mm coverslip.jpg
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The design sent to the slicer was more 'sophisticated' than this but the printer dumped my cleverness and came up with this !! -- man and machine working in harmony ;-)
Now need to see how to glue on the coverlips. (hotmelt?)

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Re: Bought in - Darkfield condenser, NA 1.35-1.45.

#19 Post by patta » Mon Feb 07, 2022 4:09 pm

Thread drift..
Here, a third slide-holder
with sophisticate "step" to keep the coverslip
still a dab of glue is needed
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WIN_20220207_17_06_50_Pro_cut.jpg
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Re: Bought in - Darkfield condenser, NA 1.35-1.45.

#20 Post by dtsh » Mon Feb 07, 2022 4:33 pm

Chas wrote:
Sun Feb 06, 2022 10:31 pm
It took 3 attempts to get it to print as it kept lifting off the bed .. I guess it needs some extra bits to get it to stick down (????)
Try adding a brim, usually helps.

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Re: Bought in - Darkfield condenser, NA 1.35-1.45.

#21 Post by patta » Thu Feb 10, 2022 9:38 pm

Here the condenser design, before forgetting! There is nothing really new (compare with post #7 above...)

The light coming from some illumination is reflected by a conical ring mirror (should be a paraboloid); enters a half-ball lens without much refraction, then concentrates up to the specimen.
The NA is controlled by the narrow baffles that restrict the converging cone of light.

I've done about 10 prototypes; the one in photos below (#5) outputs a cone of about 1.35-1.45NA, above a 1.2mm slide; there is some stray light elsewhere but not too much.
One round coverslip cemented on top stops oil infiltration and reduces bubble formation.

Can be designed also for different NAs; higher (say 1.45-1.50?) but won't reach above a 1.2mm coverslip, issue in previous posts.
Smaller NA, I'm trying to make one with about 1.1 - 1.2 , for water mounts, but the half-ball lenses needed are hiding somewhere.

It is made with 3D printer, three pieces, about 15 grams in total. The "mirror" is simply aluminum foil glued there. I publish the 3D files asap but they are made to fit my weird 39mm condenser mount and a 9.0mm half-ball lens. If somebody is seriously interested I can change the barrel to fit other condensers, maybe even redesign (several weekends) the pieces in OpensCAD so dimensions can be adjusted by anybody.
Would be cool also to have a baffle sleeve movable up and down, so the NA can be adjusted. Enjoy!

Sample photos, iris exam, apertometer, maybe tomorrow.

One extra fancy perk of this design: one can roll a film of linear polarizer and slide it between the conical reflector and the lens; the cone of light then has Radial polarization, or azimuthal!
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Condensatore_conico_sezione_colorata_1000px.jpg
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Condensatore_conico_foto_prototipo_5_1000px.jpg
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Re: Bought in - Darkfield condenser, NA 1.35-1.45.

#22 Post by apochronaut » Thu Feb 10, 2022 10:30 pm

I like the polarization idea but not the lack of correction for ca. Many DF condensers go to great lengths to solve that and are ca free, which is a big problem in DF. Am I correct in that I see ca in the photo you supplied, quite a bit just above the green bar?

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Re: Bought in - Darkfield condenser, NA 1.35-1.45.

#23 Post by patta » Fri Feb 11, 2022 11:00 am

Sure, making some more pinholes to visualize the CA, I'm curious too.

Meanwhile, found out this Chinese microscope model (BK-6000?) that lists as accessory a mystery condenser "NA > 1.3" , see screenshot below.
But as usual, it is pretty hard to find out who's manufacturing it, or at least where can we find a spec sheet. Only thing, it seems to originate from the lil' town of Chongqing. On an Aliexpress page was listed at 88 US$ apiece (but not available, and the seller didn't tell much about its NA).

I'll continue the posts in the subforum "Illumination techniques".
viewtopic.php?f=28&t=14923&p=118355#p118355
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Darkfield_condenser_1_3_Screenshot_BK6000_Chonquing_Scope.png
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