MicrobeHunter.com Microscopy Forum

Hello all,

Here is another small test of the Ultracondenser (cardiodid dark field oil condenser), pushing towards the high NA limit. I do not have any objectives of NA>1 with iris or funnel stops. This is a comparison between my three 100X objectives: a 100X1.3 Planapo Ph3 oil (the prestigious one) 160/0.17, and two simple 100X1.25 achromats (not Plan), one with a black collar and 160/-, and one that is all-metallic and unspecified about the coverslip. The front lens openings of the achromats are naturally smaller than that of the Planapo, and the two of them appear to be of the same diameter.
The test subject is a strew diatom slide, mountant - Pleurax, oiled above and below. Illumination was the 10W LED light, filtered through an intereference filter that passes light of wavelength<560nm, so violet+blue+green. I could narrow the range even to 450-500nm, but the intensity fell drastically so I could not see the specimen clearly, and gave it up.

The 100X1.3 is outside the feasible DF range. It yields a nice phase contrast image though, as shown.
The 100X1.25 (black) yields a quasi-DF. Some post processing made it look better.
The 100X1.25 (metal) yields an oblique view.

So - at least for hobby use, and unexpected (for me at least), those non-pretentious, non-plan objectives can be fun.

Hobbyst46 wrote: ↑

Tue Sep 17, 2019 5:36 pm

Hello all,

Here is another small test of the Ultracondenser (cardiodid dark field oil condenser), pushing towards the high NA limit. I do not have any objectives of NA>1 with iris or funnel stops.

Intriguing post....

I'm not familiar with the "Ultracondenser"; is that a Zeiss product and what's its NA?

Sure Squintsalot wrote: ↑

Tue Jun 06, 2023 5:37 am

Hobbyst46 wrote: ↑

Tue Sep 17, 2019 5:36 pm

Hello all,

Here is another small test of the Ultracondenser (cardiodid dark field oil condenser), pushing towards the high NA limit. I do not have any objectives of NA>1 with iris or funnel stops.

Intriguing post....

I'm not familiar with the "Ultracondenser"; is that a Zeiss product and what's its NA?

Here it is shown, the one on the left is the immersion oil Ultracondenser

It is possible that Zeiss coined the term Ultracondenser because in the early years of DF , the technique was referred to as " Ultramicroscopy" because using DF particles or inclusions could be detected that were below the theoretical limit using BF.

apochronaut wrote: ↑

Tue Jun 06, 2023 12:33 pm

It is possible that Zeiss coined the term Ultracondenser because in the early years of DF , the technique was referred to as " Ultramicroscopy" because using DF particles or inclusions could be detected that were below the theoretical limit using BF.

I think so too, since when I first read about ultramicroscopy, it referred to light scattering.

apochronaut wrote: ↑

Tue Jun 06, 2023 12:33 pm

It is possible that Zeiss coined the term Ultracondenser because in the early years of DF , the technique was referred to as " Ultramicroscopy" because using DF particles or inclusions could be detected that were below the theoretical limit using BF.

This is an effect I'd still like to learn more about. It does make some intuitive sense when you think of the DF-illuminated subjects as self-emitters, but I'd appreciate being pointed to any specific literature about it!

It would seem that there's an absolute limit to the NA of the objective of around 0.8 with (any) oil darkfield condenser. I'd have to go through the math to understand why, but there doesn't seem to be any high-mag compatible dark field condenser that has a NA over 1.4 and that doesn't limit the objective to a NA of 0.8.

I wonder if NOT using a conventional slide but a coverslip might push the NA of the condenser past 1.4. Again one would have to do the math to see what that effect would be.

The Watson DG zonal oil condenser is at na 0.9.
Either with the 50x .9 oil objective or with a funnel stop for 100x oil that is listed as a part.
Provided the subject is illuminated and the na of the objective is below the na of the dark field it should work.
If the limit is .9 anything over 90x is likely to be empty magnification.
If I were spending I'd try a 60x .85 ∞ for the iscope and expect good DF with the right subject but realistically cropping a 40x .65 isn't going to be far behind.
That or the background will not be dark above 0.9.
Always happy to be corrected.
Could maybe fake it with reversing a BF image to DF.

Sure Squintsalot wrote: ↑

Tue Jun 06, 2023 5:06 pm

I wonder if NOT using a conventional slide but a coverslip might push the NA of the condenser past 1.4. Again one would have to do the math to see what that effect would be.

Wild guess -did it work, someone would have certainly suggest it a long time ago !
Moreover, someone would have designed a DF condenser for a focussed beam across a 0.17mm slide instead of a 1-1.1mm thick slide...

josmann wrote: ↑

Tue Jun 06, 2023 3:50 pm

apochronaut wrote: ↑

Tue Jun 06, 2023 12:33 pm

It is possible that Zeiss coined the term Ultracondenser because in the early years of DF , the technique was referred to as " Ultramicroscopy" because using DF particles or inclusions could be detected that were below the theoretical limit using BF.

This is an effect I'd still like to learn more about. It does make some intuitive sense when you think of the DF-illuminated subjects as self-emitters, but I'd appreciate being pointed to any specific literature about it!

A lot of what I have read is older. There was a great deal of interest pre-phase era as well as with COL, then it tapered off. I will look into on-line sources and post some links when I find them.

apochronaut wrote: ↑

Wed Jun 07, 2023 3:05 pm

A lot of what I have read is older. There was a great deal of interest pre-phase era as well as with COL, then it tapered off. I will look into on-line sources and post some links when I find them.

Yes anything you have would be much appreciated - or if you remember the names of particular books/authors I should keep an eye out for

Here is a bit on ultramicroscopy and its application in studying colloids, by Zsigmondy :
https://www.nobelprize.org/uploads/2017 ... ecture.pdf

Here is his wikipedia entry: https://en.wikipedia.org/wiki/Richard_Adolf_Zsigmondy

I wonder if NOT using a conventional slide but a coverslip might push the NA of the condenser past 1.4

There seems to have been quite an effort to push darkfield condensers and some were used with thin slides ; the R&J Beck NA 1.25-1.37 is used with ~0.5mm slides (well it says "with .02 slips" ).

Patta had a go with twin coverslips for his high NA darkfield condenser construction : https://www.microbehunter.com/microscop ... 28&t=14923

Here is the Baker Ultra Condenser: food for thought?

Chas wrote: ↑

Sat Jun 10, 2023 11:44 am

Here is the Baker Ultra Condenser:
Baker ultracondenser.jpg

food for thought?

1. In the Baker condenser, Is that a specimen flow-chamber instead of a slide ? the specimen flows by means of gravity ? or is it a flow of immersion oil
2. Brownian motion is a fascinating demonstration of light scattering microscopy.
3. One of the previous links lead to a Watson catalogue, where a "Cassegrain" type DF condenser. But the specified slide thickness is 1mm, not 0.17mm (or 0.34mm).

1] I imagine it to be a specimen flow chamber.

3] I dont think that I have seen any reference to a commercial darkfield condenser that operated through coverslip-thickness glass, though one might imagine that the thinner the slide and the wider the top element of the condenser the higher the NA that might be achievable(?) but I understand that coverglass material was a bit special; Stokes 'Microscopical Praxis' (1894) mentions that the manufacture of thin microscopical glass was a secret known only to Chance's in Birmingham (UK) .

Chas wrote: ↑

Sat Jun 10, 2023 8:23 am

I wonder if NOT using a conventional slide but a coverslip might push the NA of the condenser past 1.4

There seems to have been quite an effort to push darkfield condensers and some were used with thin slides ; the R&J Beck NA 1.25-1.37 is used with ~0.5mm slides (well it says "with .02 slips" ).

Patta had a go with twin coverslips for his high NA darkfield condenser construction : https://www.microbehunter.com/microscop ... 28&t=14923

Thanks for that link; pretty amazing effort from Patta!

Given all of my other projects, I think I'll stay away from dark field "ultramicroscopy" as it seems to be very limited to resolving sub-micron particles. I'd have thought I could resolve sub-micron structures in plankton, but no friggin' way that's happening.