How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

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hans
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How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#1 Post by hans » Sat Jan 16, 2021 7:02 am

I have been looking into immersion darkfield condensers for a while and just impulse-bought a pair of these Zeiss ones because the price seemed right and because the Reichert 1096 for the Microstar IV appears to be very rare. I can return them within 14 days for any reason or 30 days if defective but may not have time to properly understand how they are illuminated on a Zeiss stand and rig something up on my Microstar IV within the return window. Any suggestions for quick checks I should do or common problems to look out for? Any reasons these might not be a good choice? I plan to use them with 50X 0.80 oil immersion objectives.

Visually they look pretty nice. There is some residual oil (sticky but not hardened) in where the condenser mounts into the outer carrier part and the threaded ring that retains it but none in the condenser itself that I can see. However I'm not sure much can be determined visually because no light passes and the top lens appears dark black all angles when in air. Worried me at first until I realized that should be expected given the 1.2 NA lower limit, I think? A thin ring of light does pass through the cement joint between the top element and housing at some angles.

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#2 Post by MicroBob » Sat Jan 16, 2021 7:32 am

Hi Hans,
when you put a piece of paper onto the top lens and point the bottom of the condenser towards a light source the paper should be illuminated. I think it is a good sign that no light passes through in your test as the condenser has to block it. Typical damages are paint flaking of and scratched or chipped top lenses. So probably you have not one but two good ones!
I attatch a photo made with such a condenser.

Bob
Attachments
Diatomee Dunkelfeld 100er Zeiss m.I. DSC_9773 1024.JPG
Diatomee Dunkelfeld 100er Zeiss m.I. DSC_9773 1024.JPG (168.2 KiB) Viewed 7686 times

Hobbyst46
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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#3 Post by Hobbyst46 » Sat Jan 16, 2021 10:44 am

Hans,
Here are posts about my experience with the Ultracondenser. On mine, as received, paint was flaking off but I managed to fix it. It works very well and produces excellent DF with 40X0.75, 40X1.0 (oil) and even a fairly nice DF (or at least oblique) with an old achromat 100X1.25 (oil) - see links below.
To deliver DF it must be oiled to the slide bottom.
BTW, the "D" position on the phase contrast Zeiss condenser is supposed to be equivalent to the Ultracondenser - I found a small difference in favor of the latter.
It has been said that it can perform on other microscopes than Zeiss. Provided that the condenser can be raised to nearly touch the slide bottom, and that it can be centered. Centration becomes easier with practice...

viewtopic.php?f=5&t=7653&p=67192&hilit= ... SER#p67192

viewtopic.php?f=5&t=7677&p=67444&hilit= ... SER#p67444

viewtopic.php?f=28&t=8054&p=70759&hilit ... SER#p70759

hans
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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#4 Post by hans » Sat Jan 16, 2021 9:17 pm

Lots of good information, thank you Bob and Hobbyst46. This morning I removed them from "holder Z", cleaned off the oil residue, and brought them inside for a closer look. Unfortunately the second impression is not so good.
MicroBob wrote:
Sat Jan 16, 2021 7:32 am
Typical damages are paint flaking of and scratched or chipped top lenses.
The top lenses are in good condition except for a very small nick in one but the paint has flaked off entirely from both except for a ring left near the joint with the housing:
ultracondenser-top.jpg
ultracondenser-top.jpg (96 KiB) Viewed 7642 times
I might be inclined to try to repaint them, although it sounds like Hobbyst46 had trouble finding a suitable paint, but more seriously there appears to be some delamination in both of them. I have read that some older Zeiss objectives and eyepieces are frequently delaminated, does the same apply to condensers?

Shining a flashlight in the top of one there is a cloudy fringe visible near the first reflecting element but a clear view in otherwise:
ultracondenser-flashlight.jpg
ultracondenser-flashlight.jpg (133.56 KiB) Viewed 7642 times
ultracondenser-delam-1.jpg
ultracondenser-delam-1.jpg (284.04 KiB) Viewed 7642 times
The other one does not have an obvious fringe but the view is overall hazy and "colorful" as might be expected due to reflection/interference in a thin air gap:
ultracondenser-delam-2.jpg
ultracondenser-delam-2.jpg (219.91 KiB) Viewed 7642 times
I think I will probably return them. Any opinions?

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#5 Post by Hobbyst46 » Sat Jan 16, 2021 9:52 pm

Tried to imitate your flashlight experiment on my Ultracondenser and did not find any similar effects to those on yours.

Yes, I discovered delamination in both objectives and eyepieces from Zeiss. Not on condensers (two simple condensers and three phase contrast condensers, although I did not check very carefully. But that does not mean much, really. If intense halogen light has been directed towards the Ultracondenser and caused overheating, who knows. Or if someone has tried to remove immersion oil traces from the Ultracondenser with solvents (and en route destroyed the external black coating), might have damaged the doublet.

BTW, my problem with repainting was compatibility with immersion oil. Most common paints are not. MicroBob suggested engine paints, and perhaps a direct-on-rust paint might work, but a found a different solution.

hans
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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#6 Post by hans » Sat Jan 16, 2021 11:05 pm

Hobbyst46 wrote:
Sat Jan 16, 2021 9:52 pm
Tried to imitate your flashlight experiment on my Ultracondenser and did not find any similar effects to those on yours.
Thanks for checking, based on this and looking at mine more with light from different angles I am almost certain there is some delamination happening. I may add them to the pile of projects if the seller offers a partial refund, otherwise just return them.

From this diagram:
ultracondenser-diagram.jpg
ultracondenser-diagram.jpg (123.46 KiB) Viewed 7629 times
It seem logical there would be a joint like this where I see the suspected delamination in both:
ultracondenser-joint.jpg
ultracondenser-joint.jpg (124.29 KiB) Viewed 7629 times

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#7 Post by hans » Sat Jan 16, 2021 11:30 pm

Hmm, the diagram also shows an annular stop that mine do not have but there is no obvious sign of parts missing like unused threads on the bottom. "Holder Z" I removed them from is just a straight, empty tube. Does your have this stop?
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ultracondenser-annulus.jpg
ultracondenser-annulus.jpg (124.62 KiB) Viewed 7623 times

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#8 Post by MicroBob » Sun Jan 17, 2021 12:53 am

Hi Hans,
perhaps we should have a closer look at what condenser you have there precisely. It doesn't have the ring dovetail for the Zeiss West Standard series. It is not the type for the Zeiss Jena models like the LG. There seems to be a cylindrical mounting surface, but fairly unscratched for a well worn condenser. What diameter does this cylindrical mounting surface have?

Bob

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#9 Post by hans » Sun Jan 17, 2021 1:50 am

I should have posted some photos of the complete assemblies initially but the other parts are still oily and out in the garage for COVID-19 quarantine. The diameter where the condensers insert into the holders is 30 mm exactly. These parts are what I was thinking was "holder Z" based on the catalog scan 75RR posted in Hobbyst46's thread:
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ultracondenser-holder-ring.jpg
ultracondenser-holder-ring.jpg (152.16 KiB) Viewed 7598 times
ultracondenser-holder-dovetail.jpg
ultracondenser-holder-dovetail.jpg (166.08 KiB) Viewed 7598 times
ultracondenser-holder.jpg
ultracondenser-holder.jpg (179.31 KiB) Viewed 7598 times

MicroBob
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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#10 Post by MicroBob » Sun Jan 17, 2021 11:47 am

Hi Hans,
ok, then this is the condenser I had in mind. I have checked my one and found no delaminations or whatever you see there. In a darkfield setup dirt in the mountant or on slide or cover slip show up very intensively. This might mean that damages inside a dark field condenser are also very obvious in the image, but I have no practical experience here.
In Germany these Zeiss West dark field condensers are fairly uncommon and not really cheap. Much easier to find is the Zeiss Jena version and cheaper at about 50€. So depending on your local market it might be best to start over with a different condenser. How does the condenser mount on you microscope look like? Perhaps there is a condenser typ that is even easier to adapt. If your condensers were comparatively cheap you might try to repair them. I has so-so success with soaking delaminated lens groups in xylene and then placing them in a xylene-canadabalsam-mix.

Bob

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#11 Post by hans » Sun Jan 17, 2021 6:43 pm

Thanks Bob, good to know for sure what they are, there are no part numbers anywhere on them. When you looked at yours did you notice whether it has the annular stop I circled in red in that diagram? Or maybe that diagram is a different version of ultracondenser? The diagram is from page 46 of this catalog:
http://www.science-info.net/docs/zeiss/ ... ystems.pdf
MicroBob wrote:
Sun Jan 17, 2021 11:47 am
This might mean that damages inside a dark field condenser are also very obvious in the image...
Seems likely. Also, from the diagram it looks like the light crosses at a low enough angle that delamination might result in total internal reflection within the lower element. I have not tried the test with paper you suggested to check if they pass light, will wait and see what the seller says first.

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#12 Post by MicroBob » Sun Jan 17, 2021 8:08 pm

No, my condenser doesn't have this stop. It seems to have a glass plate on the bottom, held by a screwed i ring. To me the catalog image seems to be an illustration that is 20-30 years older than the catalog itself. These Ultra condensers are not that frequent on the market and for sure nothing they would have spent much energy on. I think they were quite hot in the 1920s or so as they were able to make things visible that are below the resolution limit and were used in bacteriology. The Zeiss West Standard system started in the late 40s and then phase contrast was more attractive.

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#13 Post by apochronaut » Mon Jan 18, 2021 8:10 pm

As an aside and for future reference. The AO/Reichert cat. # 1096 condenser began life as the AO K2172 broad field DF condenser issued for the series 10/20. Both feature a toric field lens in the entry aperture and can fill the field of a 10X objective through a 10X 20mm f.o.v. eyepiece. The K2172 in turn began life as the Reichert 60-709 toric DF condenser made for Reichert Austria microscopes, perhaps the Zetopan, perhaps later infinity corrected models. AO put the bare 60-709 condenser into an AO centerable dovetail mount and placed a locking ring above it to keep it there. It looks like a Reichert condenser but has the AO series 10/20 dovetail.
More often than a 1096 condenser these days, a 60-709 shows up on ebay. Anyone with a lathe can make a series 400 dovetail for one or in fact just adapt a model 1970 dovetail to one and voila a chrome , 1096.
There was also a 1096A, which is a modified 1096, carrying centering screws. It seems that early into the production of 1096 condensers for the series 100, there was still interest in broad field DF for likely the series 20. The supply of the K2172 was exhausted so for a while they made the 1096A, with the older dovetail and the required centering screws.

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#14 Post by hans » Mon Jan 18, 2021 9:56 pm

Thanks, I have not really figured out the variety of AO/Reichert darkfield condensers yet. I have the document "AO DARKFIELD CONDENSERS Models 214F, 218F, and K2172" (from P.S. Neeley's site I think) but there are no specifications like actual illuminated field diameter and NA range or intended NA range of objective that I saw, just a mention that the funnel stop reduces the NA to 0.85. Have you seen specifications for them?

https://www.ebay.com/itm/254820638067 -- is this a Reichert Austria 60-709?

The 1096 is not mentioned in the 400-series documentation I have seen so far, or I missed it, and I'm not even sure what it looks like. Did not know it was related to the K2172. Does it look similar other than the mounting?

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#15 Post by apochronaut » Tue Jan 19, 2021 2:57 am

The Reichert condenser in that listing is not the same as 60-709, based on the machining of the actual condenser housing. There is not a picture of the bottom, so it can't be determined if it is a toric type or not. The 1096 is all black and is a sealed unit with an integrated dovetail, except for the set ring that holds the toric lens in place. That became the manufacturing style from the 80's on.The K2172 , as you know is chrome, with the dovetail added on. They look very different.

The document you reference does state that the 214F and 218F are useful for 40X and up DF. From the standpoint of the AO arsenal of objectives during the period those condensers or very similar models were used (approx. 1946 to 1980), that is true. However, if you include a 25X objective in the system, both of those condensers will just fill the field of a 25X when imaged through a 20mm f.o.v. 10X eyepiece. Thus a 214F, of which there seems to be a steady supply at this point anyway, modified to fit a series 400 condenser yoke will work with the Reichert 25X .45 planachro. Sometimes they show up on ebay. There is even a 25X .65 planapo but hard to find. Some 214F condensers will fit into the series 400 dovetail yoke and work. It is a question of their being just a few thou difference in the depth of the dovetail between one condenser and another. Two seemingly identical condensers will be just ever so slightly different . One will fit, the other not. I used a 214F on my Diastar for some time with a Reichert 25X objective for a year or so betore I bought a 1096.
The document also states that the K2172 will fill the field of a 10X objective. That is also the case with the 1096, which has basically the same performance parameters. 1.18 -1.42 N.A. I think it is.

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#16 Post by hans » Wed Jan 20, 2021 1:15 am

The seller's "microscope guy" agreed from looking at the photos that they were delaminated so they just refunded and said they don't want them back. Now I have another project, I guess.
apochronaut wrote:
Tue Jan 19, 2021 2:57 am
However, if you include a 25X objective in the system, both of those condensers will just fill the field of a 25X when imaged through a 20mm f.o.v. 10X eyepiece. Thus a 214F, of which there seems to be a steady supply at this point anyway, modified to fit a series 400 condenser yoke will work with the Reichert 25X .45 planachro.
Good to know, I had been looking at the 214F also. That manual refers to it as bispheric which if I understand correctly is the least expensive and least corrected type of reflective darkfield condenser? Have you noticed much difference between the 214F/218F and the paraboloid/cardiod/toric types?

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#17 Post by apochronaut » Wed Jan 20, 2021 4:51 am

I think bispheric refers to the surfaces of the two reflective surfaces. One convex, the other concave. The first is a first surface mirror and the other a second surface mirror albeit fully glass embedded. That is the only type of true cardioid I know of. I think the bispheric designation is to separate it from paraboloid condensers which have more air to glass surfaces and therefore lack the achromatism of a cardioid. AO , like manufacturers of all darkfield condensers attempted to tackle the conundrum of high magnification-high N.A. vs. illuminated sphere, that exists with DF. systems. High N.A. condensers can only illuminate a small field. Broad field condensers have limited N.A. Companies chose different pathways to solve it.
One approach, that favoured in the current Chinese microscope industry is to offer a dry condenser which covers the low magnifications and an oil condenser that covers the higher ones ( N.A.s really). The N.A.s of the oil objectives employed are not particularly high, normally 1.25 with Chinese microscopes, so a paraboloid of lower N.A. works o.k. I am unsure of whether any Chinese condensers are cardioid or not but if so they need not be high N.A. I have seen Chinese oil D.F. condensrrs of
1.36 N.A. but not toric. .
Bausch & Lomb used a paraboloid to cover a lower oil immersion N.A. down to lower magnifications and a cardioid for superior colour correction and higher N.A. performance. Another two condenser solution in their case but both oil immersion.
AO only ever had an oil cardioid with a slightly lower N.A. topping out around 1.3 or so with a matching lower bottom threshold, until the 1980's. This allowed for use down below 40X or so with a broader field coverage, while also accomodating 1.25 N.A. oil objectives. Actually, 25X was possible but they had only a 20X. With the K2172 and 1096, the N.A. was increased to about 1.36, , so higher N.A. better colour corrected objectives could take advantage of it's performance plus the toric lens pushed the field coverage up to greater than 2mm, so 10X. It might be technically difficult to go much higher yet be able to as well go so low.
I have used the 214F and the 1096 with both a 1.25 iris equipped objective and a 1.32 iris equipped objective. The 1096 has a slight edge in colour correction and resolution at high magnifications , I would say but not noticeably in terms of resolution with a standard N.A. oil planachtomat. What is very noticeable is the absolute convenience of being able to utilize magnificstions from 10X up to 100X with one fine oil DF condenser. It is a complete revolution , really. It is like having the rheostat , when competitors only had switches.

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#18 Post by hans » Wed Jan 20, 2021 7:32 am

apochronaut wrote:
Wed Jan 20, 2021 4:51 am
What is very noticeable is the absolute convenience of being able to utilize magnificstions from 10X up to 100X with one fine oil DF condenser. It is a complete revolution , really. It is like having the rheostat , when competitors only had switches.
Yeah seems like a nice advantage. With these darkfield condensers I assume the field diaphragm is still imaged through the condenser as usual? So illuminated field diameter can be reduced to optimize contrast when using a widefield condenser with higher magnification objectives, as in brightfield?

I have not found much technical info on darkfield and I have seen some conflicting stuff regarding how the different types are distinguished and what corrections they provide. Probably because as you and Bob have pointed out professional use peaked quite a long time ago. But I just found this which you may find interesting if you have not come across it before:

MIL-HDBK-141 - MILITARY STANDARDIZATION HANDBOOK - OPTICAL DESIGN

Published 1962 and a number of the chapters are written by people from American Optical including 23 on microscopes by Alva Bennett. Regarding cardioid vs. bispheric:
In the cardioid darkfield condenser, the light rays undergo two reflections; one from the inner surface which is spherical, and one from the outer surface, which is cardioidal as shown in Figure 23.13 (b). This condenser, as is the case with the paraboloid type, is free from chromatic and spherical aberration and, since it obeys the sine condition, is termed aplanatic. ... The disadvantage of this type of condenser is the difficulty encountered in grinding and polishing a precise cardiodal surface.
The bispheric darkfield condenser as shown in Figure 23.14 is constructed with both surfaces spherical, thereby avoiding the difficulty of precisely grinding and polishing (as is the case with the cardioid type). The highly precise spherical surfaces can then be used with only slight deviations from theoretical considerations.

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#19 Post by apochronaut » Wed Jan 20, 2021 1:28 pm

There were a couple of older mirror type condensers marked Spencer, going back to the 20's and used until the 214F arrived on the scene. They were likely spheroid, I don't know. They are easy to modify to fit on the series 10 and 20 by using the fittings attached to a 214F. In use, there is a subtle difference between them and the 214F, mostly due to a lower incidence of colour fringes at wider fields. The K2172 and then the 1096 are freer of chromatic fringing yet, so yes the 214F may be a spheroid construction. Difficult to tell really: maybe only based on a measure of performance. The lack of peripheral colour does point to a degree of achromatism.
Bausch & Lomb marked their condensers as either paraboloid or cardioid.
I have not come across a DF handbook for the series 400 microscopes.

DF illumination is not accomplished in the same fashion as the illumination for other techniques. Since the illuminating beam is a hollow cone the only requirement is that the illuminating circle be large enough to completely cover the primary mirror, or in the case of a paraboloid condenser , fill the paraboloid surface. A condition of Köhler illumination cannot really be set because the field iris cannot be viewed. The illumination is set to as bright as possible with the field diaphragm wide open. It is the condenser that regulates the illumination field, which is outside the field of view and in turn only impacts the visual field by way of total internal reflection in the slide.
For high magnification of anything much above 60X, more than the base wattage of any specific microscope system is usually required to get adequate illumination. I know many people who have used 15 to 20 watts and claim that it is enough to illuminate a 100X objective but having attempted this with numerous systems, I see an imaged field with a lack of brilliance , which translates as contrast. The darkness of the field is also regulated by the iris diaphragm, with there being an optimum brilliance/background darkness quotient. With low illumination the iris must be opened more to get adequate light, thus turning the background grey. Low wattage high magnification DF is not that successful. In some cases you cannot see anything at all.
This is the reason I question those 3 watt led microscopes for oil immersion 100X DF, so widely advertised. Even in China, their research microscopes are fitted with 100 watt halogen illuminators while they offer a low wattage led option for the standard bodied model.

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#20 Post by hans » Wed Jan 20, 2021 7:38 pm

Hmm, yeah, I guess not being able to directly view the field diaphragm with no sample present complicates things a bit. How about if you illuminate some sort of thin, uniform, diffusive specimen like a piece of thin paper in oil or a drop of milk or something and look with a low-magnification objective? Should you see a sharply-defined circle of illumination corresponding to the field diaphragm?

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#21 Post by apochronaut » Wed Jan 20, 2021 9:18 pm

It isn't necessary to image rhe field diaphragm in order to set up DF , like it is with phase. You never oil phase so it needs to be adjusted critically in order to have an even well corrected illuminated field and focus the condenser..
If your illumination system is wide open, centered , and focused for maximum brilliance at the condenser, the DF condenser, once oiled does the rest. Centering and the correct immersion gap are the most critical issues. Some condensers have centering markers. Illumination cues or physical devices such as a visible circle outside the illuminated field with which to center the condenser to. The B & L Paraboloid for instance develops a kind of specular crosshair in the field just at the precise correct focal point. Some of the 1096 have a circle. Precise centering can be done during viewing by utilizing the symmetry of imaged subjects. A decentered condenser will have a skewed illumination envelope and or possibly assymetrical details or inclusions.

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#22 Post by hans » Thu Jan 21, 2021 4:59 am

apochronaut wrote:
Wed Jan 20, 2021 9:18 pm
...correct immersion gap...
This is basically why I was wondering. Practical setup issues aside, once one of these reflective darkfield condensers is set at the correct working distance in the microscope it was originally designed for, is the field diaphragm expected to be imaged in the object plane as it is when using a normal condenser?

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#23 Post by Hobbyst46 » Thu Jan 21, 2021 10:53 am

hans wrote:
Thu Jan 21, 2021 4:59 am
apochronaut wrote:
Wed Jan 20, 2021 9:18 pm
...correct immersion gap...
This is basically why I was wondering. Practical setup issues aside, once one of these reflective darkfield condensers is set at the correct working distance in the microscope it was originally designed for, is the field diaphragm expected to be imaged in the object plane as it is when using a normal condenser?
In practice, the field diaphragm is not visible. Here is an example.
All my equipment is old Zeiss (west), originally all parts are designed to work together.
My regular condenser is a turret phase contrast condenser. For a given objective (say 40X) I set it to BF Kohler, to verify centration and proper illumination.
I then replace the condenser with the Ultracondenser. Place a drop of immersion oil on the top surface and raise it up until a flash of light indicates contact with the slide.
If I inspect the back focal plane at this point, the view is like the schematics below for 40X and 63X objective. These are drawings. We see a cross section of the light cone.
And the image of the specimen (diatoms in this case) is shown below.
So the field aperture is not visible.

Notes:
1. With the 63X1.25, DF is poor, the background is grey. The NA is simply too large and there is no iris in the objective.
2. I still do not have the expertise to produce high quality photos of DF.
Attachments
back focal plane objectives Ultracondenser.jpg
back focal plane objectives Ultracondenser.jpg (48.99 KiB) Viewed 7348 times
Ultracondenser. 40X1.0 oil planapo. Resized.jpg
Ultracondenser. 40X1.0 oil planapo. Resized.jpg (68.38 KiB) Viewed 7348 times

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#24 Post by hans » Fri Jan 22, 2021 3:26 am

Hobbyst46 wrote:
Thu Jan 21, 2021 10:53 am
All my equipment is old Zeiss (west), originally all parts are designed to work together.
Since you have the matching microscope, another related question, if you don't mind: Is there a lens (called the field lens or collimator by some manufacturers, not sure about Zeiss) between the condenser and the field diaphragm in the base? Or, closely related, do you know whether the normal condensers are finite- or infinity-corrected? (As discussed here for example: http://www.microscopy-uk.org.uk/primer/illumin.htm)

Regarding imaging of the field diaphragm, it was probably not very clear what I was trying to ask, my fault. I think there are two separate questions:
  1. Is there an image of the field diaphragm formed in the plane of the specimen? In other words, if you put a piece of ground glass or thin paper or whatever there, is there a sharply-defined circle of light that changes diameter as you adjust the field diaphragm?
  2. With no specimen, just clear glass and oil between the condenser and objective, can an image of the field diaphragm (if present) be seen through the eyepieces? As you and apochronaut both pointed out the answer is no when darkfield is working as intended with the illumination minimum NA exceeding the objective maximum NA by some margin.
I would think the answer to the first question is yes but wonder if anyone has verified experimentally. The catalog illustration of the ultracondenser above does show collimated rays focusing to a point in the specimen plane as they would with a normal infinity-corrected condenser.

Consider using a typical refracting condenser with a 100X phase annulus and 100X standard, non-phase objective. There is a hollow cone of illumination falling well within the NA of the objective and presence of the phase annulus in the front focal plane of the condenser (conjugate with the rear focal plane of the objective) does not prevent the field diaphragm from being imaged in the specimen plane as usual. Then consider switching to a lower magnification/NA objective where the 100X annulus gives darkfield. Nothing changed on the illumination side and the field diaphragm is still imaged in the specimen plane, just not visible through the objective and eyepieces. So my guess is that the situation should be basically the same with a high-NA reflecting darkfield condenser unless there is some fundamental difference in how they are designed and interact with the rest of the illumination system?

Hobbyst46
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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#25 Post by Hobbyst46 » Fri Jan 22, 2021 11:12 am

hans wrote:
Fri Jan 22, 2021 3:26 am
Hobbyst46 wrote:
Thu Jan 21, 2021 10:53 am
All my equipment is old Zeiss (west), originally all parts are designed to work together.
Since you have the matching microscope, another related question, if you don't mind: Is there a lens (called the field lens or collimator by some manufacturers, not sure about Zeiss) between the condenser and the field diaphragm in the base? Or, closely related, do you know whether the normal condensers are finite- or infinity-corrected? (As discussed here for example: http://www.microscopy-uk.org.uk/primer/illumin.htm)

Regarding imaging of the field diaphragm, it was probably not very clear what I was trying to ask, my fault. I think there are two separate questions:
  1. Is there an image of the field diaphragm formed in the plane of the specimen? In other words, if you put a piece of ground glass or thin paper or whatever there, is there a sharply-defined circle of light that changes diameter as you adjust the field diaphragm?
  2. With no specimen, just clear glass and oil between the condenser and objective, can an image of the field diaphragm (if present) be seen through the eyepieces? As you and apochronaut both pointed out the answer is no when darkfield is working as intended with the illumination minimum NA exceeding the objective maximum NA by some margin.
I would think the answer to the first question is yes but wonder if anyone has verified experimentally. The catalog illustration of the ultracondenser above does show collimated rays focusing to a point in the specimen plane as they would with a normal infinity-corrected condenser.

Consider using a typical refracting condenser with a 100X phase annulus and 100X standard, non-phase objective. There is a hollow cone of illumination falling well within the NA of the objective and presence of the phase annulus in the front focal plane of the condenser (conjugate with the rear focal plane of the objective) does not prevent the field diaphragm from being imaged in the specimen plane as usual. Then consider switching to a lower magnification/NA objective where the 100X annulus gives darkfield. Nothing changed on the illumination side and the field diaphragm is still imaged in the specimen plane, just not visible through the objective and eyepieces. So my guess is that the situation should be basically the same with a high-NA reflecting darkfield condenser unless there is some fundamental difference in how they are designed and interact with the rest of the illumination system?
Good questions. Thanks for the link - so now I have learnt about "corrected for infinity". Neither of my condensers is marked as such, but they are not supposed to be marked, according to F. Sterrenburg.
I will try over the weekend to check the condenser according to your suggestions and hopefully provide definite answers. The greatest challenge will be trying to focus on an object outside the room, since there is no direct view from the microscope to the trees and parked cars outside outside... :)
Last edited by Hobbyst46 on Fri Jan 22, 2021 3:10 pm, edited 1 time in total.

Hobbyst46
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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#26 Post by Hobbyst46 » Fri Jan 22, 2021 2:42 pm

hans wrote:
Fri Jan 22, 2021 3:26 am
Since you have the matching microscope, another related question, if you don't mind: Is there a lens (called the field lens or collimator by some manufacturers, not sure about Zeiss) between the condenser and the field diaphragm in the base?
Sorry, I missed this simple question and here is the answer: Under the condenser there is a swing-out auxiliary lens. It is used with the low-mag objectives (2.5-16X) to fill it with light. There is no other lens between the field aperture and the condenser. The collimator lenses are further "upstream", between the lamp and the field aperture.

Here is a scheme, taken from the manual of the microscope.
Attachments
illuminator of Zeiss GFL.jpg
illuminator of Zeiss GFL.jpg (101.86 KiB) Viewed 7276 times

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#27 Post by hans » Fri Jan 22, 2021 5:11 pm

Hobbyst46 wrote:
Fri Jan 22, 2021 2:42 pm
There is no other lens between the field aperture and the condenser. The collimator lenses are further "upstream", between the lamp and the field aperture.
Good to know, thank you for checking. This alone is enough to say the condenser is finite-corrected, I think: with no other lenses involved the condenser alone would have to be responsible for focusing an image of the "radiant field stop" ~80 mm below (guessing distance from the diagram) into the specimen plane. The sort of test described on that page is interesting to play around with. I have done the thing with mirror and distant scene on my Reichert Microstar IV which uses infinity-corrected condensers. The image quality is not great but actually a lot better than might be expected for a condenser.

I don't know how much any of this actually matters for adapting the ultracondenser, but the older American Optical 10 is finite-corrected with arrangement similar to the GFL, it looks like. So maybe that would be a better choice for a first attempt, and give me some more motivation to finish assembling a complete one from the parts I have accumulated.

I don't know of a nice diagram like that Zeiss one showing a complete infinity-corrected illumination system but if you are curious this patent Brian found shows one used in the AO 110:
Diagram: viewtopic.php?p=90019#p90019
Photo of inside the base: viewtopic.php?p=90085#p90085

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#28 Post by Hobbyst46 » Sat Jan 23, 2021 2:15 pm

Hi Hans,
The answer is somewhat lengthy so I will respond in parts.

a) Done the test suggested by Sterrenburg in the Mic-UK link that you provided (thanks for the link BTW !):
Turret condenser, brightfield port, 10X0.30 objective, fully open field aperture (FA). Focused on a diatom slide (frosted slide), lowered the condenser,
then turned off the microscope lamp and placed a flat mirror at anangle of ~45 degrees on the light port, and tried to focus on remote objects - 5-6 meters away, by gradually raising the condenser; it worked fine, so according to the author, the condenser is "designed for infinity".

b) Replaced the condenser with the Ultracondenser (UC for short). Replaced the 10X objective with a 25X0.8 Plan-neofluar oil objective. Placed an oil drop on the top lens and raised the condenser until a DF image was achieved. Shifted the slide to bring the frosted part above the top lens of the UC. Swept out the objective. Fully closed the FA, so only a tiny bright spot was visible on the frosted slide. Opening and closing the FA changed the glare around the spot but not its size.

c) Initial trials with the diatom slide indicated to me that the appearance of an image of the FA critically depended on the height of the UC. It was sometimes similar to the ordinary appearance under brightfield (BF), and sometimes the "reverse" of it. It was never in sharp focus as it is under BF.

d) To demonstrate the above, since the strew slide had sparsely arranged diatoms. I used another slide: micrometer-sized glass bubbles, mounted in Norland 16 glue. Recorder images of the FA- fully open (size =20), half open (10), quarter open (5), and fully closed - that is, minimum diameter, size=1.

The next sets of photos show images at ascending positions of the UC. The BF was obtained at a relatively low position (marked as 1), and the UC was then raised to yield sort of oblique/COL (position 2), then a series of decreasing FA's at position 3, finally a series of decreasing FA's at position 4 - the closest to the slide, and the one in which - to the best of my judgement - was best DF. Please note that in the file names, the term "setting" actually means position, i.e. height.

At the BF and COL positions , that is, settings=1 and 2, opening and closing the FA did not yield a focused view of the FA leaves.
Attachments
glass bubbles, condenser setting 1, field diaphragm= 20.JPG.JPG
glass bubbles, condenser setting 1, field diaphragm= 20.JPG.JPG (123.33 KiB) Viewed 7208 times
glass bubbles, condenser setting 2, field diaphragm= 20.JPG.JPG
glass bubbles, condenser setting 2, field diaphragm= 20.JPG.JPG (86.09 KiB) Viewed 7208 times

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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#29 Post by Hobbyst46 » Sat Jan 23, 2021 2:34 pm

(continued)
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glass bubbles, condenser setting 3, field diaphragm= 20.JPG
glass bubbles, condenser setting 3, field diaphragm= 20.JPG (92.58 KiB) Viewed 7207 times
glass bubbles, condenser setting 3, field diaphragm= 10.JPG.JPG
glass bubbles, condenser setting 3, field diaphragm= 10.JPG.JPG (77.49 KiB) Viewed 7207 times
glass bubbles, condenser setting 3, field diaphragm= 5.JPG.JPG
glass bubbles, condenser setting 3, field diaphragm= 5.JPG.JPG (56.83 KiB) Viewed 7207 times
glass bubbles, condenser setting 3, field diaphragm= 1.JPG.JPG
glass bubbles, condenser setting 3, field diaphragm= 1.JPG.JPG (37.75 KiB) Viewed 7207 times

Hobbyst46
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Re: How to check out Zeiss darkfield 1.2-1.4 NA "ultracondenser" without a Zeiss microscope?

#30 Post by Hobbyst46 » Sat Jan 23, 2021 2:35 pm

(continued)
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glass bubbles, condenser setting 4, field diaphragm= 20.JPG.JPG
glass bubbles, condenser setting 4, field diaphragm= 20.JPG.JPG (97.24 KiB) Viewed 7207 times
glass bubbles, condenser setting 4, field diaphragm= 10.JPG.JPG
glass bubbles, condenser setting 4, field diaphragm= 10.JPG.JPG (64.66 KiB) Viewed 7207 times
glass bubbles, condenser setting 4, field diaphragm= 5.JPG.JPG
glass bubbles, condenser setting 4, field diaphragm= 5.JPG.JPG (46.39 KiB) Viewed 7207 times
glass bubbles, condenser setting 4, field diaphragm= 1.JPG.JPG
glass bubbles, condenser setting 4, field diaphragm= 1.JPG.JPG (34.3 KiB) Viewed 7207 times

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