MicrobeHunter.com Microscopy Forum

AO had two, that you would need. 1945-1980 and 1980-about 2002. Ditto, Reichert, Buffalo. There would slso be Reichert, Austria. Bausch & Lomb Balplan is another to consider but it has a unique arrow shaped registration arm. Probably not difficult to do once you have a sample.

I can send you those plus PZO, Baker early next week.

Thanks, no rush, I was hoping that there is just "one" most common condenser mount... instead there is one "Standard", another "Universal", and many more

Any model is good; it is just to make the 3D design ready for future generations; it doesn't take much time for me to draw a couple more dovetails.

Here is a drawing. Measured with calipers.The 4mm thickness of the trapezoidal section of the dovetail is an estimate.
It fits my Standard GFL.

The Swift's 38.7mm is I am pretty sure, the standard 'English' mounting size (I dont know if its exactly 38.7 ..but I reckon it is an RMS standard ).
EDIT: Or could the 38.7 mm be 38.6mm ? - A CTS catalogue says that the outside diameter of their condenser mounts is 38.6 mm.
???
Edit: from Stephanides (1947) " The Microscope and the practical principles of observation " A bit more exacting than my wobbly calipers :

with some procrastination, I've added the add-on Zeiss dovetail - the worst and fastest design.... must be glued on the bottom of the "RMS" condenser
.

Looks nice. What is needed to fabricate a real working darkfield condenser ? will it be dry or immersion (the Ultracondenser is immersion type) ?

Hobbyst46 wrote: ↑

Wed Mar 16, 2022 6:44 pm

Looks nice. What is needed to fabricate a real working darkfield condenser ? will it be dry or immersion (the Ultracondenser is immersion type) ?

It is oil immersion (or also water for those with NA<1.3)
It needs a 3D printer, some aluminium foil, a glass half ball as optics, a round coverslip and some mountant.
I'll publish the detailed assembly instruction later

Reverse-engineered also the Leica (DM) condenser dovetail from photos on internet - turns out to be
of same size as the much older Leitz ones!

AO 1094A "flip-top" condenser:
Max dovetail diameter is 1-7/8" (47.3mm), 7.8mm [dovetail + (45mm) cylinder] depth to flange.
Flange to lens top height is about 1.55" (39.5mm), for a total height of 7.8+39.8 ~ 47.6mm.

AO dovetail coming...

I've taken back this project, and, dismal discovery, wasn't really NA 1.4
One of the testing objectives - CARL ZEISS JENA 60x 1.40 - upon closer observation turned out to have NA 1.3-ish, not the stated 1.40.
I'm in good company about NA cheating...

If somebody has a calibrated Abbe Apertometer to loan...

You can make a thin slide act like a thicker one with a more viscous immersion oil applied to the bottom

Two questions I still have about this condenser is regarding it's focus and chromatism?
In every other DF condenser I have come across, great lengths were taken to pass the light through using finely polished mirrors and glass components, whether lenses or blocks. In this condenser the reflecting surface induces a lot of scatter. Why would other designers of condensers be so persnickety about ray scatter and the sillvering of mirrors etc., and at great cost, if those details were not important?

apochronaut wrote: ↑

Thu Jan 26, 2023 2:50 am

Two questions I still have about this condenser is regarding it's focus and chromatism?
In every other DF condenser I have come across, great lengths were taken to pass the light through using finely polished mirrors and glass components, whether lenses or blocks. In this condenser the reflecting surface induces a lot of scatter. Why would other designers of condensers be so persnickety about ray scatter and the sillvering of mirrors etc., and at great cost, if those details were not important?

I think here it gets away with polished mirror because "the center stop is after the mirror":
A Cardioid has a stop patch before the mirror, so the mirror needs to direct the light truthfully, no scatter, no aberration, or it will result in haze
Here the annulus / baffles are after the mirror, so light rays out of trajectory are stopped anyway. See post #27 above. There is a substantial waste in light available, that is not efficiently collected, but who cares we have powerful LEDs that consume few watts.
That's what I could manufacture; if I had Mr. Huygens Optics at my service, sure would prefer finely polished mirrors:
https://www.youtube.com/watch?v=A0bysBIj0FA&t=9s
I do believe that standard designs (cardioid etc) can be made to higher NA; just was found inconvenient because of haze, light scatter, or low working distance (drawing in post #13). I'm a high NA freak but objectively, the gain in resolution between 1.25 and 1.4 is quite risible, while cost and hassle skyrocket. I tried to stop down high NA apo objectives, in particular a dry 40x 0.95 stopped to NA 0.65, and results are really clean - and better than an equivalent achromat. I wish all apochromat ad an adjustable iris! It may be that (slightly higher) NA is mostly a marketing hype, to motivate a 10x price increase. Would you pay 10x more for an objective that looks identical to an achromat, and has also identical specs 100x 1.25?

Chromatic aberration, the main reason are the mirrors - mirrors don't have chromatic aberration, and are mirrors that do the "heavy job" of bending the light almost 90 degs in this condenser and cardioids.
Yes there is also some refraction but not at heavy angles like in the Abbe condenser. See the designs at post #19, the light rays always enter/exit the glass almost at right angle (apart from the top, that it is oiled so no refraction).

DF oil immersion condensers have a maximum and minimum aperture, let's say 1.4 and 1.2 for instance.It is impossible to achieve DF if the objective aperture is above 1.2 in and in practice scatter precludes DF at 1.2 in such a condenser rendering a not so dark field : blue, gray, brown or even silvery., depending on the hue of the incoming light but other pollution in the scatter as well, reflection off of surfaces etc. In order to achieve true DF, which has a black background the objective then must be stopped down somewhat below the minimum aperture of the condenser or to about 1 in the case above. It is impossible to achieve DF at an objective's full aperture unless the condenser has a minimum aperture , higher than the objective by some margin.
How is does your condenser differ in this regard. You mention that your background is blue?

My condenser ain't anything special, and don't think it is better than a normal cardioid.
It is what I could make quick by myself with the materials at hand (half-ball lenses) instead of getting gouged on ebay for some antique Ultracondenser.

Perk is that it can be made with very high NA, the last photo in post #2 is an "oil condenser apertometer" (handmade, of dubious calibration) that indicates the hollow light cone has max aperture ~1.45 and minimum ~1.40.
The model tested gives DF with all oil objectives I have - but the one with largest aperture, 1.40, turned out to be a cheat, with actual NA more like 1.30. So let's assume that DF worked up till 1.30. Geometrically it seems possible to get it higher by tweaking the design. The main tradeoff are working distance (thickness of the slide) and diameter of the top (it needs to be larger and won't fit in the stage hole).

Yes the DF isn't perfect and there is some bluish background light; on camera looks black but by eye it is not. It happens also at "low" NA, so it must be some haze or scatter, maybe in the condenser, or maybe in the objective and other optics.
This background light got reduced a lot (but not disappeared) when I've blackened one in the condenser surfaces, right under the specimen - the background light was coming from the specimen itself, that glows light in all directions, then this light is reflected again upwards unless care is taken to absorb it.
I liked a lot oil with DF because it seems to get much darker; I think it is because oil reduces all scatter from a dirty slide and the dusty and scratched top condenser lens.

Maybe I should improve my marketing skills and just boast wonder features - instead of going into those dirty details?

Not all Oil DF condensers are expensive.
AO 214F ( probably bispheric) are around 100.00, sometimes less. Lots of them around. 37mm sleeve , normally carrying an AO chrome on brass series 15/35 - series 20 (35 year span) dovetail. The dovetail is removeable in the time it takes to find a 2mm flat screwdriver by loosening 2 set screws. Any other dovetail needed could be printed ,slipped over the sleeve and attached the same way. The optical section is threaded in and can be adjusted over about a 10mm range for a precise adjustment to the stage.
The previous AO/Spencer condenser has a different size sleeve and came with various dovetails to accomodate various microscope models going back to the first w.w. The optics are the same with the same 10mm adjustment, just that the older condenser is a little physically shorter, about 10mm.
Both have polished silver mirrors. The older condensor is often very cheap. I sold one recently with only a restriction on the height adjustment for 40.00.
Both will cover the field of a 25X objective and up with a 20mm 10X field.

With very tall substages, the condenser body can be mounted on top of the dovetail.

I think you might have the difference in NA between achromat and more highly corrected objectives backwards. With a 100x objective design you would start at NA 1.4, then drop it down after you realize the design of an achromat will throttle the color resolution anyway and you might as.well get a little bit more working distance

Also you can use a funnel stop on lots of high na objectives without an iris, works well even with paraboloid condensers which can be had by the bushel used.

If you are referring to my post, there was a typo I fixed. It confuscated everything so as to confusedly confuse the unconfused.

With higher N.A. objectives that have optics filling the barrel, which are most these days, a funnel stop is even simpler because it can take tthe form of a washer on the rear diaphragm, just slightly smaller than the rear diaphragm.
I have a Reichert 63X 1.0 N.A. planachro glycerin. It doesn't quite give DF with the AO cardioid condenser ; kind of a gray field but the thread in rear baffle/diaphragm from the 1.25 planachro has the same thread and a just slightly smaller hole. The 1.25 has an iris, so no loss and it's diaphragm works perfectly as a funnel stop.

Oh I was speaking to pattas earlier post about the expense of app objectives along with the wish about all app objectives having irises. Also, hello what's this about a coke can Cobb slide? Now that's a diy project with some promise...

And thank you, apochronaut. I have been meaning to test a triple alliance df condenser to see if it is any different than the later ones and this trick may come in handy.

BramHuntingNematodes wrote: ↑

Fri Jan 27, 2023 4:28 am

Oh I was speaking to pattas earlier post about the expense of app objectives along with the wish about all app objectives having irises. Also, hello what's this about a coke can Cobb slide? Now that's a diy project with some promise...

When the Reichert Univar came out and continued with the Polyvar, all objectives with an N.A. above .75 were built with an integrated iris diaphragm. Each objective could be used for all contrast trchniques, even phase because the phase annuli were placed in a separate console above the nosepiece.
With later models, such as the Polylite, they departed from that, no doubt due to cost. That is probably why my 63X 1.0 N.A. immersion objective has no iris.

About funnels, I take the bait to advertise one of my earlier DYI - 3D print creations
https://www.microbehunter.com/micro ... 8&t=14262
Sure brass would be better than plastic, but now I have funnels for almost all objectives.
The centre stop/inverted darkfield/dispersion staining funnel turned out to be a messy diffraction crap.

About funnels, I take the bait to advertise one of my earlier DYI - 3D print creations

I dont kmow if this is still the case, but when Beck made their pretty extreme (focusing) condenser they sold a 1.25 N.A objective for it and commented that in order to obtain a dark field using a stop placed behind an ordinary objective's lenses, the stop needs to cut the aperture down to about 1.05. So maybe keep your condenser and leave the stops in the draw

Chas wrote: ↑

Sat Feb 19, 2022 1:27 pm

This was the Mk.I soft drinks can Cobb slide holder:

.
Only just spotted this great project, Chas & patta … I will be following with interest now

Here’s a slick little demonstration of making a Cobb Slide : https://youtu.be/od5ARpqGmbw
Nice, if you have the right tools !

MichaelG.

Voila, here too, making those Cobb slide from a beer can, sorry for disregarding the previous suggestion by chas, and thanks MichaelG for the video link!
the aluminium is a bit too thin, like 0.1mm, while the one used in the video linked above looks much thicker (0.5mm?) It is difficult/impossible to get them flat, with the coverslip sitting parallel.
Anyway, they're really quick and easy to make.

The top and bottom of larger food cans , contain a flat section tn the middle that would be large enough and would not curl. The material is now, plated steel though and a little thicker., although still thin enough to cut with large scissors.

Too late, the 3D print bug hit again: Plastic dummy slide, coverslip holder 2.0
They're plastic, not so stiff, and they soak up water and oil. But sit flat and the slide can be put flush over the condenser or the objective.
Two model, the one on the photo need a dab of glue to fasten the coverslip.

I've loaded the models for 20mm round, 20mm square and customizable OpenSCAD:
https://www.thingiverse.com/thing:5822468
.

That’s neat !

MichaelG.

Thanks. Downloading something pre-designed is a real breeze !
(It goes without saying that after printing I discovered that I have every other shaped coverslip but the one that I need ).

A question; what are two round holes on the 20x20mm slide for ?

Here is a link to Cobb's description of his slide (and a lot of curious nematode stuff):

https://www.biodiversitylibrary.org/pag ... 6/mode/1up

Maybe there is some sense in using two different coverlip sizes/shapes, as he did, especially if one is thinking of holding one to the holder with glue.