Attempt to attach DF kit to a 1925 Ernst Leitz Wetzlar brass stand.

[charlie g]

Hi all, in a recent thread of zzffn's, apochronaut kindly posted images of his ELW DF condenser kit. I have that Dunkelfeld kit, and a sleeping on a shelf 1925 brass ELW stand. Let's see if I can use this DF-kit as apochronaut suggests?!


To be continued as soon as I dig out the stand. Happy Earth Day to all, charlie g

[charlie g]

Condenser speced: "1.20"...jet black when top or bottom lens face viewed . Does this spec imply either water or oil may be used for light bridge...no I guess it's dedicated to oil-bridge due 1.3 and 1.25 na's of the scope objectives ...so the objective iris trades down NA for high-magnification dark field.

It's a silly detail...but I note 'modern objectives are speced so they can be read when mounted on the nose-piece...I have to look at my othe vintage objectives to see if this difference in etch common.

[charlie g]

The BF condenser slides out, yet such a snug fit (!1925 stand!). No specs on this bright-field /iris condenser..yet similar style and materials as the DF condenser...DF condenser has no iris.

The cone of illumination exiting this DF condenser does not inform me weather or not this is a spherical condenser ( like the large Olympus /Tokyo Neo episcopic objectives have at their exterior faces)..or if is 'cardioid' design.

[charlie g]

The silver metal lens faces on all objectives are 'knurled'...does this imply they are all meant to screw off the objective barrels? The :" 1/12 th oel-objective" silver end face smoothly screwed off it's barrel, it mates well with the iris DF-kit objective barrel.

Now if I avoid crunching one of my diatom slides and achieve a 'first light for me' with this DF condenser kit!??

[Hobbyst46]

Condenser speced: "1.20"...jet black when top or bottom lens face viewed . Does this spec imply either water or oil may be used for light bridge...no I guess it's dedicated to oil-bridge due 1.3 and 1.25 na's of the scope objectives ...so the objective iris trades down NA for high-magnification dark field.

A long time ago - 1-2 years - I posted a comparison of the performance of a cardiodid DF condenser with different immersion liquids - water, glycerol, immersion oil. The liquids were applied between the condenser top lens and bottom surface of the slide. If I am not mistaken, both dry 40X and immersion objectives were tested. The cardioid needed an immersion liquid. I think that water yielded an acceptable result, glycerol was better, oil was the best.

[zzffnn]

Charlie G,

At high NA of 1.25 and above, oil makes a visually obvious difference.

Re parabolic vs cardioid: difference is not obvious in my hands, to my eyes, with LOMO short apo objectives. What is more important is perfect condenser alignment and sample slide preparation.

[apochronaut]

Nice to see the system being used. That condenser looks distnctly different than mine, which is cardioid or spherical but they are almost identical in construction. The difference between those mirror reflecting condensers and central spot tir reflecting condensers is fairly evident when looking from below. The spherical and cardioid show a distinct small central mirror inside when viewed from below. The paraboloid shows a large central stop. I am thinking that yours is a paraboloid. 1.20 N.A. as a minimum for the paraboloid funnel is common.
You will need a lot of light. In most cases when using an oil immersion high magnification objective, a heavy duty research illuminator of 100 watts was used or an integrated illuminator inside the condenser. The one I am familiar with used a 13 watt bulb, right inside the condenser, about a cm. or less from the convex condenser mirror.
You should get excellent imaging with that, if you can get the illumination up.

[BramHuntingNematodes]

Of course they can be sensitive to slide thickness as well. It was my understanding that cardioid condensers we're useful for unstopped immersion objectives but otherwise more trouble for little gain. All my paraboloid condensers like stops after the na gets above .7

[charlie g]

Thanks, Hobbyst, zzffnn, apo, Bram HN for your directions/ for your thoughts...apochronaut launched my attempt to 'use my vintage (1925) ELW stand with this "ELW Dunkelfield DF condenser".

As I configure this dedicated oil-bridge DF condenser..I ask a basic few questions to all, please all comment if you have the time.

Circa 1925 ( and earlier time)...was high NA/ high magnification objectives used with dedicated oil-bridge/DF substage condensers the most effective means of light microscopy visualizing bacterial pathogens ( syphylis bacteria come to mind for me)? Were these oil-bridged DF condensers the 'state of the light microscopy art' for medical diagnostics before 'phase contrast light illumination methods' were available to medical use?

I ask as this one humble setup I am attempting to give 'first light' to...is so wonderfully crafted/ so masterfully fabricated...this clearly was a: 'work horse system for a clinical need'...in my mind.

Please all opine, charlie g./finger lakes/US

[zzffnn]

Yes, lots of light is required for high NA darkfield. In my own experience (darkfield dotting of mounted diatoms), good resolution is not visualized or captured by camera, if light intensity does not catch up with the demand.

Charlie, if you are handy and comfortable with DIY, you may check out and adapt this LED headlamp as modular removable darkfield illuminator:
https://www.amazon.com/dp/B092RJ9TPV/?c ... _lig_dp_it

Its 400 lumen output is more than enough for anything, except maybe to freeze the fastest motion in darkfield for still photos. But then, if your camera can tolerate some high ISO, you can simply increase ISO without increasing light output.

I bought the following LED headlamp, but feel that it is an overkill (if I do it again, I will buy the first LED; because I very rarely use the 800 lumen mode - 99% of the time I am using its 270 lumen mode):

https://www.amazon.com/gp/aw/d/B082BGTD ... p13NParams

[BramHuntingNematodes]

Apo probably can answer the historical question better but the omnibus catalog I have from the 1930s devotes a good deal of space to darkfield condensers. I know that it was an enormously popular technique in those days but I can't say if it was used for research or clinical purposes more often.

[charlie g]

Thanks, Hobbyst, zzffnn, apo, Bram HN for your useful comments. It was apochronaut who launched me on this quest for 'first-light' with my 1925 ELW stand..and my ELW dedicated 'Dunkelfield condenser...apo's concise comments on how this DF-kit is utilized ...sparked my current setup quest.

Here I now ask for comments, for opines from all to my simple questions: 1) was circa 1925 light microscopy high NA/ oil bridged DF-condensers the 'diagnostic state of the art' for bacterial pathogen diagnostics ( sypthilis bacteria comes to mind for me).

For me clearly these fine manufactured/ fine honed optical setups were develoved for a medical need ( and not for a freshwater hobby microscopist like me)?

Was this dedicated 'oil-bridged DF-condenser' by circa 1925 in hospital labs...vrs the 'country physician office'?


Shame on me...but I wish for speculations on the: 'work-horse use' of this vintage DF-kit. I doubt it was developed for a freshwater hobbyist like me.

Please all, when you have time...please offer comments. all the best, charlie g

[apochronaut]

I would think that oblique was the state of the art prior to phase contrast but for observing very transparent bodies DF would have been the thing. Much seems to have been centered around detection of syphilis and the condenser and iris kit could easily be applied as a quick accessory to a Doctor's office microscope for an immediate diagnosis. I'm sure that thousands of such kits were used, especially duting W.W.I. By W.W.II there were dedicated DF microscopes with built in condensers and illuminators, for labs and offices.
I have used a DF condenser on about a dozen microscopes and just as with all other contrast techniques the quality of the objective being used is the arbiter of the technique's value.