Expanding Darkfield Stop

Here you can discuss different microscopic techniques and illumination methods, such as Brightfield, Darkfield, Phase Contrast, DIC, Oblique illumination, etc.
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biofilmer86
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Expanding Darkfield Stop

#1 Post by biofilmer86 » Mon Nov 14, 2022 7:58 pm

The reason these aren't made anymore is that they are expensive to make and they tend to be fragile due to the small parts they contain.

Another forum discusses them hear: https://www.photomacrography.net/forum/ ... hp?t=43399

Microscope antique site: https://www.microscope-antiques.com/VHtraviss.html

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Re: Expanding Darkfield Stop

#2 Post by biofilmer86 » Mon Nov 14, 2022 7:59 pm

How they work:


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Re: Expanding Darkfield Stop

#3 Post by Macro_Cosmos » Mon Nov 14, 2022 9:27 pm

The Heine condenser essentially does this and it is vastly superior. These darkfield stops can only support a numerical aperture of up to 0.7.
(This means the old Olympus UPlanApo 20x NA0.7 can be used, but not the newer SApo and current XApo with NA of 0.75 and 0.8 -- go figure.)

It is not made anymore, I suppose, because of the cost. I fail to see any advantages of modern phase contrast/universal condensers with the annoying wheel and need to either pre-centre or re-centre each time a different ring needs to be used. The Heine condenser looks like a device from the future because of this.

FYI, a travis stop recently sold on the bay for 51 pounds.

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Re: Expanding Darkfield Stop

#4 Post by MichaelG. » Mon Nov 14, 2022 10:51 pm

Too many 'projects'

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Re: Expanding Darkfield Stop

#5 Post by apochronaut » Tue Nov 15, 2022 4:04 pm

Macro_Cosmos wrote:
Mon Nov 14, 2022 9:27 pm
The Heine condenser essentially does this and it is vastly superior. These darkfield stops can only support a numerical aperture of up to 0.7.
(This means the old Olympus UPlanApo 20x NA0.7 can be used, but not the newer SApo and current XApo with NA of 0.75 and 0.8 -- go figure.)

It is not made anymore, I suppose, because of the cost. I fail to see any advantages of modern phase contrast/universal condensers with the annoying wheel and need to either pre-centre or re-centre each time a different ring needs to be used. The Heine condenser looks like a device from the future because of this.

FYI, a travis stop recently sold on the bay for 51 pounds.
I own one of those and it is fairly simple in construction. No more complicated than an average iris diaphragm (less actually), so some factory in India or China could knock them off for a small sum but the demand would have to be there because they don't make too many cheaper consumer goods that can't be sold in a 6 figure volume. I'm sure there is a drawerfull of them in some school somewhere.
Like all DF stop systems there are limitations to it, alluded to above somewhat, not the least of which is a dependence usually on an abbe condenser and a sized carrier. The one I have came from Leitz stock when they discontinued support for Leitz and Wild in the early 90's and sold everything off.
Stops used with an abbe condenser, in general kind of negate one of the principal benefits of DF, which when accomplished with a highly corrected condenser has high resolution and is a delight to use because of it's chroma free light source. With critical adjustment and a DF condenser you can even accomplish a form of DF oblique that has substantial three dimensionality. I'm not sure that can be done with stops. Has anyone done that?
However, DF condensers that can achieve a suitable N.A. in order to maximize the performance of high resolution objectives and as well cover the field of low power objectives are few and usually require an external mechanism in order to do so. Three I can think of off the top of my head are the travelling stop types like the Heine and similar from Reichert and others, the Reichert or AO toric and the Goerz 3-D condenser, which like the Heine uses a couple of different N.A. caps. All of these, especially travelling stop types are expensive. Sometimes a toric can be found under the radar at 30 or 40 bucks, which uses optics to cover the field and just needs some mounting adjustments for other microscope bodies.

If you are on a budget and want to cover the base for DF from 10 to 100X there are two ways to go. New and used/diy.

New Indian DF condensers can be purchased in kits of two. I have seen the kit for as low as 119.00 for the two in the past 3 months, with free shipping. A dry condenser for up to 40X and an oil condenser for 40X and up.

By far the best buy in oil DF condensers is the AO 214F. They were sold in the tens of thousands from about 1950 to about 1980 for the routine testing for the presence of Treponema Pallidum. Probably just about every AO 10 sold for routine lab work went with a 214F and a #1079 funnel stop and there were thousands of them sold for that. AO 4s before that and 15s prior to that. Many in Doctor's offices too. This means that they still show up on the used market by the dozens. Built like a piece of a ship's navigation system they are indestructable chrome on brass with a threaded condenser system allowing for a full cm. extra height adjustment above the base height . The AO dovetail can be removed with a 1/2 turn of 2 screws revealing a 37mm sleeve mount. Any other dovetail can be fitted on that. The XY adjusters extend 3 cm. out from the body.
I have seen them for as low as 39.00 recently. One of those and a few stops for the low powers would cover the full range of DF and give good to excellent quality DFas well, especially if you can muster a .90 dry achromat/aplanat condenser to use with the low power DF stops.
Testing the field coverage of the 214F , I found that it easily handles a 40X objective at a 20mm field but will just barely cover a 25X at a 20mm field as well. With the 19mm AO #176 eyepieces and a 20X objective, there is a thin unilluminated corona at the periphery, so although I have not tested one with an 18mm field eyepiece, it might be possible to get full coverage st 18mm with a 20X objective.
Last edited by apochronaut on Wed Nov 16, 2022 3:17 am, edited 1 time in total.

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Re: Expanding Darkfield Stop

#6 Post by woyjwjl » Wed Nov 16, 2022 1:24 am

More than 20X dark field, all use special condenser lens and must be oiled

None of this will make you happy......

I advise you to calm down and reflect. Do you really need it?

PC is much more enjoyable :geek:
Micrographers from China, thanks to the forum for providing a platform for exchange

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Re: Expanding Darkfield Stop

#7 Post by apochronaut » Wed Nov 16, 2022 12:30 pm

Using immersion oil to achieve the best imaging is standard practice in microscopy. If you are striving for the best imaging possible, you can't get around it. It can be breathtaking with apos. It takes 5 seconds to apply oil to the condenser and maybe 2 minutes to clean it.


Phase Contrast can also by excellent but DF and phase are different, not really in a competition. Phase is especially valuable when the user has choices of phase types beyond the standard dark medium phase. You still need to oil the objective for the best resolution. I have not come across phase or much imaging period that was much better than that using a Reichert 100X 1.32 planapo negative phase objective. It reveals highly resolved details you can't even see with a 100X 1.25 planachro negative phase. You still need immersion oil. You can't really get around it if you want highly resolved microscopy.

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Re: Expanding Darkfield Stop

#8 Post by zzffnn » Wed Nov 16, 2022 1:19 pm

Macro_Cosmos wrote:
Mon Nov 14, 2022 9:27 pm
The Heine condenser essentially does this and it is vastly superior. These darkfield stops can only support a numerical aperture of up to 0.7.
(This means the old Olympus UPlanApo 20x NA0.7 can be used, but not the newer SApo and current XApo with NA of 0.75 and 0.8 -- go figure.)

It is not made anymore, I suppose, because of the cost. I fail to see any advantages of modern phase contrast/universal condensers with the annoying wheel and need to either pre-centre or re-centre each time a different ring needs to be used. The Heine condenser looks like a device from the future because of this.

FYI, a travis stop recently sold on the bay for 51 pounds.
My experience with Heine is that although it is very convenient and great with thin and small diatoms, it is not universally superior for other protists (such as ciliates). Its narrow illumination ring means too much halo and busy background.

Personally, I prefer using DIY stops (with oiled condenser) at low magnification range to vary between COL and DF, and change to oiled DF condenser for high magnification (which can be used with a NA 1.32 apo objective for nice COL). Yes, that change is inconvenient, but I really don’t go above NA 1.1 that much, unless I find a suitable tiny protist.

I sold my Heine after trying the above DIY. So I am the right buyer for such an expandable darkfield stop. It may not be as convenient as Heine, but its illumination ring width can be controlled (along with a regular condenser iris) and resulting image quality looks better to my eyes (because my DIY hand drawn rings produced better image quality when ring size is correct and well centered).

I would think Reichert Polyphos would work better with its wider illumination ring.
Last edited by zzffnn on Wed Nov 16, 2022 1:47 pm, edited 1 time in total.

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Re: Expanding Darkfield Stop

#9 Post by zzffnn » Wed Nov 16, 2022 1:23 pm

woyjwjl wrote:
Wed Nov 16, 2022 1:24 am
More than 20X dark field, all use special condenser lens and must be oiled

None of this will make you happy......

I advise you to calm down and reflect. Do you really need it?

PC is much more enjoyable :geek:
Sorry to be blunt, but my personal experience is exactly the opposite. It really depends on who is the microscopist.

I can easily get to objective NA 0.65 using a dry DIY darkfield condenser (with hand drawn circular stops).

My eyes do not like the halos of phase contrast, so darkfield is more enjoyable for me.

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Re: Expanding Darkfield Stop

#10 Post by BramHuntingNematodes » Wed Nov 16, 2022 2:28 pm

I think the problem with this device as well as the Heine is that considering an objective, you don't need or want a continuously variable df patch or phase ring. Rather, you want the correctly sized patch or phase ring.

Df condensers on the used market are common and cheap. Aside from the beautiful AO ones apo mentioned, of course b&l had paraboloid condensers for every slide thickness. I ended up with a passel of these and they are very dependable when you figure out how to use them. A funnel stop or iris objective is a good thing to have for high NA work. Phase I find different, well suited for truly transparent subjects. AO would be the way to go with this as though Nikon did make a an apo short barrel negative phase contrast, they are not common and likely not as well done as AOs, although I have not had direct experience with either.
1942 Bausch and Lomb Series T Dynoptic, Custom Illumination

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Re: Expanding Darkfield Stop

#11 Post by Macro_Cosmos » Thu Nov 17, 2022 12:48 am

The Travis Stop should be possible to DIY, though perhaps not easily done. I know a guy from China who sells the thin membrane used for aperture blades (they are not cheap), he has the option of coat it as well. I purchased a small piece and it worked well as a light baffle for another project. I would guess the price of such a custom part without accounting for trials could be $100-$150 a piece. The price will go down for larger batches but no one is going to need over 10,000 of these.

Another crude method is the utilisation of a filter wheel. I did that with pinholes for another project, it was a stupid method but hey, it worked. Populate the filter wheel with different sized DF stops. The compatibility of DIY stops is not really about magnification but rather the objective's numerical aperture. There are 40x-100x high power objectives with an iris which makes it compatible with DF stops.

Requiring oil can be quite the annoyance when dealing with live subjects. Water can be used as a decent compromise. The oblique effect from a proper oil immersion darkfield condenser or Heine is really exceptional. Double immersion cannot be avoided if high resolution transmitted light imaging is desired. I can totally see the halos being an issue with video work though, I do stills only and replace the background. :lol:

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Re: Expanding Darkfield Stop

#12 Post by MichaelG. » Thu Nov 17, 2022 1:59 am

Macro_Cosmos wrote:
Thu Nov 17, 2022 12:48 am
The Travis Stop should be possible to DIY, though perhaps not easily done.
.

Yes … quite detailed instructions are given in the RMS publication that I linked.

MichaelG.
Too many 'projects'

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Re: Expanding Darkfield Stop

#13 Post by woyjwjl » Thu Nov 17, 2022 2:25 am

zzffnn wrote:
Wed Nov 16, 2022 1:23 pm
woyjwjl wrote:
Wed Nov 16, 2022 1:24 am
More than 20X dark field, all use special condenser lens and must be oiled

None of this will make you happy......

I advise you to calm down and reflect. Do you really need it?

PC is much more enjoyable :geek:
Sorry to be blunt, but my personal experience is exactly the opposite. It really depends on who is the microscopist.

I can easily get to objective NA 0.65 using a dry DIY darkfield condenser (with hand drawn circular stops).

My eyes do not like the halos of phase contrast, so darkfield is more enjoyable for me.
I don't know your equipment, I only have BHS.....
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Re: Expanding Darkfield Stop

#14 Post by patta » Thu Nov 17, 2022 8:55 am

Modern alternative is a stop made of an LCD screen with pixels, so can be adjusted with many configurations. It has been implemented also with micromirrors.
Or a light source made of a LED array, placed at the condenser iris position.
Goes under the name "structured illumination"

If somebody is interested, tell me, I've made drafts for it last year but left it half-way. I think it is not too difficult nor expensive. Many working prototypes have been made by researchers.
I've estimated ~100 US$ apiece if made in large (>1000) numbers.

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Re: Expanding Darkfield Stop

#15 Post by Chas » Sun Nov 20, 2022 1:46 pm

MichaelG. wrote:
Mon Nov 14, 2022 10:51 pm
See here: https://archive.org/details/journalofro ... ?q=traviss

MichaelG.
Thanks for posting that.
...I guess that it would be beyond the capabilities of a 3d printer (?)

I noticed that one on eBay appeared to have a spiral spring in the middle :
traviss stop2.jpg
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Re: Expanding Darkfield Stop

#16 Post by MichaelG. » Sun Nov 20, 2022 8:31 pm

Chas wrote:
Sun Nov 20, 2022 1:46 pm
...I guess that it would be beyond the capabilities of a 3d printer (?)
.
Not being blessed with a 3D printer, I regret I cannot say … but I think someone should have a go.

MichaelG.
.

P.S. __ thanks for mentioning that one on ebay … I grabbed all three pictures
https://www.ebay.co.uk/itm/Antique-Micr ... 4647803122
… disappointed to say that I haven’t found that patent though !!
Too many 'projects'

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Re: Expanding Darkfield Stop

#17 Post by patta » Mon Nov 21, 2022 9:07 am

Something crude can be done with 3D printer

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Re: Expanding Darkfield Stop

#18 Post by apochronaut » Wed Nov 23, 2022 12:18 am

The leaves are just like odd shaped iris diaphragm leaves but the pins are finer. I would think one could modify the leaves from a fairly large iris diaphragm. The frame/ring is about 20 gauge and the arm about 24 qauge but those thicknesses could be altered a bit. The center spring is used as a compression spring to keep the arm tight to the pins.
The one I have came with a group of other adjustable masks and a couple of DF stops. One has a frame with a deep recessed side and a shallowly recessed opposite side of a different diameter. Some of the parts can be ganged to make a wide variety of mask shapes : symetrical and assymetrical.
The variable DF stop can even be ganged with the mask carrier to make a DF oblique mask ( picture 5).
There are no markings on mine.
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Re: Expanding Darkfield Stop

#19 Post by patta » Wed Nov 23, 2022 4:27 pm

wow they're beautiful, thanks for the photos!

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Re: Expanding Darkfield Stop

#20 Post by Chas » Wed Nov 23, 2022 9:45 pm

The range of size of the Traviss stop is impressive. The adjustable two-sided oblique stop seems an interesting idea too.
That the two can be stacked is even more beguiling.
(I have been reading a book by A.C.Coles (critical microscopy 1921) and he seems to be very keen on Traviss' stop)*.
Thank you for posting these photos.

* Reading some more; Coles seems to have been keen on the stops as he was a a pathologist (in the time of unchecked syphilis) and wanted to be able to sweep across large areas of his slides looking for the spirchaetes and be able to switch out from darkfield to brighfield by swinging out the stop. He limited himself generally to dark field with an 8mm objective and the stained films were not mounted in any medium but in air ...using this approach the spirocheates "cannot be missed by the merest tyro" and recommended if for searching the brains of the insane ;-)

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