Help: has anyone ever used Olympus DCW Darkfield condenser?

[osterport]

I bought a Olympus DCW 1.4-1.2 Darkfield condenser, wishing it could provide high NA illumination.

My microscope: Motic BA300
Objective: Reichert APO 100x oil 1.30 with Adjustable Iris

If I use Olympus Aplanatic 1.4 condenser with Darkfield stop, it works properly with the objective above, this is the picture of yeast.

However, if I use the DCW condenser, it's completely a mess. the darkfield stop blocks most light, looks like it only works for high NA objectives.

Has any one ever use it before? Does it require very strong illumination underneath?

Thanks!

[PeteM]

The DC-W is a pricey, but specialized, darkfield condenser meant to be used with oil immersion and high numerical aperture objectives. You're expected to oil the slide to the objective AND the condenser to the slide. Centering is critical.

The high magnification objective might ideally have an iris to further tune things, though it should work with 60-100x oil-immersion objectives a step below the condenser in terms of n.a. Your 100x Reichert with an iris should work fine, though it will likely want eyepiece corrections for the best image.

You'll also want a bright illumination system. The Motic is a bit on the low side, but should work once you oil both sides of the slide and get things centered.

[zzffnn]

Welcome to the forum, osterport.

In addition to what PeteM suggested, you would also want to carefully adjust the X, Y and Z positions of your darkfield condenser. The darkfield condenser’s top lens should be almost touch slide bottom and have oil bridge in between. Horizontal positioning is very important (perfect centration is required).

Can you describe what the “mess” look like or what is wrong there? is the view too dark, from all directions?

Cool DIY condenser adaptations there, by the way. I adapted that Olympus oblique condenser to my Nikon Optiphot before (with Legos and super glue) and like it quite a bit.

Dedicated immersion darkfield condensers take some practice to use……..

[deBult]

Hmm this Dark field condenser looks like a BH version with an ADDED mounting ring to match the BH2/Motic. May be in error as I only have the lower NA version.

This will make the centring exercise even more important.

Plus wondering whether the optical “train” of mixed Motic and Olympus parts in condenser system will match sufficiently in such a critical setup. Apo / Scarodactyl: please chime in.

[hkv]

I use it all the time and it gives good results even with high NA objectives, but require careful alignment and oil between the top lens and the slide. Otherwise, it does not work properly. It is a picky condenser.

C0568337-Green_alga,_light_micrograph.jpg (100.49 KiB) Viewed 95571 times

[deBult]

I use it all the time and it gives good results even with high NA objectives, but require careful alignment and oil between the top lens and the slide. Otherwise, it does not work properly. It is a picky condenser.

Are you using it on an Olympus BH2 or Motic scope?

[hkv]

I use it all the time and it gives good results even with high NA objectives, but require careful alignment and oil between the top lens and the slide. Otherwise, it does not work properly. It is a picky condenser.

Are you using it on an Olympus BH2 or Motic scope?

No, I use it on a BX scope so no experience from Motic, but that does not change the facts about oil and proper x-y alignment being used.

[PeteM]

Hmm this Dark field condenser looks like a BH version with an ADDED mounting ring to match the BH2/Motic. May be in error as I only have the lower NA version.. . .

FWIW, the Motic condenser dovetails are around 43.4mm at the widest - or at least the Motic BA400 is. Both the BH and BX dovetails are around 47mm at the widest. So you're likely right about the use of a different mounting ring. It looks to me like the O.P. has cleverly 3D-printed adapters for both this and the older BH-era condensers.

The U-DCW condenser (the OEM, not the modified version) is nominally for the infinite BX series -- and should work fine once properly set up on the infinite Motic scope. It would fit and likely work OK on finite BH2 models as well.

[osterport]

Thank you all so much for the reply!

I'll take a picture tonight to show how messy it is. The most difficult part is, I can not use centering Telescope to properly center it, it's just dark, not like with other condensers where you can try different stops to see where the boundary is.

BTW, when I tried the DCW condenser, absolutely use immersion oil on both condenser and objective, but it looks like:
1. very dark unless you open the Iris to maximum
2. the image quality is messy.

How would you center it? it's very difficult.

[osterport]

How bright would you think? I put in a 30W bub and a 3.5W LED, but still not enough.

The DC-W is a pricey, but specialized, darkfield condenser meant to be used with oil immersion and high numerical aperture objectives. You're expected to oil the slide to the objective AND the condenser to the slide. Centering is critical.

The high magnification objective might ideally have an iris to further tune things, though it should work with 60-100x oil-immersion objectives a step below the condenser in terms of n.a. Your 100x Reichert with an iris should work fine, though it will likely want eyepiece corrections for the best image.

You'll also want a bright illumination system. The Motic is a bit on the low side, but should work once you oil both sides of the slide and get things centered.

[osterport]

I use it all the time and it gives good results even with high NA objectives, but require careful alignment and oil between the top lens and the slide. Otherwise, it does not work properly. It is a picky condenser.


C0568337-Green_alga,_light_micrograph.jpg

Oh, this is nice one, I almost gave up. I wish I could make it, probably take some effort to figure out. Your picture indicates it is possible at least.

[osterport]

First I took a picture of yeast with 40x Reichert NA 0.75+oblique condenser+darkfield stop

[osterport]

And then I took a picture of yeast with Reichert 40x NA0.75 objective +DCW darkfield condenser + 3.5W LED ring, it's very dark.

The yeast look like bubbles in a fog at night.

[osterport]

As the last step, I swap to 100x Reichert 100x NA1.30+DCW+LED Ring, it's a mess.

We can see some details, but very poor quality

[Hobbyst46]

Thank you all so much for the reply!

I'll take a picture tonight to show how messy it is. The most difficult part is, I can not use centering Telescope to properly center it, it's just dark, not like with other condensers where you can try different stops to see where the boundary is.

BTW, when I tried the DCW condenser, absolutely use immersion oil on both condenser and objective, but it looks like:
1. very dark unless you open the Iris to maximum
2. the image quality is messy.

How would you center it? it's very difficult.

A trick that might work is to first fit a brightfield condenser. Center it carefully. Then lower it, remove it and place the DF condenser in the holder, without any lateral movement. Assume that it is centered, place a small drop of immersion oil on it and raise it slowly. When the oil just touches the bottom surface of the slide, a very bright light ring appears and DF can be seen. The whole idea is based on the assumption that both condensers and the holder or rack are precision made.

[Hobbyst46]

As the last step, I swap to 100x Reichert 100x NA1.30+DCW+LED Ring, it's a mess.

We can see some details, but very poor quality

If the 100X Reichert has a fixed NA of 1.30, getting true DF will be (nearly) impossible. With most DF condensers, anyway.

[PeteM]

It looks like your aftermarket LED lamp is just sitting above the field lens. If so, it's not likely well collimated.

You also need to stop down the iris in your 100x objective a bit. Make sure it works by visually observing through it. Ones sold used are somewhat commonly broken.

[zzffnn]

osterport,

Your LED light may be too small (on terms of light diameter) and too weak (in terms of power). You can try raising the LED light higher to condenser bottom and maybe (or maybe not) diffuse it with layers of wax paper or printing paper. I wrote “maybe” there because diffusion takes away light and your LED is likely not powerful enough even without diffusion.

Your DCW dakrfield images suggest that your lighting may not be centrally placed, diffused or powerful enough. From those images, on most circular yeast cells, you can see, from your 40x objective DCW image, there is light at 12 o’clock position, less light at 6 o’clock position, and almost no light and 3 o’clock or 9 o’clock positions. Light positions between your 40x and 100x objectives are also a bit different.

I have used LED for darkfield in a way similar to yours, but my LED diameter is wider, more diffused and has more wattage power.

You also need to find a way to perfectly center your darkfield condenser. Maybe DIY a better adapter mount.

I find it odd that your said you darkfield inaging with the 100x iris is “ very dark unless you open the Iris to maximum”. Normally, you have to stop down iris to around NA 0.8 for too darkfield, NOT open up iris. I agree with what PeteM said, remove your 100x iris objective and inspect the iris.

I think your issues are not easy to solve, unless someone gets there in person to help you. You may upload show more photos of how your condenser back focal plane looks like (remove eyepiece and point your camera down the eye tube or capture image from your phase telescope eyepiece).

Please note that the DCW condenser and your Olympus oblique condenser have different optical construction, so even though your LED works well enough for the oblique condenser, it may not be good enough for the DCW.

Also, you said your “30 watt bulb” is still not bright enough. Is that 30 watt incandescent light? Incandescent Equivalent Wattage equivalent for some 3.5 watt LED is 40 watts! My LED is 30 watt ; I think for high magnification darkfield, 10 watts of LED is preferred. You need to put the right focusing lens over the LED, depending on how you use it too. To start, go with higher power and wider light cone is a safer bet.

[osterport]

Actually I got the NA down by adjusting the Iris. However no matter how I adjust it, it is either completely dark or bright&messy.

As the last step, I swap to 100x Reichert 100x NA1.30+DCW+LED Ring, it's a mess.

We can see some details, but very poor quality

If the 100X Reichert has a fixed NA of 1.30, getting true DF will be (nearly) impossible. With most DF condensers, anyway.

[osterport]

Thanks for the detailed suggestion. 30W LED really surprised me. One question: is your LED a ring form factor like mine? Is it very big? For such darkfield stop, probably only the outer circle light would make sense, right? Most of light is blocked anyway.

osterport,

Your LED light may be too small (on terms of light diameter) and too weak (in terms of power). You can try raising the LED light higher to condenser bottom and maybe (or maybe not) diffuse it with layers of wax paper or printing paper. I wrote “maybe” there because diffusion takes away light and your LED is likely not powerful enough even without diffusion.

Your DCW dakrfield images suggest that your lighting may not be centrally placed, diffused or powerful enough. From those images, on most circular yeast cells, you can see, from your 40x objective DCW image, there is light at 12 o’clock position, less light at 6 o’clock position, and almost no light and 3 o’clock or 9 o’clock positions. Light positions between your 40x and 100x objectives are also a bit different.

I have used LED for darkfield in a way similar to yours, but my LED diameter is wider, more diffused and has more wattage power.

You also need to find a way to perfectly center your darkfield condenser. Maybe DIY a better adapter mount.

I find it odd that your said you darkfield inaging with the 100x iris is “ very dark unless you open the Iris to maximum”. Normally, you have to stop down iris to around NA 0.8 for too darkfield, NOT open up iris. I agree with what PeteM said, remove your 100x iris objective and inspect the iris.

I think your issues are not easy to solve, unless someone gets there in person to help you. You may upload show more photos of how your condenser back focal plane looks like (remove eyepiece and point your camera down the eye tube or capture image from your phase telescope eyepiece).

Please note that the DCW condenser and your Olympus oblique condenser have different optical construction, so even though your LED works well enough for the oblique condenser, it may not be good enough for the DCW.

Also, you said your “30 watt bulb” is still not bright enough. Is that 30 watt incandescent light? Incandescent Equivalent Wattage equivalent for some 3.5 watt LED is 40 watts! My LED is 30 watt ; I think for high magnification darkfield, 10 watts of LED is preferred. You need to put the right focusing lens over the LED, depending on how you use it too. To start, go with higher power and wider light cone is a safer bet.

[zzffnn]

osterport,

I usually use my LED at original light bulb filament’s (Köhler illumination) location. Its size is slightly bigger than the original filament size, in the form of a square. I usually don’t use all 30w of its power, as I turn down its output by a resistor control.

So no, at Köhler illumination location, your light source should always be of the same size and shape of the original filament.

I use different LEDs at different locations for different microscopes. They all have different sizes, light shapes and wattages.

Yes, if you want to use LED where you had it in your photos, then a high power wide LED ring light would be ideal. I do have a wide and powerful LED ring light and I would use it the same way as you did, at your location (your location is not “Köhler”).

[Chas]

The 'old banger' darkfield condensers were often designed to be used with a small point source of light, the image of which would be focussed onto the specimen, but they had intensely bright illuminants then that we dont have now.
So it might be worth trying putting a mobile phone 'light side up' on the microscope's base and seeing how the condenser behaves.

Prompted by your post I have been playing with a CTS oil-darkground and a phone light works really well with this.

To see the structure of the illumination from the condenser put a bit of white paint, or something, onto a microscope slide and pop a cover slip on top (I used a white marker pen* ).

I wonder if the tallish condenser mounting tube on your condenser might happen to be blocking one side or another of the ring light from getting directly to the condenser's annulus?

*It was a chalk marker pen so it has some nice particles in it too

[apochronaut]

You are kind of putting the cart before the horse. Firstly, how do those Reichert objectives perform in BF on the Motic? Reichert infinity corrected objectives are somewhat different in correction than Olympus objectives. Motic might be the same as Olympus or very close. Although, because they are infinity corrected the Reichert objectives will produce an image in an Olympus system and of quite faithful magnification, there is always some corrective difference resulting in some ca. I have not had any success mixing or using Olympus and Reichert together. If you fill your nosepiece with Reichert objectives, you will need more corrective eyepieces in order to take advantage of the quality of the Reichert objectives.

I notice that the there is some ca in the 40X .75 plan achromat images but way too much in the 100X images and it is heavily skewed from bottom to top. Oil DF condensers should be ca free, although with some spherical types there can be a very little with highly refractive or diffractive structures. It would be hard to align the condenser, if the objective itself has an alignment issue, which I am pretty sure your 100X 1.30 has. It is likely a planfluor apo ( also called planfluor) but those are almost completely ca free, depending on the sample. The 100X planapo is 1.32


It is a long standing standard to use 100 watt illumination for 100X DF. 3.5 watt led probably doesn't cut it especially if the light is not ideally focused. Condensers can be a bit different but you definitely need more light. DF images with too little light can look o.k. but when compared to those with adequate illumination, they lack contrast and detail. That condition will not cause the ca. Your imaging should be similar to Viktor's just , dimmer with less contrast.
You should not need to align the condenser with an alignment telescope. Once oiled, the condenser can be aligned by looking down upon it as you move it up and down slightly in the oil. Some have a ring to use for centering and with some you will see a spot or central specular highlight to use. Final alignment is done visually by establishing symmetry around details. Depending on how parcentered your objectives are, there will be some tweaking as you go through any magnification changes.

[osterport]

Let me try to solve 40x NA 0.75 first. I found the DCW condenser is not contacting the slide bottom evenly.
Then I inserted a PVC board of 1mm at the edge of the condenser mounting area.

[osterport]

Now the condenser underneath is fully contacting the slide, it's a dark circle.

[osterport]

One more change is, I only dipped very little Yeast water, which forms a very thin layer under the coverslips.
Evenly position the condenser is very important, see picture 1,

By adjusting the PVC board direction, we can see the circle of Yeast is replenished ( see picture .

One more trick, the high NA condenser light can not go through too many specimen, if we take a look at the congregated bubble, their lights are diffusing and create a fog

[osterport]

Then I tried the oil immersion objective Reichert 100x 1.30 with this set up.

It's much improved, but still not comparable with Oblique condenser in terms of details.

One thing I've been wondering: is this achromat condenser? I see blue, yellow, red colors.

[osterport]

It's hard to measure the size of Iris NA with this picture, definitely not 1.32, far from that.

My dream is, someday I just use a normal objective 100x oil NA 1.25 in Darkfield, looks like it's hard.

[osterport]

This is how it looks like under Motic 100x oil 1.25, this is not darkfield.
To make, high NA darkfield, Iris objective is a must.

[apochronaut]

Then I tried the oil immersion objective Reichert 100x 1.30 with this set up.

It's much improved, but still not comparable with Oblique condenser in terms of details.

One thing I've been wondering: is this achromat condenser? I see blue, yellow, red colors.

The blue, yellow and red colours are chromatic aberration and less likely to be condenser born. The Reichert 100X 1.30 objective is a planfluor objective, sometimes it was marked planapo fluor but they are the same and are a very chromatic aberration free objective. I own one, as well as a 1.32 planapo in both iris format and phase contrast format so I know it's performance level.
The last photo is better than the previous ones but the chroma should not be there and it is still assymetrically skewed with red on the bottom and blue on top of the cell wall and membrane border, the same as in previous images but with less coma. I would check the objective first and determine if it is sound. Try setting up and taking a photo. Then unscrew it 1/2 turn, refocus and take another image. It doesn't matter if the sample moves, what you are looking for is a reversal or even rotation of the colour banding at the borders of the cell wall.

That's why I asked how the Reichert objective compares to the Motic in BF. It should be much superior, aside from some possible peripheral ca.

Your DF condenser should be a mirror/reflectingcondenser of some type. Perhaps Viktor knows which for sure. The degree of ca produced in high N.A. DF condensers is from very low to none. Paraboloids have a small amount, spherical too but cardioids, none. All of those are reflecting condensers. The fact that a condenser produces a small amount of refraction does not directly translate as ca in the image. Abbe condensers are riddled with ca, which translates as a loss of coherence and N.A. of the illumination beam. An abbe 1.25 N.A. condenser is only well corrected over about 40% of it's central area. Most of it's complete N.A. is unuseable for high resolution microscopy. A DF condenser on the other hand must have peak resolution from the lowest N.A. of it's illumination cone to the highest., so are usually built to minimize ca. That's why they are expensive. The older one's used silvered mirrors, the more modern ones's use aluminum.

I did some checking and the BH2-DCW condenser model # based on it's specs., likely translates as For BH2 model microscope, .dark field condenser, cardioid design, wide field. It's high cost , likely stems from it's wide field design, which can go as low as a 20X objective at an F.N. of 22, which is pretty good. An average oil immersion high N.A. DF condenser would get to an F.N. of about 18 with a 20X. That is one rational for many older microscope systems using 25X objectives, rather than 20X, allowing more conventional DF oil condensers to cover the field at 25X.
The best I have seen are the AO/ Reichert toric DF condensers, which cover an F.N. of 20 at 10X.