Condensers, how do you properly use them?

[Seta]

Hi,

I started my microscope project few weeks ago, never used them before but have experience with bellows/microscope objectives set ups.

The condenser is maybe the most differentiating item between both systems as well as transmitted vs reflected light and although the condenser seems quite simple I am sure has its own tricks.

So here are some questions I have:

- How do you properly focus a condenser ( I have no idea, right?.. )? I focus on the subject, close the iris, center it and move the condenser until the iris blades are in focus ..is this the right way to do it?

- Does closing the iris and closing the objective iris have the same effect (reduce NA and give greater DOF)? Then why are there objectives with an Iris?
So you can use them with a condenser without Iris?

- Is using an abbe condenser with a DF filter the same as using a DF condenser?

- I read Abbe condensers have to be oiled with higher than NA 1.0 objectives; is that so? can all abbe condensers be oiled?

- Do you need an apo condenser to use high end apo lenses? like those 60/1.40 Oil ones..

Javier

[apochronaut]

Hi,

I started my microscope project few weeks ago, never used them before but have experience with bellows/microscope objectives set ups.

The condenser is maybe the most differentiating item between both systems as well as transmitted vs reflected light and although the condenser seems quite simple I am sure has its own tricks.

So here are some questions I have:
- How do you properly focus a condenser ( I have no idea, right?.. )? I focus on the subject, close the iris, center it and move the condenser until the iris blades are in focus ..is this the right way to do it?

That depends on whether you have a field diaphragm or not. Typically, you want the field diaphragm and the subject in a conjugate plane, using the closed field diaphragm( iris) as a focusing target. Normally, that would mean that the condenser iris would be de-focused but still parcentered. It is then adjusted for each objective used by viewing it down an eyepiece tube with the eyepiece removed. Adjust it to about 3/4 if the objective aperture, then fine tune that while viewing the subject.
If there is no field diaphragm and no köhler or köhler type illumination system, you would adjust the condenser center and height with each objective as it was used. Focus the leaves to center the condenser, then adjust the condenser diaphragm as above. Fine tune it for maximum resolution, contrast and ideal brightness by viewing the subject. Backing off the condenser too much or closing the iris too much will increase contrast at the expense of resolution.

- Does closing the iris and closing the objective iris have the same effect (reduce NA and give greater DOF)? Then why are there objectives with an Iris?
So you can use them with a condenser without Iris?

The purpose of an integrated objective iris diaphragm is to lower the N.A. of the objective or increase depth of field. Sometimes both are beneficial. Lowering the N.A. is critical with high N.A. objectives used for DF. There must be a separation of between .2 and .4 N.A. between the condenser and the objective, otherwise the objective absorbs peripheral rays and the dark background washes out. You do not need a condenser iris for DF. The iris in the objective essentially acts as the condenser diaphragm in DF.
Sometimes an iris is used as a photographic iris, similar to that in a camera lens but just as with a camera lens the resolution of the objective is reduced by closing the iris.
In fluorescence microscopy an iris is sometimes used to increase depth of field and reduce flare.

- Is using an abbe condenser with a DF filter the same as using a DF condenser?

Not really but if you had a very precise and centered DF patch and a superior oil immersion condenser, it would approximate it. I'm not 100% sure about the cheaper dry DF condensers on the market but most dedicated oil DF condensers are superior designs that limit or eliminate ca. Using a DF patch with an abbe condenser will only get you as good as the abbe condenser is capable of.

- I read Abbe condensers have to be oiled with higher than NA 1.0 objectives; is that so? can all abbe condensers be oiled?

It is best but not necessary to oil any condenser rated above 1.0. Using any condenser dry with objectives up to 1.0 is o.k, as long as it and the illumination system are properly adjusted. With objectives above 1.0 N.A. however, the peak resolution of the objective begins to be limited by the dry condenser and the limitation increases with objective N.A.. With standard 1.25 N.A. oil immersion objectives, using an unoiled 1.25 abbe condenser unoiled will limit the objective's N.A. to around 1.13. Using a .90 achromat or abbe aspheric condenser however, will maintain that limitation but improve the peripheral corrections of the condenser, so with plan imaging, the entire image will be improved.
For this reason, since many microscopic investigations do not require peak resolution, manufacturers of quality microscopes began introducing .90 to .95 achromat/aplanat condensers for routine use in the 1970's or so. A dry 1.25 abbe condenser cannot duplicate the performance of one of those, despite the fact that it's N.A. is about the same.
You only oil those condensers that are for sure oil immersion and have an N.A. over 1.0

- Do you need an apo condenser to use high end apo lenses? like those 60/1.40 Oil ones..

Ideally, yes but in practice seldom. Generally, an achromat/aplanat is sufficient and some abbe aspheric very good too. What is required though and does help a lot is to oil the condenser and get it as close to the aperture of the objective as possible. Most good companies offer(ed) achromat 1.4 N.A. condensers. I have seen them as high as 1.52.
In the past, some companies made condenser bodies that had a lens section threaded in with an R.M.S. thread. You could then use an identical objective as a condenser: a 20X .65 apochromat objective condenser to match a 20X .65 apochromat objective for instance. The condenser lens would then be oiled if it was an oil objective.
I have such a set up but have never taken the time to do it. I should.

Javier

[Seta]

Thanks,

- The BH-2 (BHT) has field iris, so Köhler it is. I will practice focusing as you say

- Does not closing the condenser diaphragm also change NA? the effect it produces would suggest so, greater DOF, same as lowering it like you say

- I am getting one of those 3d printed Condenser filter kits Saul is making..looking forward to see the effects I can achieve with it.

- No oiling the condenser for now, but good to know an average condenser may be enough. That RMS adpter seems like a expenssive way to get close to perfection..which at the end may be worth it once you have mastered the business, whic is still far away for me.

By the way, I received the MIP-5 head, updated the original post.

[apochronaut]

Yes. closing the iris in the condenser reduces the available objective N.A.

[Wes]

- I read Abbe condensers have to be oiled with higher than NA 1.0 objectives; is that so? can all abbe condensers be oiled?

- Do you need an apo condenser to use high end apo lenses? like those 60/1.40 Oil ones..

I use water instead of oil on the condenser for high NA objectives, its a decent compromise (according to my math it allows a cone of light with NA=1.2) and its really easy to clean compared to oil which makes a mess. You know in principle if you get an identical objective to the one you are using it will make a perfect condenser because the NA would be nicely matched.

[apochronaut]

yep.

Some time ago, quite a few years now, I was looking for the 1.4 N.A. achromat aplanat condenser for my Diastar. It seemed impossible to find, however silosurplus had blanks of the factory condenser housing containing the interface 1.4 N.A. lens ( still do). I obtained a couple of those and set about building several designs into the housing . One of them uses an apochromatic triplet as a bottom lens. Shortly after completing that project ; there is a thread here, I think entitled " a condenser quest ", I found the ellusive cat. # 1973 1.4 N.A. condenser, which works extremely well with the 1.30 and 1.32 oil objectives.

For some time, I didn't work with those diy condensers .
About a year ago, I finally did a broader test of them, this time with the diatom amphipleura pellucida and a 1.32 N.A. 100X planapo.
While neither of my diy condensers worked out very well as oil condensers, I did end up with the best of both worlds because one works really well as a dry condenser; better than the factory # 1202 .90 achromat aplanat( mainly brighter...seems to be working at a slightly higher N.A.) and the other seems to shine as a water immersion condenser, something sorely lacking from microscope companies.

Neither work well for phase. I continue to use the .90 achromat aplanat as a phase condenser, even with the 1.30 planfluor and 1.32 planapo phase objectives. The focal point of a phase condenser is very critical.

[hans]

I use water instead of oil on the condenser for high NA objectives, its a decent compromise (according to my math it allows a cone of light with NA=1.2) ...

Is that number less than 1.33 because it is based on some criteria like 50% transmission rather than critical angle?

[Hobbyst46]

- I read Abbe condensers have to be oiled with higher than NA 1.0 objectives; is that so? can all abbe condensers be oiled?

- Do you need an apo condenser to use high end apo lenses? like those 60/1.40 Oil ones..

I use water instead of oil on the condenser for high NA objectives, its a decent compromise (according to my math it allows a cone of light with NA=1.2) and its really easy to clean compared to oil which makes a mess. You know in principle if you get an identical objective to the one you are using it will make a perfect condenser because the NA would be nicely matched.

May I ask, how can one be sure that the (oil immersion) objectives are impervious to water vapor ?

[apochronaut]

The upper lens of the condenser is sealed into it's housing in such a way that the mfg. is confident that oil will not bypass the seal. Imperfections can happen and it can be assumed that most of the time this is the case and that sometimes the oil does enter the lens pack. Fortunately, ebay exists and it further can be assumed that the oil impregnated lenses gravitate to ebay, where they can be distributed evenly amongst the faithfull.
Does water vapour bypass the seal more than oil? Through the bottom lenses yes I would assume. I am very carefull to dry the condenser out thoroughly after I have been using it in the sauna however, even a hot bath.

The lens seal, if perfect, would inhibit water as much as oil, would it not?

[Wes]

I use water instead of oil on the condenser for high NA objectives, its a decent compromise (according to my math it allows a cone of light with NA=1.2) ...

Is that number less than 1.33 because it is based on some criteria like 50% transmission rather than critical angle?

I never said I was good in math I don't remember how I got to the NA=1.2 value but I redid the calculation and arrived at your value NA=1.514*sin(arcsin(1.33/1.514)) = 1.33

- I read Abbe condensers have to be oiled with higher than NA 1.0 objectives; is that so? can all abbe condensers be oiled?

- Do you need an apo condenser to use high end apo lenses? like those 60/1.40 Oil ones..

I use water instead of oil on the condenser for high NA objectives, its a decent compromise (according to my math it allows a cone of light with NA=1.2) and its really easy to clean compared to oil which makes a mess. You know in principle if you get an identical objective to the one you are using it will make a perfect condenser because the NA would be nicely matched.

May I ask, how can one be sure that the (oil immersion) objectives are impervious to water vapor ?

Not sure about water vapour but water itself has a high surface tension but I wouldn't count on that if the seal is broken.

[viktor j nilsson]

I use water instead of oil on the condenser for high NA objectives, its a decent compromise (according to my math it allows a cone of light with NA=1.2) ...

Is that number less than 1.33 because it is based on some criteria like 50% transmission rather than critical angle?

Glycerol would probably work even better than water (100% Glycerol has a NA=1.47) and is also very easy to clean.

[Seta]

Interesting talk about Oil,
Will receive the 100 Oil soon and will star using it and the 40/1.0 Apo

- As Glycerol NA is close to that of Oil, would it also work instead of oil on the lens side?

- How do you apply oil, just put a drop on the slide?

- Would lens cleaning liquid be enough to clean lens afterwards?
People mention Isopropyl alcohol...can it damage the lens coating or is it safe to use? Can be used with any lens?

- Would oil used as a mountant have any benefits over water or canadian balm?

- To prevent accidents, at least for now, I will only use long working distance (over 2mm) dry lenses when using oil, no fluors or the 40/0.70
CFN achromats 4, 10 and 20 should be safe to use.. is this a common practice?

[Hobbyst46]

The upper lens of the condenser is sealed into it's housing in such a way that the mfg. is confident that oil will not bypass the seal. Imperfections can happen and it can be assumed that most of the time this is the case and that sometimes the oil does enter the lens pack. Fortunately, ebay exists and it further can be assumed that the oil impregnated lenses gravitate to ebay, where they can be distributed evenly amongst the faithfull.
Does water vapour bypass the seal more than oil? Through the bottom lenses yes I would assume. I am very carefull to dry the condenser out thoroughly after I have been using it in the sauna however, even a hot bath.

The lens seal, if perfect, would inhibit water as much as oil, would it not?

...

I realize that my question was a setup for a spike (or slam dunk {pun}). So let me describe my thoughts. Agreed that the surface tension of water, that is roughly thrice that of oil, will probably prevent penetration of liquid water into the objective during immersion. However, water is much more volatile than oil. The objective front, which dips into immersion water for a long time, is definitely exposed to water vapor at the same time. Since (probably) the objective is colder than its surroundings, vapor can condense inside the objective, IF it has penetrated. The same does not happen with oil because the amount of oil vapor is negligible.
Objectives that are designed for water immersion are most certainly impervious to water in all its forms, by design and construction. Not to mention water-dipping objectives. I am simply not sure about oil immersion objectives when used with water.
Glycerine is more like oil in this respect so I would not worry. It is easy to clean since it is totally miscible with water.
It all the above sounds too theoretical, my apologies.
And, since I have a 63X1.25 objective that I rarely use, will try it with water instead of oil.

The condenser is a different story. Dripping liquid (al liquids) can crawl and reach the non-sealed space beneath the front lens of my turret condenser, and invade the inside of the condenser. Water will corrode the brass or steel inside. So great care is required. Perhaps only with Zeiss turret condensers.

[apochronaut]

Yes, there are probably situations where water vapour will condense on the inside of the objective. Living in a cold country and sometimes using a microscope in cold conditions, I have certainly seen my breath condense all over everything. I never had to worry about condensation inside objectives though, whether immersion sealed or dry.
I have trialled various objectives that were designated as oil immersion with water and in general have not found that it works well at all. In fact, I did a post covering a few of them some time ago. There was only one oil objective that worked well with water and that was an AO # 1026 50X oil immersion achromat with iris. Maybe vapour could get into the internals through the iris control ring but I am pretty sure it won't around the front lens. I don't use that objective much with water anyway because it's mate , the #1027 100X with iris prefers oil.

The post above though, was mostly about condensers. Oil invasion hasn't been an issue with condensers that I use a lot, which admittedly are mostly of U.S. design. I use some Baker and Austrian Reichert too but by and large they are Spencer, AO or Bausch & Lomb. I have never experienced an oil leak into an AO or Spencer condenser but I have come across some that were so saturated in oil, that it crept UP into the condenser from below, fouling the threads of the lower set ring. Spencer front condenser lenses seem to be press fitted into a precise relief and then possibly furled. They seem pretty fast. One would assume that manufacturers pay close attention to how secure the top condenser lens is, since it is likely to be driven against the slide a few times. Setting the condenser height stop on microscopes, seems to be about # 300 on microscope set up check lists.
B & L are different. The top lens does not seem as secure as on Spencer/AO. I have encountered several, with the top lens dislodged and one had a lot of oil in it. I epoxied it back in and I am in the process trying to build a 1.4 N.A. condenser into a Balplan condenser housing and that top lens has also been epoxied in. B & L never got around to making a compatible condenser for the protoype flat field apochromat 125X 1.4 objective I have for the Balplan. Or at least not one that I have ever come across. It would be rare. The objective works o.k. with a 1.25 abbe aspheric, showing remarkable detail of a pumping belloid rotifer mastax for instance in bright field but I would really like to give it a run at a full 1.4. The objective is corrected at 4 wavelengths. I won't be using water with that one.

[Tom Jones]

You might find this (long) video explanation, by Peter Evennett (Royal Microscopical Society and Quekett Microscopical Club) , of how microscope optics work useful:

https://www.youtube.com/watch?v=60_jgZtyR6U

It answers a lot of questions and I really wish I'd had it as a reference when I was first starting out. It's very well done.

[Greg Howald]

I want to thank everyone who participated in this post. I read things on the forum often and if you ain't careful you might just learn something. Thanks. Greg

[hans]

I never said I was good in math I don't remember how I got to the NA=1.2 value but I redid the calculation and arrived at your value NA=1.514*sin(arcsin(1.33/1.514)) = 1.33

I had been thinking about this recently, for the similar case of using an immersion darkfield condenser with water sample. I never got around to it but it would be interesting to work out actual transmission vs. NA since it is already falling off quite a bit before reaching critical angle, so a more realistic "effective" NA number based on that would be a bit lower.

[Hobbyst46]

Out of curiosity, I tried to observe a 50-60um diatom with a Planapo 40X0.8 oil objective and a Neofluar 63X1.25 oil objective, in three modes: dry, water immersion, oil immersion. Just glimpses, no photography. Both water immersion and oil immersion (as expected) improved the view relative to the dry. On the 40X, water gave the same (visually) improvement of sharpness and resolution as oil. On the 63X, water immersion was marginally inferior than oil. More experiments are needed to decide.

I then switched to the Neofluar 40X dry objective and tried the D position of the phase contrast, turret condenser. Normally, with the 40X0.75 objective (all dry), darkfield is not so good. Zeiss tells us to oil the condenser to the slide, for DF. I placed a very small drop of water instead. The view improved a lot, and calls for further experimentation, including the Ultracondenser. I believe it will work, because there is some similarity between the D position of the turret condenser and the Ultracondenser (despite their different principles of operation: a stop in the turret condenser, a cardiodide in the Ultracondenser).

And DF of the same diatom with the D position watered to the slide, and the Planapo 40X0.8 (oil immersion) objective watered to the coverslip, gave very good DF indeed. Eye view, that is. The apo vs fluorite here is not important, I think. Just mentioned.
After all, oil is less likeable than water....

EDIT: I checked the Ultracondenser as well. It is a 1.2-1.4 NA, oil immersion Cardiodid. Checked it twice, with water and immersion oil between the top lens and the slide bottom, respectively. The objective was the 40X0.8 oil condenser: the same as above. In fact it is a 0.6-1.0 NA with iris. So, It gave good DF up to ~0.7 with water, but up to 1.0 with oil. So for this DF condenser, water immersion (lens->slide bottom) is not as good as oil immersion. Still, water is quite good. And less messy.

EDIT (2): A 50% mixture of glycerine and water will have an even better RI than water and be less tacky and viscous than glycerine. Does anyone know if someone has tried it ?