Condenser Alignment.

[apochronaut]

To most microscopists, this means centering the condenser under the objective. What if the condenser itself isn't aligned?
A condenser is an optical device that focuses light along an axis but also usually includes a mechanical device that reduces the intensity of the light by vignetting the periphery of the beam, usually an iris diaphragm. For certain illumination techniques such as phase contrast, interference contrast or dark field patches to name the most common, a further beam modifying device is inserted under the condenser. Each component that modifies the beam needs to be in axial alignment.
Now some of these devices, such as a phase contrast diaphragms are adjusted to be in alignment with the objective and while they will work under such a condition, they may still not be in alignment along the condenser's optical axis. The light still gets where it needs to go in order to perform it's needed function but follows a zig-zag pathway, thus carrying a degree of distortion and or aberration to the eyepieces. This can be anywhere from dramatic to subtle but once proper alignment is attained, there is usually a noticeable improvement in image quality and never a deterioration. Mis-alignment is much less of a problem in BF but usually worth attending to when the condenser is called upon to focus specialized illumination beams. It is one of the principle culprits when someone is having trouble with DF patches and is particularly nasty at flumoxing attempts to align a 40X patch.
Condenser housings are all similar in function but of variable construction. They aren't normally part of an adjustment routine but I have long ago included it in my routine of microscope set up.
To adjust it, a condenser must have a way of adjusting the condenser lens pack relative to the condenser iris diaphragm and thus perfectly align the condenser iris with the field diaphragm. Sometimes the field diaphragm is independently adjustable relative to the condenser iris and sometimes not but ideally both need to be on the same axis as the condenser lens pack, which we have to assume is internally axially well aligned. If the condenser is a sealed unit you just have to take it as it is and assume it was aligned in the factory. Almost all of this type will be BF condensers, so outside of attempts to install DF patches, they should work o.k. This little article is related to condensers that are mostly used for enhanced contrast techniques and need to be critically aligned for best performance. Many used ones have been taken apart and reassembled without due attention to alignment.
So I have a couple of condensers at hand here, a Bausch & Lomb 1.25 abbe aplanatic from a Balplan and a 1.25 abbe phase contrast condenser , also from a Balplan. I guess this is Balplan week. I also re-aquainted myself with just how good those Balplan planachros are. They were the first long barrel objectives at roughly 60mm parfocal , coming out in the mid-70's and blew everything away at the time and for many years after. The 40X .65 in particular will image punctae on diatoms where most .65 objectives can barely image the striae. It functions more like a planfluor and seems to function at a higher N.A. than .65. ....and they made a 50X .80 planfluor as well!
I used that objective to test a newly aligned condenser in BF but also it's phase analog objective for the phase condenser. So, the alignment was successful. Excellent imaging for both.
Here is the simplest way to align one.

The BF condenser I have in hand has 3 set screws around it's perimeter. Loosening the set screws allows the condenser lens section to be removed from the diaphragm housing and adjusting them differentially to align the condenser to the condenser iris . The phase condenser has three cap screws on top that fasten the top plate including the lens section on to the phase diaphragm section and the iris section. It can be aligned by orbiting the optical section in the xy plane against the condenser iris or visa versa, if you see it that way. To adjust the phase condenser, you do it with the open port and once aligned each phase diaphragm is adjusted to it's corresponding objective, through the aligned condenser.

Bring in a 10X objective then, and focus it on some slide.
The first thing is to just barely loosen the screws that fasten the condenser into it's housing, then install the condenser and establish Köhler with focused field iris leaves and center the contracted leaves of the field diaphragm. Then using either screwdrivers or allen keys on the side or your fingers on top for condensers that have top screws,, establish that you can move the condenser lens pack manually while looking through the eyepieces. You will see the field diaphragm move while you manipulate the slightly loose condenser lens section. Then center the field diaphragm again at it's completely closed position and lower the condenser about a cm. You will see the edges of the field diaphragm blur considerably. Then close the condenser iris. By focusing the condenser a little up or down, there will be a point where both the field diaphragm and condenser diaphragm leaves are both enough in focus to see each closing on the other. You want to get them completely concentric. Usually, by centering the field diaphragm and then by manipulating the condenser lens pack manually you will get one overlaying the other perfectly. It will take a few recenterings of the field diaphragm because every time you move the condenser lens pack you will mis--align the field diaphragm optically. Once you have the two irises opening and closing centered on each other, you have to carefully tighten the condenser lens pack down without disturbing it's centering. For those condensers with top fastening screws, an L-shaped scewdriver helps or gently removing it to tighten it down. Might take a few tries.
With a phase condenser you can then align each phase diaphragm to it's objective. You can test your alignmrnt by looking through the 10X phase objective with the open port of the condenser, focused on a slide , then closing, centering and focusing the field iris until it is the smallest. Then close the condenser iris completely, which should just dim the bright center spot . Then switch to the 10X phase diaphragm. There should be no light. As you open the field diaphragm then to fully, you should have a large black center spot surrounded by a complete dull but clearly light halo. Opening and closing the condenser iris should cause the spot to increase and decrease in the center of a well lit, even field. If it is seriously skewed, either your phase alignment is off or the condenser alignment is. Check your phase alignment first.

[deBult]

Ha great info -again! Thanks for sharing this “how to”.

[Hobbyst46]

An excellent guide, Apo, thanks !

How would you suggest to test and align a turret achromat-aplanat 1.4 phase contrast condenser ? the basic lens gives an NA=0.32. It is fixed inside the body and I did not see any set screws around (though never seriously checked). The top lens, which makes it NA=1.4, is screwed onto the body, and can in principle be aligned by means of three very tiny set screws (slotted screws actually, it is a very old Zeiss). To complicate it further, it seems that the distance between the top lens and basic lens varies, depending on how many rotations of the top lens are made when it is assembled onto the condenser's thread. Would you test and align it in along the same steps as for the Abbe condensers ?

Another question: alignment of the phase rings (condenser against objective) is done by means of two small knobs (X and Y motions) of that condenser. Would you say that such alignment (the dark and bright rings overlap each other) is not in itself an evidence of adequate phase contrast setting ?

[apochronaut]

I would have to think on how to image mis-alignment within a condenser's optical path a little. That post was primarily to do with aligning the mechanical parts of a condenser to the lens axis, which would be a line drawn between the center of the front and back lenses of the condenser. I just assumed that most condensers are precise enough and squat enough to be pretty optically aligned internally but realized that some have alignment screws. There might be a way of using a Bertrand lens or similar with a longer focal length to view down into the condenser's intestines.
Regarding the alignment of the phase diaphragm and phase annulus guaranteeing phase alignment. Yes, it does but it doesn't also guarantee condenser alignment. The optical pathway could still be zig-zag. That black central spot created by the phase diaphragm I suggest eclipsing and declipsing ( is that a word?) the partially closed field diaphragm as an alignment test can be way off center, only capable of causing a partial eclipse and the phase rings could still be aligned. In this scenario , the ordinary and extroardinary rays that hit their target to create a phase image do so but various of those rays transit through the condenser non-symmetrically in a skewed path resulting in a loss of full coherence and some backgound tonal unevenness and contrast reduction. Another thing to look for is when you look at your phase alignment with the Bertrand lens, the ghost circles you see in the center should be in the center and as concentric as possible.

I have done a few tests aligning phase with and without full centration ( is THAT a word? ) of the condenser and the precisely centered system has a deeper grey, more even background and seems to have better contrast.
Thanks to both of you sbove for the thumbs up on this wordy step by step. I hope it helps some people improve their imaging or get those DF patches refined.

[Hobbyst46]

centration - from the Merriam Webster Dictionary it appears to be a synonym of centering.
declipse - sounds to me a great and meaningful word, that is apparently missing in the same dictionary...

[StargazerX5]

Apo, a splendid contribution as well as thought provoking.

Like Hobbyst46 I have Zeiss scopes fitted with the same AchApl 1.4 phase condensers. Never thought of centering lens of condenser proper. However below the condenser lies an auxiliary lens that does have centration control which I have never touched. For the WL its 2 thumbscrews and the GFL has set screws, likely captive - not sure.

But I do notice a small coloration off to one side of field dia. during Kohler alignment. This is more obvious when condenser is oiled which minimizes reflections between condenser and slide. I'll have to examine this later thanks to your post.

Thanks,
Glenn

[Hobbyst46]

Apo, a splendid contribution as well as thought provoking.

Like Hobbyst46 I have Zeiss scopes fitted with the same AchApl 1.4 phase condensers. Never thought of centering lens of condenser proper. However below the condenser lies an auxiliary lens that does have centration control which I have never touched. For the WL its 2 thumbscrews and the GFL has set screws, likely captive - not sure.

But I do notice a small coloration off to one side of field dia. during Kohler alignment. This is more obvious when condenser is oiled which minimizes reflections between condenser and slide. I'll have to examine this later thanks to your post.

Thanks,
Glenn

Likewise, I never tried centration of the auxiliary lens (I have GFLs). However, if that lens is even slightly swung out and is not strictly on the optical axis, assymetric blue and yellow fringes appear in the field diaphragm. Looks like worthy of investigation, indeed.

[bkt]

But I do notice a small coloration off to one side of field dia. during Kohler alignment. This is more obvious when condenser is oiled which minimizes reflections between condenser and slide. I'll have to examine this later thanks to your post.

Thanks,
Glenn

Likewise, I never tried centration of the auxiliary lens (I have GFLs). However, if that lens is even slightly swung out and is not strictly on the optical axis, assymetric blue and yellow fringes appear in the field diaphragm. Looks like worthy of investigation, indeed.

You mean such an effect or asymmetry? I quickly checked, don't believe mine will be adjustable...

[Hobbyst46]

Yes, as shown in the photo.
When the condenser and auxiliary lens are aligned, any blue fringe (if at all) will be symmetric, around the open iris.

[apochronaut]

I don't think that example is with an aux. lens. In this example the condenser lateral plane is not perpendicular to the optical axis of the objective. Racking the condenser up and down a little will bring the 5 :00 condition into view at 11:00.and visa versa. In this case the hemisphere centered around 5:00 needs to be lifted and the hemisphere centered around 11:00 consequently or alternately lowered. This condition does slso decenter the condenser axis.
The first thing to do is level the condenser unless it is of crappy mfg. and poor machining or burrs on the shoulders or collars setting the lenses, or cheaply finished lens edges are inhibiting alignment.
If one does a check to see if the iris is on axis when the condenser is not perpendicular and it is, then making the condenser axis perpendicular will put the iris off axis. Since there is no way with this condenser to align the lens pack and iris laterally ( according to the poster)the best case scenario is to have the condenser level. In BF , having the iris a bit askew isn't going to affect it much at all but it would some in phase. Since the objectives in this microscope are all over the place in terms of ca distribution, wavelengths and radial symmetry without a condenser, I suspect this is just a case of typical poor q.c. during production and inspection if there is such a thing, and not a lot can be done about it.
Remember that Motic started out in an independant country but has since come under management by a planned economy rule for 25 years now. Slowly, Hong Kong gets bent to conform. They have managed to some degree to stay ahead of the game but looking at their product line , they are selling the same low cost optics and frames churned out of huge centralized Chinese facilities by the hundreds of thousands. Amscope and many others sell the same stuff and it's a crap shoot whether you get s good one or a bad one but to them, they are all good. They need a lot of microscopes. There are 300,000,000 students in China and they finish them only up to a point.

Motic may make their own higher corrected higher resolution objectives and better aligned systems applying appropriate q.c. too but then the price gets normalized closer to where it should be.

[bkt]

Since there is no way with this condenser to align the lens pack and iris laterally ( according to the poster)

Please, care when you add such sentences... might give me some bad ideas. After the outside, I had now a look inside also. The iris fall out. Now I'll have to clean things up. I see nothing in all those parts that could allow any tweak/alignments

[apochronaut]

Give it up! Did I tell you to take your condenser apart? I made a post about adjusting it laterally, not disassembling it. Maybe there is some software that can fix it.

[Phill Brown]

But I do notice a small coloration off to one side of field dia. during Kohler alignment. This is more obvious when condenser is oiled which minimizes reflections between condenser and slide. I'll have to examine this later thanks to your post.

Thanks,
Glenn

Likewise, I never tried centration of the auxiliary lens (I have GFLs). However, if that lens is even slightly swung out and is not strictly on the optical axis, assymetric blue and yellow fringes appear in the field diaphragm. Looks like worthy of investigation, indeed.

You mean such an effect or asymmetry? I quickly checked, don't believe mine will be adjustable...

LED? Yellow and blue fringing is what I like least about diffused LED with pretend Kohler.

[bkt]

Give it up! Did I tell you to take your condenser apart? I made a post about adjusting it laterally, not disassembling it. Maybe there is some software that can fix it.

No problem, don't worry, I'm too curious... and ended joking Fixed and clean again

[bkt]

LED? Yellow and blue fringing is what I like least about diffused LED with pretend Kohler.

Yes, 4500k LED (AWB shifting this a bit). Didn't test with halogen.

[bkt]

They need a lot of microscopes. There are 300,000,000 students in China and they finish them only up to a point.

Makes me now think Motic is a lot of marketing. The badly aligned condenser I dismantled so is a Motic achromat, worth €450; their basic abbe condenser price is €80, I won't look in there, works nice, shouldn't be much different.

According to my seller, the achromat might be useful for 100x oil... I noticed nothing to tweak in there. Lenses being pushed in, or lenses holders being glued in place. The iris blades are in their rails, again; nothing to tweak there either.

Marketing and communication campaigns via social networks, to share there how their solutions can be efficient? Their hardware bases, options and objectives look much more affordable than those of other well known brands. Is this forseen to target amateurs and education, with all the many features, regardless of the images qualities? Could allow students to evaluate a lot of different techniques on "cheap" hardware before they get later their hands on more serious equipment?

So far, as newbie, I've no regrets. I'll deal with the base I got so, and its limitations.

Maybe there is some software that can fix it.

Software may add or fix a lot for amateurs... My Bresser Erudit DLX 600x I could get for €200 wasn't that bad.

Motic may make their own higher corrected higher resolution objectives and better aligned systems applying appropriate q.c. too but then the price gets normalized closer to where it should be.

I'm waiting for an advice from a "historical brands" seller, for their opinion about objectives and CA; prices look very different. I won't test Motic's apos, even thought their costs look very attractive, like their other hardware... Meanwhile, I followed your previous advice and I ordered two "Chinese" fluor objectives designed for education, to see how they could deal with CA.

I'm pretty sure that somehow you may be opening up a can of worms regarding other distortions too. The microscope optics can be repaired.

After having that look inside a condenser, and earlier, at the objectives CA, I'll soon have a look at:
- the tilting / poorly aligned trino head
- the positioning of my camera CCD using the stock 1x adapter

sorry again

[Phill Brown]

Think you'll find the yellow and blue fringing is how the subject edges are illuminated,the objective can't do a busting lot about it.

[bkt]

Think you'll find the yellow and blue fringing is how the subject edges are illuminated,the objective can't do a busting lot about it.

I got this achro condenser as used, but it seemed new (now I dismantled it...). I'll wait and see what I could get out of it. Maybe any artistic effect, if any noticeable by my eyes

The basic abbe doesn't show that effect. But it is much more diffused: