Help needed - 1) Faulty phase contrast, 2) re-assembly of field diaphragm leaves Zeiss standards

[Hobbyst46]

Hello

They say that a felony leads to more felony...

Phase contrast problem
The phase contrast on my microscope deteriorated suddenly overnight. Could not get a sharp image of the condenser phase ring in the back focal plane of the objective. Could not align the phase ring of the objective with the phase annulus of the condenser. The problem was observed with the 16X Ph2, 75X Ph2, 63X Ph3 so I thought it was not related to the objectives.
I removed the condenser and cleaned it (it was not really dirty) - no change.
I suspected the illumination 45 degrees mirror, below the field diaphragm, deteriorated or disengaged. So I removed the field diaphragm unit.
But the mirror appeared to be unharmed and in good condition.

Field diaphragm assembly problem
The phase problem unsolved, I "jumped" into another problem. My field aperture has been half-frozen for some time. I always thought of cleaning it, but the three screws on top were stuck, so I left it alone. Apparently, because of the terrible summer heat (temperatures 32-35C) the metal collar holes expanded and suddenly I was able to unscrew them and expose the aperture leaves. Indeed, the inside needed cleaning. There was a layer of dried oil or grease on both the seat that I could clean. But although I tried to do it very carefully, the leaves were disturbed, broke loose from their seat so I cannot just "close" it back but have to re-arrange the leaves. The leaves were also stained with dried oil so I had to clean them with Petrol (octane, isooctane etc) and dried them. But reassembly is a problem. There are 13 leaves!

Any advice please? I found these instructions posted by PeteM some time ago, for a different scope, are they applicable to the Zeiss as well?

As you probably observed in disassembly, the iris leaves go in one at a time with one pin down and the other hoping to align with slots or holes in a part above (and now likely apart, since you got the leaves out).

So you start assembly one leaf at a time -- one over another -- resting the leaves toward the fully open position -- and get maybe half way around when things start flying apart. At this point you'll want to conjure up some sort of very light clamp or restraint to hold the previously assembled pin ends lightly in place. You may have to make up something like a bit of stuff foam cut in a circular arc and held between clamp type tweezers. Whatever holds most of the already-pinned ends in place.

As you get to the last few iris leaves you need to start tucking them under the already installed leaves, fiumbling to align the pin and its hidden hole. I use a tiny spatula to lift the leaves already in place. Not so bad if you have secured the ends of the previously installed leaves. Seemingly impossible if you haven't.

After much consternation and a few tries you've got all the iris leaves with one end pinned in place. You carefully arrange them to the outer wide open position; using that as a reference so all the pins now facing up are equally spaced.

At this point you take the top portion, try to carefully drop it over the pins, jiggle things a bit, and if you're lucky capture all the upward facing pins.

Next you do something stupid like drop the entire assembly and start again -- this time with a bit more dexterity.

Not sure if this is the right way; but it has (eventually) worked for me on several scopes.

[75RR]

Any advice please? I found these instructions posted by PeteM some time ago, for a different scope, are they applicable to the Zeiss as well?

Yes, pretty much.
Most of us have had to do it at one time or other. It's the price one has to pay for fiddling with the field iris housing.
It takes dexterity and a lot of patience - it is a one step forward two steps back sort of thing at first and then suddenly it is back together.
I found dropping the top portion onto the pins the hardest part. It is very easy to disarrange the leaves again.
I am now extra careful with it!

[Hobbyst46]

Thanks 75RR!
There must be an easier way, a trick - I cannot believe the Zeiss workers assembled it it in such a frustrating way...

[apochronaut]

Some iris diaphragms have a ring that the follower pins slide in, like yours and some have a ring that the pins get drawn in but otherwise they are about the same. Probably the ones with the sliding guides are a little easier to fix.

Pete M's instructions are pretty much what I have found but having done about 20 or more of these from about 6 different mfg. I learned a few tricks. I don't recall ever doing a Zeiss , though.

The first thing is, take the time to clean all the leaves meticulously, so that they have no tendency whatsoever to stick to each other. If they are steel leaves, check them one by one against a common one to see if any are at all magnetized. If they are at all and you have a way of demagnetizing them, then do so.

If they are lightly magnetic, that isn't really a problem, except that their tendency to stick together during assembly will be. I guess, try anyway. Any that seem more magnetic, should be assembled first.

I usually place a very tiny dab of hi-tack grease( damping grease) on the rotater pin and just around it on the leaf before I set it in it's hole. This helps stick the leaf in place because as you get to the point where you must lift leaves in order to install the last 5 or so under the rest, it is very easy to lift installed leaves out of their seats. Once you get into that, you can very easily transit to the start over phase of the operation.
If you do lift one or more out and they lose their registration, keeping all the leaves as open as is possible , you can visually move them a bit fore and aft, circumferentially one by one and because the radial registration is provided by the open position, you can usually find the circumferential registration.

Two points; make sure the direction of rotation isn't backwards, when you start and when installing the rotating ring, make sure to locate it unconnected, by hovering it over the assembled mechanism to determinine if the degree of rotation is correct for complete opening and closing. If you put it in place and then have to adjust it later, it can happen that the ring will pick up a bunch of leaves and disturb them enough that S.O. is in order....especially if magnetism is involved.

To hold assembled leaves in place, if need be, I have used a paper shafted swab. I gently bend one end at a right angle for a handle, snip off the other end then gently arc the shaft to follow the curve of the leave seats. Pipe cleaner or aluminum wire twist tie might work too.

[apochronaut]

Regarding your phase problem, have you checked your phase telescope or bertrand lens for a loose element, or other focusing issue?

[zzffnn]

You can search on YouTube how people repair their camera lenses with stuck aperture blades. Their techniques are similar. You may need two fine tip forceps.
This one is a good start https://youtu.be/wyOfC-Zrmpw

This does not help you now, but may help you next time:
My way of repairing aperture stuck with oil is soaking the entire assembly (without taking it apart, but remove all glass) in xylene for an hour. Then open and close blades. It worked for two fully frozen (by oil) lenses that I have. Taking apart the blades makes repair much more difficult for myself.

Your phase issue:
I don't know for sure, but check for other optical alignment issues. Mounting (screws) for head, condenser and mirror, for example.

[75RR]

I removed the condenser and cleaned it (it was not really dirty) - no change.

Can you be more specific as to what you did.
Did you open it?
It could be that the ball bearing is no longer sitting on the spring.
This would affect the click stop (port positioning) and probably the x axis movement of the annulus as well.

If you are going to open it make sure to place a towel on the work surface to catch the ball bearing when you drop it. ;)

[Hobbyst46]

Thanks folks for the super-rapid and helpful information!! Field aperture is back in one piece!

What I did, following all advice (and PeteM's instructions, and everyone's suggestions):

1. After soaking the leaves with light petroleum, and drying, I wiped them one by one with a petroleum-moistened Q-tip.
They are steel indeed, Not magnetized. At first I suspected they were, but what was magnetized was my tweezers... the leaves are free.
2. Arranged them neatly under the light of a magnifier - desk lamp, stabilized the chassis and placed them carefully, one over the other. Up no No. 8.
I decided to try dry installation, without the grease on the axis pins - I thought that if the dry attempt fails, I would re-try with the grease.
3. Then attached a cellotape, taped over half of the aperture, to prevent assembled ones from falling out. See photo.
4. Grasped each of the remaining 5 leaves with a flat (non-magnetized) tweezers, and very slowly inserted it and tweaked its position until registered.
5. For the next stage, i decided to separate the rotating wheel (sort of cogwheel with a lever) from the outer top collar. See the first photo. The wheel is lying in a petri dish.
6. I verified that all leaves are as radially oriented as possible, this represented an open aperture.
7. Aligned the rotating wheel with the leaf pins, and placed it over the aperture. verified that it rotates and open and closes the aperture properly. Surprisingly, this was easy!
8. Assembled the top collar, glass window. This was a nuisance - the alignment of screw holes on both parts.

And after a year of a harsh resistance to rotation, due to dried oils/grease on several surfaces inside the aperture, the field diaphragm can be pushed with a finger!

Thanks again!

The next step to do is the phase contrast, who started all this...

[Hobbyst46]

@75RR
@zzffnn
@Apochronaut

Thanks for response about the phase contrast issue as well!

That was really stupid of me. Indeed, one of the elements of the phase telescope got loose - guess I did something with it and forgot about it!!
Here is how it looked like through the fauly telescope, then after I fixed it:

[apochronaut]

always good to have a cheap and easy repair. i'll bet you are liking the field diaphragm, that you didn't like before!

[Hobbyst46]

Hello again, I apologize for adding one more question:

The view of the closed field aperture (pinhole) through my phase contrast condenser is shown below. I mean, the actual is what I see. Instead of a nice bright circle, it is overshadowed with an ellipsoid light stain.
Is not related to the field aperture, neither to the condenser BF iris.
It is visible through all objectives.
Lowering or raising the condenser - the ellipse shrinks or grows with the central spot.

The condenser is clean and aligned - I did not take it completely apart, only the top lens.
The light beam coming out of the field diaphragm is a plain circle, no distortion.

What can it be?
My simple Abbe condenser yields the same ellipse of light - but much weaker, relative to the brightness of the central circle.

Will appreciate your opinions!

[apochronaut]

what happens when you open the field diaphragm up slightly and then , more?

[Hobbyst46]

what happens when you open the field diaphragm up slightly and then , more?

The image of the field diagram, that is the bright circle, grows continuously, its diameter increases smoothly, and so does the "halo" or "stray light". Also, the shape of this stray light depends on the auxiliary lens (the one beneath the condenser). If it is within the light path, the stray is an ellipsoid. If it is swung out, it is much more elongated. but always coincides with the main beam, the bright circle.

[Hobbyst46]

I removed the condenser and cleaned it (it was not really dirty) - no change.

Can you be more specific as to what you did.
Did you open it?
It could be that the ball bearing is no longer sitting on the spring.
This would affect the click stop (port positioning) and probably the x axis movement of the annulus as well.

If you are going to open it make sure to place a towel on the work surface to catch the ball bearing when you drop it.

I just removed the top lens assembly. Removing two small side screws enables removal of the holder of the top lens of the condenser. That is what I did. I Looked inside all ports and saw nothing unusual. It rotates OK, with a click stop at every port position.

This condenser has seen heavy use in the past, I am sure; its (plastic) top plate is somewhat deformed, less convex apparently than its original form, since the rim does not touch the steel ring; I mean, there is a 1mm space between the plastic top plate and the steel ring, along the rim. Tightening the screw at the center of the top plate does not help. The top lens holder (that I removed this time, but of course put it back on) was touching the top plate at some point. This has caused friction during rotation of the condenser, so I had to cut off a small part of the top plate below the top lens holder. I did that a long time ago; performance was in my opinion so-so, but can I perhaps get rid of the "halo" or "stray light" ?

[apochronaut]

I think it is caused by internal reflection, bouncing back to those little finger indents in the field diaphragm collar, and reflecting back up off of them, possibly?

[Hobbyst46]

If I cover the field diaphragm including all polished metal surfaces with an opaque black paper with a small hole in the middle, there is no change. Apparently it is not related to the field diaphragm. But I think it might be internal reflections within other optical parts. I suspected the internal coating or paint of the objectives, but it happens in all of them at the same azimuth, and rotation of the objective does not change it. Likewise it persists after replacement of eyepieces. Same result after replacement of the binocular head.
So internal reflections inside the condenser maybe...Perhaps the condenser rack is not exactly vertical... I guess I will have to live with it.
At least, owing to such superb support, I have quite good DF and the PC is back.
Thanks Apo.

[75RR]

Can you post a photo of your condenser - that should give us an idea of what could be wrong.

I just removed the top lens assembly. Removing two small side screws enables removal of the holder of the top lens of the condenser.

If all you touched was the top lens and the lens holder of the condenser then you might want to take it off and reassemble again. It might have gone on a little skew.

[Hobbyst46]

Thanks 75RR. I will try it.