Partially stuck Zeiss phase contrast condenser for the Zeiss W GFL microscope

[Hobbyst46]

Hello

I would appreciate an advice for maintenance of a phase contrast Zeiss condenser, Achromat-Aplanat model Z III 6 (or similar) for an old but usable Zeiss W GFL microscope.

It has the following positions: brightfield, darkfield, (missing) DIC prisms, Ph2 and Ph3. There are three separate problems:

1. Racking the condenser up and down is somewhat difficult - possibly due to dried grease.
The microscope has not been used or serviced for years before I bought it.
2. Condenser ring rotation in order to change brightfield -> darkfield -> phase etc is slightly less smooth than expected.
3. Most annoying - centration of the phase rings. The knob that moves the phase annulus "up and down" works fine. But "horizontal" movement of the phase annulus, by means of the small knurled wheel, is difficult. This wheel, that protrudes from the condenser front, is nearly frozen.

Should I try to oil it, or perhaps use a silicon vacuum grease which is immune to oxidation?

Thanks in advance.

[photomicro]

Hi there,

first, can you confirm which microscope. I assume from what you say, it is Zeiss West, but the GFL has a round base, and the WL a rectangular base.

The substage being stiff is common, and as you say, not helped by an unused microscope. The first question asked above is because the substage is fixed on the GFL, but removable on the WL. In both cases, it is normally best to use cloth to remove excess grease, and quite possibly dust. A light application with a cloth of something else plus use of the mechanism should have it moving freely.

In relation to the turret condenser, again I am a little unsure which model you are referring to. Perhaps a picture would help, though the principles are the same. Both the mechanisms you mention are prone to sticking, partly because they are used so much, by hand, and this introduces much dust and such. Mmm...just read again; there isn't a knob that moves the annulus up and down..unless you mean one moves it side to said and the other up and down, but they both work in the same (horizontal) plane. Anyway, again, clean off excess grease. The large plate overing the top of the condenser comes off, revealing the mechanism, which is quite fiddly. Be careful.

I may be able to put up some photos of one to explain better.

Hope that is of some help.

Mike

[Hobbyst46]

Thanks photomicro,

here are some photos.

The base is round, the substage plate is removable, no model name is inscribed on it so I thought it was GFL...
I have upgraded the condenser rack by adding a third filter/lens holder (from a spare condenser rack), but this change is not related to the problems.

In my description of the phase annulus movement, if the view through the focused phase telescope is an X-Y plane, the condenser knob (on the left in the photo) controls the Y axis movement, the knurled disk/ring (up front in the photo) controls the X axis movement.

Would you recommend removal of the condenser top plate to reach inside and force some oil inside (e.g. with a syringe?)

[photomicro]

The photos help a lot. It is a GFL as you say (and said) the W part confused me, I guess now you meant it to mean West.

Anyway, I would try some light sewing machine oil or something, essentially to clean the rack on the condenser rack. Then just move it up and down a few times to loosen up. There should be a screw that you could loosen too. I sold my GFL earlier this year, so can't check. A WL is by my feet.

Whilst still on the sub-stage...is there a supplementary (auxiliary) lens in one of the filter trays? There should be.

You have the achromatic-aplanatic bright-field dark-field phase-contrast condenser V Z. The Z just refers to the dovetail fitting.

The screw in the middle at the top comes out, and is all that is holding the top plate, which essentially just covers the mechanism. I hope the picture I have used shows this. You will see there is a small registration pin near the screw to stop the plate turning when fitted. The central part, where the round brass part moves around in a bigger circle, is what will be stuck, and careful coaxing of this with the edge of a screwdriver may ease it. It is more a case of removing hard grease than having to add anything. You certainly DON'T want any oil on the phase plates.

Just a note on the lever to the side. It does lock, just check yours isn't locked in position.

Mike

[Hobbyst46]

Mike - many many thanks!!!

Yes, the lever ("knob") is lockable and functions OK. Only the other level ("knurled disk/ring") is troublesome. I will try and follow your advice.

[Hobbyst46]

Mike - indeed, the major problem was dirt and dried grease around the brass disk under the condenser top plate. I cleaned it carefully with a minimum of light petrol, which improved the phase allignment tremendously.

Regarding the condenser rack, I loosened the counter-screw (the one that is coaxial with the condenser focusing knob) and applied two oil drops to the rack top, inside the vertical groove, but those actions only helped a bit. Raising the condenser to within 2-3 cm of its uppermost position is difficult. Luckily, removing the stage is a cumbersome job, enough to deter from removing the condenser rack altogether for service...

Anyway, many thanks again.

[Charles]

The front knurled unit can only be cleaned and lubed by taking off the back plate. You have to be carefull when you remove the back plate, because there is a small ball bearing on a spring which rides along the edge of the condenser and 'clicks' into grooves for each of the positions on the condenser. By moving the knurled knob, it also controls the one of the directions for adjusting the phase annuli. These can all be gunked up and hard to move properly unless cleaned. Replacing the back plate, you need to make sure the ball bearing is on the spring as you put it back together. There was a detailed discussion on cleaning this a couple of years ago on this forum. Do a search and you may find it.

[Hobbyst46]

Hello again.

Mike - sorry I forgot to answer your question, but yes, my condenser rack for the Zeiss GFL carries three holders: The top is the original auxiliary lens, the middle is a filter holder
and the bottom one is a similar auxiliary lens salvaged from a spare, unused rack. I find that using the two auxiliary lenses "in series" widens the field of view when using low power objectives (mainly 6,3X) without having to unscrew and remove the top condenser lens (it is an Achromat-Aplanat). This is a primitive shortcut, useful for my occasional use of these objectives.

Charles - Thanks a lot for the info. I will look for that article. I have already removed the back plate once, a long time ago, but was unsure of how exactly to fix it, so I re-fitted it back... Let's see once again...

[Hobbyst46]

Thanks Charles,

Yes, I found the long forum thread initialized in 2015 by markG, and your very helpful remarks. His condenser rack was apparently much worse than mine. Otherwise, his challenges and doubts of that time appear familiar to me now. I must preserve this condenser for the GFL with great care, since such gadgets are very expensive. And I am aware of the small ball-with-leaf spring mechanism. I will postpone the mission for some time.

[Charles]

To clean the rails and gear of the condenser rack, the easiest way is to remove the stand from the base. It is held with four bolts which can be access from under the base. After removing from the base, you can slide the condenser rack off to get things clean and re-lubed.