Cleaning, lubricating and centering a Zeiss GFL Pol Scope

  • I bought a Zeiss GFL Pol mikroskope which needed cleaning, lubricating, centering and other maintenance.
    I partially dismounted the micro and macro gears, cleaned as much as possible and remounted again.
    I am going now to center the scope.
    To do this I dismounted the analyzer holder, and placed a simple straight tube (no other optics inside) in its place, equipped with a non centerable objective and a simple ocular).
    I placed a proper specimen on the rotating table, and tried to make the tube coaxial with the table, rotating the three screws available for centering it.
    Unfortunately it was not possible. To center the tube I should displeca it more than possible, and at the best the table axis seems located in the upper left quadrant of the ocular field.
    Obviously I will try again, but I would like in the meantime to ask you the following:

    The rotating table of Zeiss GFL Pol has some centering screws, may be hidden somewhere, or cannot be centered and must be taken as the reference axis for all the equipment?
    Thanks to everybody for the attention.
    Regards,

    Salvatore Previtera

    • Offizieller Beitrag

    Hello Salvatore,

    at first the centre of the tube must match to the centre of the objective. You need an ocular with crosshair and a special point-objective with a crosshair. The cross is in the middle of the ocular field. This is the basic adjustment.
    At this point should be the axis of the rotating table. The table for polariation has no hidden centering screws. You must loose the four screws at the carrier and fix in right position. This reference position can be reached with every centerable objective.

    Regards
    Bernd

  • Dear Gernd,
    many thanks, I am going to try and will let you know.
    Regards,
    Salvatore

  • Hi Bernd,
    I tried your way, but with no success.
    The four screws you mention have a very limited play, and only in the front-back direction, while I need a displacement to the right.
    The displacement I need is about 2 mm.
    After half an hour of contemplation of the scope, I noticed a slight deviation from the perpendicular of the straight tube.
    Since the nosepiece is fixed to the arm of the scope by means of a screw, can it be that during shipping or othe bad treatment the nosepiece was tilted from its original position?
    To verify my hipothesis I to-morrow will perform a test by observing at high enlargement a specimen, and note if there is a focusing loss from the center of field to the left and right border, as expected if the specimen plane is not orthogonal to the optical axis.
    I'll let you know for additional advise.
    Best regards,
    Salvatore

  • Hi Bernd,
    I saw your article and the last picture showing the objective revolver.
    But while it is clear how to proceed for the check of aligmnent of condensor and table, how do you measure the gap between table and revolver?
    I can put a parallepipedal piece on the table, but I have no piece to fit the revolver.
    Best regards,
    Salvatore

  • Hi Bernd,
    thanks for the explanation.
    I used another approach to detect a possible tilt.
    I assumed that the simple ocular tube was perpendicular to the mounting flange.
    When the tube is mounted on the computer arm above the objective revolver, I try to align it visually with a vertical line, like one side of a table top computer, and I perceived some gap as you saw with your test of the table.
    However, if I detect some tilt, how can I deal with it?
    The screw which secures the dovetail to the computer arm (which needs a special tool to be unscrewed) is accompanied by two teeth which will probably hinder any displacement.
    If the dovetail cannot be shifted to its proper position I have to think to some mechanical device to compensate the skewness. =O

  • Hi Bernd,
    Thanks again. I will verify the possible tilt of the revolver in the way you suggested. Afterwards I will try to dismount the revolver and see if the pins are straight or not.
    In any case I must provide a remedy.
    If the revolver is really skewed the possible actions are, at least to my imagination
    Straighten the bent pins,
    or remove the pins and put a thin sheet of rubber between the revolver and the scope arm to block the position of it in a vertical way,
    or machine by lathe a device to be placed between the revolver and the analyzer intermediate tube to tilt this last part to the vertical. This device will lengthen the optical path between objective and ocular by about 5 mm, but it should not affect too much the quality of the image.

    If the revolver is not skewed, I can machine a similar device to be placed between the table holder and the table, with the possibility of regulating the shift of the rotation axix.
    This device will raise the table by 5 mm, but will not affect the tube length and the main optics.
    Now, why this defect? Not difficult to imagine: during shipping a lot of shocks can be made to the poor scope.
    Ten years ago I bought fro the States a GFL naked stativ (with a non rotating table) . It arrived well packed by bubble plastic, but unfortunately the external package was of light cardboard.
    One of the knobs of the table was heavily bent, the last tooth of the clockwork lever was distorted, and the revolver had a stamp of the small balls on the round guide, as after a powerful shock.
    So, everything could have injured my actual scope... <X

    • Offizieller Beitrag

    Hi Salvatore,

    this is another thread descring the repair at a damaged revolver:

    https://mikroskopie-forum.at/index.php/Thre…agsch%C3%A4den/

    Klaus, you can see him on one of these pictures, comes very often to me with such complicated repair cases.
    Prudence is the better part of valour. ^^

    Best regards

    Bernd

  • Hi Bernd,
    you are a treasure of informations!!!
    Thank you very much and
    Best regards,

    Salvatore Previtera

  • Hi Bernd,
    to day I made a simple test for the orientation of the objective revolver with the method you suggested and noted a skewness of around 1 degree.
    Looking at the arm of the scope, which seems very robust, I wonder how strong a shock shoulf have experienced to bend...
    Tomorrow I will continue the test and let you know.
    Best regards,
    Salvatore

  • Hi Bernd,
    yes it is what I plan to do, but for that I should find a proper tool to dismount the revolver (a snake eye screw driver). (Where in Germany?)
    By the way, the scope had some grub screw badly torn and quite difficult to unscrew. A measurement with the caliper showed a diameter of 3.5 mm but since I could not fine any grub screw of this diameter I built some by threading, cutting and filing a brass bar of 3.5 mm diameter. It works fine but I feel some play between the screw and the hole. Do you know which was the true threading of the Zeiss scopes? Metric or Imperial? There is an imperial thread with a 3.6 mm diameter which could fit the hole in a more tight way, and probably I will buy some grub screws of this type at the end of my refurbishing task, where I will see perhaps other screw to change.
    Best regards,
    Salvatore

  • Hi Bernd,
    Yes, for positioning the dovetail, and on that, to position the ocular tubes (the simple vertical straight one or the inclined one, equipped with Bertrand lens).
    In both cases I found three grub screws to center the device plus three grub screws to block them.
    Apart from making such grub screws by myself ( I could not find a supplier for them) I bought from England some normal screws 1 inch long and 3.5 M thread which fit well, even if with a little play.
    I use these screws to check the possibility of alignment, while I will use the self made scrubs to set it up definitively.

    Regards,
    Salvatore

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