It is advisable to cover the top lens of the lens groups. Because the screw connections of the lens groups can be very tight due to their age, it is easy to slip with the lens opening tool and damage the lenses! Please be careful with adhesive tape. On the one hand, it leaves behind residues that are difficult to remove and, on the other hand, the ingredients may attack the coating.

I use a piece of cotton wool from makeup pads to cover the lens. I press it carefully onto the lens group. Using the imprint, I cut the cotton wool pad to size so that it fits exactly onto the lens group. Then I use adhesive tape to attach the cotton wool pad to the edges so that the tape does not touch the lens.

There are two lens groups. One at the front and one at the rear. Both are screwed onto the shutter. The groups themselves do not need to be dismantled. They only need to be unscrewed from the shutter!

I strongly recommend taking a picture before each step! Preferably from different positions. This makes assembly much easier! Make sure that the pictures are as high-resolution as possible so that you can zoom in accordingly.

If you disassemble the helicoid, first measure (with lens focus to infinity) the distance from the mount to the front of the lens. Since the entire lens group moves back and forth, this can be an indicator that the distances are correct after assembly. See ‘Lens To Mount Distances’ for more information. Also mark the position where the two threads diverge! The helicoid has several threads, but there is only one correct starting point. You can screw it together at any point, but then the distance to the start will not be correct.

The Zenzanon PS lenses (at least the ones I have) are well constructed in terms of the helicoid. It can be adjusted using a threaded construction in conjunction with a guide ring. Nevertheless, it is advisable to mark and measure before disassembling.

Remove the name ring. There are special silicone cylinders available for removing the name ring. Alternatively, a cylinder that is the same size (or 3D printed) as the flat part of the name ring, covered with a latex glove, can also help.

Loosen screws A, remove parts B and C, and remove ring D.

Assembly note: The rotating ring for the aperture has a small notch into which part B fits. This connects the outer rotating ring with the aperture inscription to the inner ring. The inner ring is in contact with the two protruding pins of the shutter and rotates them. (The shutter pins protrude slightly and face each other.) See the drawings for how to reinsert the ring. To do this, adjust the aperture ring so that the movable part with f2.8 is on the fixed part with f2.8. Part B should fit in approximately at the level of the f8 mark on the rotating ring. (This applies to my 80mm f2.8; it may differ for other lenses.)

Loosen screws A, remove ring B.

Loosen screws A and pull out switch B.

Remove the retaining ring A and pull out the pin B. Caution! There is a small ball under the metal plate C! Once the pin B has been pulled out, it will fall through! Without this ball, the pin will no longer lock into place! Therefore, take care when disassembling!

Assembly Note: To reinstall the ball, insert the pin B, loosen plate C, and insert the ball.

In case you lost the ball, it has a diameter of 1.58 mm.

Loosen screws A, remove ring B.

The lens group can remain screwed into the shutter and can be removed later. This is easier to do with the shutter removed.

Note: This group can be very difficult to remove. The normal opening tool for lenses may not be sufficient here, as it can easily slip. I printed an opener with a 3D printer. Alternatively, openers for preserving jars could also help.

Remove screws A and lift out back plate B.

Remove lens group.

Desolder the cable to the shutter.

Remove the ring that holds the shutter to the lens housing.

Provided that the partial removal of the front has been taken into account, the shutter should now be easy to remove (from the front).

The pins are located on the back and connect to the camera when attached to the camera body.

The resistance of the coil should be approximately 420Ω here (testet on the 50mm f3.5, 80mm f2.8 and 150mm f4).

Note: The measurement is taken across the entire control circuit (see below) and not just the coil itself.

The resistance variates between these two pins according to the chosen aperture value. See the following page for measurements on real lenses.

The ribbon cable connects the pins to the cables from the shutter. To do this, the back of the lens must be opened.

The shutter contains a circuit board to which the cables connected to the ribbon cable are soldered. The circuit board itself contains a diode, an adjustable resistor, and various switches. The cables from the coil are also soldered here.

The electromagnet serves to delay the closing of the shutter. If the electromagnet is not activated, the shutter closes in 1/500 of a second. (However, the camera also controls the magnet at 1/500 second, but only very briefly. See ‘Camera Control Times’. I haven't been able to find out why this is, but it's probably due to the design.) For longer exposures, the camera must activate the magnet to delay the shutter. An iron piece connected to a lever is attracted by the magnet, and the shutter only closes when this lever is released.

The coil is controlled via the orange and blue cables. A diode and an adjustable resistor are connected in parallel.

The resistor-diode combination has two functions.

When the coil is no longer controlled, the magnetic field dissipates and induces a current that runs in the opposite direction to the control direction. This is conducted through the diode to prevent the current from flowing into the camera housing.

The variable resistor is used to control how quickly the coil discharges. This allows you to set how long the magnet holds the lever for the shutter release after the camera removes the control. This is why the variable resistor can also be adjusted from the front without having to completely dismantle the lens. (Only the name ring at the front needs to be removed.)

The variable resistor has the type designation 502 and is therefore a 5kΩ potentiometer. I was unable to determine the type of diode, but I was able to replace it with a 1N4148.

A: Control voltage, B: Control time, C: Voltage from the reduction of the magnetic field of the coil

The camera controls the electromagnet when triggered. Measurements were taken with an oscilloscope at the coil contacts on the ribbon cable (I soldered wires and routed them to the outside). The lens was attached to the camera and the control times and voltages were measured.

The following times were measured on an 80mm f2.8. The Control Voltage was on every measurement on 5.8V (A to A).

The measured current on a shutter speed of 8s was 6mA with 5.8V.