Servicing a Kiev MC Vega 28B 2.8/120mm lens
Marwan’s step by step guide to servicing a Kiev MC Vega 28B 2.8/120mm lens
By Marwan el Mozayen.
One of my absolute favorite lenses in the Kiev system is the Vega 120mm. Mechanically this lens is very well made. The construction is quite elaborate, for example the aperture mechanism is double ball bearing. From an optical point of view, together with the 2.8/80mm MC Volna 3 and the MC Telear 5.6/250mm, it is one of the most modern lenses in the entire system.
With its compact overall length, and is hardly longer than the 80mm standard lens. It has a decisive advantage over the 120mm Carl Zeiss Jena Biometar, in terms of size. It can be used on the Kiev 88 using the plug-in bayonet as well as the Pentacon Six mount. With a front thread diameter of 62mm, you only need one filter size for the 80mm and the 250mm lenses.
The Kiev 28B 120mm lens has a minimum distance of 1.20m. It also has a pleasant neutral bokeh, and this makes it is ideal for portrait photography. It is also among the best medium format lenses from the former USSR in terms of optical performance, and in some respects it is even superior to Carl Zeiss Jena lenses.
I have been using my Vega 120 since the end of the 90s. I have not had any problems with this lens. However, some time ago I got my hands on a defective and heavily soiled Vega for a relatively small amount of money. Since I had never disassembled a Vega before, this lens offered itself as an object for a dissection.
On closer inspection, however, it turned out that it was still salvageable. I documented the process step by step.
The focusing worked flawlessly on my target lens, so only the lens barrel, which also contains the aperture mechanism, was removed. In this regard, the Vega is built to be very service friendly and you should allow about 1- 1 ½ hours for disassembly and reassembly.
Tools needed are a set of slotted watchmaker’s screwdrivers, various tweezers, and a lens wrench. A bellows for dust removal as well as optics cleaning paper and a set of clean anti-static gloves for clean removal as well as installation of lenses is recommended. White spirit, brake cleaner and sugar soap are suitable for cleaning the removed components.
Since we are only looking at the lens barrel and the aperture mechanism on this lens, I am not re-greasing the worm gears.
The next step is to disconnect all mechanical connections between the outer lens mechanism for focus adjustment and the tube with the aperture unit inside.
At about the 7 o’clock position, there is a larger slotted screw with a flat head that must be loosened. The aperture ring can then be lifted off.
Pay attention to the two steel balls of the f-stop ring.
Mark all adjusted parts of the orifice mechanism in their position before disassembly.
When the return spring of the diaphragm mechanism has been carefully unhooked, the inner tube together with the diaphragm unit can now be pulled out. To do this, loosen the three screws on the front side.
Again, make sure that the correct position is marked for later correct assembly.
The tube is then simply pulled out on the front side.
The retaining ring of the front lenses can now be loosened with a suitable lens wrench.
Carefully remove the lenses and arrange them in the correct order on a clean soft surface and, if necessary, carefully remove dust with compressed air and then clean them free of streaks using suitable utensils.
Proceed with the rear lens elements of the tube in the same way.
Before removing the orifice assembly, mark the position of the component in relation to the tube.
Now unscrew the three retaining screws on the tube.
The entire ball bearing unit can now be easily removed and further disassembled for cleaning.
To do this, first loosen the retaining ring with the correctly set lens key.
Before further disassembly, again mark the individual components in their position relative to each other.
Carefully remove all orifice plates and, depending on the degree of contamination, rinse all orifice plate unit components in brake cleaner until they are free of oil and other contaminants.
In my particular case, the contamination was so extreme that the cleaning had to be done in several steps.
Once all parts have been cleaned, the assembly of the orifice unit can be started.
The hardest part is getting the last element over the first.
Once the diaphragm unit has been reassembled, it is essential to check that it runs smoothly.
If everything runs correctly, it can then be reinserted into the tube in the marked position.
After correct insertion, the unit is fixed in the tube with the 3 screws. The screws are to be provided with a screw lock against unintentional loosening.
From this step comes the famous phrase: “Reassemble in reverse order”.
One more note, the two aperture detent screws should be treated to a small amount of suitable grease.
Once everything is assembled, briefly check that everything works smoothly.
Images © Marwan el Mozayen 2023.
You might also be interested in this article on repairing the Leica R4 https://silvergrainclassics.com/en/2022/12/a-leica-r4-rises-from-the-dead/