Operations carried out
Cameras and lenses
Leica M - Black viewfinder
Old Leica M often have the problem called “black viewfinder”.
The viewfinder only lets you see the frames and the central part of the rangefinder, aiming is impossible.
This phenomenon is the consequence of the degraded bonding of the viewfinder prisms.
As a result, the semi-transparent mirror placed at 45° between these two prisms no longer lets the light of the viewfinder pass through.
If the mirror itself is not degraded, it is possible to do a restoration.
It is obvious that for this operation, the rangefinder must be removed from the camera, this is another subject developed in other pages of this site.
You should know that the Leica M rangefinders have undergone many modifications depending on the models, especially the M3 which was equipped with 3 different rangefinders.
However, apart from a few details, the restoration procedure is almost identical.
You must start by removing the prisms, there are several fasteners (depending on the model), the part of the sight frame and the flat pressure spring on the side.
Micro-screws adjust the position of the two prisms when they are glued, and resin that stabilizes them.
You must identify the original positions of the screws before loosening them slightly, and gently remove the resin. Then, with a wooden object (so as not to scratch or break the glasses), lift and remove the two detached prisms.
The old glue is cleaned with acetone-free nail polish remover. Only the glued surfaces should be cleaned, without insisting too much (aged Canada balsam does not resist), because overflows can remove black paint.
My method is very artisanal, but it has proven itself…
Not having to redo the mirror, I do not need specific materials and products, used by professionals more specialized for this work. (vacuum chamber).
If the mirror is partially damaged, you have to choose between continuing, entrusting it to a professional, or another method which is currently in the test phase…
I use silicone for dental impressions, UV glue and a UV lamp for its hardening.
Once the two prisms are cleaned, I apply an extremely thin double-sided adhesive to reposition the two pieces of glass.
Provide a small pull tab to facilitate the demolding and removal of this double-sided adhesive.
I make a position mold in a small rigid plastic container with a flat bottom.
The two prisms held by the double-sided adhesive are then placed in the silicone with the flattest part (front of the viewfinder) touching the bottom of the container. This stabilizes the assembly.
The silicone mold must be allowed to harden well before removing the prisms.
Once the silicone has hardened, the entire container must be removed, as the silicone is flexible and will facilitate the removal of the prisms that have retentions due to their shapes.
This is the time to separate the two prisms and remove the double-sided tape.
Logically, you have to clean the surfaces again and remove any glue residue from the double-sided tape and, as a finishing touch, a sensor cleaning product perfectly finishes the preparation. Isopropyl alcohol is less aggressive than solvent.
The first prism is placed in the mold in place.
The UV glue is a micro-film.
(I don’t have a favorite brand, I’ve tested several which, if you pay the price, are always satisfactory)
It is applied in a drop which, by pressure, spreads over the entire surface to be glued.
The second prism is positioned by sliding, following the retentions then lightly pressed. The mold must be replaced in the container for its rigidity and check that the prisms are in place.
A UV lamp (a simple battery-powered flashlight) placed on top of the mold polymerizes the glue. In principle, it takes less than a minute for it to harden. I leave the lamp on longer for safety.
For this repair, the mirror was too degraded, it did not cover the entire viewfinder and consequently, the frames were partially visible.
So I used another prism/mirror in very good condition and the result is particularly satisfactory…
As with most repairs, reassembly is the reverse of disassembly.
LEICA the legendary brand
I disclaim all responsibility if you damage your toys!!! There are also professionals to do this job!
