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The silvering in Leica Rangefinders can oxidise after many years. The balsam used to cement optic groups together , being an organic compound , crystallises and the reflected image becomes weak and sometimes yellowed with age.Oxygen gets to the silvered surfaces and these then degrade.
Restoring a rangefinder in a M camera requires complete dismantling of the optical system , splitting the prisms , cleaning with nitric acid , and placing a layer of aluminium onto the optic by vapour deposition in a vacuum chamber. The prisms & optics are then re-aligned and recemented and refitted into the rangefinder chassis with final calibration left to last. This whole process entails heating the assembly to about 200 degrees c , before the lenses and prisms can be removed from the rangefinder.
The M3 Rangefinder is a totally different design to the M2 or M4/M6 telemeter. Apart from the obvious differences in magnification , the frame lines ( mask ) is parallel to the camera body , in the other M cameras the mask is at an angle. The M3 has a ground glass diffuser to allow illumination of the mask . The other M cameras have a perspex , fluted diffuser and an internal reflector which , although does the same job , some degree of flare can result in the viewfinder which can 'white-out' the RF secondary image . The original M3 rangefinder was expensive to produce , the viewfinder assembly alone had 2 optics and 2 prisms cemented together , which makes re-silvering more difficult , as these 4 elements have to be aligned and re-cemented exactly after restoration .A lot of effort went into the production of the the M3 RF unit . The mask , itself , is composed of two pieces of glass , each less than a 1/10 of a millimeter thick , cemented together , with the photographically reproduced frame lines , sandwiched bewteen . This is why the image on some M3's becomes yellowed as the balsam deteriorates and crystallises. Leica in Solms, Germany will only fit the M6J rangefinder (which is similar to M6 ) and the internal chassis of the M3 has to be milled out slightly to take the new type unit. Their cost for fitting a new rangefinder is about £ 650 , so having your original rangefinder re-silvered gives a great saving , at approximately one fifth of the cost , and you get to keep the original frames and 1:1 Viewfinder .
RESTORATION & RESILVERING OF LEICA TYPE M2 & M4 RANGEFINDER
The main reason for a completely 'blacked out ' rangefinder on any M camera is due to the balsam , holding the beam-splitter together , deteriorating. Oxygen , from the air , attacks the silvering , as the balsam crystallizes and ' breaks-down. The final straw is when the camera is knocked or dropped and the prisms separate completely , leaving you with just the tiny rangefinder rectangle in the centre of the viewfinder , visible . In some cases it may be possible to remove the old balsam and just recement the prisms without re-silvering , but this usually gives an inferior rangefinder image as the old silvering has tarnished and may be missing altogether in certain areas. To restore a Leica rangefinder to good condition it is neccessary to replace the 'semi-silvered' coating before recementing the beam-splitter.
The frame lines for the rangefinder are made up of two glass plates less than a 1/10 mm thick. one of these plates has the frame lines photographically reproduced on one side . To keep the emulsion from deteriorating , Leitz cemented these two plates together ( with balsam ) so that the emulsion side was sandwiched between glass and , consequently , the ageing of the balsam , gives a yellow tint to many rangefinders . These masks are now no longer available . Up to a few years ago they could be purchased as a spare part at UK £ 130 each ! The later M4 and M6 cameras overcame this problem by manufacturing the frame mask from aluminium of a similar thickness but with the frame lines and RF aperture cut out of the metal so that there is no optical or glass component bewteen the projected secondary image and the beam-splitter. That is why you will not see a 'yellowed' rangefinder secondary image in the M6 .
M2 Rangefinder dismantled for cleaning & prisms (lower) stripped for re-silvering
The above shows an M2 rangefinder with some of the component parts removed for chemical cleaning. The chassis , to the left , still contains the frame-line mask , the reflector and auxillary prism . To the lower part of the picture the two prisms making up the beam-splitter are seen stripped of paint and silvering . Immediately above is the front rectangular optic of the viewfinder and to the right is the mobile optic assembly which is operated on by the roller & arm mechanism in the throat of the camera. Immediately above the front viewfinder optic is the field lens doublet which is mounted into a metal frame with the two screw locating holes. This is composed of two glass elements cemented together with the metal frame sandwiched in between. After all optical components are chemically cleaned the prism can be resilvered . This is done in a vacuum chamber where aluminium is vapour deposited onto the hypotenuse. Once the correct thickness of metal is deposited the two prisms can be aligned and cemented together prior to painting. The paint is neccessary to help prevent internal reflections within the beam-splitter.
The completed beam-splitter after re-silvering , cementing ,alignment and re-painting
Once the mask , reflector & auxillary prism have been cleaned ( or replaced if neccessary ) the beam-splitter , mobile optical element and field lens can be replaced . As long as the beam-splitter has been aligned and cemented correctly , it is then secured with epoxy resin into the rangefinder chassis where slight adjustment of the height of the prisms can be achieved by two grub screws. More adjustment is available by lowering or heightening the position of the front rectangular optic with another two grub-screws. This can also be moved sideways to adjust the overall horizontal position of the rangefinder secondary image by a third grub-screw. Epoxy resin is used to secure all optics once the calibration of the rangefinder has been completed .
The finished rangefinder unit can be refitted to the camera body . Final adjustments are made after the body collimation has been checked and adjusted .
All Leica M cameras sufffer parallax error to a greater or lesser extent . This is evident when looking through the viewfinder and observing the RF rectangle . If you move your eye up/down or left/right from the centre of the eyepiece , the secondary rangefinder image will shift slightly. Moving the eye down will make the RF image go up and vice-versa. The Leica M3 does not exhibit this phenomenon to any great extent and this is partly due to the design of the optical system which is significantly different than the later M2 type finder , which is basically the same as used in the current production cameras .
Variations of M3 DS Rangefinder
The development of the Leica M3 , which came directly after the IIIg , shows numerous changes were made to the internal parts as well as the external construction , such as strap lugs and top-plate fixings. The rangefinder in the first double stroke M3's went through several modifications before finally being discarded in favour of the M2 type , of which the basic design , is still used in the latest MP cameras and continued after M3 production ceased . In fact it is safe to say that the M3 developed into the M4 via the M2 .
The photograph shows , partly dismantled ,three variations of the first type M3 rangefinder chassis which was fitted to the double stroke camera. The casting of the chassis in all three is from a different mould .
The black arrows show that the locating arrangment for the auxlliary prism is different in each case. In RF unit A the prism is fitted into a tubular section of the chassis with half of the tube cut away. In RF unit B the location has rectangular sides and comprises a glass block which is cemented to the prism. In the RF assembly C the prism is again fitted into a tubular construction in the chassis , but this time the tube part is complete and not cut away. The red arrows show the different arrangement for selecting the individual bright-line frames in each unit.
The optical components are also arranged differently in each unit , with the later rangfinder having air-gapped field lenses as opposed to cemented doublets . The earliest rangefinder has the main viewfinder prism with four components cemented together , two prisms and two lenses all in one optical unit. This makes alignment , after re-silvering , more difficult and it is probable that the modifications to the later rangefinder made assembly and calibration easier in the factory .
Modifications to the mask ( bright-line ) was also made and in each unit there are slight differences. When the single stroke M3 arrived the rangefinder also changed . It lost its built in viewfinder lens and this was then fitted to the camera top-plate instead of the internal chassis.
It appears to me that , in a very short space of time , the M3 rangefinder underwent several changes before being dropped in favour of the M2 rangefinder which was possibly easier to produce and less expensive and easier to calibrate , although , in my opinion the M3 was a better unit , with the frame mask parallel to the body making it less prone to flare than the M2 system which is basically the same as that used nowadays
Camera Repairs & Restoration - Luton , Bedfordshire - England
We can re-silver your M1/2/3/4 ( M5 & M6 POA ) rangefinder for GBP £ 145 plus postage . As long as the prisms are in reasonable condition your rangefinder can be restored. Sometimes it is not possible due to third party damage caused by previous repairs that have been done to the rangefinder before , resulting in badly chipped or damaged prisms . In these cases it may be necessary to replace optical components and an estimate would be given prior to any work taking place. A complete Leica replacement rangefinder unit is about UK £ 650 plus fitting , so restoration of the original part is an economically sound alternative .
EXTENDING THE RANGE OF EARLIER M3 RANGEFINDERS : Not all M3 cameras can be adjusted to focus down to 0.7 metre . The early M3's just go to 1 meter . There is , on later M3's that only focus to 1 mtre , an extra lever in the throat of the camera that stops the roller arm coming out further . This can sometimes be , straightened slightly so that the roller arm comes out further allowing focusing below 1 mtre . The reason that Leitz did this was because below 1 mtre the rangefinder and parallax correction was not as accurate. Some of the early M3's did not have this extra 'stop' and , whatever you read on the internet about extending the range , this is not true for all M3 's . There were 3 different rangefinders for the first design ( double stroke ) M3 , and the problem with extending the range is that the moving objective ( the lens that moves when you focus the camera ) hits the inside of the top-plate before it reaches 0.7 mtre. There is a possibility with some M3's that the prisms can be removed and reset in a different position so that the lens will be able to focus below 1 mtre , but this requires that the rangefinder is heated to 200 degrees C to soften the cement and then loosen the prisms/beam-splitter so that it can be repositioned to extend the range . If you check your camera , and look in the throat where the rangefinder roller arm is attached you may see a small lever that acts as a stop and hits the centre eccentric screw post . You will see that this is bent slightly. If you are very careful you may be able to bend this lever so that it is a little straighter and thus allow the roller to come further out . You would have to be very careful , and use a long nosed pair of good quality pliers. Do not attempt to unscrew the roller arm because the span of the rangefinder is adjustable on an eccentric cam and unscrewing this will upset the calibration . Straightening the stop lever may give you a little more on the focus scale below 1 mtre but it normally will not focus all the way down to 0.7 . If there isn't a stop lever ( which is normal for early M3's ) then the only way to extend the rangefinder is to reposition the internal beam-splitter optics , which entails removing the rangefinder and heating the optics up to remove and reposition them . This is not a small job .
The difference bewteen these two M3 double stroke cameras is about 38,000 units .The one on the right is 748 xxx and the left is 786 xxx
This is the normal balsam separation found in many M3 cameras . It entails heating and removing the prisms & separating the optic , cleaning and recementing. The rangefinder then has to be re-aligned & recalibrated .
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