When you book your camera in for a full service, we also service your rangefinder. All optics are cleaned and adjusted, including any minor optical repair work and accurate calibration, which is included in the service price. Screwmount cameras have a simpler rangefinder setup. Cleaning the optics and fitting a new beamsplitter can dramatically improve the rangefinder. A new screwmount beamsplitter is fitted as standard during a service.
If any of the optical components in a Leica 'M' are chipped or damaged, we will endeavour to restore them so that they are serviceable and in many cases, this is covered by our standard service charge. In the unlikely event that any of the optical components have to be replaced, this may incur additional costs.
This is an expensive, time-consuming and complicated job to do, requiring specialised tools and equipment. If you carry on reading below, you'll understand that the rangefinder is as complicated as the rest of the camera. Thankfully, not all cameras need a rangefinder rebuild but if yours does, you know it's in good hands.
Remove your rangefinder and send it to us for repair
If you wish to remove the rangefinder from your camera, to send to us for repair/service/prism rebuild. This is a useful option for overseas customers, for avoiding customs charges based on the value of the entire camera.
Rangefinder Calibration only
We offer a fast rangefinder calibration service for all film 'M' cameras and the digital 'M' range. We will calibrate your rangefinder accurately for infinity and also close focus. It is possible for your rangefinder to indicate infinity accurately but this does not mean it is accurate at close range. We also check and calibrate vertical alignment, that is to say, horizontal subjects, such as rooftops align perfectly as you focus. In some cases, we may be able to improve close focus range on earlier M3's if you ask. This isn't always possible without dismantling the camera.
PLEASE NOTE: Calibration is an adjustment not a repair. Your rangefinder may have been badly adjusted in the past, or the tech didn't understand the close focus adjustment but if you find that your camera regularly needs calibrating, it could be a couple of things. The adjustment screw at the centre of the roller on the rangefinder arm might be loose. The rotation of the roller as you focus the camera could cause the adjuster to turn - although this isn't very common. Another scenario is where the camera has been dropped or knocked. The drop does not have to be severe. It can cause the main prism epoxy pads to lose adhesion. Over time, vibration will allow the prism to shift and if that happens - you lose rangefinder accuracy. If after calibration, it continues to lose accuracy due to a shifting prism, we may have to secure the main prism with epoxy and re-calibrate and additional charges will apply. If you are aware of any mishap with your camera, please let us know. A loose, shifting prism isn't obvious to us when calibrating your camera.
and how things work...
In our pricelist, alongside our standard service prices, we have a category that deals with additional work. When we service a Leica, we clean your rangefinder optics and even carry out various minor repairs but in certain circumstances, the rangefinder will have blacked-out, or it will be heading that way. The Leica M3 and M2 rangefinders are very complex and hopefully, as you will see, the work we do is significant and complex. I'm not aware of any other repairer that carries out this level of detailed work.
This article discusses the Leica 'M' rangefinder, in this case specifically the M3 rangefinder. The rangefinder design and layout changed somewhat by the time the M2 was introduced but the principle is the same. In fact the M2 rangefinder remains the same in all cameras right up to the M11. There have been some changes and improvements but the general operating principle remains unchanged.
I would like to explain how the rangefinder works and also give you an idea of the kind of work we undertake when we carry out a rangefinder/prism rebuild. If you are interested in the technical aspects of Leica cameras, you'll probably find this interesting.
Perhaps the most common reason for a prism rebuild is the dreaded 'blacked out' viewfinder. This happens because the main prism, which consists of two triangular sections, separates at the point they are cemented. The original optical cement was canada balsam – a form of purified tree resin. As the balsam ages, it can become discoloured, cloudy and brittle. The slightest knock may cause the prism to split. Because of the angles involved, total internal reflection will then stop light from the viewfinder from getting to the eyepiece, although you can usually still see the RF patch and framelines as they are still reflected from what remains of the beamsplitter on the part of the prism nearest the eyepiece.
Georg Friedrich Brander
The first true 'coincidence' rangefinder, or telemeter, was invented in 1778 by the Bavarian engineer and mathematician, Georg Friedrich Brander. It was based on two mirrors set apart horizontally and used trigonometric principles to determine the distance of a visible object. This information is crucial for various operations, such as artillery targeting, anti-aircraft gunnery, and long-range sniping. Miniaturisation allowed these devices to become adopted by photographers. To begin with, they were sold as accessories. The rangefinder would be pointed towards a subject and a dial turned. When the images coincided, the distance scale would indicate the actual distance to the subject and this could be transferred to the camera lens. Eventually, rangefinders were miniaturised and were built into cameras, with the lens mechanically coupled to the rangefinder. One would adjust the lens focus until the two images coincided (the viewfinder image and the RF 'patch' (as it has become known), at which point the lens would be accurately focussed.
The rangefinder used in the screwmount range of Leica cameras is relatively simple, not unlike the diagram below. It is often maligned because the eyepiece is small and many vintage cameras have dusty optics and faded beamsplitters, so the experience is often uninspiring. These little rangefinders however are capable of really accurate and critical focusing, however, during the development of the M3, it was clear that improvements and additional functionality were required in order to bring the Leica range up to date. The Leica M rangefinder is vastly more complex than before.
There is as much complexity within an 'M' rangefinder as there is in the rest of the camera! Much of the development cost of the M3 went into the rangefinder design. Not only is it an reliable distance measuring device but it also includes mechanisms for correcting parallax and the means of projecting framelines into the viewfinder that automatically represents the angle of view of the lens attached to the camera. It is a superbly designed instrument but it is complicated and the optical components are extremely fragile. For this reason, many camera technicians refuse to work on them. In the past and when spare parts were available, a faulty rangefinder would simply be replaced. They were not considered to be serviceable items.
The viewfinder section of an M3 is based on a reverse Galilean telescope with a magnification ratio of 0.91. This comprises a bi-convex ocular or eyepiece and a plano-concave objective. In front of the objective sits the trapezoidal prism (12). The purpose of this prism is to correct the viewfinder parallax. The M2 uses a similar type of viewfinder but the magnification ratio was reduced to 0.72 to accommodate the wider angle of view needed for 35mm lenses and framelines.
In the image above, I laid out the various optical components of an M3 rangefinder in the order they would be fitted inside the rangefinder chassis. Here is a description of how it works:
The main prism on an M3 comprises of two triangular sections of high refractive index flint glass, cemented together, with the beamsplitter applied to the hypotenuse of the prism closest to the eyepiece. The concave objective is cemented to the front of the prism.
The field lens (8), that can be seen in the illustration is a cemented achromatic doublet that usually sits in an adjustable frame to the side of the prism. In our case, the doublet is actually cemented to the main prism (10), so the prism consists of five cemented components. This particular arrangement gives little margin of error when we carry out restoration work, as everything has to be perfectly centered and aligned.
Light (the secondary image or 'patch'), enters the small rangefinder window and is reflected by 90 degrees by the fixed pentaprism (1), which also flips the image horizontally. A more complicated arrangement than the simple swivelling mirror as shown in our simple rangefinder diagram or of the type fitted to screwmount cameras. There is a small doublet lens (2), that we call the telescope, that is fitted to a bracket that moves horizontally in an arc. It is indirectly connected to the camera rangefinder arm via an arrangement of cams. The telescope performs the same function as the swivelling front surface mirror of our simple rangefinder. It indirectly scans the view in front of the camera, via the pentaprism.
As you turn the focus ring on your screwmount or 'M' lens, there is a rangefinder coupling at the back of the lens moves in and out relative to the focus position. The position of the coupling is accurately transferred to the camera via the roller (cam follower) on the rangefinder arm. The position of the arm determines the position of the telescope. If you gently push the rangefinder arm in and out on your camera, the telescope will swing from side to side.
The cam follower of the rangefinder arm is secured with an eccentric adjustment screw. The position of that eccentric determines the maximum or minimum deflection of the telescope. The rangefinder arm is also fitted with an 'eccenter'. This has the effect of either lengthening or shortening the rangefinder arm. This determines the range of deflection of the telescope. Using these two adjustments, we can acheive a high degree of accuracy from infinity down to 1 metre or less.
Vertical alignment is accomplished by raising or lowering the telescope via a small adjustment screw. The term vertical alignment causes some confusion. Imagine a horizontal rooftop in the distance. As you focus the camera, the ridgelines should coincide. If you can see that one is slightly higher than the other, the vertical alignment needs to be adjusted. Although in this case we are concerned about the alignment of horizontal objects, the telescope has to be physically adjusted vertically to correct the error.
The vertical adjustment screw on an 'M', is behind a small cover screw on the top plate of the camera, or behind the Leica red dot on later cameras. The adjustment screw was eventually removed by Leica. A special tool is now needed.
The vertical alignment adjuster is NOT behind the cover screw on a screwmount Leica. That is actually the horizontal alignment adjuster. Vertical alignment is corrected out by rotating the left window (looking at the front of the camera). The window has a slight prism. Once vertical alignment is correct, it is likely that horizontal alignment will be necessary. Back to our M3 rangefinder...
The image from the telescope passes through the roof prism (3), which reflects the light by 90 degrees and also flips the image 'upside down'. A tiny lens (4), is cemented onto this prism with the point of focus coinciding with the plane of the brightline mask (5). This arrangement allows the edges of the rectangular RF aperture, or patch to be sharply in focus when viewed through the eyepiece. Usually, we remove and re-cement the lens tiny lens onto the roof prism since old balsam can degrade the RF patch. It is also worth pointing out that the telescope (2), is adjustable but under normal circumstances, it should never be touched. In the context of a rebuild, a poorly adjusted telescope can result in the edges of the RF patch being out of focus, the actual RF patch image being out of focus, also, as the eye is moved around the axis of the eyepiece, the RF image may appear to jump around. This adjustment can be tricky, requires a special tool and should only be adjusted by someone who knows what they are doing! Incidentally, an inaccurately cut roof prism can also cause the RF image to jump, if the eye is moved up and down in relation to the eyepiece.
The RF image passes through the clear rectangular aperture of the brightline mask and then to a 90 degree prism, the delta prism (6), that has a correction lens cemented onto it (7). The RF image from the small window is inverted once more.
The centre rangefinder window, called the illuminator window, allows light to pass through the brightline mask. It plays no other part in the operation of the rangefinder, other than to illuminate the framelines. M3 centre window is made from ground glass. The M2 and later cameras use a plastic prismatic window. Due to the different internal design, illuminator light needs to be directed sideways to a small internal mirror, before it can illuminate the framelines. The prismatic design accomplishes this.
After the rangefinder image and the image of the framelines have passed through the delta prism (6,7), the image passes through a field lens (8) – an achromatic doublet, that depending on the age of the camera, it may or may not be cemented directly onto the side of the main prism (10). Once the image enters the main prism, it is reflected and essentially mixed with viewfinder image thanks to the beamsplitter (10a). Light from the main viewfinder passes through the beamsplitter and the image from the small window reflects off the beamsplitter and finally enters the eyepiece (9).
The brightline mask unit comprises of the actual glass mask, which is cemented into the mask frame. The frame is capable of moving left to right at an angle of about 40 degrees and is activated by the rangefinder arm. This forms the parallax correction. The mask frame unit also holds a secondary metal mask, we call the sliding mask. Its function is to hide/reveal the different framelines as determined by the focal length of the lens fitted or by operation of the frameline preview lever if fitted. There are various adjustable linkages that connect the sliding mask to the rangefinder chassis and then to a mechanism inside the shell of the camera containing the lens mount and preview lever.
The original brightline mask for the M3 and M2 etc comprise of a photo-lithographic image attached to one side of a very thin glass window. Because the emulsion is delicate, another thin glass window is cemented to the emulsion side in order to protect it. There are a number of adjustments possible that set the position of the sliding mask, so that the displayed framelines correspond with the lens fitted, as well as parallax.
Because the mask can become permanently damaged by the sun, or delaminated due to age and the fact that they haven't been available for many years, we designed our own Free to Air replacements. They are glassless and and balsam-less, so they should last as long as the camera. In most cases, the original mask will clean-up well and not require replacement. If the only problem with the rangefinder is mask related, we can replace it and a rangefinder rebuild may not be necessary. Unfortunately, in some cases, the rangefinder and prism will need rebuilding and the mask may have also deteriorated severely, requiring replacement.
Re-coating the beamsplitter is a tricky process. Silver was used for many years before being replaced by aluminium. Before application of the beamsplitter, the prism components have to be thoroughly cleaned and the surfaces finely polished before the silver is deposited under vacuum conditions using a physical vapour deposition process. We do this in house. The amount of silver deposited is critical. Too much and the viewfinder image will be too dark, too little, and the RF patch will have poor contrast.
Above is the beamsplitter part of the prism. The beamsplitter is clearly in poor condition but we will clean and polish these parts and replace the beamsplitter using physical vapour deposition which we do in house. Both prism parts are then optically aligned and then cemented using UV cure optical adhesive. In addition, there is a concave objective as well as a a doublet field lens that has to be optically centered, cemented and then attached to the prism.
The rangefinder is now ready for reassembly. Parts are loosely fitted before the rangefinder is attached to a special jig. This allows us to make all of the necessary adjustments to all of the components before they are finally screwed into position. The last job being to secure the main prism by using three pads of epoxy adhesive, as originally used at the factory. After a final check and clean, the rangefinder is ready to be fitted back into the camera.
My rangefinder constantly needs calibrating - why?
I often tell people that there should be no reason to have your rangefinder adjusted regularly, unless the camera has been dropped or had a knock. The only exception is if the adjuster screw on the rangefinder arm is very loose. If this happens, the screw could turn along with the roller on the end of the rangefinder arm. This can be checked easily. Normally, they are quite tight and as long as the roller is free to turn, it is unlikely to give any trouble.
A common problem is where the main prism can shift slightly as the camera is being used. The prism is epoxied into place and any To prevent the fragile glass parts from damage caused by shock and vibration, Leitz came up with is a method of injecting epoxy through three holes, when cured, becomes hard enough to support the prism but with enough 'give' to have a shock-absorbing effect. The face of each pad also adheres to the painted surface of the prism.
If a camera receives a knock, the prism may shift slightly inside the rangefinder housing. The epoxy still has a clamping effect but the adhesion has been lost. This is the usual reason for a rangefinder losing accuracy. Always let us know if you think this is the case because a shifting prism isn't always obvious. We can re-epoxy your prism in place and calibrate your rangefinder.
Much thought went into equipping the rangefinder with sufficient adjustments in order to ensure complete accuracy, including framelines that shift position as the lens is focussed to provide parallax correction. When we rebuild a rangefinder, it is attached to an alignment jig. This is vital in order to ensure that everything works properly and allows us to calibrate everything correctly. Once we are happy that everything is working correctly and that distant focus, close focus and vertical alignment are within limits, we epoxy the components into their final positions.
Rangefinder Rebuild/Blacked-out Viewfinder - Leica 'M' - more technical details below