An Electronic Viewfinder 100th Anniversary Leica M?

We asked a physicist to design one, and here’s what he came up with!

As you a know I’ve been breathlessly speculating about what Leica (a company founded as E. Leitz Wetzlar in 1849!) will bring forth to celebrate the centennial of the Leica camera in 2025, and the concept of a sensational new Leica M with unimaginably advanced features has continually crossed my mind more than once. The main problem with executing such an idea is that the Leica M3 was remarkably close to perfection when it was released in 1954, and it has been continually refined and improved in countless ways in the ensuing 74 years. Is it truly possible to improve upon the current analog Leica M6 or MP or the digital M11-P in any meaningful way while still retaining the Leica M’s unique character and charm. I batted this around with my dear friend Bill Maxwell, the president and founder of Maxwell Precision Optics (who happens to be a physicist, inventor, and a longtime camera maven) and we came to the same conclusion—yes, it can be done, but it would entail nothing less replacing the venerable, much-admired optical-mechanical M range/viewfinder with a digital electronic equivalent that yielded noticeably improved performance parameters but also delivered the visceral shooting experience M users love. Here is my edited version of Bill’s proposal, complete with a very rough conceptual diagram to give you a better idea of what it entails.

How the original Leica M opto-mechanical range/viewfinder works:

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The original Leica M rangefinder/viewfinder employs a small lens that looks through the “small rangefinder window” and moves in an arc to shift the secondary image inside the patch.  A beam-splitter combines the main viewfinder image with the secondary image of the rangefinder “patch,” and when the two images of the subject are superimposed on one another, the subject is in focus.  The M viewfinder also has frame lines for different focal length lenses that are superimposed (projected) onto the main image for the purpose of composition and are illuminated by light coming through the central translucent window on the front of the camera. These frame lines move down and towards the lens as the lens is focused closer to compensate for parallax error. 

However, in the original configuration of the Leica M rangefinder the frame lines move at a fixed rate as the lens is focused, technically a design flaw since the parallax between the main viewfinder window and the lens only becomes significant at the very closest focusing distances. Ideally, the frame lines should have moved very slowly through most of its travel, and then moved faster as the lens approached the near end of its close focusing range. To minimize the effects of any parallax-compensating discrepancies, the original M frame lines also show a smaller area than the full frame captured on the film or sensor. This built-in “safety factor” prevents cutting off any part of the field of view thar may not be shown within the frame lines.

An Electronic Simulation of a Leica M Coincidence Optical/Mechanical Rangefinder/Viewfinder by Bill Maxwell of Maxwell Precision Optics

The optical/mechanical multi-frame range/viewfinder in the Leica M3 of 1954 and its successors was and is a magnificent achievement, but it has some inherent limitations and imperfections that can be easily corrected using today’s technology. These limitations include fixed parallax-compensating frame lines that only show about 80-85% of the captured image, do not provide perfect compensation for parallax error, and cannot shift in and out to compensate for the narrowing of the image field as you focus closer. Some photographers who’ve used these cameras in the days when they were hailed as state of the art might appreciate such an updated viewfinder presentation in an upgraded “Leica M12 or a “100th Anniversary Leica M.” Our goal: to preserve essence of the “Leica M shooting experience” while taking it to a higher level of real-world performance.

Note: One obvious solution to achieving perfect viewing accuracy would be taking a “Live View” feed off the image sensor, creating an M-mount camera with a built-in eye-level Electronic Viewfinder (EVF). Indeed, it’s entirely possible that Leica will bring forth such a “Mirrorless M” with a high-spec EVF to mark its centenary, but it probably won’t have an electronic rangefinder or be marketed as part of the Leica M rangefinder series. Another possibility is creating a hybrid M that combines an electronic viewfinder (EVF) with a traditional optical-mechanical rangefinder and lets the user select either option. However the most comprehensive and best integrated solution is an all-electronic range/viewfinder as Bill Maxwell envisioned.

Basic concept of an Electronic Leica M range/viewfinder. How it works:

A miniature high-resolution camera (A) is placed behind the main M viewfinder window. A second similar camera (B) is placed behind the smaller secondary rangefinder window. The middle window which was used to illuminate the original optically projected frame lines serves no purpose and could be eliminated or repurposed.

A nearly 100% reflective mirror, located behind the first camera (A) reflects an image off a miniature high-resolution monitor (inside the camera) located off to the right from the point of view of the photographer behind the camera. The eyepiece itself is placed conventionally on the back of the camera body toward the left end.

Seat of the pants conceptual sketch of proposed Electronic RangeViewfinder Leica M by Jason Schneider.

Camera (A) provides the main full view image that was originally provided through the large M viewfinder window and includes a narrow band outside the periphery of the widest-angle frame lines that define the image area, providing an electronic simulation of the original Leica M viewfinders. Camera (B) provides the secondary image which will be superimposed in the center of the main view as a brighter small rectangular “patch” to recreate, in effect, an electronic version of a “coincident image” rangefinder.

The two images of the subject, seen from different angles, are imaged by the two different cameras spaced apart horizontally; this constitutes the “rangefinder base.” As the lens is focused, the two images are brought together until they coincide at the point of focus. In other words, the lens is focused by triangulation, exactly as in a classic M rangefinder camera.

An image processing chip superimposes the secondary image in the center of the viewfinder image. This chip takes the larger image from camera (B) and scans a smaller rectangular shaped area across the image which results in the image inside the “patch” moving left and right to allow triangulation of subjects at distances ranging from the closest focusing distance of the lens in use to infinity.

The electronic version of the viewfinder could have the frame lines shift more precisely, as alluded to above, to provide nearly perfect correction for parallax error. The frame lines could also move inward and outward to define a more accurate field of view, expanding and contracting to better show an accurate crop as the field of view expands and contracts as the lens is focused at different distances.  The degree of expansion and contraction of the field of view is specific to the focal length of each lens, and that could easily be compensated based on the algorithms or programming of the imaging chip. Lastly, the secondary rangefinder patch could be moved to remain in the center of the frame lines, with the secondary image in the patch shifted to the proper position to allow for proper triangulation.  A sliding utility on the screen on the back of the camera could allow entering lens focal lengths from 21mm to 200mm manually or auto-indexing of focal length in use could be accomplished internally using AI simulation.

Because Leica made several different versions of M viewfinders with different magnifications and different selections of frame lines, a menu on the touchscreen on the back of the camera could allow the simulation of any of those versions, and the possibility of customization of the frame lines that appear in the viewfinder as well. For example, the frame lines could be milky white (as in the original M Leicas) or darker, with the color and contrast of the viewfinder lines fully customizable.

In all current and previous Leica M range/viewfinders the main viewfinder image is less than half as bright as the scene when viewed with the naked eye. The secondary rangefinder patch is also less than half as bright. However, when the primary image and the secondary image “patches” are superimposed on one another the result is approximately twice as bright as the surrounding view but still somewhat less than the brightness visible with the naked eye.

The electronic version of the M viewfinder would allow you to adjust the brightness of the view to your taste—for example, to be much brighter in dim lighting situations compared to what is visible with the naked eye. It would also allow adjusting the contrast between the main view and the rangefinder patch. The viewing image brightness could also be manually or automatically adjusted.

New electronic M-mount lenses?

Newer electronic M-mount lenses could be made to communicate with the imaging chip to electronically transfer specific lens and focus distance data, and could also be used to compensate for the precise focal length of each individual lens, which inevitably varies slightly due to manufacturing tolerances.

Because many photographers would want to use their current or original M lenses, the electronic M camera body could have a pivoting arm with a roller bearing inboard of the lens mount to engage the cam on the back of the lenses (basically the same setup as the original M).  This arm would move a sensor that would communicate the focus position of the lens to the imaging chip which in turn would move the secondary focusing image inside the “patch” according to the programming in the chip, allowing precise manual focusing of any camera/lens combo.

Lastly, if anything ever got misaligned due to a nasty bump, you could just aim the camera at a point on the distant horizon, a star at night, or the moon, with the lens set to infinity, push a button and presto, the camera will realign itself!

Engineering challenges, solutions, and likely outcomes

Is it possible to cram all the complex electronics required for a state-of-the-art electronic range/viewfinder into all the right places and still retain the timeless Leica M form factor? The answer is a resounding yes. With today’s miniaturized digital components—just think of the 3 48MP cameras built into the slim 0.32-inch-thick Apple iPhone 15 Pro Max—it’s clearly not a problem. What about battery power and battery consumption. Having a camera with two integrated miniature cameras and a touchscreen LCD would undoubtedly require more battery power than the current digital top-of-the-line Leica M11-P, but a somewhat larger Li-ion battery, and a circuit that activates the camera only when it’s raised to eyelevel would go a long way to solving the problem. Also, the translucent frame line illumination window in the traditional Leica M could be retained and used as a supplemental battery charger.

Will we ever see a Leica M rangefinder camera with a fully integrated electronic range/viewfinder like the one Bill Maxwell envisioned? It’s possible, but highly unlikely, primarily because the existing optical-mechanical one, which will turn 75 next year, provides a uniquely satisfying shooting experience and is still the best of its kind.

Profuse thanks to Bill Maxwell for presenting his ingenious ideas, and to James Lager for furnishing the illustrations and schematics of the classic Leica M range/viewfinder accompanying this article.