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"M" rangefinder lens connection/parallax correction


p__2

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Hello:

 

I am new to this forum and Leica. Although I have several books now

and have searched online, I cannot find or determine exactly HOW the

rangefinder is connected to the lens for parallax.

 

I can of course see the lens at 11 o'clock for the ttl meter,

however, curiously cannot see anything or imagine just how it works.

 

Can anyone shed some light or direct me? I am curious and have

reached the point where I MUST figure it out.

 

Thank you in advance.

 

 

Kind regards.

Paul

M6 Ti

50mm 'cron

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As to the mechanics of how it works, I'm not competent to answer. But the view in the viewfinder changes slightly as you focus a rangefinder coupled lens. The easiest way to see this is to mount the camera on a tripod and focus the lens. Ignore the rangefinder patch. You will see the entire image in the viewfinder move. As you focus from infinity to close-up, the view will shift down and to the right. The idea is that the viewfinder frame is always centered on the area that will be in focus on the film. Since the viewfinder is up and to the left of the lens (from the point of view of the photographer) if the view through the viewfinder pointed straight ahead all the time, only at infinity focus would the viewfinder's image coincide with the lens's image. At closer distances, the viewfinder's image crosses the lens's image.

 

Of course, this parallax correction only places the area in focus in the same point. The foreground and background will still be different.

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Take the lens off. At 12-O'clock is a small wheel; that is the cam follower that touches the rear of the lens as it is focussed. Focus the lens; see how the rear moves as you focus it? That's what moves the wheel in the body which triangulates the rangefinded; much like our eyes. Ninth grade physics lesson.
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Subject: Response to "M" rangefinder lens connection/parallax correction

 

Thank you both kindly for your replies.

I understand this of course, but my question I suppose is more technically based.

 

Simply, in my mind at least, unlike an SLR where one views the image ttl, the rangefinder on the IIIG (and later "revised" on the M3) are connected to the lens..as you well know.

 

My question .. HOW DOES IT WORK?

 

There must be some sort of lever(s) and or lens (I would imagine connected to what exactly I do not know) to allow as we adjust the focus ring on the lens to compensate or change the binocular type image giving that alignment within the viewfinder. As it is directly SOMEHOW connected directly to the lens.

 

Does the rengefinder mechanism move within the upper housing?

 

Is it a strictly mechanical (unseeing) device, or does it work with additional lenses, reflections, and/or levers/mechanics?

 

I of course have the instructions and the idea behind rengefinder technology and specifically Leica's, however, I have not seen or figured out exactly "how" the rangefinder is "connected" to the lens on the later model Leicas.

 

I hope I am making some sense. I hate to type..where in life be only 1 min. conversation..it is very frustrating, I know!

 

Thank you for your patience and understanding.

 

Paul

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The lens bone is connected to the cam bone.

The cam bone is connected to the follower bone.

The follower bone is connected to the lever bone.

The lever bone is connected to the mirror bone.

The mirror bone is connected to split-image bone.

The split-image bone is connected to the frame-line bone

The frame line bone is connected to the viewfinder bone.

The viewfinder bone is connected to the eye bone.

The eye bone is connected to the brain bone.

I hear the word of LEICA!

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Just a brief note on terminology: the rangefinder compensates for field, not parallax. Field refers to the borders of the frame, which increasingly differ between your eye and the lens as you pull focus. Parallax refers to the way near objects appear to change position relative to distant ones when viewed from your eye or the lens. But even Leica calls it <a href="http://www.leica-camera.com/produkte/msystem/m7/tecdat/index_e.html">parallax compensation</a>, so what can I say?
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And to make things more complicated, the M does not compensate for the changing effective lens focal length as the lens is focussed closer -- as a lens is focussed closer, it's effective focal length grows, so it's field-of-view gets progressively smaller. 'Course, this correction IS made by my $500 Hexar AF and is also included in some of the Japanese fixed-lens RFs from the '60s and '70s.
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>>> as a lens is focussed closer, it's effective focal length grows

 

This is completely incorrect terminology. The focal length is the focal length. The field of view does get narrower as you focus closer, however.

 

This is actually the same cropping effect as with a subframe digital chip. The focal length does not change because you put a smaller chip behind the lens, and it doesn't change because you moved the film backward relative to the lens by focusing closer. In both cases you're simply cropping a smaller portion of the image circle.

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It's not germane to P*'s question, but Mark and Harry are wrong. Mark is correct in his statement that "The focal length is the focal length. The field of view does get narrower as you focus closer, however", but incorrect in his conclusion. The second portion of that sentence describes an increase in the <i>effective</i> focal length. Look it up in any decent lens or lens design book.
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