M9 engineering geek question

[jrc]

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I was out with the D3 and the Zeiss ZF25, manual focus, shooting in manual mode. When the lens is in focus, an unobtrusive focus-light indicator comes on. When it is not in focus, a < or a > sign pops up, telling you which way to turn the focus ring. And, when the indicator is on, the lens is, in fact, in focus, allowing you to focus accurately even without wearing your glasses, if need be.

 

Does anybody know how this is done? Where is the D3 taking the reading? Is the sensor involved? If, hypothetically, Leica wanted to do this with an M9, would it be complicated, novel engineering problem? Or has the problem really been solved, and it's just a matter of applying it?

 

JC

[Overgaard]

Canon does the same with R-lenses attached. And so does the Digilux 3.

 

But don't ask how. Just why not.

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[sdai]

I was out with the D3 and the Zeiss ZF25, manual focus, shooting in manual mode. When the lens is in focus, an unobtrusive focus-light indicator comes on. When it is not in focus, a < or a > sign pops up, telling you which way to turn the focus ring. And, when the indicator is on, the lens is, in fact, in focus, allowing you to focus accurately even without wearing your glasses, if need be.

 

Does anybody know how this is done? Where is the D3 taking the reading? Is the sensor involved? If, hypothetically, Leica wanted to do this with an M9, would it be complicated, novel engineering problem? Or has the problem really been solved, and it's just a matter of applying it?

 

JC

 

It's an electronic rangefinder, John. The camera beams infra red light on the object and clock the time the light bounces back to measure its distance.

 

This requires the lens could transfer its distance information to the camera so the camera could compare the distance setting on the lens to its calculation and decide when the object is in focus.

 

Since Leica's M lenses have no electronic linkage to the camera, it can't transfer the distance info to the camera so it can't be done unless Leica re-engineer the mount.

[ammitsboel]

I was out with the D3 and the Zeiss ZF25, manual focus, shooting in manual mode. When the lens is in focus, an unobtrusive focus-light indicator comes on. When it is not in focus, a < or a > sign pops up, telling you which way to turn the focus ring. And, when the indicator is on, the lens is, in fact, in focus, allowing you to focus accurately even without wearing your glasses, if need be.

 

Does anybody know how this is done? Where is the D3 taking the reading? Is the sensor involved? If, hypothetically, Leica wanted to do this with an M9, would it be complicated, novel engineering problem? Or has the problem really been solved, and it's just a matter of applying it?

Some people hate this.

It's for square heads.

[earleygallery]

It was also fitted to most electronic SLR's in the early 80's before AF became more commonplace. Back to the future eh?!

[jrc]

It's an electronic rangefinder, John. The camera beams infra red light on the object and clock the time the light bounces back to measure its distance.

 

This requires the lens could transfer its distance information to the camera so the camera could compare the distance setting on the lens to its calculation and decide when the object is in focus.

 

Since Leica's M lenses have no electronic linkage to the camera, it can't transfer the distance info to the camera so it can't be done unless Leica re-engineer the mount.

 

As far as I can tell, the ZF has no electronic link to the camera. Perhaps I'm missing it.

 

My Nikon 14-24 f2.8 zoom has 10 small contacts on the edge of the mounting ring. The ZF does not. Thats' why I was curious - I was wondering if it was reading microcontrast or micro edges off the sensor input somehow...this same technology is used with even ancient Nikon and Pentax lenses, before there were any electronics at all...

 

JC

[jrc]

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Some people hate this.

It's for square heads.

 

In American slang, "square head" is a derogatory term for Germans or Scandinavians. Is that what you mean? Germans or Scandinavians?

 

JC

[jaapv]

No. He means Sponge Bob. He is a Scandinavian himself....

[rob_x2004]

Is Sponge Bob an Iiikia man?

[AlanG]

As far as I can tell, the ZF has no electronic link to the camera. Perhaps I'm missing it.

 

My Nikon 14-24 f2.8 zoom has 10 small contacts on the edge of the mounting ring. The ZF does not. Thats' why I was curious - I was wondering if it was reading microcontrast or micro edges off the sensor input somehow...this same technology is used with even ancient Nikon and Pentax lenses, before there were any electronics at all...

 

JC

 

It works via contrast detection. Either on the sensor itself (slower for use when the mirror is up) or via AF modules in the camera. IR is sometimes is used in low light. Some cameras have a little IR emitter for this or use the one in the flash. But I don't believe the IR itself is used to measure distance but merely is supplying the illumination for the contrast detection.

[mjh]

Canon does the same with R-lenses attached. And so does the Digilux 3.

 

But don't ask how. Just why not.

This is based on the very same phase-detection autofocus sensor used for focusing automatically. The sensor detects whether the image is in focus, and if it isn’t, in what direction one should search for optimum focus. No communication between body and lens is required, which is why it works with all kind of lenses. This requires a dedicated AF sensor, though, which is available with SLRs only, so don’t expect this technology to find its way into the M9.

 

BTW, this would not work at all with an active IR autofocus, a some have suggested, as that would require some communication with the lens. And neither is it based on contrast detection. For one thing, DSLRs usually don’t use contrast detection except in live-view mode. And then, contrast detection cannot tell whether you have focused too near or too far.

[AlanG]

The sensor detects whether the image is in focus, and if it isn’t, in what direction one should search for optimum focus.

 

 

This assumes the threads on all lenses turn the same way.

[sdai]

As far as I can tell, the ZF has no electronic link to the camera. Perhaps I'm missing it.

 

My Nikon 14-24 f2.8 zoom has 10 small contacts on the edge of the mounting ring. The ZF does not. Thats' why I was curious - I was wondering if it was reading microcontrast or micro edges off the sensor input somehow...this same technology is used with even ancient Nikon and Pentax lenses, before there were any electronics at all...

 

Sorry, John ... I didn't read your post carefully, in this case, the camera is still using phase detection with its AF sensor, of course, there's no feedback to drive the lens and you have manually turn the focus ring to put it to work.

[sdai]

WRONG WRONG WRONG!!!!

 

YES, YES, YES ... I AM WRONG ... SEE MY POST ABOVE.

[george +]

But Leica Camera Company could incorporate a laser rangefinder - made by another Leica company (now unrelated except for name) and couple this to the rangefider cam. It seems easy. (?) And logical. (!) And could do away with all that complex prism setup.

[sdai]

In fact, if you use a dumb adapter, the focus confirmation on a Canon EOS won't work. That's why people buy those "AF confirmation" adapters, and you can code this adapters with your specific focal length and maximum aperture to guarantee proper metering with the EOS camera.

[henning]

The autofocus sensor module is usually located in the floor of the mirror box. The main mirror is half-silvered, and the light is re-directed to the bottom by a secondary mirror that is hinged from the main mirror.

 

It's because the main mirror is semi-silvered that a circular polarizer is needed instead of a regular polarizer. The semi-silvered mirror is itself a polarizing filter, and if the filter on the front were not a circular polarizer, AF would not work in some filter positions.

 

Phase detection allows the camera to determine whether the subject is behind or in front of the plane of focus; lens construction, features or thread direction have nothing to do with it.

 

Henning

[jrc]

This is based on the very same phase-detection autofocus sensor used for focusing automatically. The sensor detects whether the image is in focus, and if it isn’t, in what direction one should search for optimum focus. No communication between body and lens is required, which is why it works with all kind of lenses. This requires a dedicated AF sensor, though, which is available with SLRs only, so don’t expect this technology to find its way into the M9. <snip>

 

Okay. But is there *some* existant technology that would do it for a rangefinder? The laser thing seems problematic to me -- I have used laser rangefinders both on survey total stations and to play golf and hunt, and the quality of return depends too much on the target's surface, and the response isn't always quick. Perhaps because it would only need to work at relatively short range, it would be okay...On the other hand, the lasers I've used don't work at very close ranges...I do know that Nikon is now offering a rifle scope with a built in rangefinder good out to several hundred yards, so lasers can work in conjunction with precision optics.

 

JC

[offshore]

What's a M9?

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Hallo,

Look here: Leica M

[sdai]

Okay. But is there *some* existant technology that would do it for a rangefinder?

 

That's the electronic rangefinder I mentioned about before I read your post carefully, Contax G1/G2 uses a electronic rangefinder, all Nikon DSLRs have electronic rangefinders too.