A dumb question about Leica and rangefinders in general

Discussion in 'Leica M Forum' started by Ray Sachs, Mar 28, 2011.

  1. Ray Sachs

    Ray Sachs SC Legend Subscribing Member

    Sep 21, 2010
    Not too far from Philly
    Real Name:
    you should be able to figure it out...
    This may be a dumb question (I was once told there's no such thing, but think that's hogwash - I've heard some and no doubt asked some that qualify BIG time!). I haven't used a true rangefinder camera in probably 30-35 years. And the ones I used in my youth were relatively cheap ones and had fixed lenses, not interchangeable. The idea of having two focus windows and lining up the images to focus makes good sense to me with a fixed lens - it should be a fairly simple calculation to do the triangulation and bring the two images together in sync with the focal range of the lens.

    But how does this work with an interchangeable lens rangefinder like an M8 or M9??? I look at these things, I know they're manual focus, I see the two windows on the front of the camera that feed light to the OVF and I understand that you focus them the same way we did with the old ones - line up the two images in the viewfinder to achieve focus. But wouldn't this change with the focal length of the lens? Wouldn't a 28mm lens focus at a different point than a 35mm than a 50mm? Or maybe not? I guess distance is distance is distance and as long as the lens is designed to work with the Leica standards, the rangefinder focus could work regardless... But I have to admit I'm having trouble wrapping my feeble mind around this. The X-100 got me thinking about this even though it doesn't use anything LIKE the same mechanism, but it being a modern "rangefinder" knockoff, it made me start thinking about the real thing...

    -Ray
     
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  2. TraamisVOS

    TraamisVOS SC Hall of Famer

    Nov 29, 2010
    Melboune, Australia
    I've got an M8 and I sometimes wonder about this too, particularly since I'm using uncoded non-Leica lens.
     
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  3. Streetshooter

    Streetshooter Administrator Emeritus S.C. Charter Member

    Jul 12, 2010
    Philly, Pa
    The Leica RF has a cam in it. It will focus any lens designed for it.
    10' is 10' no matter what lens is being used.
    The cam rolls on the inner barrel of the lens and sets the patches to focus.
    In a nutshell, that's the idea.
     
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  4. Ray Sachs

    Ray Sachs SC Legend Subscribing Member

    Sep 21, 2010
    Not too far from Philly
    Real Name:
    you should be able to figure it out...
    But it works, right - your shots are in focus when the lined up images tell you they are?
     
  5. Ray Sachs

    Ray Sachs SC Legend Subscribing Member

    Sep 21, 2010
    Not too far from Philly
    Real Name:
    you should be able to figure it out...
    I guess this makes sense. As long as the assumption is that the lens and camera start out at some 'zero' point, whether 5 feet or 10 feet or whatever, and the rotation of the barrel (or at least the cam) is consistent in terms of focal distance from lens to lens...

    It would seem it would be awfully easy to get something out of alignment and not know it until you review a batch of photos, but I guess they're smart enough to take that into account. And I assume for critical focus, you can still check it on the LCD in real time...

    -Ray
     
  6. Streetshooter

    Streetshooter Administrator Emeritus S.C. Charter Member

    Jul 12, 2010
    Philly, Pa
    Well, M cameras used to be very hard to damage.
    Even after a drop, the RF would stay aligned.
    With my film M's... It never mattered which Leica lens I used, it was perfect.
    Now I hear that some lenses need an adjustment for the cam...
    Dunno.
     
  7. deirdre

    deirdre SC Top Veteran

    652
    Sep 26, 2010
    I have an old 135mm Hektor. Its cam is out of adjustment, so I learned something from that.

    I asked on a thread over on l-camera-forum asking about my inability to get an in-focus shot with the rangefinder images, but it scale focuses just fine.

    First test was to try infinity. That focused just fine. Great, even. I'm actually still stunned at how good that is. (Especially for a $100 Leica lens!)

    Anyhow, they offered advice on getting it back into alignment, which I need to do this weekend before my trip.
     
  8. TraamisVOS

    TraamisVOS SC Hall of Famer

    Nov 29, 2010
    Melboune, Australia
    I guess it works... but I'm not entirely sure sometimes because some of my shots aren't always spot on with the focus. I don't know if it's me, or if there is some kind of a back focus issue or whether as Don said it's a cam thing.

    Speaking of infinity, I know that when I turn the focus wheel all the way to infinity, it's not exactly at infinity. When I'm trying to focus on a building far away in the distance, I always have to turn the focus all the way to 'infinity' but it's not in focus until I pull the wheel back just a smidgen. Is that normal or does 'infinity' mean 'infinity' when the focus wheel is turned as far as it can go?
     
  9. Streetshooter

    Streetshooter Administrator Emeritus S.C. Charter Member

    Jul 12, 2010
    Philly, Pa
    James, that is not normal although, it is a common problem on M's after the M7.
    It's an easy adjustment.
     
  10. TraamisVOS

    TraamisVOS SC Hall of Famer

    Nov 29, 2010
    Melboune, Australia
    Which part is not normal? The infinity thing? So it's supposed to be spot on with infinity after turning the wheel hard to infinity?
     
  11. Streetshooter

    Streetshooter Administrator Emeritus S.C. Charter Member

    Jul 12, 2010
    Philly, Pa
    Infinity is infinity. A Leica is a very precise camera.
    Once adjusted, it's just that way.
     
  12. TraamisVOS

    TraamisVOS SC Hall of Famer

    Nov 29, 2010
    Melboune, Australia
    eek!

    Is that what people have been talking about when they say they have back focusing problems?
     
  13. Streetshooter

    Streetshooter Administrator Emeritus S.C. Charter Member

    Jul 12, 2010
    Philly, Pa
    Pretty much so. Like anything mechanical, adjustments are sometimes needed.
    My Black Laq M4 was in for adjustments back in 1978.
    Not since and still perfect in every respect.
     
  14. Streetshooter

    Streetshooter Administrator Emeritus S.C. Charter Member

    Jul 12, 2010
    Philly, Pa
  15. Archiver

    Archiver SC Top Veteran S.C. Charter Member

    610
    Jul 11, 2010
    Melbourne, Australia
    Early this year I was at the local camera repair centre (Camera Clinic in Collingwood, Melbourne), and they told me they were getting quite a few people coming in with M9's and their lens collections. These were people who shot with film Leicas for years, and when they got the M9, they found that what they thought were perfectly focusing lenses were not quite that. It appears that film had more 'slippage' in the old days, as there was no pixel peeping, and that sensor resolution is very high now.

    With the purchase of M9s, some found their old lenses to be less precise than they thought, hence the desire to have all their lenses focus-matched to their M9's. I have been fortunate as all of my lenses have been good. Mind you, they are all modern lenses made in the last four or five years, most in the last three.
     
  16. Brian

    Brian SC Top Veteran S.C. Charter Member

    638
    Jul 7, 2010
    The Leica RF is calibrated for a 51.6mm focal length. The Cam of a 51.6mm lens moves 1:1 with the optics of the lens as you focus. With different focal lengths, cams are used to translate the motion of the optics moving in the helical as you focus to the RF cam, which drives the rangefinder of the camera.

    The position of the optics with respect to the RF cam and the image plane is critical to this system working. A difference of 0.02mm makes a noticeable difference with an F1.5 5cm lens. Problems arise as film does not sit perfectly flat in the camera, and manufacturers make assumptions on film curvature in THEIR camera line. To make things worse, digital cameras have flat sensors with IR absorbing glass in front of them. That IR glass enters into the optical path.

    I throw a layer of copper tape on the Cam of the lens for a quick-fix.
     
  17. deirdre

    deirdre SC Top Veteran

    652
    Sep 26, 2010
    Brian, when you say copper tape -- you mean like the 3M brand roll of stuff?
     
  18. Brian

    Brian SC Top Veteran S.C. Charter Member

    638
    Jul 7, 2010