Focusing scale on Nikon Manual Lenses

Discussion in 'Nikon' started by hjoseph7, May 9, 2011.

  1. I was testing the focusing scale on various MF lenses and was surprised by the variation. As a matter of fact I came to the conclusion that the focusing scale on these lenses are totally worthless just like on the AF lenses.

    What I did was to try to focus on the small Logo on my TV set right under the screen from m y living room couch which I assumed was about 8 feet away. With a 105mm lens I achieved perfect focus at a bout 7 feet, close enough. With the 85mm I achieved perfect focus at about 6.5 feet. With the 55mm 4.5 feet, 35mm 2.75 feet(1.08 meters) and with the 20mm 1.5 feet.

    Can anybody explain all these variations ? Am I missing something here, I thought the focusing scale was a g iven, but apparently there is more to it than just lining up the scale to the middle pointer.
  2. To start with, 1.08 meters = 3.54 feet, not 2.75 feet.
    Where are you measuring from?
    The lens scale is distance from the film plane, which is indicated by a circle with a line through it on top of the camera.
    Short focal length lenses have greater depth of field which makes manual focusing less accurate.
    - Leigh
  3. Leigh has it, I suspect. I have lots of old manual focus Nikkor lenses and the scales are quite accurate when measured from the focal plane and if set to the measured distance will always be in focus (rather than focusing and then trying to measure the distance, which is asking for DOF variation, much less over-rating the untrained human eye).
  4. With a 105mm lens I achieved perfect focus at about 7 feet.
    and with the 20mm 1.5 feet.
  5. There's something wrong with your camera, or your eyesight.
    I'm not sure what constitutes "perfect" focus with a 20mm lens.
    How large is the subject feature you're supposedly focusing on in the viewfinder?
    I've been shooting Nikons for over 50 years and never had a focus problem with any of them.
    = Leigh
  6. Harry,
    What aperture , on which camera are you testing ?
    At what size are you examining the results ?
    If you set your 20mm to 7ft does it still have "Perfect Focus" ?

    Looking at your result : the wider the lens , the larger the DOF, so if you ljudge at the "Nearest "setting on your lens that stuff seems to be in focus, this all makes perfect sense....

    Mostly with a 20mm and aperture smaller than f4. almost everything from around 2.5 ft on will seem in focus, "Perfect Focus" is something different for which you will need to start "Pixel Peeping" ...
  7. I have done the same test as you have on a few lenses.
    I found the best way to test is to actually shoot a resolution chart and the distance where you have the highest resolution is the point of focus. This takes the viewfinder out of the equation.
    It's also difficult to judge a visual resolution chart so I used a slanted edge chart and software to determine resolution.
    What I found out is that the camera's register distance (sensor to f-mount) have a big impact on the accuracy of the focusing scale. The only time you will really notice this is when you focus by distance.
    On motion picture film cameras and pro video cameras they can adjust this distance (called back focus adjustment) . If it's not correct the lens' focusing scale will never line up with the right distance.
    So what I'm saying is that if your lenses distance scales don't line up it may be the register distance on you camera that is off. On Nikon it should be 46.50 mm +/- 0.02mm (less variation on some cameras). Wide angle lenses and large aperture lenses will be the ones that differ the most.
  8. Pete I'm using a Nikon FE2, there is no such thing as "register distance" on this camera and if there were, the camera has been CLA'd about a month ago. This is pretty elementery stuff, the distance scale is on the lens, it has nothing to do with the camera. I am focusing on a single spot the TV set, once the TV set is focused, then the lens should give me the exact distance from the TV set to my NON-DIGITAL camera. I tested 5 different MANUAL FOCUS lenses and they all give me different results. I could understand 1 foot or even 2 feet, but 5+ feet difference ?

    [This is what the NYIP says about Methods of Focusing(circa 1980's): ... One way to focus your lens is to measure the distance to your subject and then set your lens for this distance. As you well know, this is not the typical approach, but it is a starting point for your understanding the focusing systems. It may surprise you to learn that one of America's most famous studios, Bachrach, use this very technique. They shoot all their basic portraits using a string attached to the camera. Knots on the string mark off each foot.

    By stretching the string to the face of the subject, they know exactly how far the camera is from the face. ... Focusing Scale: One way they know the distance on which their camera is focused is by looking at the distance scale on the lens. You'll probably find such a scale on the lens of your camera. It is a series of numbers marking the distance in feet or meters.
    Let's say you want to focus on a point that you know is 10 feet away. You rotate the barrel of the lens until the number 10 on the distance scale lines up with the center marker, as in the picture on this page. Relaize that by turning the barrel to line up the number 10 with the marker you were also moving the lens in or out. At the point when 10 on the scale lines up with the center marker, you have produced the sharpest possible image of any object 10 feet from the lens. Obviously, if your subject is four feet away, you rotate the barel until the number 4 lines up with the center marker. if the object is 15 feet away, you line up the number 15 with the marker, and so on. ]
  9. Again, are you measuring distance from the film plane?
  10. Peter the film plane is 2-3 inches from the front of the lens not 5 feet.
  11. I sent the question to Nikon Customer service, they should get back to me in about a day. My guess is that the scale is not an actual distance scale, but a DOF scale which takes into account the focal length of the lens. For determining the hyperfocal distance this is great, but for determining Macro Focusing distances, or the flash exposure based on the GN this does not help any.
  12. This is pretty elementery stuff, the distance scale is on the lens, it has nothing to do with the camera.​
    Harry, it can't be too elementary since you got it wrong :)
    Focusing by distance is how motion picture films are shot. But they have better lenses with better distance markings.
  13. there is no such thing as "register distance" on this camera and if there were, the camera has been CLA'd about a month ago.​
    The more you post, the more obvious it is that you have no idea what you're talking about.
    The flange focal distance of 46.50mm that Pete mentioned is correct.
    It's the basic specification for all Nikon F-mount bodies and lenses since they were invented.
    It should be measured when the camera is sent in for a CLA, but it may not have been. It takes special equipment that some shops don't have.
    - Leigh
  14. Leigh thank you I called Nikon Customer service because they are professionals and they don't automatically assume you dont know what you are talking about, or do they raise your blood pressure with silly nonsensical and provocative comments that have nothing to do with the original question. Learn how to read and spare me the mumbo jumbo.
  15. Register distance being off between the lens and the film would normally involve some sort of visible damage to the body, warping of the mount ring or problem with the film back. But what you're seeing is problems with focusing in the viewfinder, so - have you shot film recently and does it come out in focus? My thinking is that you might have a problem in the focusing screen, mirror or finder prism...
    Do you have another camera body you can try the lenses on to narrow down whether it's a lens problem or a body problem?
  16. they don't automatically assume you dont know what you are talking about​
    I never assumed that you didn't know what you were talking about, I allowed you to demonstrate that fact.
    When you make comments like "There's no such thing as register distance on this camera...", it demonstrates a fundamental lack of understanding of the subject under discussion.
    Andy's suggestion regarding the focusing screen is a good point to pursue. The focusing screen may have been replaced with an incorrect part. Also, the mirror mount may have sustained damage, which can throw off the image on the focus screen but will not affect the image on film.
    Have you tried the lenses on a different camera body?
    - Leigh
  17. Please all, just accept the fact that the focusing scale/markings on Nikon/Canon/Olympus/etc lenses--of any vintage-- are not accurate, period. If one of the distance markings actually agrees with the focused distance, it is an[almost] random coincidence.
    If you really want to accurately scale focus, you need to calibrate each lens and scratch your own markings on the barrel.
    In the past, I've found that Leica M and R lenses had the most nearly accurate focusing marks.
    The cinema lenses mentioned above are accurate because they equipped with high-precision 300ยบ-rotating focusing mounts, and are individually calibrated and marked by the manufacturer, and checked regularly by the owners/users. But no one here is willing to pay $13,000 for a 28mm f/2 lens with no AF or auto diaphragm, are they?
  18. You'll forgive me if I don't choose to accept a false statement as "fact".
    - Leigh
  19. Nikon just got back to me. There is nothing wrong with the camera, or lens. According to Nikon, wide angle lenses have a larger DOF and take into account the viewing angle so there is more room for an 'acceptable range of focus'. Therefore, trying to use Zone focusing(pre setting the lens to a given distance) will not work very well with wide angle lenses.
    Standard focal length lenses are a little better, but still unreliable. According to Nikon, Zone focusing can be used with short telephoto, or telephoto lenses because the DOF as well as the angle is very shallow on those lenses.
    According to Nikon, at very close focusing distances the distance scale on wide angle lenses can be pretty reliable, this I tested.

    After taking the NYIP course years ago, I always assumed that the Distance scale worked the same for all focal length lenses, even though I never used it much. It was only recently that I decided to test that theory out.
    I'm still confused as to why Nikon would mark the lens with numbers that are practically irrelevant for every day use, there must be a reason.
  20. Thanks keith, you answered my question.
  21. Harry wrote:"I'm still confused as to why Nikon would mark the lens with numbers that are practically irrelevant for every day use, there must be a reason."
    Well they sure aren't irrelevant on mine, just tested the following lenses at a 5 foot distance, all are in perfect focus reading 5 ft on my F3 with a split image screen: 24 2.8 AIS, 50 1.8 pre AI, 50 1.4 pre AI, 105 2.5 pre AI, 200 f4 AI micro nikkor. Now any distance over 5' on the 24 is a guess, as the next mark on the focus scale after 5' is the infinity symbol. An E series 75-150 was out about the width of the "5" on the focus scale at 5 feet, indicating a distance of 61" give or take.
  22. Bob I think you got a point there.

    At 5 feet with FE2 the numbers did not vary as much but there is still some varience. I'm using a type E2 Matte/Fresnel focusing screen with etched grid, not the split screen.

    here are the numbers with the FE2: with a 24mm f2.8 AI the marker pointed to 2.5 feet, with a 55mm 4 feet, 85mm 4.3 feet, 105mm 4.5 feet, 180mm could not go 5 feet because 6 feet is minimum; at 6 feet marker pointed to 6 feet
    But wait...

    Here are the numbers with my FM2 with split screen: 24mm 4.8 feet, 50mm 5 feet, 55mm 5 feet, 85mm 5 feet, 105mm 5 feet, 180mm could not go 5 feet because 6 feet is minimum; at 6 feet marker pointed to 6 feet
  23. ...why Nikon would mark the lens with numbers that are practically irrelevant for every day use, there must be a reason.​
    Setting flash exposures was one very good use: as in dividing the guide number by the distance, which I always read from the lens.
    The only time I have seen a problem such as you describe was on an FE that had gone down with me on an icy sidewalk; the mirror was loose in its mount. Easy to fix, it just snapped back in.
  24. Curt I just got off the phone with the camera repair shop, they also think it's a loose mirror, or it could be a loose focusing screen. I looked inside and the mirror looks a little out of place, but I'm afraid to touch it.
  25. Your FM2 results suggest that there is something out of adjustment in the viewing system of your FE2.
  26. Well I found out what is wrong, the focusing screen was installed backwards. I probably can fix it myself if I can find the little tweezer tool that with the screen.
  27. Very good.
    Any small pair of tweezers will work. You just need to grab the little tab.
    - Leigh
  28. Since the shop put it in the wrong way they probably didn't do a good job of the A in the CLA.
    So there might be shims on the focusing screen that they possibly forgot to put it.
    You can check your focus screen calibration visually by focusing at infinity on a 50mm f/1.4 or similar. The screen should show that the image is in focus.
    This is how Nikon calibrates it but they usually put in a split-screen when calibrating, have a calibrated 50 f/1.4 and use a collimator for infinity.
    Coarse adjustments are with shims and fine tuning with the mirror stop. When everything is correct it also means that the distance from the focusing screen to the lens mount is the same as the film plane to the lens mount.
  29. So "to answer the question" is to agree with the OP? Seems about standard around here.
  30. It was the focusing screen - aww yeah, who da man? :)
  31. Ohhh Boy, . . . Ohhhh Boy . . . . !?????? After 50 year of photography I have to learn that.

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