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  1. #1
    DanielStone's Avatar
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    Possibility of having Nikon AI/AI-S lenses re-engraved for T-stops?

    Hey all,
    Has anyone here, reading this post, had 35mm system lenses re-engraved(or a scale made) for T-Stops instead of(or in addition to) F-Stops?

    I'm asking because I shoot primarily chrome, and have found some discrepancies in resulting density of exposures in series of DOF tests, (say, 1/60@f8, then 1/30@f11, etc...).

    Now, while it isnt "impossible" by any means to work this way, and the discrepancy is hard to see unless really scrutinizing the film on the light box, but its noticeable to me

    I know that in the pro cinema industry, t-stops are STANDARD affair, but it seems us 'lowly' stills people get only f-stops!

    Guess this same question can also apply to MF and LF shutters/lenses as well. That way each lens is individually tested for transmissive value.

    -Dan

  2. #2
    Ricardo Miranda's Avatar
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    This may explain why you get discrepancies in exposure:
    The FA has a closed-loop exposure system. This means that while displaying the exposure any time the meter is on, the FA measures the actual exposure after the lens stops down to its taking aperture, just an instant before the actual exposure. This way the FA corrects for any errors in the lens' diaphragm mechanism, so I get exposures more consistent from lens to lens than on newer cameras. Some lenses have diaphragms which are calibrated so that they may over or under expose a little, but on an FA, they all expose perfectly.
    http://www.kenrockwell.com/nikon/fa.htm

    As you are using manual AI/-S lenses, there are tiny differences when the diaphragm closes. The FA is the only Nikon that corrects that difference with manual lenses. Others, like the F4 have a open-loop exposure system.
    My cameras:
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  3. #3

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    Quote Originally Posted by Ricardo Miranda View Post
    This may explain why you get discrepancies in exposure:


    http://www.kenrockwell.com/nikon/fa.htm

    As you are using manual AI/-S lenses, there are tiny differences when the diaphragm closes. The FA is the only Nikon that corrects that difference with manual lenses. Others, like the F4 have a open-loop exposure system.
    no wonder I hate the FA.

  4. #4
    ic-racer's Avatar
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    Most all Nikon cameras since the 1970s have built in meters. Perhaps their intention was that the users would actually use the camera's built in meter?

  5. #5

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    Quote Originally Posted by Ricardo Miranda View Post
    As you are using manual AI/-S lenses, there are tiny differences when the diaphragm closes. The FA is the only Nikon that corrects that difference with manual lenses. Others, like the F4 have a open-loop exposure system.
    I'm not going to comment on Mr. Rockwell as a source in general, but as a long time FA owner, I can tell you that the FA only applies "last look" corrections in S and P modes and not A nor M modes. So for DOF purposes, Mr. Rockwell's claim is a red herring. If you think about how Nikon's aperture lever works, you'll see this has to be the case. (From language in the manual, I think it only applies such corrections when it can't detect an AI-S or Series E lens, but I'm less sure of that.)

    You might be able to get a lens re-engraved with T-stops, but unless you also recalibrated the detents you'd still be shooting in f/stops. Since DOF is a subjective "acceptably sharp" criteria to begin with, I suggest you relax, don't worry, and save your money for outings, film, prints, etc.

  6. #6
    brucemuir's Avatar
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    How do you know it's not the shutter causing the discrepancy?

  7. #7

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    I have checked my Nikon AI/AIS lenses and found although the T stop is a bit different from the mark f/stop but by the same amount for all stops. The variation between clicks are much less, 1/5 of a stop at most. Depend which camera and condition the shutter speeds generally aren't as accurate as the apertures.
    I think the FA does the last look on P and S because the aperture stop down level on the AI lenses is not linear. However the aperture ring is accurate as I have stated above.

  8. #8

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    I would think the T-stop difference from the F-stop would be a consistent offset, not different for each stop. So if the offset was 1/2 stop, it would be 1/2 stop for all aperture settings. But the only way to really know this is to have a lab do the T-stop testing and calibration for you. $$$

    As was mentioned, I think the first suspect in your exposure difference would be the shutter.
    Since you are talking about spending $$$ on this endevor...
    First I would get all your camera shutters cleaned and adjusted to spec.
    Then get the specs of the measurement of the final adjustment and variation for each speed.
    Then you know how close it is to marked speed, for each speed.
    Example final adjustment could be average of 1/3 stop slower than 1/125 sec (within spec), but with up to a +/- 1/3 stop variation for say 20 shots.
    So, with the variation, the shutter could be 2/3 stop slow to dead on.

    I think re-engraving would be difficult.
    On the cheap, you could put a strip of white tape or label over the aperture ring and relabel it for the T-stops.
    I think that is what I did back in the 70s when I was using a hand meter.
    Today, with a computer, a color printer and some experimentation to work out the scale and spacing, a label would probably look pretty good.

    As for the detents, I would have a tech remove the device making the detent and just use the aperture ring smooth, w/o detents. The detents would be in the wrong place anyway in relation to the recalibrated T-stops.

  9. #9

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    I have a Bell and Howell Foton with a 50 mm T2.2 engraved in T stops.... Would trade for an M2 with 35cron....

  10. #10

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    I've tried de-clicking an AIS Nikkor. Removing the click-tab also removes any and all resistance on the aperture ring, so it's free to just turn on its own. In addition to feeling like garbage and occasionally making a fingernails-on-chalkboard noise, the aperture ring moves on its own when attached to the camera since the metering coupler on the camera is spring-loaded. I took some pictures of the lens parts below so you can see how de-clicking/re-clicking the aperture ring would work in theory. I don't know if all Nikkors are built like this, however.


    Nikon 50mm f/1.2 AIS by LJ Slater, on Flickr

    Nikon 50mm f/1.2 AIS by LJ Slater, on Flickr

    Regarding the exposure discrepancies, I too would be interested to know which camera was used? The F5/F6 are supposed to have shutter monitoring systems that makes corrections as needed. My guess would be that the manufacturing tolerances in Nikkors are not up to your standards, Mr. Stone :P

    There are lots of "T-stopped" cinema lenses for F-mount bodies, but they appear to be upwards of $3K each.

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