How to open 1/3 stop with ISO dial.

Discussion in 'Exposure Discussion' started by kbrede, Jun 25, 2012.

  1. kbrede

    kbrede Member

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    I've got a 1/3 stop filter compensation to work with. Not all my lenses have aperture stops of 1/3 and shutter speed is only full stops. So to make things easier, when using a handheld light meter, I thought I'd dial in the compensation with ISO on the camera.

    I've got 160 speed film. I leave the light meter at 160 ISO and set the ISO dial on the camera to 200 ISO. Is that right?
    Thanks,
     
  2. Christopher Walrath

    Christopher Walrath Member

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    What camera are you using. Would help to know.

    Keep it light.
    ChrisW
     
  3. E. von Hoegh

    E. von Hoegh Member

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    Wrong. To give 1/3 stop more exposure you need to set to 125 ISO.
     
  4. markbarendt

    markbarendt Subscriber

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    Filters reduce exposure.

    Moving the meter's/camera's, EI/ISO setting, from 160 to 200 also reduces camera exposure, in this case by 1/3 stop.

    To offset a 1/3 stop filter's reduction in exposure move from a setting of 160 to 125 to add that exposure back in.
     
  5. Terry Christian

    Terry Christian Subscriber

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    E. van Hoegh is correct. Your filter blocks 1/3 stop of light, so you need to trick your camera into thinking the camera has slower film in it so that it'll let in more light. Opening your aperture to a lower f-stop number, or lengthening your shutter speed, will have the same effect.
     
  6. Bill Burk

    Bill Burk Subscriber

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    When factoring in filters, I set the EI for the film & filter factor combination on the handheld meter, (as pointed out for 160 and 1/3 stop filter factor, 125 is the answer).

    I set that on the handheld meter as ISO B and use that.

    I would leave the camera at 160, for example an SLR with through-the-lens metering would attempt to compensate anyway.
     
  7. jeffreyg

    jeffreyg Subscriber

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    My understanding is that published filter factors are not always correct and can vary from mfg to mfg as well as with the color of the filter and the colors of the subject. It would be best to meter through the filter and without the filter to see the difference before making the adjustment if that degree of accuracy is important.

    http://www.jeffreyglasser.com/
     
  8. E. von Hoegh

    E. von Hoegh Member

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    Wait a minute. Are you metering with the camera's meter or the handheld meter?? Changing the ISO setting on the camera and then metering with the handheld set to 160 will compensate for nothing. If the camera has TTL metering, it will (as has been pointed out) automatically compensate for the filter factor
     
  9. E. von Hoegh

    E. von Hoegh Member

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    This will work only if the meter cell and the film have identical spectral response, which is not often the case.
     
  10. ic-racer

    ic-racer Member

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    You can't make a 1/3 stop exposure adjustment with that camera.
     
  11. E. von Hoegh

    E. von Hoegh Member

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    Why can't he?? Did you read anything other than what you quoted? About the ISO setting on the camera's meter, perhaps?
     
  12. Bill Burk

    Bill Burk Subscriber

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    True, but the correct EI setting (this example at 125 on the hand-held meter, 160 on a through-the-lens meter) combined with the existing light may lead to a recommended exposure that can be set on the camera.
     
  13. JBrunner

    JBrunner Moderator Staff Member Moderator

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    If it were me (and it isn't), I'd just overexpose the sucker a half stop or what have you. A neg you can call fatty is a friend.
     
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  15. kbrede

    kbrede Member

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    Some of the lenses I have do not have 1/3 stops on the aperture ring. Some of them have a mixture of 1/2 and full stop increments on the same ring. So I was just looking for an easy way to open 1/3 stop, no matter what lens I'm using. I'm not going to be using TTL.

    What I've been doing is metering at 160 (film speed) and then opening the aperture by 1/3 or 1/2, depending on the lens.
    My thought was to meter at 160 and then open 1/3 stop, via ISO dial.
    This should give me the same exposure as opening aperture, but be easier since I could just apply the meter reading, and not worry about the filter factor. The filter compensation would already be dialed in. That's my thought anyway.

    As Bill mentioned, setting "ISO B" to 125 might be the way to go.

    1/3 of a stop may not matter that much, but I have other filters with larger filter factors.
     
  16. BrianShaw

    BrianShaw Member

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    I was about to say something like this, but I was so completely wrong earlier this AM I'm almost afraid to speak!

    I never worry too much about 1/3 stop adjustments -- 1/2 at most.
     
  17. kbrede

    kbrede Member

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    I used 1/3 stop as an example, bad one I guess. :smile: I have other filters with larger filter factors that I want to apply what I learn here. Also some of my lenses only have full stops between clicks. With a camera that only has full stops for shutter and a lens with full stops on aperture, knowing how to change the ISO dial to compensate is something I'd like to learn.
     
  18. E. von Hoegh

    E. von Hoegh Member

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    If you are metering with a handheld meter, and setting tha camera with that reading, it will not matter what the ISO setting on the camera is, as you will not be using the meter in the camera. If you are using a handheld meter, set that meter at ISO 125 and use those readings. If you are using the meter in the camera, and it is a TTL meter, simply screw the filter on and continue using the 160 setting on the camera's ISO dial. Why are you using two meters and two settings?

    What camera are you using?
     
  19. Bill Burk

    Bill Burk Subscriber

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    Aha,

    Setting the ISO dial on the camera adjusts the camera's meter - which you are ignoring anyway when you use a handheld meter and manual camera settings.

    So changing the ISO dial but not using an "Auto" exposure mode, doesn't link camera meter to f/stop or shutter speed so it would have no effect.

    (same thing E. von Hoegh just said)
     
  20. E. von Hoegh

    E. von Hoegh Member

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    Yeah, and it's only the second time I said it.....:confused:
     
  21. kbrede

    kbrede Member

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    EDIT: OK I just read the two posts above. I understand now. The ISO dial doesn't really open via shutter or aperture, it just changes the in camera's meter reading. I didn't know that.

    This confuses me. If I use a handheld meter and apply the meter settings and then open the aperture 1/3 stop. How is that different from applying the handheld meter reading and opening 1/3 stop via the ISO dial?

    EDIT: And therefore it doesn't matter what the ISO dial is set at.

    But leave the ISO setting on the camera at 160, right?

    I am not using the camera's meter.

    I'm not using two meters. I'm not 100% sure what "two settings" you're referring to. I can program my meter for two ISO settings, 'A' and 'B.' So I could program 'A' with ISO 160 and 'B' with 125. This could be used to more easily meter. One setting for when filter is off, one for on. Maybe that's what you're referring to?

    I'm using a Zeiss Ikon ZI and a Pentax Super ME.
    Thanks,
     
    Last edited by a moderator: Jun 25, 2012
  22. artonpaper

    artonpaper Subscriber

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    Just to chime in, if you are using the in-camera meter there is no reason to adjust for the filter factor, at least in theory. When using an external meter tean lowering the ISO is called for. Each ISO designation is a 1/3 stop increment. Using a lower ISO will increase the exposure called for by 1/3 stop. The 1/3 stop convention was determined to be the least noticeable significant exposure change one can make. This was more important to those exposing chromes. If you have difficulty finding the third stop point on the aperture ring, or on those few older lenses with half stop clicks, the 1/2 stop point will do. The difference between 1/3 and 1/2 stop is negligible, especially when shooting negative film. Also my rule of thumb for shooting negative film is to err on the side of overexposure.
     
  23. markbarendt

    markbarendt Subscriber

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    The ISO setting on the camera is only for the camera's meter. If the camera is in manual then the ISO setting on the camera meter has no effect on exposure, period. Only when a camera is in an auto mode does it matter.

    In manual you set the ISO with your film choice, 160 here.

    The other controls you have to affect exposure are aperture, time, and filters.

    Your handheld meter will give you the aperture and time, set them then open up by whatever filter factor is in use.


     
  24. Thomas Bertilsson

    Thomas Bertilsson Subscriber

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    Film: ISO 400
    Filter: 2 stops compensation
    Set meter at: EI 100

    Film: ISO 160
    Filter: 1/3 stop compensation
    Set meter at: EI 125
    Filter: 2/3 stop compensation
    Set meter at: EI 100
    Filter: 1 stop compensation
    Set meter at: EI 80
     
  25. Bill Burk

    Bill Burk Subscriber

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    To clarify for OP... How the ISO dial links to camera behavior seems to be the point of confusion...

    The Pentax ME Super doesn't have an automatic aperture. The f/stop you click is the one you get.

    Some cameras override the aperture in program and shutter priority mode (OM-Program comes to mind). Pentax ME Super doesn't mess with your f/stop once you set it.

    The camera has an electronic shutter. When using Auto - Automatic mode, shutter speed varies automatically and the speed will change by 1/3 stop if you make 1/3 stop change to the ISO dial. (But don't do that for filters since it reads the light through the lens).

    When using M - Manual mode, you get the shutter speed displayed in viewfinder - the shutter does not change 1/3 stop when you change the ISO dial.

    Going to the original plan: Setting meter ISO "B" to 125 is a good idea. Leaving the camera at 160 is a good idea.
     
  26. kbrede

    kbrede Member

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    Thanks all for your help and sticking with it, until I got it. :smile: