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  1. #1

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    Reciprocity Failure

    A question about reciprocity failure. If you use an in-camera ttl light meter, does the camera give you the proper exposure regardless after 1 second? I don't entirely understand...

    Thanks -

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    DWThomas's Avatar
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    Quote Originally Posted by mporter012 View Post
    A question about reciprocity failure. If you use an in-camera ttl light meter, does the camera give you the proper exposure regardless after 1 second? I don't entirely understand...

    Thanks -
    No, reciprocity failure is a deviation from expected behavior of the emulsion, I can't see how the camera could deal with it. Unless perhaps it was a super smart camera that could have it's exposure system programmed to compensate for a particular film, as not all films behave the same way. Given the current status of film cameras in the market, that feature wouldn't seem likely to appear.

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    At a very basic level, the film loses sensitivity after it's maximum exposure has been reached, manifesting as poor contrast, colour shift/cast and other anomalies. You can see reciprocity failure in action if you use, for example, Provia 100F (slide film) for star trails. Set the camera up, trigger the shutter and lock it open for say 6 hours. This exposure time is way, way beyond the film's design intent for correct exposure over a given range. What happens over that long period of time is that the colour shifts to a strong magenta (with Velvia, it is a strong green) and gains contrast. Provia 100F, along with Velvia (used correctly) is a beautiful film with no casts whatsoever. It's what happens when you make very long exposures how the film's design breaks down. It's often exploited by traditional arts students in the street / documentary photography oeuvre.

    You can hedge against reciprocity failure by providing additional exposure, but at some stage RF will still creep in. There is no camera that corrects for reciprocity because it is a characteristic of film, not one that a camera has control over (but to some degree, the photographer does, for the same statement above, by providing additional exposure and corrections). RF is a journey of discovery and is well worth experimenting with when you have selected a film you like and which you will use quite often, getting to know how it behaves beyond it's limits is one of the more interesting investigations you can do.
    .::Gary Rowan Higgins

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    Eastman Kodak USED to include Reciprocity Failure charts in the leaflet that was packaged with every "Professional" film they sold. Sure took a lot of experimenting out of it. Who wants to experiment, re-inventing the wheel? I certainly do not. I do not know if EK still does this. Right now, EK is on a heart-lung machine. So I fear all this knowledge is forever lost.

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    Poisson Du Jour's Avatar
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    Two things. Reciprocity information is available in data sheets as pdf documents. Has been since Nelson lost an eye.
    You don't need to experiment if you expose film well within it's intended limits; outside those limits though you do need to understand what the film's individual response will be like and formulate a strategy for dealing with it as necessary.
    .::Gary Rowan Higgins

    A comfort zone is a wonderful place. But nothing ever grows there.
    —Anon.






  6. #6
    LJH
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    I'm with Gary on this one; you will need to experiment in order to know what to expect.

    Exposure is only part of the Reciprocity equation (B&W). A degree of processing compensation is often needed to compensate for the change in contrast.

    Like Gary wrote, colour shifts also can be expected with colour films in long exposures.

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    Nothing replaces doing it yourself but the Pinhole Assist app comes close. They have reciprocity failure charts included for a number of common emulsions and it will do the calculation for you based on light levels and your camera settings.

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    No, reciprocity failure is different from film to film, so a light meter cannot know how to adjust for that. Some films don't need any adjustment up to a minute or longer, and some need adjustment after just a second.

    Basically, you find the datasheet on the film you're using, and that will tell you what sort of correction it needs. If it requires 1 stop of correction, just keep your shutter open for twice as long, if it needs 2 stops, then it's 4 times as long, 3 stops, 8 times as long etc. You double the amount of exposure for each stop.

    Generally I find that you can be pretty lax though, if you're doing long exposures, it's likely at night, and overexposure matters less, i.e. a black sky is a black sky, but during the day a blue sky will turn white with overexposure.

    Trial and error is the order of the day really.

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    http://www.willwilson.com/articles/0...ciprocity2.pdf

    This gives really great information for several films. Look on the last page.
    "Often moments come looking for us". - Robert Frank

    "Make good art!" - Neil Gaiman

    "...the heart and mind are the true lens of the camera". - Yousuf Karsh

  10. #10

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    OK. So if my light meter reads f/8 at 2s, this will be inaccurate then and I need to use one of these charts? Dammit, there goes a ton of long exposures down the drain!

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