Author Topic: strange lighting related story.  (Read 2982 times)
Roi_hartmann
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strange lighting related story. « on: September 07, 2010, 01:56:39 PM » Author: Roi_hartmann
Sometime ago, I remembered this story that one of my friend had heard from his teacher long time ago. that teacher was visiting in a factory that produced harvesters with his class. he had his film camera with him and took some pictures(I dont know exact year of this trip, but presumably it has happened in 80's or early 90's) later, when he developed the film, all the pictures that were took inside the factory hall were completely black. Ofcourse its possible that teacher just had done something wrong when photographing inside but I was just wondering is there some light sources that could distract normal film camera. My friend did not know what kind of camera(ecxept that it was film camera) teacher had, but I would guess it was that kind of camera that automaticly adjust right exposure time(sorry, dont know the right english term for that)If I remember right, teacher had told that lights inside the factory hall were orange. so that would indicate those were hps or lps lamps.
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Medved
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Re: strange lighting related story. « Reply #1 on: September 07, 2010, 02:29:19 PM » Author: Medved
If the camera used monocrystal silicone light sensor without filter (so most sensitive in IR) for light measurement, it could be fooled by the lack of IR (as it was likely calibrated for black body radiation, where the visible energy is by given formula proportional to IR) in the illumination, so it set too long exposure. But the film is sensitive only for visible (and UV), what was there in excess (compare the IR measured by the sensor), so severely overexposed the film.
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Roi_hartmann
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Re: strange lighting related story. « Reply #2 on: September 11, 2010, 08:41:41 AM » Author: Roi_hartmann
That is interesting. But I think that if the photos were completely black, wouldnt that mean too short exposure time. Ofcourse, clear answer could be difficult to get due to many unknow details of this case. I have not seen those pictures or even have had change to meet this teacher. thanks for answering thou.
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SeanB~1
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Re: strange lighting related story. « Reply #3 on: September 11, 2010, 08:59:32 AM » Author: SeanB~1
If it was a film camera it most likely had a focal plane shutter, and this, combined with the flourescent lighting in the factory, has the effect that portions of the film that are exposed when the light from the tubes was off ( near mains crossings) were underexposed.

See http://en.wikipedia.org/wiki/Focal-plane_shutter for more.

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Medved
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Re: strange lighting related story. « Reply #4 on: September 11, 2010, 09:40:26 AM » Author: Medved
@SeanB:
These move ~20ms or longer, shorter exposure times are made by forming only narrow gap rolling across the frame. So if the interference would be an issue, then it would made effects like this one

@Roi_hartmann:
In fact there are two points in the photo processing chain, that need exposure adjusting, what might be fooled: First is when the photo is taken to the negative and second is, when the negative is transferred onto the paper.
The second is usually automatically controlled in the processing machine, set to get equivalent brightness between all pictures in the batch, while compact color of totally black or totally white pictures might cause this second exposure control to act weird...

Or the problem with the sensor was all the way opposite: It was sensitive only for the yellow, so based on it's level it "think", then there is way more light then in reality  and severely underexposed the film.
And if it was BW film, there is another problem with the sensitivity curve of these films: They are most sensitive i the blue end of the spectrum (where HPS does emit only very little amount of light, LPS obviously no at all), while not as much in the red part. This might make the situation even worse: Sensor set the camera for the amount of yellow, while the film is not sensitive there.

And other cause might be the wrong timing alignment between shutter and the flash lamp (if flash was always used inside): The automatic set the exposure for the flash, but it flashed at the time, when shutter was closed. So the picture was taken effectively without the flash, but rather fast shutter, yielding again severe underexposure.
« Last Edit: September 11, 2010, 09:52:21 AM by Medved » Logged

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kai
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Re: strange lighting related story. « Reply #5 on: September 14, 2010, 07:29:26 PM » Author: kai
My friend did not know what kind of camera(ecxept that it was film camera) teacher had, but I would guess it was that kind of camera that automaticly adjust right exposure time(sorry, dont know the right english term for that)If I remember right, teacher had told that lights inside the factory hall were orange. so that would indicate those were hps or lps lamps.

I would also not rule out 3000 K standard halophosphate lamps, seen in a mixture with daylight. In such a setting they could be described as "orange", too.

And I can not imagine that the outcome as described, frames without any trace of an exposure, had anything to do with the lighting, since such an outcome needs more than just a modest misadjustment. I'm not aware of specific exposure problems from lights with different colour, also not of particular issues with using a camera with focal plane shutter under standard FL or HID lighting, simply because it is hardly bright enough for allowing exposure times shorter than 1/30 second, unless ultra-fast film stocks are being used.

I think a scenario of an automatic exposure control being so severely fooled by the discharge lamps (of whatever kind) is pretty unlikely.
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