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Reciprocity failure in digital camers?
I like to take night shots. I've had some success at it with my film
SLRs, but there was always some voodoo involved; taking several shots on B, holding the shutter open for 2 seconds, 5 seconds, 10 seconds, etc. I just got a Kodak P880. I chose it mostly for the wide angle capability and the reasonable price. While on vacation in Montreal and Quebec City I got to experiment a bit with it. I have to say that the ability to view the night shots on the screen was a real blessing. It allowed me to fine-tune the exposure and be sure I got a decent shot. I have to say that sometimes (not all the time) it was almost too easy. In certain modes the auto-exposure will use shutter speeds up to 16 seconds. It got the exposure pretty close to "right" a fair percentage of the time. That notwithstanding, I'm curious about reciprocity with digital sensors, if only to know what is going on a bit better. Is there a point at which doubling the exposure time doesn't produce a "one stop" change, as with film? Or makes a color change? I also did a litle experimenting with the ISO settings but not in a systematic way, I'm afraid. Assuming no camera shake, and a stationary subject (buildings, etc.), would you use a lower ISO and longer exposure or the other way around? I'm wondering which results in less noise. Greg Guarino |
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Reciprocity failure in digital camers?
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Reciprocity failure in digital camers?
wrote:
That notwithstanding, I'm curious about reciprocity with digital sensors, if only to know what is going on a bit better. Is there a point at which doubling the exposure time doesn't produce a "one stop" change, as with film? Or makes a color change? Well, here are a couple examples: http://www.pbase.com/image/34152731 "This is a long (almost 9 minutes) exposure that I took last night using only the light from the moon." - Annika1980 (circa Sept 2004) Here's one I took under moonlight as well: http://www.photosig.com/go/photos/vi...KI2?id=1716559 I also did a litle experimenting with the ISO settings but not in a systematic way, I'm afraid. Assuming no camera shake, and a stationary subject (buildings, etc.), would you use a lower ISO and longer exposure or the other way around? I'm wondering which results in less noise. Lower ISO will generally mean less noise, but remember it also needs a wider aperture for the same exposure time, which will lose some DOF, and that a longer exposure will eat up more batteries. |
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Reciprocity failure in digital camers?
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Reciprocity failure in digital camers?
wrote in message ups.com... I also did a litle experimenting with the ISO settings but not in a systematic way, I'm afraid. Assuming no camera shake, and a stationary subject (buildings, etc.), would you use a lower ISO and longer exposure or the other way around? I'm wondering which results in less noise. Greg Guarino I have the Kodak P850 (for the zoom) and I have found that in certain shots, going over iso 200 produced a lot of noise, really an unreasonable amount. For example, we were at the fair with our daughter and she was on a ride, Trying to get the shot of her moving, boyfriend turned the iso up to 200 and the pictures are really pretty bad. Unusably bad because of the noise. That being said, I've taken pictures of other things at the higher iso and not gotten them so noisy, things that weren't moving as much. |
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Reciprocity failure in digital camers?
Greetings Greg,
Glad to hear about the shots of Montreal. Great city and the P880 could capture most all scenes. You do not have to worry about reciprocity in digital, variations are accounted for in the camera. Reciprocity is really more related to film and some paper. With Film, if you use long exposures the sensitivity of the film is reduced slightly which can cause a shift in color. With a digital camera that problem is removed and most cameras can handle exposures of several seconds or longer. What you should consider is that low light or higher ISO settings in digital camera can yield an increase in 'noise' the digital equivalent of grain. You may want to get a good filter for it, or in your case improve on some shots with flash. The P20 can talk to your camera and would be an advantage. Talk to you soon, Ron Baird Eastman Kodak Company wrote in message ups.com... I like to take night shots. I've had some success at it with my film SLRs, but there was always some voodoo involved; taking several shots on B, holding the shutter open for 2 seconds, 5 seconds, 10 seconds, etc. I just got a Kodak P880. I chose it mostly for the wide angle capability and the reasonable price. While on vacation in Montreal and Quebec City I got to experiment a bit with it. I have to say that the ability to view the night shots on the screen was a real blessing. It allowed me to fine-tune the exposure and be sure I got a decent shot. I have to say that sometimes (not all the time) it was almost too easy. In certain modes the auto-exposure will use shutter speeds up to 16 seconds. It got the exposure pretty close to "right" a fair percentage of the time. That notwithstanding, I'm curious about reciprocity with digital sensors, if only to know what is going on a bit better. Is there a point at which doubling the exposure time doesn't produce a "one stop" change, as with film? Or makes a color change? I also did a litle experimenting with the ISO settings but not in a systematic way, I'm afraid. Assuming no camera shake, and a stationary subject (buildings, etc.), would you use a lower ISO and longer exposure or the other way around? I'm wondering which results in less noise. Greg Guarino |
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Reciprocity failure in digital camers?
Ron Baird wrote:
... What you should consider is that low light or higher ISO settings in digital camera can yield an increase in 'noise' the digital equivalent of grain. You may want to get a good filter for it, or in your case improve on some shots with flash. The P20 can talk to your camera and would be an advantage. ... I'm not an expert on this, but I hypothesize that the explanation for Ron's comment is as follows: A digital sensor accumulates charge (i.e., electrons) in each pixel position as a response to light falling on the sensor in that position. The sensor also accumulates charge in each pixel simply as a result of the random motion of electrons (due to heat, radiation, and perhaps other factors other than stimulation by light.) We see digital "noise" when the ratio of random charge becomes a significant percentage of the total charge in a pixel, causing the value of that pixel to have a noticeable random component to it. The sensor accumulates random charge as a function of time. The sensor is discharged just before the image is made, and read after the image is made. In bright light, the time between pre-image discharge and post-image reading is short, allowing little random charge to accumulate. In dim light the time is long, allowing more random charge to accumulate. Hence the extra noise in low light situations. Dark areas of an image are most subject to this because the random charge in all areas of the image is the same, but the dark areas have a higher percentage of random to light stimulated charge accumulation. The "filtering" that Ron talks about is the digital process of averaging adjacent pixels with similar values in order to eliminate differences that are due to random factors. But no filter, no matter how smart, can truly distinguish differences due to random charge as distinct from differences due to different amounts of light. It uses heuristic algorithms to make intelligent guesses, which are often but not always right. Hence there is always some loss of detail when aggressive noise filtering is performed. Alan |
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