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Old Dec 1, 2006, 10:46 AM   #1
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In my physics course we just began studying optical modeling and my instructor made a comment about digital camera sensors that I'm not entirely convinced was correct and I wanted to hear what y'all had to say.

Basically he said that if you decrease the physical size of each pixel on the sensor but do not increase the light sensitivity that you would actually worsen the photo. He thinks that each pixel needs to return the same light intensity no matter how many pixels there are on the sensor.

Wouldn't the light supposedly being missed by the smaller pixels be picked up by the other pixels around them thereby preserving the exposure intensity of the entire sensor?
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Old Dec 1, 2006, 11:10 AM   #2
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The larger the photosites for each pixel, the larger their surface area, so that more light hits them. That means that they produce a stronger signal. As a result, your signal to noise ratio is much better using a sensor with larger photosites, requiring less amplification for equivalent ISO speed sensitivity.

Any sensor has a noise floor, where you need a given amount of light to generate a strong enough signal to get above it. So, the better the signal to noise ratio, the weaker your light can be and still allow you to get usable photos.

You've got noise generated by the sensor electronics, amplfiers, A/D converter, etc.. So, your signal from light in your photo needs to be stronger than the signal generated from other sources.

That's why most DSLR models have higher usable ISO speeds compared to most non-DSLR digital cameras. Their sensors are larger, and the photosites for each pixel have a larger surface area. So, they generate a stronger signal compared to noise from other sources.

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Old Dec 1, 2006, 1:15 PM   #3
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Another (side) issue is lens resolution vs. sensor resolution.
If you have a fixed-lens camera and lens can only resolve a certain number of lines per mm, then there is no point adding a sensor which can resolve less data than the sensor can. You're buying a sensor which is "too good" (unless it has other benefits like having more dynamic range.)

And you have the issue that Canon is starting to run into. The sensors that they are using (on the high end) are starting to out resolve all but their best lenses. They will either have to start selling even better (and more expensive) high-end lenses, or start improving their sensors in other ways.... because they won't resolve any more detail once they reach that wall.

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Old Dec 1, 2006, 6:44 PM   #4
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I suspect that theclass involved signal/noise ratio somewhere. If it didn't, it should have.

borntoworship09 wrote:
... Wouldn't the light supposedly being missed by the smaller pixels be picked up by the other pixels around them thereby preserving the exposure intensity of the entire sensor?
Yes, but at some point the signal from each small pixel would be swamped by noise. That can be "corrected" by downsizing the imagethus "averaging" adjacent pixels. If the number of pixels is cut in half, the signal/noise ratio should increase by a factor of the square root of 2.
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Old Dec 1, 2006, 10:42 PM   #5
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Surprisingly you don't suffer a lot of resolution loss with the smaller sensors. These are the test results from dpreview of an 8Mp DSLR and an 8Mp superzoom with a small sensor. The DSLR has all the advantages in dpreview's tests. They use a non-zoom prime lens and find the aperture with the highest resolution. With non-DSLR cameras they basically aim it and shoot, and a 12X zoom is generally lower resolution than a good prime.

There isn't a lot to choose in the resolutions they derived from what they could see on standard resolution charts.

Everything that has been said in the thread is true. You will get more noise with the small sensor, but evidently not so much you degrade the detail when you provide enough light to shoot at low ISO. If you apply noise reduction you will degrade the resolution to some degree if you don't just remove noise from flat areas. The larger sensor sites become far superior in both quality and resolution when the light is limited enough to require higher ISO settings.

Light overlap will not increase the quality. If adjacent sensors did pick up light that should have been picked up by specific sensors it would degrade the image. You get resolution because light from a specific point hits a specific array of sensors.

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