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#1 |
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Join Date: Feb 2003
Posts: 11
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Hi everyone!
I work for a retailer of cameras, and I've been selling digital cameras now since thier inception. I like to consider myself fairly knowledgable about them, and I like keep up on the technology as a matter of professional pride. Now, every once in a while I get a customer who, in the process of researching his first digicam purchase, digs up some obsure tidbit of information that I've never heard before. Usually a quick bit of internet research is all it takes to find the answer, but I've had no luck so far; so here I am! This customer started going on about pixel size, telling me that bigger was better. I'd never heard this before, and I can't for the life of me figure how it could possibly matter. Little help? ![]() |
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#2 |
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Join Date: Jun 2002
Location: Hay River Township, WI
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It very well can make a difference. A larger pixel size means it can gather more light - hopefully with the same noise level as a smaller pixel. That would mean a higher signal/noise ratio and thus a higher useable ISO.
In addition, pixels act somewhat like a detector at the bottom of a pipe so light that is not in line with the "pipe" doesn't reach the detector. That can cause vignetting which might be less pronounced with larger pixels. Of course if you are comparing cameras with different pixel sizes, there are going to be other differences as well that could negate those effects. |
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#3 |
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Hi Chris,
I believe the customer is referring to number of pixels rather than the size of a pixel. Anymore, consumers are misguided to think a higher pixel count means better quality images. Most users of digital camersa just want 4x6 prints with a "feeling" they can get 8x10 if they want and they rather not use software to edit their pictures so a good 2mp - 3mp digital will do just fine. The storage media needed for 4, 5 and 6 mp digitals can get rather expensive. Rodney |
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#4 | |||
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#5 | |
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My research thus far is leading me to conclude that this was an example of a person who knew just enough about the subject to be dangerous. It's a phenomonon that I've commonly encountered throughout my experience in various technical sales fields ![]() |
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#6 | |||||
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ISO in digital cameras is a bit murky (at least to me), but less noise means a higher ISO. I think of it as a finer grain film being able to be "pushed" futher to get higher ISO. Certainly ISO and noise are tightly related in digicams. Quote:
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1) There aren't really very many different sensors out there. They don't really want to advertise that (e.g.) the guts of a Canon are the same as a Casio. 2) To talk about those issues highlights the problems with digital cameras - never mind that there are exactly analogous problems with chemical cameras. Nothing is sold by talking about the problems with the product. Not much is sold by pointing at problems in your compeditor's products either. 3) The gain in signal/noise and vignetting reduction is fairly small in consumer-level cameras because there isn't much difference in sensor size. To see a big change in sensor size, there is a big change in price. |
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#7 | |||||
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As an aside, something else that occured to me when I was considering the possible advantages of large vs. small sensors was their respective heat (and therefore noise) generation. I know from circuitry that larger chips require higher voltages and thus generate more heat. This is the primary reason behind most (computer) chip manufacturers steady drive to reduce thier core sizes. Would you consider this much of a factor in CCD design? |
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#8 |
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Join Date: Jun 2002
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The customer is right, but really not using the correct terminology. A pixel is the unit of display produced from the output of the photo diode (photosite) on the sensor.
Professional level cameras have larger sensors with larger and deeper photo diodes. With electronic noise being somewhat consistent at a given temperature, signal is relative. The larger and deeper "wells" of the pro-level photodiode collect more signal than their smaller counterparts on consumer cameras. Thus the signal to noise ratio is favorable on the pro cameras. In practical terms what this means is more information detail and less noise in the image. There are only a few manufacturers of consumer level sensors. The vast majority excepting Fuji are made by Sony and purchased by other manufacturers. For example, all 5 megapixel sensors in consumer cameras are made by Sony. Yes, the Minolta, Olympus, Sony, etc., all have identical sensors. The differences in their respective performance comes from differences in their electronics, lenses and designs. Over the years Sony has used several small sensors, sometimes crowding more photosites on the same size sensor. This has contributed to adjacent sensor voltage "leakage" which causes the purple/blue fringe called "blooming" and commonly mis-identified as "chromatic aberration" which is usually red/green and caused by lens design. The actual photo diode size is relatively greater on the lower resolution cameras. Perhaps this is one reason why the Olympus C2100UZ has such an outstanding image for a 2 megapixel camera with an incredible 10x optical zoom lens. It represents the zenith of 2 megapixel iterative design. The same size sensor was used in subsequent 3 and even 4 megapixel cameras - crowding more and more photodiodes onto a relatively small space. Professional cameras and removable lens dSLR models like the Canon D30/D60 - Nikon D100, Fuji FinePix Pro S1/S2, etc., use much larger sensors and larger photodiodes which allow much lower noise. Lower noise at low amplification (low ISO) allows using higher amplification of signal (high ISO) while keeping noise to a low enough level to permit useful images. Consumer cameras start with much more noise and the more the signal is amplified, the more the noise becomes an issue. So "pixel size" (in the customer's terms) or more properly photoreceptor size, does play a major role in the quality of the image. But because the consumer cameras excepting Fuji all share primarily Sony sensors, there is little relevant difference in photoreceptor (photodiode) size at a given pixel count. Lin |
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#9 | |
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It also explains ISO in digital camera terms. Let me see if I have this right: The photoreceptor's properties (as I suspected) do not change, the ability to increase ISO is really the ability to increase the amount of signal amplification, which is limited by the signal-to-noise ratio of the photosensor; a higher noise photosensor allows for less amplification than a lower noise photosensor. By Jove, I think I have it. ![]() Thanks again. |
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#10 |
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Join Date: Dec 2002
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Crispy & others,
Actually, the topic of what ISO is has been talked about recently. Here is the thread: http://www.stevesforums.com/phpBB2/viewtopic.php?t=7078 And thanks to everyone in thread for helping me to understand more about CCDs and photoreceptors. I seem to remember a press release about an interesting idea in CCD design. The company was suggesting that there were better layouts/patterns for the photoreceptors. Specifically, they tried modling the eyes of some animals and found that they got less noise and better overall pictures. Did anyone see this? Is this just the usual marketing spin/garbage or is there something to that? Eric |
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