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Old Jun 12, 2003, 4:16 PM   #1
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Default ccd area

can anyone explain the how relationship between ccd area, and pixels, relate to quality.

eg, the canon s45 and the s50 both hav a 1/1.8 inch ccd.
one is 4megapixel,and the other is 5mp.
will the s45 have less noise, as it has larger ccd elements?
(these cameras are almost identical, apart from that.)

as the top end digital SLR's tend to use moderate pixel count (6 megapixels) but have larger ccd area to get the quality, so resulting image is a copable size 3000x2000, but has less noise.
(i know some use cmos sensors, that's going to be another topic)

I guess the dSLRs can rely on the user having appropriate lenses, to acheive the desired level of zoom, whereby the consumer/compact cameras, don't have detachable lenses, so make up for this, with extra megapixels, which can aid zooming/post production.

I'm thinking that the s50's 5MP ccd is still not particularly noisy, plus any extra ccd noise would be overshadowed by other noise in the system, lens, jpegging etc.

any views?
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Old Jun 12, 2003, 6:45 PM   #2
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I used to have an Olympus E-10, with a 2/3" ccd, and now use a D100 with a nearly APS sized sensor (about 2.5x larger sensor area than 2/3"). From my experience this larger sensor is is more sensitive to blue than was the 2/3", allows for much higher ISO equivalencies (up to 6400 ISO, very little noise up until ISO 1250), and the larger sensor area produces shallower depth of field (great for portraits and other creative work).
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Old Jun 12, 2003, 11:21 PM   #3
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First a little technical detail, which will help understand how CCDs work. I've learned this by reading forum posts around the web. If I have it wrong, I'm sure someone will correct me (as they should!)

The sensor is covered with photosites. One photosite for each color Red, Green & Blue. A triplet of photosite is combined to make the data for 1 pixel - RGB. What matters is how deep the photosites are, how large they are, how many there are and how closely they are packed together.

The deeper the photosite, the closer to perpendicular the light needs to be. Film still works correctly even when the light hits the film at a very shallow angle. Digital sensors require that the light hit the sensor at an angle closer to 90 degrees than for film. If the physical CCD is small, then the angle will always be close to 90 degrees, but if the CCD is large, then the steeper the angle the light is when it hits the sensor on the edges. To get around this, special micro lens is placed over the sensor to bend the light back closer to perpendicular. For example, the Canon 1Ds has to have extra microlenses to improve the light angle... raising the cost of the sensor.

How large around a photosite is effected how much light will hit it. This (partially) effects how sensitive the sensor is to light. I don't know what is a good size. But the designers of the CMOS/CCD sensors have to choose how large they are and how densely packed they are. Too close together leads to (I assume) interference between each photosites and therefor more noise. But too far apart causes light to be lost when it hits the sensor where there isn't a photosite. Therefor you really do want to pack the sensors as close together as possible without them being so close the noise is bad. This is where the Fovion chip has an advantage because the sensors for the different wavelengths of light are physically stacked over each other. This allows for the same location of the sensor sampling each wavelength of light… much better than having three closely packed sensors each sample one wavelength.

Some say that the Canon 10D has photosites that are packed very closer, but it still produces very little noise. A very nice trick indeed. A side effect is that it causes the defects in lower quality lenses to shows up more.

Now to how this effects the "relationship between ccd area, and pixels, relate to quality. " Lets look at your example:

S50 = 2560 x 1920 = 5MP (roughly) @ 1" by 1.8"
S45 = 2272 x 1704 = 4PM (roughly)@ 1" by 1.8"

You can't know which camera will produce less noise based only on that information alone. Assuming the photosites are the same size, then the S50's will be packed closer together. That might mean more noise (assuming everything else is equal.) But they could also have improved the CCD in other ways to reduce noise. Or they could have reduced the size of the photosites, and had the same amount of space between each of them. You can't know.
Quote:
Originally Posted by iodine
as the top end digital SLR's tend to use moderate pixel count (6 megapixels) but have larger ccd area to get the quality, so resulting image is a copable size 3000x2000, but has less noise.
I believe this is a true statement. In general the sensor size on DSLRs is larger than on consumer/prosumer grade cameras. This gives them more space to play tricks to reduce noise (but too much spacing between photosites reduces quality, so it's more than that.)

I'm not sure I understand this sentence:
Quote:
Originally Posted by iodine
I guess the dSLRs can rely on the user having appropriate lenses, to achieve the desired level of zoom, whereby the consumer/compact cameras, don't have detachable lenses, so make up for this, with extra megapixels, which can aid zooming/post production.
The first part is true. The DSLR owner picks the mm lens they want to satisfy their needs. But I don't get the consumer camera comment at the end. They trade flexibility for cost. The built in lens is (in most cases) cheap or cheaper than a stand-alone lens, and this translates into a cost savings. Also, they can mate the smaller sensor to a smaller lens that reduces materials and therefor reduces cost. My 10D is using lenses that are designed for a 35-mm sensor (film/1Ds) so part of the image that it thrown on to the sensor plain is wasted because there is no sensor there. In a fixed lens camera, the lens is made to match the smaller sensor.
Quote:
Originally Posted by iodine
I'm thinking that the s50's 5MP ccd is still not particularly noisy, plus any extra ccd noise would be overshadowed by other noise in the system, lens, jpegging etc.
Canon probably made improvements to the CCD to reduce noise beyond the size and density of the photosites. It's possible that the greater resolution in the same size sensor caused them to have to use a better quality lens (better coatings, better materials, fewer allowed defects) but if they did it is anyone’s guess.

Does this help make anything clearer, or did I just confuse you with too much detail?
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Old Jun 13, 2003, 12:10 AM   #4
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excellent, I've been looking around the web for hours, and people seem to gloss over this detail.

What i meant, by
Quote:
"whereby the consumer/compact cameras, don't have detachable lenses, so make up for this, with extra megapixels, which can aid zooming/post production."
was that, in the consumer market, there's a bit of a race for extra megapixels,
this mainly gives users scope for zooming into the image in post production (or live, if your camera can do that)

in the dSLR market, they are happier to go towards higher quality ccd/cmos sensors rather than chase after megapixels, eg the 1D is just 4Mp.
As these users can attach their prefered lens, they can get all the zooming they want(mostly), by optical means.

i think the 5ish megapixel mark is going to prove a bit of a plateau, for consumer cameras (for a while)
It seems that that gives reasonable scope for printing, and consumer monitors can't even display those resolutions anyway. (probably why there was a plateau at 3.1Mp for a while too.)
plus it just costs more to store.
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Old Jun 13, 2003, 8:24 AM   #5
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Longer glass costs more money, althought I bet the sensor is the #1 cost in a camera (and the lens #2, unless it's really cheap.) So ya... I'd agree that (assuming customers realize it) more MP allow you to get the effect of a zoom without it having to be built into the camera (and therefor cost more $$.)

The 1D is a bit old, though. I view it as a trade off of pics per second vs. megapixels. The main reasons to use the 1D over the D60/10D/D100 level camers are: better build quality, much better AF system, more pics per second. I've heard it argued that the 10D has a good a sensor noise wise, don't know myself. And the reason to use it over the 1Ds is: its cheaper, the smaller images are easy to manipulate, cheaper, faster pics per second, probably others.

If you haven't guessed, I've worked on a consumer electronic product or two. It's really frustrating (as an engineer) how many good ideas are scuttled for cost reasons. Even what I think of as just a little cost (a few dollars.)
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Old Jun 13, 2003, 10:45 AM   #6
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so the drive for megapixels in the mass market consumer sector, should help to drive down cost in the low volume pro market.

bound to get faster too,
1-2 fps, seems quite doable now, at 5Megapixels, (until the memory buffers run out)
but at some point it all stops being still images, and turns into video. i wonder if we lose something, when that happens.
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Old Jun 13, 2003, 2:35 PM   #7
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Yes, most certainly. The consumer market might not care as much as a Pro (and therefor the parts aren't as fancy/expensive) but the lessions learned from making all those consumer cameras will help them do a better job on the low volume Pro market.

Even the decent consumer cameras can do 3FPS at 5MP. Only a few pro 35-mm can do more than that with their fancier/better sensors. I only know of the Canon 1D (8 FPS)and the Nikon D1H (5 FPS.)
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