New Canon 5D

[Wade]

OK, here is kind of what happened in the Canon progression. The 10D has a 6.2 Megapixel sensor. When they were developing the 20D, they kept the exact same sized sensor from the 10D, but managed to pack more pixels into it increasing the density of the pixels. So, in the 20D and consequently the Rebel XT and 30D, they have the same sensor size, but higher number of megapixels.(8.2). For the 5D, they increased the area of the sensor up to the same size as a full frame of 35mm film. But, they lowered the density of pixels packed into it back down. That’s why the extra size of the sensor didn’t keep pace with what it would have been by growing from the 20D/Rebel XT/30D sensor and keeping that density of pixels packed in.

[Bevan]

Originally Posted by Bevan

I guess that is what I was thinking larger Pixels like large Grain Film
If the sensor Pixel spacing and size remained the same as the area
of the sensor increased you would have to have a 40 or 50 mp sensor
to match the quality of the 30d right.

I found a place that explains it tech

5d is good for lower light levels
30d is good for high light levels
both are sharp in there proper shooting enviroment
but the nikon d200 is better as compromize for me LOL

http://www.pbase.com/lou_giroud/camra

this is very teckie but explained a lot.

[CatCynic]

Originally Posted by Bevan

I guess that is what I was thinking larger Pixels like large Grain Film
If the sensor Pixel spacing and size remained the same as the area
of the sensor increased you would have to have a 40 or 50 mp sensor
to match the quality of the 30d right.

No. It's not like large grain film, not at all. Pixel pitch influences how noisy the image will be. A tiny point-and-shoot with an 8Mpixel sensor the size of a fingernail will capture images with lots of noise because the pixels are tiny and so get very little light each - the sensor has a high pixel pitch, but this doesn't equate to fine grain film. For digital we want bigger pixels for lower noise. The 30D has an 8Mpixel sensor, but it is much larger than the point-and-shoot, and therefore has a lower pixel pitch - that's one of the reasons why the 30D produces images with less noise than the point-and-shoot.
The photosites on the 5D sensor are larger again than on the 30D. This means that each one gets more light. They can be more accurate at reading the level of that light, so the image that they produce is less noisy - you get the effect of LESS grain, not more (digital "grain" is more about noise).
The difference in size between the 30D sensor and the 5D sensor isn't as much as you think - full-frame is 36x24mm=864mm**2, APS-C (like the 30D) is 22x15mm=330mm**2. The ratio is 2.6, so a full-frame sensor with the same pixel pitch as the 30D would have 21.5 Mpixel, not 40 or 50.
The important question, however, is NOT the pixel pitch of the sensor. It's the detail in the finished image. For this the absolute number of pixels is important - the sensor size is irrelevant. If you make a 20x30" print from a 30D, and I make a 20x30" print from a 5D, you have 8.2Mpixel contributing to the print, and I have 12.7Mpixel contributing to the print; more pixels = more detail (everything else being equal, of course). Add in that the 5D has an inherent advantage as far as noise level goes, and I'd expect the 5D to produce a better image, but it might not be too easy to tell .
In essence, the 5D is better than the 30D. It has inherent advantages from having a bigger sensor, and it has numerous other advantages from its more sophisticated technology.
We could consider the Nikon D200, which has a 10.2Mp sensor that isn't much bigger than the 30D's 8.2Mp, but they are different technologies - the Nikon is CCD, while the Canons are CMOS - so there are numerous other factors that intrude.