Re: |GG| Re: The Joy of Pixel Density

Roger N. Clark (change username to rnclark) wrote:
Paul Furman wrote:
John Sheehy wrote:
Paul Furman <paul-@xxxxxxxxxxxxx> wrote in
news:qw4gk.15728$uE5.3878@xxxxxxxxxxxxxxxxxxxx:
The way I understand, the over all well size *does* change for a given
area. As pixel size changes: the depth matches the width. Or are they
all the same depth of a silicon chip? Or is depth even the right
measurement?

There is not much variation in the total number of photons capturable per unit of area; most of the variation is in the rate they are caught. So, it seems that "depth" (whether literal or metaphorical) has a fixed maximum in current technology.

Could someone elaborate on this please? It seems critical to this question. Which 'catches faster'? I've never heard of that. Are there different depths or it's just widths?

Paul,
This is more obtuse language that is meaningless.

There is no "variation in the rate they are caught."

Devices have a Quantum Efficiency, which is the fractional number
of photons that are captured, generating electrons that create a
signal in the electronics. Quantum efficiencies in consumer cameras
are pretty close. What has historically changed over the years
is fill factor, mostly through the use of micro lenses,
read noise and fixed pattern noise.

From:
http://www.clarkvision.com/imagedetail/digital.sensor.performance.summary
"Fundamental factors set sensor performance of semiconductors
like CMOS and CCDs. These include the absorption length in silicon,
the efficiency of photon absorption (which is very high, typically
40-50% for modern digital cameras), and electron charge density
in the silicon. Blue wavelength photons have shorter absorption
lengths in silicon than red or green photons. Major factors in
limiting the maximum number electrons captured in a semiconductor
image sensor are the absorption length and electron densities. "

See Table 1B for absorption lengths. Note the absorption lengths
are 5 microns for red wavelengths of 6000 angstroms.

So an I understand from that, small pixels get muddled data from deeper penetrating photons as they cross under to adjacent pixels. Presumably by the time that happens, the highlights are well blown out anyways.

--
Paul Furman
www.edgehill.net
www.baynatives.com

all google groups messages filtered due to spam
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