From: acl on
On Apr 4, 4:11 am, "David J. Littleboy" <davi...(a)gol.com> wrote:
> "acl" <achilleaslazari...(a)yahoo.co.uk> wrote:
> > "David J. Littleboy" <davi...(a)gol.com> wrote:
>
> >> You are sounding as though you are saying the same thing that I was. The
> >> effective size of each sensel in a 3-color system is 1/3 that of the size
> >> of
> >> each pixel in a Bayer system.
>
> >> So at the base ISO, for an exposure that puts 18% gray at 18%, the
> >> 3-color
> >> system's red sensel has sqrt(3) worse noise than the Bayer red pixels.
>
> > You are assuming that the well capacity is the same (total) but is
> > split in 3 for each channel. Why are you assuming this? (It may well
> > be true, I am not disagreeing).
>
> Basic physics: charge storage takes space. Put three charge storage devices
> in the same area, and they'll each have 1/3 the capacity. The technology
> used also has a large effect, but these things are all fabricated using
> essentially the same technology.
>

Well, I suppose you're thinking of the fact that any dielectric will
break down if the electric field is high enough, ie a finite charge
density can be supported per unit volume before breakdown, and that
this is an upper limit (probably a very generous one). But this is not
about the area, it's about the volume. Now for these sensors the
volume is fixed because a) the area is fixed by sensor size and number
of pixels (and perhaps necessary electronics), and b) the depth is
fixed by the characteristic absorption depths for photons of a given
energy. For a CFA sensor, the area is fixed by similar considerations
(of course the necessary electronics will be different), but I have no
idea what fixes the depth.

So the whole relationship between well capacities for these Foveon
sensors and the more usual sensors is unclear to me.

From: David J. Littleboy on

"acl" <achilleaslazarides(a)yahoo.co.uk> wrote:
> "David J. Littleboy" <davi...(a)gol.com> wrote:
>> "acl" <achilleaslazari...(a)yahoo.co.uk> wrote:
>> > "David J. Littleboy" <davi...(a)gol.com> wrote:
>>
>> >> You are sounding as though you are saying the same thing that I was.
>> >> The
>> >> effective size of each sensel in a 3-color system is 1/3 that of the
>> >> size
>> >> of each pixel in a Bayer system.
>>
>> >> So at the base ISO, for an exposure that puts 18% gray at 18%, the
>> >> 3-color
>> >> system's red sensel has sqrt(3) worse noise than the Bayer red pixels.
>>
>> > You are assuming that the well capacity is the same (total) but is
>> > split in 3 for each channel. Why are you assuming this? (It may well
>> > be true, I am not disagreeing).
>>
>> Basic physics: charge storage takes space. Put three charge storage
>> devices
>> in the same area, and they'll each have 1/3 the capacity. The technology
>> used also has a large effect, but these things are all fabricated using
>> essentially the same technology.
>
> Well, I suppose you're thinking of the fact that any dielectric will
> break down if the electric field is high enough, ie a finite charge
> density can be supported per unit volume before breakdown, and that
> this is an upper limit (probably a very generous one).

Well, I wasn't trying that hard<g>. Merely pointing out that charge storage
capacities are finite, whatever the technology.

> But this is not about the area, it's about the volume.

It's about the area when that's the parameter that's changing.

> Now for these sensors the
> volume is fixed because a) the area is fixed by sensor size and number
> of pixels (and perhaps necessary electronics), and b) the depth is
> fixed by the characteristic absorption depths for photons of a given
> energy. For a CFA sensor, the area is fixed by similar considerations
> (of course the necessary electronics will be different), but I have no
> idea what fixes the depth.

The depth in the above is unrelated to the way capacitors are formed. That's
the depth of the photodiode. The photodiode is a photo-triggered switch that
dumps some amount of charge from the power supply into the charge storage
device when a photon is detected (3 of every 10 photons).

Whether or not you can stack capacitors in the fabrication technology is
independent of whether or not you put three photodiodes at different depths.
And if you can stack capacitors in the Foveon technology, you can stack them
in CFA technology as well. It's all the same CMOS.

> So the whole relationship between well capacities for these Foveon
> sensors and the more usual sensors is unclear to me.

I think you are trying too hard. A pixel has a given area. For a given
fabrication technology, the charge storage capacity you can put in that area
is limited and a function of that area. You can use it for one capacitor, or
three. But the well depth will differ by a factor of three. And the well
depth determines the SNR (and dynamic range) at the base ISO.

David J. Littleboy
Tokyo, Japan


From: John Turco on
nospam wrote:
>
> FOR IMMEDIATE RELEASE
>
> 37 Megapixel Direct Image Sensor brings the revolutionary patented
> Foveon X3 Full-Color Technology to Nikon's forthcoming full frame
> Digital SLR, the Nikon D3F.
>
> Tokyo, Japan, April 1, 2007 � Foveon Inc., a technology leader of
> award-winning high-quality digital camera image sensors, and Nikon
> Coporation, industry leader in photographic equippment for nearly a
> century, announced their partnership for the forthcoming Nikon D3F Full
> Frame Foveon Digital SLR Camera.

Hello,

Stop! Go no further! Nikon has existed, since 1917, but the company
didn't become internationally prominent, until after World War II. I'd
hardly call that being the "industry leader in photographic equippment
[sic] for nearly a century."

If you're going to post an April Fools' joke, get the basic facts right,
at least. <g>

> "There has been a longstanding rumour that Nikon was not interested in
> the full frame format," says Richard Kabuki, product marketing manager
> at Foveon. "Working together, we perfected the technology to
> manufacture a larger sensor to Nikon's high standards, eliminating all
> noise and color anomalies which plagued earlier Foveon sensors, and
> bringing to fruition photography's first full frame Foveon based Nikon
> camera."
>
> The new Nikon D3F camera has 37 million pixels, arranged as 12.3
> million pixel locations in 3 seperate layers, the highest of any 35mm
> DSLR. "The image quality is like nothing you've ever seen before,"
> explains Mr. Kabuki.

<edited, for brevity>

Kabuki, eh? Is that Japanese or Polish? :-)


Cordially,
John Turco <jtur(a)concentric.net>
From: ASAAR on
On Tue, 03 Apr 2007 22:16:04 -0500, John Turco wrote:

>> The new Nikon D3F camera has 37 million pixels, arranged as 12.3
>> million pixel locations in 3 seperate layers, the highest of any 35mm
>> DSLR. "The image quality is like nothing you've ever seen before,"
>> explains Mr. Kabuki.
>
> Kabuki, eh? Is that Japanese or Polish? :-)

Huh? The name is Mr. Kabuki, *not* Mr. Kielbasa. :)

From: acl on
On Apr 4, 5:38 am, "David J. Littleboy" <davi...(a)gol.com> wrote:
>
> Well, I wasn't trying that hard<g>. Merely pointing out that charge storage
> capacities are finite, whatever the technology.

Yes, of course.
>
> The depth in the above is unrelated to the way capacitors are formed. That's
> the depth of the photodiode. The photodiode is a photo-triggered switch that
> dumps some amount of charge from the power supply into the charge storage
> device when a photon is detected (3 of every 10 photons).
>
> Whether or not you can stack capacitors in the fabrication technology is
> independent of whether or not you put three photodiodes at different depths.
> And if you can stack capacitors in the Foveon technology, you can stack them
> in CFA technology as well. It's all the same CMOS.

OK I think this would need more understanding of how conventional CCDs
operate on my part (I mean the nitty-gritty details, which I never
bothered to find out). I also don't know anything about fabrication
technologies, so...

Anyway, there is not much practical point to the discussion, as unless
they improve their sensors dramatically (and judging from some samples
I've seen, the image quality is still rubbish), not to mention their
cameras, they're not interesting photographically.

>
> I think you are trying too hard. A pixel has a given area. For a given
> fabrication technology, the charge storage capacity you can put in that area
> is limited and a function of that area. You can use it for one capacitor, or
> three. But the well depth will differ by a factor of three. And the well
> depth determines the SNR (and dynamic range) at the base ISO.


Well that is what I do not understand, the relation between
fabrication technology and what you call capacitance (not that I'm
claiming it's not capacitance, I just don't think of it this way).

Maybe if I think about how the junctions work a bit more it'll become
clear.

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