From: acl on
On Mar 18, 3:00 am, "Roger N. Clark (change username to rnclark)"
<usern...(a)> wrote:
> acl wrote:
> > But I find it very hard to believe that this limit is at 6 microns, or
> > that the performance of the canon cameras in terms of read noise
> > cannot be duplicated and improved.
> 6-micron limit? Who said 6-micron limit? I haven't said anything
> about a 6 micron limit.

Nobody mentioned 6 microns. But 6 microns is the current smallest size
of DSLR pixels, and you wrote:

2) Current DSLR cameras, like the Canon 20D, Nikon D50, and all other
DSLRs tested on my web pages and other people testing cameras

So read noise isn't the limiting factor for current dslrs, but the
ADC. If the pixels were significantly smaller (thus lower well
capacities), eventually read noise would become limiting (and yes,
shot noise too, but we can bin them and get rid of that, while we
cannot reduce the significance of read noise by binning, as has been
gone over ad nauseum by all sorts of people here). Since current
sensors aren't limited by their read noise, but smaller pixels would,
I concluded that the argument was that we are well-balanced now. Maybe
I misunderstood.

But I cannot see why read noise can't be reduced further. Also, I
cannot see why on-chip binning cannot be implemented, so that the read
noise (or the part of it that is purely due to reading out the
charges) can be independent of how many pixels are binned (thus, r per
pixel for unbinned pixels, r per binned pixel for binned). I do not
know how much of it is indeed due to readout and how much due to other
stuff (eg the structures around the sensing area), though. It's one
thing to say it's not done now, and another to say it cannot be done
(which you didn't, I know; nor did anybody else).

> I've only argued that the premise
> of binning smaller pixels can equal the performance of larger pixels.
> That goes for 8 versus 16-micron pixels or 2 versus 6.
> I also said given the choice of a 200+ megapixel camera with
> 2-micron pixels or a 24 mpixel camera with 6 micron pixels,

> I would choose the 200+ camera for static shots and the
> 24 mpixel camera for fast action and low light work.

And a very expensive lens, and a very heavy tripod...

From: acl on
On Mar 18, 5:21 am, Lionel <use...(a)> wrote:

> >But I find it very hard to believe that this limit is at 6 microns, or
> >that the performance of the canon cameras in terms of read noise
> >cannot be duplicated and improved.
> Who said either of those things? I haven't seen Roger do so, I
> certainly haven't, nor have I noticed anyone else saying that.

No point in rewriting my reply, read the one to Clark.

> You seem to be arguing with something that nobody has said.

Maybe. Happens often! I don't think so in this case, though.

From: John Sheehy on
Lionel <usenet(a)> wrote in

> Explain to me how a small photodiode under a microlens can possibly
> have a well size as large as that of a photodiode the size of the
> microlens itself.

I can't explain that; I'm not sure it's possible. However, it has nothing
whatsoever to do with the fact that a microlens only affects how fast a
well fills, not the ratio of max signal to lowest usable signal (DR).


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John P Sheehy <JPS(a)no.komm>
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From: Paul Furman on
John Sheehy wrote:
> Lionel <usenet(a)> wrote
>>On Sat, 17 Mar 2007 21:40:31 GMT, John Sheehy <JPS(a)no.komm> wrote:
>>>Lionel <usenet(a)> wrote:
>>>>Exactly. And he's also neglecting to account for (in his analogy),
>>>>the drops that hit the lips of the smaller containers, & are lost,
>>>Apparently, not many photons are lost with the 1.97u pixel pitch in my
>>>FZ50. It captures almost exactly the same amount of photons per
>>>square mm at ISO 100 saturation as the 1DmkII! Even photons that get
>>>close to the edge may still go into a well,
>>No, that's not how photodiodes work. Those photons are lost.
> Which ones are lost? You made a very vague reference to drops on the
> edge; I can only guess the scenario in which they occur. I don't know
> how thick the walls are in your mind, etc. I get the feeling that you
> meant imply "in the worst and most impractical manner possible". The
> fact is, current tiny-sensor pixels are not losing many photons the way
> they would in your horror story.
>>>whether it is the next one over is
>>>irrelevant, as the resolution is still more precise than if you had
>>>large pixels, where any collected photon could have been in any of a
>>>number of pixel wells on a finer-pixel-pitch sensor.
>>>You're talking boogey-men. Talk facts, from real world stuff, please.
>>>No cultish hand-waving.
>>And you're calling names, not supplying facts.
> I hope I didn't offend any boogey-men, but then again, they *want* to
> scare you.
> I am supplying facts about various cameras and how much noise they have,
> and how they bin. You're just making up worst-case scenarios.
>>>>(equivalent to the extra fill-factor loss), & the fact that the
>>>>smaller containers will fill & overflow more easily at points with
>>>>heavy exposure (which is equivalent to lowered well capacity in the
>>>>smaller photodiodes, thus a reduced maximum photon capacity).
>>>You're getting very funny now. Go back and look at what you just
>>>wrote; you just complained about resolution!
>>I did? Where?
> You complained about a small container filling up, while its neighbors
> didn't.
>>>What if there was a pattern of extra drops in every second row of
>>>small containers? How would you see that with the larger containers?
>>How would you see it if you're binning all these drops? - You /are/
>>still talking about binning all these samples, aren't you?
> Binning is optional. It's saves space on memory cards, and speeds up
> their writes.

I really don't get this binning. Does anybody do that (half the
megapixels) because they can't afford memory cards?
From: John Sheehy on
Lionel <usenet(a)> wrote in

> Suppose you have two photodiodes next to each other on the same piece
> of silicon. One can hold a maximum of 1000 photons. The second has
> only half the surface area of the first, & can therefore hold only 500
> photons at most. The second photodiode, however, has a microlens in
> front of it, so it will collect photons from an area exactly the same
> size as the surface area of the first photodiode.
> Now, send a stream of photons at both photodiodes & measure the output
> signal from the diodes. Everything is equal from 0-500 photons/diode,
> but the smaller photodiode tops out at 500 photons, whie the larger
> photodiodes keeps on providing a useful signal right up to 1000
> photons. Therefore, the larger photodiode has double the (linear)
> dynamic range of the smaller one.

I qualify my statements much more thoroughly than most of the population,
and even I wouldn't consider it necessary to qualify for your hypothetical
"mixed capacity" sensor. We were discussing whether or not "microlenses"
affect DR. You had to come up with a scenario that adds another factor,
and the discussion is not about microlenses anymore. You are going to
comical lengths to try to find me wrong about something.


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John P Sheehy <JPS(a)no.komm>
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