Bart van der Wolf wrote:
>
> "Scott W" <biphoto.RemoveThis@hotmail.com> wrote in message
> news:1157072868.581178.149830@b28g2000cwb.googlegroups.com...
> SNIP
>
>>
>> If we take this a step further an idealized sensor would have 100%
>> quantum efficiency and record the precise location where each
>> photon was detected. Then the trade of between noise and
>> resolution could be done in post processing. This is of course not
>> a realistic sensor for a digital camera but it can be used as a limit
>> to what could be done if no practical consideration needed to be
>> taken into account.
>
>
> Other scenarios can be considered as well. How about a sensor array that
> can sample at half pixel positions by e.g. piezo controlled
> repositioning. With adequate sampling density, this might even allow to
> reduce the strength of the AA-filter a bit. Thus we can combine the
> larger sensel area with higher resolution and less aliasing tendency.
> That also would allow to employ techniques known as 'Drizzling',
> allowing even higher resolution in postprocessing.
>
You are all forgetting that photons are finite. For a typical
daytime scene, you want an exposure time of a small fraction
of a second, you only get so many photons/second per square micron
delivered to the focal plane. It is not a large number.
Somewhere I have those calculations, probably back a year or so
ago in a response to Ilya, who was advocating really tiny
pixels.
For example, in a 1D mark II with 8.2 micron pixels, 67 sq microns,
you get 80,000 electrons (photons) per pixel, or a maximum of 1195
photons per square micron. Increase quantum efficiency to 100%
(about a factor of 4), and you get 4780 photons/sq micron. But that
is max signal. The typical 18% gray level would have only 4780*.18
= 860 photons /sq micron: a signal to noise ratio of 29 for 1-micron
pixel. It would be an OK (not great) image, and worse than current small
pixel P&S cameras. Then of course, as your light levels fall and
you boost iso (the above is for iso ~80), you would have very few photons,
e.g. at ISO 800, you would get only 86 photons on the gray card.
Note that the dynamic range also decreases as the photon count goes down.
All this also assumes that the full well electron problem gets solved.
Currently, full wells max out at about 2000 electrons/square micron, and
it isn't clear that you could have much of a well at all with 1-micron
pixels. There must be a "wall" to hold the electrons (it is a potential
well in a CCD).
Back to the original question, are 22 megapixel APS-C cameras
possible? Yes, but performance would be low. That is my fear,
that the megapixel wars will degrade image quality. Image quality
in DSLRs is so high because the pixels hold 50,000 electrons and
above. In my opinion, 50,000 electrons should be a threshold
that should not be crossed. For current sensors, that means
pixels in the 6 to 8 micron range being the sweet spot.
The some DSLR cameras are pushing that limit down, and that is bad
in my opinion.
Roger
>> Stay informed about: Are 22 megapixel APS-C sensors realistic? 
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