Re: How would lens optics/engineering drive toward an optimal sensor/film size?

Roger N. Clark (change username to rnclark) wrote:

Philip Homburg wrote:

In article <lxAYf.8381$4L1.5623@xxxxxxxxxxxxxxxxxxxxxxxxxx>,
Paul Furman <paul-@xxxxxxxxxxxxx> wrote:

Philip Homburg wrote:

However, for this to be true, the larger format has to be as sensitive
(per pixel) as the smaller format, and this require a much higher
ISO sensitivity.


This is why smaller formats perform better in low light.


I don't see why this has to be true. Nobody makes 6 Mpixel medium format backs
in the same process technology as is used for 6 Mpixel P&S sensors.


The quantum efficiency of sensors doesn't change with sensor and pixel
size, so sensitivity does not change. But larger pixels (in larger
sensors) collect more photons per pixel. See:

The Signal-to-Noise of Digital Camera images
and Comparison to Film
http://www.clarkvision.com/imagedetail/digital.signal.to.noise

The f/ratio Myth and Digital Cameras
http://www.clarkvision.com/photoinfo/f-ratio_myth

from the last paragraph on that page:
"If you tried to make a smaller camera that collects the same number of photons as a larger camera, you must keep the aperture constant. Given a camera, for example, with a 50 mm f/1.4 lens and then shrink the camera 2x, you would need a 25 mm f/0.7 lens that had double the resolution if you wanted to keep the same detail in the image. That means the smaller camera would not be much smaller, and might be more expensive due to the lens specifications."

Just to be clear though about this f/ratio Myth, the exposure time remains the same for f/stops on different size sensors, it's just the signal to noise ratio or degree of detail that's compromised by not using a larger aperture. And the DOF change.

And to get the miniature camera with high performance you describe would have to be some magical high-res film? If you were willing to make small-format fast lenses, at what point does the pixel size limit things? 6-9 microns?


Another factor is that as sensor size shrinks, a wall
between sensors must be maintained between pixels. That wall
is not photon sensitive, so the fractional photo
sensitive area goes down.

In the data I've seen on read sensor noise, some of which
is presented in tables on the first web page above, the larger
sensors with more expensive electronics have lower read noise
than cheap P&S cameras.

Camera performance is about lenses and sensors. Collecting
adequate photons for good signal-to-noise ratio images
was something not appreciated before digital cameras came
along. So having pixel sizes large enough to collect lots
of photons is important. That means larger pixels, but too large
and you can't pack as many in the camera or it becomes too
large. The sweet spot is currently 6 to 9 micron pixels
in my opinion. This also happens to be a good size
for lens aberrations, including diffraction.
.

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