[Foto] Re: uj Nikon bajonett?

[Zabb Csaba]

--- dMT alias Medve <moso-t at prolan.hu> wrote:
(Valahogy kulonbozok a bajok a CCD-nel
> es a CMOS-nal. Persze az en egyszeru agyam azt sem erti, hogy ez
> miert ket komplementer halmaz. A CCD egy aramkor soros
> kiolvasasra, a CMOS egy felvezeto technologia.

Egy ertekezes a temaban (CCD/CMOS/35mm):

Kyocera pulled back N Digital to upgrade the firmware and add in
better cooling devices. I have not heard anything regarding to what
sensor they will use for the next high end digicam though. With the
lesson learned from N Digital and Kodak's 14n, I think Kyocera will be
super conservative this time.

The N1/ND was a very ambitious project. Probably it was too ambitious.
Kyocera underestimated the engineering efforts around the 6MP Philips
sensor. The Philips sensor specs look very good on paper; however, for
real world application, it has two major problems: 1. It eats up lots
of power. 2. It can generate lots of heat which will increase the
noise level. Kyocera had lots of troubles with these two issues. The
Philips sensor is Ok for med format digiback because it has the space
to install good cooling devices. This is not an option for N1. At the
end, Kyocera had to lower the ISO rating to reduce the noise. Also,
Kyocera was short of software and firmware engineers. Many things
could not implemented correctly and on time. Another minor issue is
the corner performance. Even with larger N mount and larger image
circle of N lenses, the angle which light strikes the micro-lense at
the border of CCD is still off too much. This causes some performance
degradation with the 17-35 lens.

CMOS sensor indeed has more noises than CCDs. Another problem with
CMOS sensor is that it does not have the idea of shutter. I.e. CMOS
sensor is always ON. The good news is that the CMOS process allow the
designer to put lots of extra circuits to the same chip. A sampling
circuit can be added beside a sensor to monitor its value all the
time. When the camera is not doing the shot, the sampling circuit will
record down the noise level in the sensor. When the camera is taking a
picture, the sampling circuit will act like an artifical shutter,
record down the sensor value at the end of the shot then decrease the
recorded value with the noise value sampled last time to get the real
picture value. With this, you will see a very clean image with little
noise. The penality is that this will reduce the dynamic range of the
sensor. It hurts the tonal gradation as well. This is the main reason
you can see why pictures from Canon D60 and 10D all look very clean;
however, they look just more fake than S2Pro and D100's. Anyway,
almost all CMOS sensor are using this multi-sampling noise reduction
circuit now. Canon is just the first one which used it on consumer
digicams.

One more good thing about CMOS sensor is that the sensor pixel is
shaped like a tile, more or less like an area sensor. The light which
hits any spot on the tile will be recorded. On the other side, CCD
sensor pixel shaped more like a well. A micro lens has to be added to
the top of a sensor to focus the light to the right spot. This is the
main reason that with the Nikon F-mount, Nikon will never be able to
produce a full-frame digicam with CCD sensors. The angle of the light
path to the film boundary is too narrow for a micro lens to focus
light to the sensor.

With CMOS sensors, Canon has more design freedom. The 1Ds uses
bascially a sensor made up by two D60/10D sensors.

Kodak's 14n uses a 14MP CMOS sensor from FillFactory. The sensor is
actually more hi-tech than Canon's; however, since it has more pixels,
each pixel has to be smaller than Canon's. Small pixels means that
each pixel will have less area to accept light. With the smaller Nikon
F-mount, the pixels around the border have the light angel issue
again. Kodak had to add in complex exposure compensation function to
correct this problem. Another issue is that the FillFactory chip was
noisy... something Kodak had not expected. On paper, the sensor should
have a dynamic range around 11.5bit(69db?) but in reality, it is less
than that... I think probably FillFactory has tried too many fancy
things with their noise reduction circuit which may not work well all
the time. On the other side, Canon just relies on some proven
brute-force apparoach.

Sure, Kodak also has lousy software engineers such that the post
imaging processing is simply not as good as Canon's. It will take a
while for things to improve...."

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