Digital BW, The Print

Truman

Thanks for the reply and the references.  But have you seen any reviews of
the high end digital SLRs vs digital backs?  It seems like these two markets
are kept well apart.  I suspect the 35mm guys simply don¹t yet want to rate
their product against the 1 shot per second backs¹ quality and are focused
on their own closer-to-home competition.  I fear the MF guys see no need to
make the comparison or display the stats because it could undermine the
significant premium they can extract from studio photographers that want to
stay looking studio-pro rather than sports-pro/prosumer.  If a PhaseOne H10
uses a 35mm-sized mosaic sensor like the 1 Ds (albeit one is CCD and the
other CMOS) how much noise cuts the price in half (even ignoring all the
other benefits of faster fps and portability)?  Ask a dealer of both why
there is such a difference in price and he will say that the PhaseOne/Leaf
delivers a much better image, lower noise etc.  But no one I have spoken too
is able to tell me the noise stats.  Canon brags about the high signal to
noise ratio of the new MK II.  Yet I can't find that stat on their website.
16 megapixels at a decent price (let alone the other features) becomes a
powerful proposition vs film if the image quality is close to that which I
have seen from an old 6 mp H10.  Like I said, how much noise cuts the price
in half?

Steve


From: Truman Prevatt <tprevatt@...>
Reply-To: DigitalBlackandWhiteThePrint@yahoogroups.com
Date: Sun, 29 Feb 2004 09:03:42 -0500
To: DigitalBlackandWhiteThePrint@yahoogroups.com
Subject: Re: [Digital BW] S/N figures etc for digital cameras

The noise is electrical noise. Every electrical circuit has noise - it
is a results of random motion of electrons. The power of that noise is
proportional to the temperature and something called "bandwidth." In
fact there is a ever present electrical back ground noise on the earth
of about 10^-15 watts. The only way to avoid electrical noise is to cool
the circuit to absolute zero where it would be a little uncomfortable to
take pictures and the shutter wouldn't work.

How this impact the image is when the sensors that count photons are
characterized by the electronics (there is some photon noise but
electrical noise is by far the limiting factor). The S/N (signal to
noise ratio)  is the measure of the signal power -" number of photons"
vs. electrical noise background in the circuit. The reason there is
higher noise at higher ISO is the signals are amplified prior to the
analogue to digital conversion to bring the voltage into the range of
the A/D so another type of noise won't be a problem (quantization
noise).  The amplification amplifies the noise along with the signal.

The 12 bit A/D will perform better than the 8 bit mostly because there
is more margin in the dynamic range. It is unclear if 16 is needed but
the more bits the better. I have seen RF sensor system where 24 bits
were required.  One way to get better S/N is with "bigger" sensors (more
are at each sensor location)  in the array that count more photons in a
fixed shutter time vs. a small sensor. You don't eliminate the noise but
provide a bigger signal to the A/D for a higher S/N. That's why the new
Sony F585 is so noisy compared to the DSLR out there. However to get
bigger sensor at each location you need a bigger array - the bigger the
array the more expensive it is to produce ( cost will go up with area).

The noise in a Canon, Nikon, etc. is going to "look different" than in
the Sigma because of the interpolation. The noise that exist in nature
is what is called "white" that is there is no correlation between
neighboring pixels. Because of the interpolation to get a full number of
pixels in the mosaic sensors the noise is correlated in neighboring
pixels. See  http://www.dpreview.com/reviews/sigmasd9/page15.asp where
this is shown and is pretty clear what is going on.

Dpreview has pretty good reviews of digital cameras, http://www.dpreview.com

Truman




[Non-text portions of this message have been removed]