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Dear Christophe and Jim,
  I have been made aware that messages related to Nüvü Cameras' technology 
were exchanged on confocalmicroscopy. As the CTO of Nüvü Cameras, I would 
like to add my 2 cents to this discussion.

  We do build EMCCD cameras and we use the same EMCCD chips as every 
other EMCCD camera maker (from e2v technologies). However, what 
differentiates our cameras from the others is not only a photon counting 
option: every camera maker has this function. The main difference between 
our cameras and the others is the low level of spurious Clock Induced Charges 
(CIC) that are generated during the EMCCD read-out, which is lower than 
0.002 electron/pixel. And when it comes to photon counting, which, as Jim 
noted, is restricted to low flux levels and/or high frame rates to avoid losses 
by coincidence, the low CIC level is of extremely high importance as it is the 
dominating source of noise. I must stress this: we do not filter the noise. We 
just don't generate it. We achieve this by using an electronic controller (the 
one that produces the electric signals used to clock the pixels out of the 
EMCCD) that generates electric signals that are different from the controllers 
used in the other cameras. By doing so, we generate less spurious charges 
when we move the electrons around the EMCCD.

  Another differentiating aspect of our cameras is the higher achievable EM 
gain. This is of importance, as a higher EM gain allows, in photon counting, to 
extract more photo-electrons out of the read-out noise. Its like having a 
higher Quantum Efficiency (QE). There is no big magic here: it is only a 
matter of producing a clock that has a higher voltage. However, a higher EM 
gain also means a higher level of CIC. With out controller, we can reach a high 
(>3000) EM gain while generating less CIC than our competitors.

  In photon counting, the lower dynamic range can be compensated by using a 
higher frame rate and adding frames together by post-processing. Of course, 
this requires a higher frame rate, which generates a higher total level of CIC 
(CIC is read-out dependent, as compared to dark noise which is time 
dependent). Once again, the low CIC level generated by our cameras has its 
advantages.

  The use of this controller also has the advantage of yielding a higher charge 
transfer efficiency (CTE). Some research fields, especially the ones using high 
resolution spectroscopy, are rejecting the EMCCD technology because of their 
less-than-optimal CTE. We hope that our higher CTE cameras will allow them 
to re-think the usage of EMCCDs for their applications.

  For higher flux applications, the EMCCD can be operated at a lower gain to 
avoid saturation, and get sub-electron read-out noise. Of course, you are then 
plagued by the Excess Noise Factor that has the same effect on the SNR as if 
you would halve the QE. However, if you get a single photon in a pixel, you 
will see it with >5 sigma confidence level (read-out noise wise), which is 
impossible to do with a sCMOS or a conventional CCD. At the same time, you 
will be able to image the brighter regions of your image and be shot noise 
limited there. EMCCD cameras also have the advantage of being operated at a 
lower temperature than sCMOS, and benefit of a lower dark noise (about a 
hundred times lower). sCMOS also have a lower QE (peak at 55%) while the 
EMCCD peaks at around 92%. Divide that by 2 and you are not that far from 
sCMOS, have lower dark noise, lower read-out noise, better pixel response 
uniformity, Gaussian noise, etc. Of course, sCMOS can reach hundreds of FPS, 
and it is 3 to 5 Mpix. It is just a matter of time before larger format EMCCD 
will be out. Still, for some applications, sCMOS is better than EMCCDs. The 
reverse is also true.

  These were my 2 cents. If you have questions, feel free to write back to me 
at odaigle __at__ nuvucameras dot com.