Thinking in Photons.


Researchers interested in understanding how to compare CCD and CMOS technologies.


A different way to evaluate microscope cameras that's critical for accurate assessment of CMOS technology.

A simplified signal to noise equation

There is a disconnect in imaging: we image photons but we talk about camera specs in electrons. This gap can be bridged easily, making camera comparisons more meaningful. Consider the difference between Gen I sCMOS and Gen II sCMOS. On the face of it, read noise specs seems rather equivalent (be careful to compare rms to rms, median to median under analogous modes and speeds). But, if the read noise is considered first in electrons rms and then converted to photons, using QE at a particular wavelength, the differences are pronounced. At 100 fps in rolling shutter mode, the Gen II ORCA-Flash4.0 has 1.9 e- rms while Gen I has 2 e- rms. The QEs at 550 nm for Gen I and Gen II are 54 % and 72 %, respectively. Using these numbers, the read noise in photons for Gen I is 2/.54 = 3.7, while the Gen II is just 1.9/.72 = 2.6. So now, in photons, the Gen I sCMOS has 42 % higher read noise than the ORCA-Flash4.0.


Finally, consider the outcome of this exercise when the ORCA-Flash4.0 V2 is running in slow scan mode with only 1.5 e- rms noise. The read noise is a mere 2.08 photons.

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