1 electron = 1 photon?

Started Apr 12, 2013 | Discussions thread
Jack Hogan
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Re: Internal vs external QE: KAF 8300 data sheet
In reply to alanr0, Apr 14, 2013

alanr0 wrote:

For a Bayer sensor the colour filter array is going to have a big impact of the spectral response.  Within the 500-600 nm range, the green filter transmission will peak near 550 nm and drop by around 50% at 500 or 600 nm.

There is useful info in the KAF 8300 data sheet.  Page 17 shows the external QE for each of the four colour channels (R Gb Gr B), and also for monochrome variants with and without microlenses and glass windows in the package.  This is a relatively old Kodak CCD design, now supplied by Truesense.  I believe it was used in the Olympus E300 and E500 DSLRs, so dates back to 2004 or earlier, and won't be representative of more recent designs from other manufacturers.

Peak monochromatic QE is near 550 nm, as one might expect.  Microlenses improve QE by 50% or so.  The angular response is asymmetric, presumably a combination of microlens performance and sensel shape.  QE falls for angles greater than 10 - 15 degrees, so there will be some loss of efficiency for lenses faster than f:2, increasing rapidly beyond f:1.4.  Current versions use offset microlenses, so the acceptance angle tilts across the frame (p 18) to improve performance with non-telecentric lenses.  I don't know if Olympus' 4/3 DSLRs used offset microlenses - older (2005) versions of the data sheet don't show this feature, and the 4/3 specification calls for near-telecentric lenses.

Note that compared to the KAF 8300, some Bayer sensors appear to have rather lower red and blue sensitivity relative to the green channel.  This will degrade the noise performance to a small extent, but greatly improves tolerance to changes in colour temperature which might otherwise saturate the red or blue channels.

Alan

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Alan Robinson

Thanks Alan, I remembered the KAF 8300 data sheet that you had linked a while back only after all the questions came up

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