Using Brain to compare camera sensitivities

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donboy
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Joined: Sat Mar 25, 2017 1:57 am

Using Brain to compare camera sensitivities

#1

Post by donboy »

Hi Robin,

Wondering if the Brain can be used to compare sensitivity of some ZWO cameras. Thus being able to determine in a comparison how much one camera is more sensitive or less sensitive than another?

Don
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admin
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Re: Using Brain to compare camera sensitivities

#2

Post by admin »

Hi Don,

you *can* compare the sensitivity, but you need a constant light source to do that - one that you can illuminate both sensors evenly with. The way I've done it is this...

* Do sensor analysis of both cameras with the brain in 16 bit mode
* arrange for identical illumination levels for each camera - I did this using a PK Pentax camera lens and adaptor, with the lens sitting glass down on an electroluminescent panel and the camera in the adaptor. Then I could vary the aperture of the lens to get a reasonable illumination level
* measure the histogram peak on both cameras in the SharpCap histogram - note down the electron rate (e/s/um^2) when hovering over the peak for each camera - this takes into account the gain you have chosen and the pixel size of the camera to find the number of electrons being created by the sensor per second per square micrometer
* because you have arranged identical illumination for the two cameras, the photon rate (photons per second per square micrometer) will be the same for both cameras
* so the only reason the electron rates will be different is that the cameras have different QE - you can work out the ratio of the QE values of the camera from the ratios of the electron rates.
* If you know the true QE of one camera you can work out the true QE of the other from the ratio

Note - this measures the QE ratio averages over the range of frequencies that your light source produces. A colour camera will appear to have about 1/3 the QE of a mono camera by this measurement because of the effect of the colour filter array.

cheers,

Robin
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