# Amount of photons per pixel

1. Feb 23, 2008

### Theraven1982

A fresh question.
I want to find the number of photons falling on a pixel in a CCD. A very simple model:
* bigger source area gives larger response ($$A_s$$)
* when object farther away, smaller response: $$\frac{1}{R^2}$$
* bigger detector area gives larger response ($$A_d$$)
* size of the lens is $$\pi r^2$$, with r the radius of the lens
* the larger the focal length, the smaller the amount of light on the detector: $$\frac{1}{f^2}$$
* atmospheric damping gives extra coefficient of D
* spectral response dependence: $$QE(\lambda)$$
* amount of energy from the source: E

gives something like this:

$$A_s A_d\frac{1}{R^2}\int^{\lambda_e}_{\lambda_s} QE(\lambda)E d\lambda$$

If I understand correctly, if this is calculated (the quantum efficiency can be modeled like e.g. 3 small parts), and the answer is divided by the photon energy, the amount of photons per pixel should appear.

I don't really know how to put in the energy from the source. The radiant exitance looks good, but I don't know what to do with it. And I can't find a source of information on how large these quantities should be.

Last edited: Feb 23, 2008