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Selection of optical lens matching light source and accessories

To understand the performance of wholesale infrared Germanium lenses, it is necessary to understand what is the EMVA1288 standard. The EMVA 1288 full name, the European Machine Vision Association 1288, is a set of performance characterization standards for image sensors and cameras developed by the European Machine Vision Association.
Quantum efficiency η
Transient dark noise (Dark noise)
***Absolute sensitivity threshold
Dark signal non-uniformity (DSNU)
Quantum efficiency: the ratio of the number of electrons produced by a camera chip to the number of photons received, which can also be said to be conversion efficiency. Quantum efficiency is related to the ability of an optical lens to respond to multiple faint light.
“Dark noise” refers to a signal produced by the thermal excitation of electrons from the read and amplify circuits when there is no illumination and the exposure time is zero. Obviously, the wholesale large size infrared Silicon optics only wants to get the electronic signal generated by the photon, which is undesirable for the camera. Dark noise affects many other characterization projects and largely determines the quality of the camera.
*** Sensitivity threshold is a very intuitive performance characterization that directly tells us how much the camera will produce a numerical signal when the number of photons hitting the optical lens is reached.
“Dark signal non-uniformity” refers to the difference in the dark signal generated by the thermal excitation of each pixel on the camera chip. This reflects the level of the chip manufacturing process. Theoretically, the dark signal generated by each pixel should be the same. .
For us, if we can know the “underlying cornerstone” – the number of photons and the “top building” – the value of the digital signal, we can find the intermediate parameters according to the relationship.
The expression for the number of photons is:
1.A is the effective area of ​​the pixel, and the international unit is square meter.
2.E is the irradiance, the international unit is watts per square meter.
3.t is the exposure time, that is, how long the camera has received

  1. The Et multiplication, ie the total energy energy of the photon per unit area, multiplied by the area A, then the physical meaning of the numerator of the expression is the total energy of the photons received in the pixels of area A during the exposure time t.
  2. For monochromatic light of frequency v, the energy of a single photon is e = hv, then the energy of dividing the total energy by a single photon is equal to the number of photons.
  3. The digital signal value can be used to measure the gray value of each pixel by computer.
    The summary of the measuring device to be measured and the corresponding is summarized as follows:
  4. Irradiance E – Irradiance meter
  5. The pixel “effective” area A – given by the CCD itself data
  6. Exposure time t – controlled by the camera’s software
  7. The frequency or wavelength of light – determined by the light source
  8. Digital signal value (gray value) – read by computer software
    Select purchasing large size ZnSe optics matching light source and its accessories: several requirements for light source
  9. Must be “uniform light”. The meaning of uniform light is that the “irradiance” or light energy of each point is the same at the same vertical distance from the illumination source. The image sensor contains a lot of pixels (typically 2048*2048), and the performance parameters represented represent the overall performance of the camera. Therefore, the same light should be given to each pixel on the camera to eliminate the difference in illumination. The resulting performance difference.
    In order to obtain uniform light, the high-quality method is to use an integrating sphere, and place the LED lamp on the integrating ball into the optical port. After the incident light is reflected multiple times inside the integrating sphere, uniform light will be formed at the light exiting port. The radius of the light exit port should be larger than the size of the CCD, but it should not be too large, otherwise the uniformity of the emitted light cannot be guaranteed.
  10. For black and white optical lenses, monochromatic light should be selected, and the wavelength of the monochromatic light should be the wavelength corresponding to the large sub-efficiency of CCD/CMOS. This is because what we want to represent should be the ideal performance of the camera, and the greater the quantum efficiency, the better the performance.
    In general, for different CCDs, we can choose a single red LED light (LED is the abbreviation of light-emitting diode, corresponding to wavelength 625 nm), or green LED light (corresponding to wavelength 525 nm) color camera, white light, Because color cameras contain three colors, R, G, and B, the light source should also contain these three colors, so white LEDs can be used. The quantum efficiency measured at this time is obviously the average quantum efficiency of the CCD full-band.
  11. The accessories that control the irradiance of the light source or light are DC stabilized power supply and diaphragm. Wherein, the DC stabilized power supply is used to control the voltage (or current) of the LED lamp bead, thereby changing the irradiance of the outgoing light; and the pupil is located in the integrating sphere, and the incident in the integrating sphere can be changed by changing the size of the pupil. The amount of light thus changes the irradiance of the outgoing light. In actual testing, these two methods can be used to regulate.

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