What Is a CCD Camera?
A CCD Camera is a camera that uses a CCD as its image sensor. CCD stands for Charge Coupled Device.
In recent years, technological innovations have replaced CCD cameras with CMOS sensors, which are superior in terms of performance and cost. However, they are still in use in some research applications, and some hobbyists prefer them because of their tendency to produce stronger contrast in photographs than CMOS.
Uses of CCD Cameras
CCD cameras are used in some compact digital cameras, but development of CCD cameras for general use are being produced. It is highly likely that they will be replaced by CMOS cameras in the future.
They are often useful in research applications. For example, they are used in combination with microscopes in imaging biomolecules. CCD cameras are characterized by their high sensitivity.
CCDs are characterized by their high sensitivity. Furthermore, the detection sensitivity can be increased up to 1000 times by amplifying the detection signal with an EMCCD (electron multiplying).
Recent CMOS sensors can also detect single molecule fluorescence by improving quantum yield. However, when single molecule fluorescence is weak, an EMCCD camera that can amplify the signal is more advantageous.
Principle of CCD Cameras
CCD cameras use a lens or other optical system to form an image on a CCD sensor, which consists of an array of photodiodes (CCD elements).
When a photon strikes a light-receiving CCD element, the photoelectric effect generates electrons, and the element stores an electric charge. The charge accumulated in each CCD is transferred to the CCD for transfer, and the current is amplified by an amplifier. The amplified current is calculated by the CCD camereas control board and converted into image data.
In EMCCD, a voltage is applied to the transferred charge before it is sent to the amplifier to double the number of electrons. This is done using a phenomenon called collisional ionization. The EMCCD can also detect single photons and can measure the number of photons.
However, charge transfer does not take place until enough charge is accumulated in all CCDs in a row. This is the rate-limiting factor in the transfer rate.
Types of CCD Cameras
1. CCD Element Type
Full-frame type
Full-frame CCDs are standard CCDs and have the highest sensitivity and dynamic range for physical and chemical measurements. A light-shielding shutter is required to prevent light from shining on the element during readout.
Frame transfer type
The frame transfer type has two types of CCDs, one for light receiving and the other for image storage. The received image is transferred to the CCD for temporary storage, and the stored charge is read out during the next exposure. While a shutter is not required, a CCD with twice the area is needed.
Interline type
The interline type CCD is a type in which the light receiving and storing sections are arranged in a single element. This type of CCD element is used in video cameras. A shutter is not required, but the aperture is smaller than that of a full frame.
2. Types of CCD Cameras
Spectroscopic camera
This is a camera that can obtain the spectral spectrum of an image. It can measure spectral characteristics within the shooting range at once. Applications include diagnosis of food freshness, detection of foreign substances, and in the industrial field, management of product color.
Camera for biological observation
Cooled CCD cameras are widely used for the purpose of observing microscopic movements of living organisms and images of extremely low light by attaching them to microscopes. The key factors are high sensitivity, high resolution, and high speed.
X-ray camera
X-ray CCD cameras are becoming widely used in the soft X-ray to hard X-ray range. CCD cameras are superior to other detectors because of their high sensitivity and wide dynamic range.
High-speed cameras
Cameras capable of 100 frames per second or more are called high-speed cameras. They are increasingly used in industrial applications such as automobile crash tests and factory manufacturing process control.
Other Information on CDD Cameras
Differences From CMOS Cameras
A CCD sensor extracts charge from electrodes to the outside like a bucket relay, whereas a CMOS sensor has a photodiode in each pixel and reads signals directly from the pixel while switching at high speed with a semiconductor switch. Thus, there are the following differences:
CCD = power consumption x / image quality ◎ / price x
C-MOS = power consumption ◎/image quality ◎/price ◎
Thus, CCD is superior in terms of image quality, while CMOS is less expensive.