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In this article we introduce and review CCD and scientific CMOS cameras, compare the advantages and disadvantages and introduce the research applications suited to both CCD and sCMOS cameras.
In a camera a light sensor converts light into an electrical signal which can be amplified, digitised and mapped to produce a digital image.
CCD stands for Charge Coupled Device. In a CCD the sensor is an array of pixels. These are connected in series. Charge travels from one pixel to the next in a column until it reaches the end pixel. This is a slow process compared to the highly parallel process of CMOS sensors. It then moves to the readout phase, where it is converted to a digital signal and amplified.
There are now enhanced types of CCD detector that have improved performance such as back illuminated CCDs. These are more efficient (higher quantum efficiency) and more expensive.
CMOS stands for Complementary Metal Oxide Semiconductor. The detector consists of silicon and a mix of other trace metals. It is essentially a silicon chip. As these are mass produced it is cheaper to produce than a CCD. However, CMOS cameras were originally not suitable for scientific research because of high signal to noise levels, and lower image quality.
Andor technology was one of several partners to see the potential for the development of CMOS to contribute to scientific research. It invested in a collaborative programme which resulted in sCMOS technology, or scientific CMOS. The limitations of the earlier CMOS cameras were overcome, leading to fast, sensitive and high-resolution cameras perfectly suited for scientific research. In the following years these new sCMOS cameras soon replaced the CCD cameras across many application areas.
The light sensor is again an array of pixels but in this case, charge is converted into voltage inside each pixel. Each pixel contains its own amplifier and the readout process is in parallel rather than in series. This offers many advantages over the CCD model, most obviously in faster processing times because the charge doesn’t need to travel across the array before amplification. Also extremely low noise, high resolution, and a large field of view.
When compared to CCD, sCMOS sensors require less power and so are extremely low noise, they are faster to convert images into digital data leading to rapid frame rates. They offer:
They offer great performance overall, however, in low light conditions, such as single molecule studies, an EMCCD (Electron Multiplying) camera would often be preferable. Under these conditions the signal to noise ratio is better allowing for improved detection of faint signals inherent in single molecule imaging experiments (EMCCD is described elsewhere).
To choose the best camera, it is necessary to consider conditions and requirements of use. No one camera does everything. Here are some examples.
A. In Life Science
For histology imaging, there are high light levels, low magnification needed and low speeds or static conditions. For this a good and cost-effective option will be a basic colour CMOS camera.
For widefield fluorescence microscopy, you would need good sensitivity, a wide field of view, dynamic imaging capabilities for imaging at moderate magnification. We would recommend an sCMOS model, either front or back illuminated models.
For confocal flurorescence microscopy, we have lower light levels, a wide field of view, and are studying dynamic processes. We would choose either a higher performance sCMOS or EMCCD or a combination of both cameras (Andor Dragonfly).
For radiometric imaging eg Calcium imaging there are dynamic changes with wide dynamic ranges of signals. We would choose sCMOS again to allow high speed imaging, or an EMCCD that can provide high speeds with even the weakest signals, but not over as wide a field of view as sCMOS.
For super resolution microscopy we need high sensitivity, high signal to noise, small pixels and high-speed imaging. We would choose sCMOS or EMCCD. sCMOS offer higher speeds over wider fields of view - however EMCCD remains a more sensitive sensor technology so remains an option when signals are below the working range of sCMOS.
See ZL41 Cell and Sona (sCMOS cameras) specification sheets for detailed information.
B. In Astronomy
The particular features of sCMOS - a large field of view, high resolution and fast readout are also ideally suited to astronomy applications. Our Balor cameras are suitable for applications including solar and exoplanet studies and looking at near earth objects and space debris.
C. Physical Science
Applications include Neutron Tomography, Cold Atoms, Bose Einstein Condensation and Quantum Optics.
The performance of a sCMOS camera compared to a CCD is outstanding for speed, sensitivity and resolution. Pick up our specification sheets for ZL41 Cell and Sona sCMOS cameras which show their life science imaging capabilities. For high-speed, high-sensitivity, high-resolution imaging, our sCMOS cameras are pushing the boundaries of research in a wide range of applications. For example, in developmental biology, gene editing and neurophysiology. For large scale applications such as astronomy the Balor sCMOS camera is ideal for large sky studies.
There are imaging conditions where CCD cameras are still preferable. Deep cooled CCD cameras have significantly less thermal noise than any sCMOS. This means that for long exposures that are limited by thermal noise (also called dark current), deep cooled CCDs remain the best solution. Since the general imaging market has moved to sCMOS there are only a small number of these specialised cameras that are suitable for these applications.
For bioluminescence we need very high sensitivity sensors and the lowest thermal noise to maximise collection of weak signals over long collection times of many minutes or even hours. We would choose deep cooled CCD camera or EMCCD that offers a CCD mode like iXon Ultra as these cameras offer high sensitivity sensors with the lowest thermal noise.
Imaging experiments that involve long exposures include in vivo imaging, plant imaging or any imaging application that is based on luciferase-based reporter systems.
For the lowest light levels such as some single molecule biophysics experiments, or quantum imaging, EMCCD remains the best imaging technology read more in our article on Single-Molecule Studies - EMCCD or sCMOS?
Date: December 2022
Author: Jo Walters
Category: Technical Article