Here's a table I made that has some basic info regarding commonly used Digital Production Cameras i.e., most of Sony and Panasonic's, Genesis, Arri D-20, Red One, etc. I hope you find it to be useful. Enjoy!
The two most commonly found sensor types in both video and stills cameras are CCD (charge coupled device) and CMOS (complementary metal oxide semiconductor). Both are available in a single sensor version and more commonly for video cameras, an array of 3 sensors; Red, Green, and Blue which allows for Chroma Subsampling to compress picture information for storage and transmission. This is not an article on Chroma Subsampling, YCbCr vs. RGB, or 3 chip vs. single Bayer array. That's a whole other topic and I'll be addressing the issue at some point on this blog. The goal of this entry is merely to introduce an overview of both technologies and how they compare on a basic level.
Both basic classes of digital sensors, CMOS and CCD, accomplish the same task of capturing light and converting it into electrical signals.
CCD, Charge Coupled Device:
3CCD cameras have three separate charge-coupled devices, each one taking a separate measurement of red, green, and blue light. Light coming into the lens is split by a trichroic prism assembly, which directs the appropriate wavelength ranges of light to their respective CCDs. By taking a separate reading of red, green, and blue values for each pixel, 3CCD cameras achieve much more precision than single-CCD cameras. In a CCD, when light strikes the chip it is held as a small electrical charge in each photo sensor. The charges are converted to voltage one pixel at a time as they are read from the chip. Additional circuitry in the camera converts the voltage into digital information in the A/D or “analog to digital” conversion process. This ability to resolve colors in the A/D process is quantified in terms of Bits per color channel, 8 and 10 bit being the most common for HD video. Common production cameras using 3CCD's: Most of Panasonic's cameras, Sony F900/23, Viper, etc. CCD's also come in single chip "striped" versions. A single, striped, Super 35 sized CCD is found in both the Panavision Genesis and Sony F35. These sensors are incredibly expensive to manufacture but are arguably the highest quality with the least amount of drawbacks other than the price tag.
CMOS, Complementary Metal–Oxide–Semiconductor:
Two important characteristics of CMOS devices are low noise immunity and low static power consumption. Significant power is only drawn when the transistors in the CMOS device are switching between on and off states. Consequently, CMOS devices do not produce as much waste heat as other types of sensors. CMOS also allows a high density of logic functions on a chip. Single chip CMOS cameras use a Bayer Mask Filter in which each square of four pixels has one filtered red, one blue, and two green (the human eye is more sensitive to green than either red or blue). This results in luminance information collected at every pixel, but the color resolution is lower than the luminance resolution. Like CCD's this color information is separated into channels and put through a chroma subsampling scheme to reduce bandwidth. In the case of RED Code RAW, the information from the chip is output as Raw Bayer data and must be “De-Bayered” (interpolated using a demosaicing algorithm) in order to be viewed. Common production cameras using single CMOS sensor: RED One, Arri D-21, Phantom, etc. 3 CMOS cameras similar to 3CCD, or 3MOS cameras are becoming increasingly common with Sony's XDCAM EX line and the Panasonic HPX300. CMOS chips tend to be more prone to non-visible infra-red (IR) light that can contaminate color saturation in video images. Though not always necessary, IR Cut filters in front of the lens is an effective way of dealing with color contamination.
CMOS vs. CCD:
Neither technology has a clear advantage in image quality. CMOS can potentially be implemented with fewer components, use less power and provide data faster than CCDs. CCD is a more mature technology and because of its "global/synchronous shutter" is far less prone to sensor artifacts than a CMOS sensor which are more commonly equipped with a "rolling shutter". This is the most immediately apparent issue between the 2 different technologies.
- Both CCD and CMOS can exhibit several of four different types of sensor artifacts: Smear, Skew, Wobble, and Partial Exposure. CCD's can suffer from vertical smearing on bright light sources, while CMOS sensors are immune to that artifact. To date, most CMOS sensors are equipped with a rolling shutter which can exhibit skew, wobble, and partial exposure. The well documented and highly undesirable problem of "Jello Cam" is caused by the way the rolling shutter scans the sensor from top to bottom. CCD's and CMOS sensors equipped with a global shutter are immune to this effect because the entire surface of the sensor is scanned simultaneously. Global shutters on CMOS sensors do exist but are extremely complicated and expensive to manufacture so are only found in more high end digital camera systems such as the high speed Weisscam HS2.
Read this in-depth and informative article on sensor artifacts by Barry Green of DVXUSER >>>
-CCD sensors, as mentioned above, create high-quality, low-noise images. CMOS sensors, traditionally, are more susceptible to noise.
-CCD's require a good deal of stable power to operate compared to higher efficacy CMOS sensors. CCDs consume as much as 100 times more power than an equivalent CMOS sensor.
-Because each pixel on a CMOS sensor has several transistors located next to it, the light sensitivity of a CMOS chip tends to be lower. Many of the photons hitting the chip hit the transistors instead of the photodiode.
-CMOS sensors can scan and offload their footage quicker, making CMOS a more appropriate choice for high-speed cameras.
-CMOS chips can be fabricated on just about any silicon computer chip assembly line so they tend to be extremely inexpensive compared to CCD sensors.
-CMOS sensors are catching up quickly to 3CCD’s with their ability to capture a large picture on a single chip. Most Super 35 sized digital sensors are CMOS i.e., Arri D-21, RED One, etc.
-Perhaps the most hotly contested topic relating to CMOS vs. CCD is whether a Bayer array (CMOS) can match the color resolution of a 3 chip camera or striped CCD sensor. Cameras with a large, single CMOS sensor that's laden with photosites such as the Arri D-21 claim that through oversampling, true 444 RGB can be captured. Numerically speaking, the way a Bayer filter is arranged will always have twice as many green photosites as red and blue. The argument is whether or not through oversampling equal parts of RGB can be derived. One thing that isn't debatable though is that high end 3 chip cameras that are 444 capable do in fact output equal parts Red, Green, and Blue.
Choosing a CCD or CMOS system can have a very real impact on the quality of footage your camera can shoot. While CMOS and CCD sensors do the same basic job of gathering light and turning it into a video image, they go about it in very different ways and just being aware of your camera's strengths and weaknesses is the best practical solution to the inherent limitations of the technology you're working with.
MORE TO READ:
A simple explanation of CMOS vs. CCD from Dalsa >>>
A very technical article on the topic >>>
A good article on Bayer Sensors from Cambridge in Colour >>>
Lenses designed for 35mm Motion Picture format will "crop" or become more telephoto when used on the smaller imagers found in digital cameras. Because of this, every digital format has a specific crop factor that you can use to find an equivalent 35mm format lens size. By taking the lens focal length of your format and multiplying it by the crop factor, you can determine a 35mm format lens that will produce the same Field of View (FoV). You can also use these crop factors to find equivalent lenses across various formats.
CROP FACTORS FOR DIGITAL FORMATS:
2/3", multiply Lens Focal Length x2.5 to arrive at 35mm equivalent
1/2", x5.4
1/3", x7.2
1/4", x9.6
To those transitioning to digital this info is useful in figuring out what size lens on HD cameras is going to correspond to what you already know from shooting on 35 and Super 16. Currently the 3 most commonly used sizes in digital camcorders are 1/3", 1/2", and 2/3" available in both 3CCD or 3CMOS versions. Each of these sensors require different size optics to deliver the same relative Field of View (FoV) and Depth of Field (DoF). If as a cinematographer you know exactly what a 28mm lens is going to look like when you put it on your Super 35 camera then wouldn't it be nice to know what lens you need to put on your 2/3" HD camera to get the same Field of View? Let's figure it out.
Based off of crop factor of x2.5 for 2/3" HD, we can divide 28mm by 2.5 which gives us an equivalent lens of 11mm for the smaller format.
The above illustration shows a lens image circle created by an 85mm lens. Lens make circular images, not rectangular ones. They are matted down to a rectangle when they pass through the gate and onto the film plane. As you can see, a lens designed for 35mm cinematography is optimized to create the largest possible field of view on 35mm motion picture film. The frame extends as close to the edge of the circle as it can before vignetting becomes apparent. The same size lens when used with a smaller imager does not perform the same way because it does not have the physical area to cover the image circle the same way Super 35 does.
This is why optics designed for 16mm can't be used on 35mm cameras; they're designed for a far smaller frame and will produce an image similar to this when used on a larger format:
Additionally a too large image circle when used on a smaller imager may let in unwanted light which reflects off the sensor and causes flare. Many people think that 35mm format lenses behave more telephoto when used on smaller sensor digital cameras. In fact they do but what is actually happening is by the default of its own size, the chip is just cropping in on the available image. So for example, if you put 25mm lens on a 1/3" camera, because of the 7.2 crop factor, that 25mm lens will behave more like a 180mm would on a 35mm film camera.
Reading the various online forums and books on optics, I've found there is a great deal of confusion as to what constitutes a "normal" lens. First of all, what do camera people mean by normal? By all accounts, a normal lens is one that is neither wide nor telephoto. In other words, one that approximates "normal" human perspective and field of view without creating unnatural distortion. In HD video, the exact same lens will create a totally different image depending on the size of your camcorder's sensor.
So how do how do you figure out how to create a "normal" Field of View for whatever format you're shooting?
In the world of 35mm still photography, a 50mm lens is considered to be a good choice for reproducing the human field of vision. The renowned French photographer, Henri Cartier-Bresson, shot his entire career on a 50mm lens for this reason. This is because a 50mm is quite close to the diagonal measurement of the film plane in 135 format (aka 35mm still) which is 43mm. To create a natural, undistorted perspective in photographic images you must first determine the diagonal measurement of the film plane or image sensor and then match the lens accordingly. A smaller size (mm) than this diagonal will result in a wider image and a larger will result in a more telephoto image.
So if the old rule of thumb is that a 50mm lens is normal in 35mm still photography and we also shoot on 35mm film in cinematography then wouldn't a 50mm be a normal lens for that format as well? Many people seem to think so but this is incorrect. The reason is that the size of the camera aperture is totally different in both formats. In still photography the film goes through the camera horizontally where there is more surface area between the perforations. This results in a larger negative area than the vertical movement motion picture cameras create. Compare the difference:
If this is the case then what is a normal lens for Super 35? According to the rule of the diagonal; to capture a perspective that is undistorted for this format you would use around a 28 or 30mm because the diagonal measurement of the negative is 28.48mm. This seems a hair wide to me though so I would err on the side of a 35mm as a normal perspective lens for this format.
As far as finding a normal lens for your HD camera goes, it's a little bit more nebulous than for film cameras. Because each camera uses different dimensions of active pixels and pixel aspect ratios as well as pixel sub-sampling and host of other specific factors, determining a precise "diagonal" can be challenging. The actual active size of 2/3" 3CCD sensors can be wildly different from manufacturer to manufacturer so there is no way of systematizing this at the moment. That being the case, many shooters just use the crop factor formulas to arrive in the ballpark of what they're going for. If you know your crop factors and sensor sizes then it's easy to predict your field of view before you set your lens.
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