Camera Input
What features should I look for in a camera?
Following are a number of features common to many cameras currently on the market. Becoming familiar with these features and their functions will help you pinpoint which features, and ultimately what type of camera, will best suit your next project's needs.
Automatic Exposure [AE Mode] - This feature automates camera adjustments to maximize effectiveness in for a wide range of lighting conditions. A camera equipped with Automatic Exposure can successfully shoot and quickly adjust for lighting conditions that a camera lacking this feature would have difficulty with.
Automatic Gain Control [AGC] - AGC refers to special circuitry that automatically adjusts the camera or recording device’s gain level to allow for the optimum output signal without causing potentially damaging circuit overloads.
Auto Iris - An automatedIris will automatically read and interpret lighting conditions make adjustments by either opening or closing to compensate for them. This allows for more consistent output, and frees the operator to focus on other elements of the recording or shoot.
CCD Iris ™ - A feature developed by Sony that adjusts shutter timing to produce consistent video signal output levels regardless of varying lighting conditions. A CCD Iris effectively allows for optimum light exposure to be achieved with the use of a fixed iris lens.
Digital Signal Processing [DSP] - Cameras emit digital signals (as opposed to analog) to store information about their collected images. A camera that is DSP enabled will be able to remove unwanted noise or other variables from these signals on-unit. This essentially means that the processing will occur within the camera and does not require any further accessories to apply digital signal manipulations to the camera’s signal.
Donpisha™ - Means “immediate” in Japanese. The Donpisha shutter allows camera operation to occur at a particular point in time and is used to shoot moving objects without a time delay. The Donpisha shutter can capture flicker-free images of fast moving objects
Electronic Shutter - This is generally a mode that can be set on a camera that allows for exposure length to be precisely controlled in order to reduce smear when recording quickly moving objects.
Field Integration/ Frame Integration - This mode adjusts the CCD’s normal charge to occur for 1/60th of a second. This greatly reduces blur but only allows for ½ vertical resolution. Frame adjusts the CCD’s normal charge to occur for 1/30th of a second. This allows for full vertical resolution, but can result in blurring if recording quickly moving objects.
HAD ™ - A new technology developed by Sony, Hole Accumulated Diode improves camera performance in spectral response, vertical smear and sensitivity. The sensor also allows for an electronic shutter capacity for IT type sensors.
HyperHAD ™ - A derivative of the HAD sensor that also incorporates OCL which results in nearly doubled sensory sensitivity and produces images with no perceptible smear.
On Chip Lensing [OCL] - A camera with OCL has microscopic lenses mounted over each sensing pixel. This results in nearly doubled sensory sensitivity.
Progressive Scan CCD - Progressive scan allows for the simultaneous acquisition of odd and even fields which allows for full vertical resolution in Sony’s Donpisha mode.
Restart/Reset - This function allows the camera’s normal charge accumulation cycle to be stopped and reset to the beginning of a new cycle. This function primarily is used to allow for synchronization between the video camera and an external strobe event.
White Balance - White Balance is a means of adjusting the color balance of a camera. Often, particularly with video camera’s, white balance is automatically adjusted per a sensor that reads light levels as the subject is photographed.
White Chip - This is a special filtration circuit which limits signal amplitutde levels to remove readings in excess of its user-established level. This is a particularly important feature for those interested in broadcast as the NTSC signal amplitude max is below the signals produced by most cameras.
Zoom Lens - Generally speaking, a lens with a focal length that can be adjusted. A zoom lens will allow the operator to change magnification and angle of view without moving the camera or changing lenses.
What are some important elements that vary between cameras?
Given that all cameras were not created equal, an awareness of the general qualities and categories that vary from camera to camera is crucial to making an informed decision about the piece of equipment that it is most appropriate for your project. Following is an index of specifications that vary widely from camera to camera and have a significant effect on the type of output a particular camera is capable of producing.
Angle of View - The angle of view is essentially the portion of a scene available for viewing through a particular lens. The focal length of the camera’s lens is the primary determiner of this property; wide angle lenses provide a more wide and zoomed out view while a telephoto lens provides a closer image of the subject but less of the landscape surrounding it.
Aspect Ratio - This is a ratio that quickly communicates the proportions of a camera output. The variables x:y stand for the ratio of height to width of an image. A standard video monitor has an aspect ratio of three units high to four units horizontal; this is expressed 4:3.
Depth of Field - The distance between the closest and furthest object in focus with any given lens. Depth of field depends greatly on the choice of lens focal length and aperture. Generally, a shorter focal length and smaller aperture will increase a camera’s depth of field.
F/Stop, F/Number - A system of gauging the calibrated measure of an aperture lens opening. F/Stop and F/Number are often used interchangeable. Common F/Stops include f/1.4, f/2, f./2.8, f/4, f/5.6, f/8, f/11, f/16, f/22. As the numbers increase the light let in on the imager decreases as the lens opening becomes incrementally smaller. In low-light situations a small F/Stop produces the best results.
Focal Length - The distance between the optical center of a lens and the camera’s image plane. The focal length influences a camera’s depth of field and angle of view. Often times the term Zoom Lens and Variable Focal Length Lens are used interchangeably, as the manipulation of focal length results in what is more commonly known as a zoom effect.
Gain - The amount of amplification applied to an electronic signal. This term is often used interchangeably with amplitude of volume. Particular to camera considerations, gain, or signal amplification, allows the light present in dimly-shot pictures to be amplified, thus clarifying the image.
Minimum Object Distance [MOD] - The minimum distance between a camera and an object at which the camera can focus on the object.
Modulation Transfer Function [MTF] - MTF can be understood in very simple or very technical terms. Spoken simply, the MTF is a function that evaluated the resolution capacity of a lens in a given scenario, with any given subject. The details of the function are thus. As a disclaimer, this does not represent a standard or official means of measurement, but a simplified version of the function that has been created to clarify the concept. Let us understand modulation as a quantity defined by (Lmax - Lmin ) / (Lmax + Lmin), where Lmax and Lmin are minimum and maximum luminance levels for a given grating. This is known as the Michelson contrast. The Modulation function (M) is then applied to the modulation of the image (Mi)/ the Modulation of the object Mo. In our equation (v) stands for a specific frequency, thus: b)MTF(v) = Mi / M0.
Sensitivity - The amount of light required to produce a peak white signal (brightest possible signal) given a specified lens aperture. The less light required to produce a peak white signal, the more sensitive the greater the camera sensitivity.
Signal to Noise Ratio [S/N] - A ratio between the normal signal output and the noise (extra data) level within a particular signal; the higher the ratio (5:1 over 2:1) the more pure the signal.
Smear - An image smear is the undesirable product of CCD chips. A smear appears as a vertical stripe across the image and is caused by distortions in high brightness values.
Spectral Response - Spectral response is the measure of a sensor’s ability to transfer light frequencies into digital images. Ideally, a camera should be able to sense and accurately output all frequencies within the spectrum of visible light, however, cameras will usually vary on frequencies on the extremes the spectrum as frequencies near red or infrared.