MegaVision has an interesting approach to optimizing the signal-to-noise ratio of a capture. While one of the better known brands uses an actively cooled chip (with its resultant condensation problems), MegaVision makes a map of each and every pixel (we call this map a dark capture) and subtracts each pixel’s value above black, if you make a map and choose to implement its application.
Dark Correct is that vehicle and it will be necessary on some cameras all the time, on other cameras most of the time, and on some cameras very seldom. Why this difference in the use of this important feature? Because different chips have different noise signatures and because newer chips benefit from the recent advancements in chip manufacture and are therefore less noisy. When do you need to enable Dark Correct? When shadows start to look noisy. Noise shows up looking very much like grain in film.
What causes noise? Several factors can cause noise, the most tangible factor is environmental; heat in the form of high ambient temperatures contributes to the noise in a digital capture. If the shooting conditions feature ambient temperatures above 75 degrees Fahrenheit, start looking to enable Dark Correct. Temperatures in excess of 90 degrees Fahrenheit may find Dark Correct falling short of truly effective. In reality, temperatures in the 80’s are not considered optimum for the operation of a computer and will therefore not be optimum for any digital camera. While we have generally become ambivalent about lofty operational temperatures for computer equipment, lower temperatures will extend the service life of any electronic component including computers. Most professional installations of digital cameras include a stable, cool ambient environment. Do not under estimate the value of an air conditioned studio.
To evaluate the effect of temperature on the T2 you’ll need to be aware of the dark value of the camera. The T2 conveniently takes its own “temperature” and displays it as a dark value. This dark value on average runs between 10 and 100 on a scale of 0-4,096. To view the dark value, start a Setup>Balance. The first field suggests doing a new Dark Correct capture if the dark value has appreciably changed since the last Dark Correct capture. Reference this dark value and make a new dark capture if the value moves more than 2 whole units. Generally, you won’t see the dark value change a lot. If the dark value does move around indiscriminately, let us know, we’ll probably want to look at your camera.
When noise does show up in a capture you should be aware of it. You should be checking low values as a matter of course before saving any image. Close inspection of low values; for general placement of important reflectances and verification of adequate transition of tone is mandatory. This is where you will notice noise. Do not fall into slipshod technique by failing to evaluate the fit of your image to your intended target. When you do see noise and it cannot be temperature related, it will fall into four general possibilities: 1. A Sensitivity setting greater than normal, 2. an overaggressive Capture Curve, 3. a Gamma value in excess of 2.0 in addition to the above two conditions, and 4, a lengthy shutter speed.
Sensitivity electronically “pushes” the exposure index of the chip. Just like film, pushing the development pushes up the grain, which in digital speak is called noise. If you see noise in the shadows, check the Sensitivity you’re using. Noise generation may be normal if you’re really pushing the exposure index. Consider a new dark capture if you suspect Sensitivity playing a part in noise generation.
Capture Curve can add noise to a low value if you’re under lit and you’re using an aggressive curve to open up the low values. The display of noise is a physical reminder to light your way to better images, rather than wiggling software. Evaluate the shadow end of the Capture Curve. If it starts essentially straight up from the shadow on its way to the highlight corner, you may want to add some fill or increase the density range a bit.
An elevated Gamma value can create noise. Usually, an elevated Gamma value does not significantly affect the noise in an image. However, it can; in concert with an aggressive Capture Curve and/or Sensitivity push and/or lengthy shutter speed. These aggregate conditions may be reason for a new dark capture.
Lengthy Exposure times will up the noise generation in a capture. The Photoshoot™ software will actually ask for a dark capture for each shutter speed. If you make a shutter speed change and the software does not detect a valid dark capture for that speed, a pop up dialog box will alert you to that fact. Make sure you have a recent dark capture by capturing a new one every time you use a long shutter speed.