Lighting-up Time
was a valuable specification. A good colour camera would have a sensitivity of between 5 and 7 lux, and an average rating was between 8 and 10 lux. Nowadays, you regularly see sensitivity
figures of 0.01 lux, and even 0.001 lux. Does this mean that the cameras are really that much better than those of 15 or 20 years ago? Sadly, it doesn’t. What has changed is the way in which sensitivity is quoted. Increasingly figures are taken with processing and slow shutter on, set at their maximum, and the resultant video image isn’t a full signal but a 20IRE one. If that doesn’t work, there are a few other tricks that can be used. Interestingly, Benchmark still assesses
camera sensitivity in the traditional way. It means every device we test undergoes the same process, so the figures can be compared to give an indication of performance. Just as an aside, the actual performance figures from 15 or 20 years ago haven’t changed much! One thing that our numerous tests have
In any video application, light is a very important element. Without light, cameras cannot define an image. You may hear talk of so-called ‘zero lux’ cameras, but the reality is that if someone had created one, they’d either be living a life of luxury, or be hidden away in some military research centre! All cameras need light of some form, and with HD video, light quality is also an issue!
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f you ever want a prime example of how specsmanship can get very confusing, consider something that should be simple, such as camera sensitivity. Traditionally, this is a measure of the level of light, at the viewed scene, that is required to allow any given camera to deliver a 1 volt peak-to-peak video signal with all processing functions - such as gain or slow shutter - switched off. Back when everyone (or at least every credible manufacturer) tested sensitivity in this way, it
proven is that despite what some might tell you, HD cameras do struggle to meet the levels of low light performance achieved by analogue CCD-based cameras. However, this does not simply mean that HD video cameras require more light than analogue cameras; the light quality is also very important.
Dark times?
There are two main reasons why HD cameras can often deliver inferior low light performance to traditional cameras. The first has to do with the sensor type. Many HD cameras make use of CMOS sensors, which are attractive to manufacturers as they are simpler - and therefore cheaper - to manufacture. The process follows along the lines of other chip manufacturing. Traditional CCTV cameras - and some HD
cameras - use CCD sensors. These chipsets are older and more established. They are more costly as they have a proprietary manufacturing process, but their performance is proven to be superior in low light applications. In everyday use, away from laboratories and test equipment, the difference isn’t always that obvious, because much of the low
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