Sens Up is For SuckersBy John Honovich, Published Apr 07, 2012, 08:00pm EDT
Run as fast and far as you can, if you are looking for a good low light camera and the manufacturer cites 'Sens Up.' This is a sneaky trick that vendors play when rating low light performance. Instead of admitting that there cameras suck at night, they say things like 'min illumination only 0.000001 lux with Sens Up 512x', etc.
Let's break down what Sens Up is and how it is used to trick people.
'Sens Up' implies that low light sensitivity is increased (i.e. sensitivity up - which seemingly is a good thing - who wouldn't want their cameras to be more sensitive to light? However, the problem is how this is done.
To make the camera more light sensitive, the shutter is open longer so that the camera can capture more light but there is a major downside to this.
The longer the shutter (i.e. exposure), the more moving objects will blur. See it below:
The image with the longer shutter is brighter but the moving person is blurred out. Bad tradeoff.
Sens Up Relative to Default Shutter
Here's how 'Sens Up' comes into play. The default shutter in most cameras is 1/30s because the default number of frames in a second is 30. To get 30 frames in a second, the shutter cannot be open longer than 1/30s for each frame.
Sens Up signifies how much longer a shutter is than the default 1/30s:
- If a camera is at 'Sens Up 2x', then is has a 1/15s exposure (2 x 1/30)
- If a camera is at 'Sens Up 4x', then it has a 1/7.5s exposure (4 x 1/30)
- If a camera is at 'Sens Up 32x', then it has a ~1 second exposure (32 x 1/30)
The more you 'Sens Up' the brighter the image will be but the blurrier anything that moves with be. Go back and look at the 1 second exposure image above - that is 'Sens Up 32x' - unusual for most applications.
[NOTE: In analog NTSC cameras, default shutter is typically 1/60s because each frame consists of two fields. As such, 30 frames per second requires 60 fields per second. To get those 60 field, you typically need a shutter of no more than 1/60s.]
How Bad Sens Up Gets
Manufacturers often run wild with Sens Up ratings. Numerous Samsung cameras are rated with a Sens Up of 512x - which is insanely misleading:
The shutter needs to be held open for over 8 seconds (1/60s x 512) to achieve 'Sens Up 512' [note: this is an analog camera, that is why 1/60s is used]. Even a slug would be blurry at such an exposure setting. Even more crazy, this is included in PTZ specifications [link no longer available] as well, where presumably the camera is moving.
Many many manufacturers do this - Samsung is not alone. Google results for 'Sens up 512', 'Sens up 256', 'Sens up 128', etc. return numerous results.
If you want a good low light camera, you should almost certainly disqualify any camera that lists its low light performance using 'Sens Up', it's a dirty trick used to confuse non experts into thinking a camera that is bad at low light is actually good.
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