Nokia camera mechanical shutter explained by Damian Dinning

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Damian Dinning is the person responsible for many awesome camera innovations at Nokia. Before leaving the company — his place was taken by Juha Alakarhu — he brought PureView to the world, first, in the form of the Nokia 808, then, the Lumia 920 with PureView stage-two.

The Nokia 808 PureView features, among many other camera innovations, a mechanical shutter. While the Nokia EOS is nothing but a (recurring) leak at the moment, it is rumored to have a camera system which heavily relies on the one used in the 808. A recent leak tries to depict the same construction, including a mechanical shutter.

Damian Dinning felt the need to comment on Nokia camera mechanical shutter. He made it clear that the comment was only referring to that, playing it safe so that we don’t misinterpret his thoughts and consider them a confirmation of any sort of the Nokia EOS.

Nokia mechanical shutter

Here’s his input on a recent MyNokiaBlog post:

Hi everyone, there are so few factually correct statements in the original piece or related comments (no disrespect intended) I felt compelled to help explain. :)

Please note, my comments are ONLY addressing the general topic of mechanical shutters – no more.

Keeping it simple, the main reason for fitting mechanical shutters is for use with xenon flash. Typically CMOS sensors read light across the sensor from left to right and top to bottom. The time each pixel is ‘read’ is the effective shutter speed. This is OK in most cases and OK with LED flash as the light is effectively constant/continuous. LED flash in most cases being the equivalent of turning on a torch before the exposure and turning it off after the exposure has been made, effectively increasing the amount of light in the scene more or less for the duration of the picture.

In the case of xenon, the flash fires a very short ‘pulse’ of light. This pulse can be as short as approximately 1/25,000 (hence why xenon can freeze high speed movement). With a typical CMOS sensor the time difference between the 1st pixel being ‘read’ and the last is greater than this time. The result would be some pixels would be correctly exposed whilst others would be dark or even potentially black. To overcome this, the pixels are effectively read all at the same time. But to achieve this all pixels are turned on, the shutter opens, the flash fires, the shutter closes and the pixels turned off. And that’s why typically mechanical shutters have been needed in products such as n8, n82, n808. In some cases some latest generation sensors can read all their pixels at very high speed (note: again don’t ask me to comment on speculation or rumour) allowing xenon to be used. In some cases e.g. Nikon 1 series these later generation sensors are allowing for electronic shutters which can provide potential advantages in high frame rate scenarios which mechanical shutters would not be suitable for.

In some cases a hybrid approach maybe used e.g. a SE product of a few years back which featured xenon only used the mechanical shutter for flash but not other situations, which meant in that case it didn’t provide the following potential advantage….

With mechanical shutters, because the pixels are effectively read all at the same time it overcomes the motion skew effect which can typically occur with CMOS sensors due to the time difference between the first and last pixels being read. As the read time from CMOS sensors is increasing (shorter read times) this is becoming less of an issue in some cases.

Mechanical shutters do require additional space, there are no space advantages to them.

As for dust protection there is some theoretical advantage to them but in practice (at least in my experience) I have seen dust penetration in all cameras, there is a fundamental limit to what can be done to prevent dust penetration.

Hope that clarifies things.

Source: MyNokiaBlog

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About The Author
Anton D. Nagy
Anton is the Editor-in-Chief of Pocketnow. As publication leader, he aims to bring Pocketnow even closer to you. His vision is mainly focused on, and oriented towards, the audience. Anton’s ambition, adopted by the entire team, is to transform Pocketnow into a reference media outlet.Given his background, and knowing his potential, something tells us he will succeed this time too! Stick around!Read more about Anton D. Nagy!| Google+