Rolling Shutter - simple quetsions

W

W.bat

Member
I'm really new to video but an old hand at stills (pro). Can I ask what is rolling shutter?

Also if I set the shutter speed at say 500th of a second when shooting video as opposed to a 50th what happens? ie does the shutter speed have a bearing on the video shot.

Thanks in advance.
 
Rolling shutter and shutter speed are different.

Rolling shutter is that the whole frame is not photoraphed in one go but over a set of time - lets say 1/100th of a second

That means that the moment captured at the top of the frame is 1/100th later than the moment captured at the bottom

(bascially the sensor is a scanner that rolls up the image area)

This leads to 'skew' in a fast changing image - google video jello

Shutter speed is how long the sensor (each bit of it) is exposed for

typlically a normal shutter speed is 50% of frame rate - say 1/50th at 25 FPS

You will know from still that a 1/50th shutter creates blurred image on a moving subject

in stills this blur is (generally) not good, but in video the blur helps the frames meld together into 'motion'

Shooting a 1/500 would not be typical as there would not be a blur in the frames, this gives the video a very staccato feel to watch - can give you a headache

So for video stick to 50% of the frame rate for your shutter speed

Of course rules are for breaking and the high shutter stacato look is often used in action sequences - 'saving private ryan' look

A slow shuuter gets really blurred frames, typically used for 'drugged out' sequence..

S
 
W.bat said:
I'm really new to video but an old hand at stills (pro). Can I ask what is rolling shutter?

Also if I set the shutter speed at say 500th of a second when shooting video as opposed to a 50th what happens? ie does the shutter speed have a bearing on the video shot.

Thanks in advance.
Click to expand...

A 'rolling' shutter is similar to the 35mm still 'slit' shutter which would travel across the film plane, to obtain the 'high shutter speed'. Typically one would see this at shutter speeds above the 'flash sync' speed, if one used 'flash'... one would have a narrow band of image... and black elsewhere depending on the high shutter speed setting and when the flash actually took place.

In 'motion picture' capture DSLR's often do not capture the entire sensor field 'in one shot' but read out areas of the sensor, which leads to 'rolling' shutter effect (think of it as an 'electronic' slit), a banding or distortion of the image, depending on the speed of the camera in motion, as well as more obvious in some situations than others.

There are panning speeds or object 'angular' speeds relative to the camera that either enhance or minimize the effect, a stationary camera, an object coming directly at the camera, will probably not show the effect. A moving camera with background objects, such as a 'whip pan', will have high speeds across the film plane, and show the effect more. Handheld camera on a bumpy truck... more obvious...

While the artifact is some what different from 'film film' motion picture cameras, even they have certain artifacts that 'speed' rules apply. The 'general' rule is an object should not take shorter than 5 seconds to traverse the entire frame, either from camera motion, or object motion.

Test will allow one to 'refine' this to one's own camera...
 
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