1/30 sec shutter, 30p or 60p best?

[Paul Anderegg]

If I were to lock my 790 into 1/30 second shutter speed, because i shoot everything at night in the dark, would the results look/work better shooting 30p or 60p? The final edited and broadcast files will be 60p, but I hear 1/30 shutter has weird effects on 60p recording?

Also, would 30p recording offer better video quality in general over 60p when shooting HDV 18Mbps? I am not sure if half the frames being recorded means each frame is twice the bitrate and quality????

Paul

[Garrett Low]

You can't have a shutter speed of 1/30 with 60p. It is impossible to have the shutter open longer the length of the frame. Slowest shutter speed you could use for 60p is 1/60th.

[William Hohauser]

If you are at 1/30th then 60p is a waste of frames as you are duplicating images and potentially you are lowering the quality of the image as the camera has to compress twice as many frames into the same bit rate.

I am not sure about the 790 but I have had cameras that allow you to record slower shutter speeds than the recording rate, certainly the 700 and the 600 allow you to do this with 60i.

[Garrett Low]

Originally Posted by William Hohauser

If you are at 1/30th then 60p is a waste of frames as you are duplicating images and potentially you are lowering the quality of the image as the camera has to compress twice as many frames into the same bit rate.

I am not sure about the 790 but I have had cameras that allow you to record slower shutter speeds than the recording rate, certainly the 700 and the 600 allow you to do this with 60i.

60i is 60 half frames per second. The frame rate is actually 30fps (29.97fps). In any case, the frame would only be exposed for 1/60th of a second at the longest. It is pure and simple physics. The camera may let you set the shutter speed longer than the frame rate, but the actual exposure time cannot be longer than the frame rate.

[William Hohauser]

Sure it can. The entire recording method is done by frame buffer. There are no physical restraints on shutter speed as in film or analog recording with old video tubes. 1/15, for example, is stored and then distributed over two frames in 30p. This is all happening in data to non-moving storage. It doesn't make a difference if the actual writing of the data is much later than the event. I'm talking within a second here. The HM600's shutter goes to 1/7.5 and the shutter on a Panasonic GH3 goes to 1/2. Try it yourself, there is no way to create the resulting motion blur except if the camera is holding the imaging chip open longer.

60 interlaced (60i) is 60 captured frames of movement per second, the frames are half the resolution of the chosen format intertwined so to create the illusion of full resolution at 30fps. Works great with most recordings. However it does create issues with recording action which is why many sports broadcasts are shot in 720p60. Now that 1080p60 is becoming feasible, people will switch to that for filming action although not for final broadcast yet.

[Garrett Low]

OK William, I got what you're saying. But wouldn't that create very disturbing and unnatural image. If say you shoot at 60fps and you're holding the shutter open for 1/30 of a second. The first frame's end position will be 1/30th of a second after the beginning of the next frame. As you noted for sports or actually virtually any shot with moderate motion, it would appear to jump back 1/30th of a second every frame.

I'll have to try that, just never thought of even trying it.

[William Hohauser]

Without getting detailed into the very interesting research into frame rate and perception, I can summarize it this way: The faster the frame rate, the more real the image looks. The slower the frame rate, the more dreamlike the image looks. 60fps says news - 24fps says entertainment. 24fps is a good compromise between fantasy and reality. Slower frame rates than 24 start to look odd not to say that that can't be used to good effect. Music videos and horror films use slow shutters often.

[Taky Cheung]

Years ago when 60i is the only frame rate available in consumer cam, setting shutter speed to 1/30 is the poor man progressive camera. While seeing all the interlace lines at other shutter speed settings, they all disappear if the shutter speed is 1/30.