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Movie mode - technical discussions Still imaging is complicated enough but for most of us video and movie making is a whole new world to get to grips with - here is the place to request help and advice and to post it too.

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Old 5th November 2013
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Rawcoll Rawcoll is offline
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30fps and PAL

I really only dabble in video, and then I've used the GH2 which can be set to a 50fps frame rate. But both Olympus and Fuji are based around 30fps. I've looked through the tutorial and found that useful, and I can understand the origins of flicker when 30fps is used in lighting that flickers at 25/50 per sec. However, what I'm not clear about is how 30fps footage plays on a tv designed for PAL (or 24fps for that matter). Do you get flicker, or does the movie go a little bit slower (faster). Or does the tv just adjust its frame rate to match? Video technology is a whole new ball-game to me and I don't know enough about it. Could one of you video techies explain what goes on please?
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Old 7th November 2013
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Re: 30fps and PAL

It's down to your editing software. You have to choose at the outset what frame rate the final video will be, and then the software will sort out the frames from your source material.
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Old 8th November 2013
raichea raichea is offline
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Re: 30fps and PAL

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Originally Posted by Rawcoll View Post
Or does the tv just adjust its frame rate to match?
Modern TVs usually adjust to 25 or 30fps as needed.
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Old 8th November 2013
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Re: 30fps and PAL

Thank you both.
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Old 19th January 2014
davidfarquhar davidfarquhar is offline
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Re: 30fps and PAL

My understanding is that the flicker in artificial light is not related to the fps of the video being taken. It is actually related to the shutter speed used in the footage.

UK electricity runs at 50 Hz, so every 1/50 of a second the lights go through an entire cycle. During the cycle the colour and intensity of the light varies slightly as the electricity cycles (thats about as technical as I get on that part of it).

If you are shooting at 1/60 shutter speed then every frame on your video will capture 5/6 of a cycle, and given that each frame starts 1/30 second after the last, you cannot ensure that the same 5/6 of a cycle is captured on every frame. Hence the colour and intensity of the light will vary slightly from frame to frame. This gives rise to the flicker as you see different intensities on each frame

The solution to this is to shoot at 1/50 second shutter speed. Every frame will capture a full cycle of the electricity, regardless of when you start it. Thus each frame will capture the same average light colour and intensity, and the resulting video will have no flicker.

I believe (from distant memory) that the E-M5 will default to the conventional norm of "shutter speed half your frame rate" in automatic mode. This norm is there to give your footage a "normal" feel to it. If you shoot 30fps at a shutter speed of 1/120, then the footage will appear very jerky. Shooting it at 1/30 will appear sluggish. So over time the normal convention has arisen.

However if you shoot in manual mode you get to control both shutter speed and aperture, so you can manually set shutter speed to 1/50 (not quite half frame rate but so close as to not be noticeable), and then use aperture and ISO to adjust to give the correct exposure. I always shoot movies in manual for this reason, with shutter speed 1/50 indoors to avoid flicker.

I hope this long explanation helps - try it out on manual mode its really easy to see the effect even in the viewfinder. Please note I'm not a professional videographer so if any of my above is slightly wrong I apologise - I do know however that 1/50 will sort out your flicker

David
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Old 22nd January 2014
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Re: 30fps and PAL

Thanks David, I see where you are coming from here. The only problem I see is if you want to shoot at 60fps, where 1/50th would be too long.
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