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What was the judgement about sodium?


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#1 G McMahon

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Posted 31 July 2006 - 11:44 AM

Hello all,

In my search through the manual (I was concerned whether I should be shooting at 1/50 shutter speed PAL, since I believe video does not run of a mirror), I stumbled on this portion which I have noticed around the forums but cannot fully decipher it.

The luminance level of artificial lighting ? particularly that of a fluorescent lights and mercury lamps ? changes in synchronization with the power line frequency of 50 Hz, the vertical sync frequency (approx. 60 Hz) of the camera recorder and frequency of the lighting (50 Hz) will interfere with each other, possibly causing the white balance to change cyclically. When shooting under artificial lighting or when adjusting the white balance, set the shutter speed as shown below. (Chart)

From operating Instructions manual ? Model Ag DVX100Ap

Is this referring to shooting out of synch, when say Pal is used under lighting power supply in non-PAL countries? Is this referring to the spectral range of the sodium is too great for the camera to render all colours (past forum)or, it cannot keep its white balance consistent under those lighting conditions as fluctuations from the light source of the sodium render it difficult to reproduce?

Shooting under sodium?s this Saturday. Was planning on shooting natural at 4500K colour temperature, and subtlety mixing corrected lights on the faces to ease some of the sting from the colour. Now I?m have second thoughts and thinking I should ease back a touch on the saturation and colour of the sodium?s and going 3200K. I don?t want to leave much correction in post (I believe you do not have much play in post with video on a budget). Was I being too over zealous or I am getting slightly gun shy now?

We are motivated in the script by letting the colours of the city in the BG to come alive, lots of colour and movement to influence the state of the characters in reference to their setting.

I am right in shooting at 1/50th?

Thanks all for sitting through the mammoth piece. I hope all can benefit and I look forward to the scrutiny after I post some grabs after the shoot.

Graeme
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#2 Stuart Brereton

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Posted 31 July 2006 - 01:00 PM

Shooting at 1/50th should eliminate problems from sources powered on 50hz mains.

Sodium and Mercury lamps do not emit the full spectrum of light. Large parts of it are missing from these lamps, and they exhibit huge spikes at other frequencies.

Sodium lamps, as you've probably noticed, are a kind of pinky orange (unless they are the older Low pressure sodium lamps, which are much more saturated orange). Because of the discontinuous spectrum of these lamps, you cannot correct them back to white, there is simply too much of the spectrum missing.

I would use a tungsten white balance on the camera, and try to use the sodium sources as backlight or kickers, and use a soft tungsten source as a key for the talent.

If you need to gel your lamps to a sodium look, I suggest you check the archives for Michael Nash's gel pack of CTO and bastard amber (I think), which is a very good match.
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