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Old October 6th, 2007, 07:24 AM   #1
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Sony V1U (North American) shooting in 50hz Australia

Hi everyone.

I know there's probably hundreds of threads out there devoted to overcoming this problem but I've had no luck in searching for them.

I'm shooting a concert tour in Australia and have run into several venues that use fluorescent lights backstage. The 50hz "dance" is killing me with my North American (60hz) V1U. Does anyone have any suggestions for overcoming this problem? The CMOS chips seem to make the problem more pronounced than I was used to seeing with my 60hz DVX-100a in 50hz countries.

Also, while I'm on the subject, why did Sony remove the 50/60hz switchable feature from the V1 after it worked so well with the Z1?

Thanks,
Adam
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Old October 6th, 2007, 07:29 AM   #2
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The answer to your last question is a one word 'price', Adam. With the V1's spec being so good the Z1 had to be allowed some USPs to keep it shipping.

I'd suggest you try different shutter speeds to eliminate the flourescent flicker. If you can put the camera on fixed aperture and variable (auto) shutter speed (as I could with my VX2k) you can lock that down at the point where flicker dissapppears.

tom.
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Old October 6th, 2007, 09:31 AM   #3
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I've never tried, but I wonder if using the V1's 24p setting would do a better job since it closer the 25 fps PAL standard?
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Old October 12th, 2007, 05:05 PM   #4
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A 100Hz shutter should do, but it also cuts a lot of light...
It's better the other way round, a 60Hz shutter with a PAL cam doesn't hurt that much, does it?
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Old October 13th, 2007, 06:09 AM   #5
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You mean 1/60th sec shutter speed? It's fine to use that with your PAL camera - only thing is the camera becomes less light sensitive - as all NTSC versions are.
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Old October 13th, 2007, 07:24 AM   #6
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There is a formula for figuring out all this with 50 or 60hz low frequency lighting and is applicable to both HMI and fluorescent (magnetic ballasts usually but there are actually electronic ballasts that operate at this lower frequency too):

Safe camera speeds with 60hz lighting :

Camera speed in fps = shutter angle / 3 / LPEP

Where LPEP = number of light peaks that you want to capture per exposure
period (typically 2 per cycle, or hz).

Safe shutter angles with 60hz lighting :

Shutter angle = speed in fps * 3 * LPEP

For 50hz power replace 3 with 3.6 in both formulas.

What all this means is that if you don't capture at least two cycles of light output during your exposure then you start to get flicker.

So for example in 50hz situations and assuming you want 30fps it would be as follows to figure out shutter adjustment:

30*3.6*2 = 216
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Old October 14th, 2007, 12:39 AM   #7
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Richard

If I'm reading this right, what you are saying is that SLOWER not faster shutter speed is the way to go in order to capture 2 cycles. I forget the angle to fps conversion, but in dumb terms, it seems that you would need a shutter speed of half the frequency to capture two cycles. ditto for fps.

Is this close to correct?
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Old October 14th, 2007, 04:49 AM   #8
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Absolutely. Think about it like this. Each shutter moment is a moment where we're capturing light. If you're light is flickering that means that its not refreshing at a very high rate. 50 to 60 times per second is not so much! You are practically guaranteed to see flickering if you're shuttering is open at a moment the light is refreshing and not fully lit. The faster your shutter the more likely you are to be open at such a moment. Many feel that you need at least two refreshes of your light per shutter moment to be safe and not see flicker. For this reason, many of us that are manufacturing electronic ballast-oriented solutions for fluorescent or HMI are interested in the output driving frequency of the ballasts we source. 40,000 times per second is not uncommon nowadays for a fluorescent ballast (like Cool Lights) and 75 to 150 times per second is common for metal halide / hmi. When you're updating 40,000 times per second on a flo--flickering is a non-issue at any shutter speed and normal FPS setting.

There are very few solutions around that can drive HMI higher than 150hz and you will get some bulb noise when you do this as the bulbs were all originally designed for magentic low frequency ballasts. This bulb noise manifests itself as a slight humming.
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Old October 14th, 2007, 08:44 AM   #9
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Hmmm. Is there any such thing as a HD-PAL camera?
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Old October 14th, 2007, 08:46 AM   #10
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Hmmm. Is there any such thing as an HD-PAL camera?
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Old January 28th, 2008, 05:04 PM   #11
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Interesting

Thanks for this in-depth explanation.
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