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SDX900 video level


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#1 Craig Needelman

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Posted 06 October 2006 - 10:10 AM

I'm on a shoot in Maine with 3 SDX900's. We set up the cameras shooting the same CU and set the video level to match on each camera using a scope. The new SDX900 is about a stop slower than the other 2. All cameras are set to 0DB and the knee is identical. We even swapped lenses and the new camera is still a stop slower. Any ideas? Please reply on list.

Craig Needelman
DP Philadelphia

Edited by Craig Needelman, 06 October 2006 - 10:10 AM.

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#2 John Ealer

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Posted 06 October 2006 - 10:22 AM

I'm on a shoot in Maine with 3 SDX900's. We set up the cameras shooting the same CU and set the video level to match on each camera using a scope. The new SDX900 is about a stop slower than the other 2. All cameras are set to 0DB and the knee is identical. We even swapped lenses and the new camera is still a stop slower. Any ideas? Please reply on list.

Craig Needelman
DP Philadelphia


Check that PHALFSHUT is the set the same on all cameras.

If the new camera is set to ON, it will default to a 180 degree default shutter, meaning that if you're shooting 24P, you're using a 1/48 shutter speed. That's your one stop difference.

This setting is hidden in the OPTION menu. Hold the MENU button down and the LIGHT button (by the LCD display) to access it.

J
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#3 Craig Needelman

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Posted 06 October 2006 - 10:43 AM

PHALFSHUT is set to on, on all cameras. what now
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#4 Craig Needelman

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Posted 06 October 2006 - 10:53 AM

Just tried turning PHALFSHUT ON AND OFF and didn't see any difference on either camera.
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#5 John Ealer

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Posted 06 October 2006 - 10:59 AM

PHALFSHUT is set to on, on all cameras. what now


Did you load all the same scene files into all three cameras before you started? You mentioned shooting a chart and scoping it, checking the knee, etc., but GAMMA slope and type could be different, among many other things.

You might want to try saving the settings on the "dark" camera and loading them into one of the other ones to see if that changes anything...

Just to cover the obvious:

Shutter is set the same on all cameras?
Does the problem persist at different filter wheel settings? (Could be a filter wheel anomaly...)
Do all the cameras have the SDI card installed? (i.e. are you sure you're monitoring the same signal with ?)
There's no chance of a cable problem (i.e. splitters if using composite analog), or a termination problem?

PHALFSHUT is over-ridden if you turn the SHUTTER ON with the main switch, which is why you're not seeing any difference. So I think you're probably looking at a situation where the shutter speeds are slightly different, so I would look there first.

J
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#6 Craig Needelman

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Posted 06 October 2006 - 01:08 PM

Did you load all the same scene files into all three cameras before you started? You mentioned shooting a chart and scoping it, checking the knee, etc., but GAMMA slope and type could be different, among many other things.

You might want to try saving the settings on the "dark" camera and loading them into one of the other ones to see if that changes anything...

Just to cover the obvious:

Shutter is set the same on all cameras?
Does the problem persist at different filter wheel settings? (Could be a filter wheel anomaly...)
Do all the cameras have the SDI card installed? (i.e. are you sure you're monitoring the same signal with ?)
There's no chance of a cable problem (i.e. splitters if using composite analog), or a termination problem?

PHALFSHUT is over-ridden if you turn the SHUTTER ON with the main switch, which is why you're not seeing any difference. So I think you're probably looking at a situation where the shutter speeds are slightly different, so I would look there first.

J



I'm working off the same scene file on all cameras. I've got 2 cameras straight into the scope comparing, no splitters. Shutter is set at 47.2, a number we got early on that seems to be the best speed to limit strobing. I've compared different filter wheel settings. Everything so far is exactly the same. Any other ideas? By the way, why would you use PHALFSHUT on if you get a better stop with it off. We didn't see any strobing difference on or off. Thanks for all your suggestions so far. Craig
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#7 John Ealer

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Posted 06 October 2006 - 01:26 PM

I'm working off the same scene file on all cameras. I've got 2 cameras straight into the scope comparing, no splitters. Shutter is set at 47.2, a number we got early on that seems to be the best speed to limit strobing. I've compared different filter wheel settings. Everything so far is exactly the same. Any other ideas? By the way, why would you use PHALFSHUT on if you get a better stop with it off. We didn't see any strobing difference on or off. Thanks for all your suggestions so far. Craig


As I mentioned, PHALFSHUT is over-ridden as soon as you turn on the shutter, which you've turned on and set to synchro-scan if you're using a 1/47.2 shutter speed. PHALFSHUT only takes effect when the shutter is OFF. It's basically a way to default to a "film style" 180 degree shutter "angle".

Have you checked that SETUP level is the same (i.e. 0 or 7.5 IRE) for both cams?
Stating the obvious, do the bars from both cameras match up on the scope?

J
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#8 Craig Needelman

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Posted 06 October 2006 - 02:52 PM

Well I think I've solved the issue. On the 3 cameras we have 1 Fuji 7.5-133 lens and 2-Canon wide angle zooms, a 4.5-50 and a 5.2-47. The 2 Canons are a stop slower than the Fuji. I don't understand it, but they are. To match the video levels out of the camera you have to open up the camera that has the wide angle on it a stop more. It's the same no matter what camera I stick the wide angle on. Any thoughts?
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#9 Michael Collier

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Posted 06 October 2006 - 03:32 PM

Sounds like a result of a lens marked in Fstops, not in Tstops. I would set the two up based on a waveform reading (with a chip chart in view), if you know its the lens thats the issue. That way the cameras recieve the same amount of light to the sensors. The only difference between cams will be the DOF.
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#10 John Ealer

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Posted 06 October 2006 - 03:41 PM

Well I think I've solved the issue. On the 3 cameras we have 1 Fuji 7.5-133 lens and 2-Canon wide angle zooms, a 4.5-50 and a 5.2-47. The 2 Canons are a stop slower than the Fuji. I don't understand it, but they are. To match the video levels out of the camera you have to open up the camera that has the wide angle on it a stop more. It's the same no matter what camera I stick the wide angle on. Any thoughts?


Most EFP lenses like the ones you're using are marked with F-stops (relative apeture) rather than T-stops (absolute transmission). [Modern film lenses are marked with T-stops]. A lens with more light loss through the optics will yield a lower video level than a lens with less light loss even though the F-stop of the two lenses are the same. In sum, two lenses with the same F-stop can transmit differing amounts of light to the sensor, two lenses set to the same T-stop will always transmit the same amount of light.

Also, and probably most importantly, most EFP lenses have a significant degree of ramping at the long end of the lens...i.e. many get a half-stop or more darker over the last 10% or so of the zoom range. So if you were at the long end of the Canon wide angle lenses to frame up your chart, say past 45mm or so, then you'd definitely get a significantly darker image than on your Fujinon, even though the F-stop is set the same. I think this ramping issue is probably the main factor in your problem.

In general, avoid doing any critical set up work at the long end of an EFP lens because the ramping characteristics are so severe.

Hope this helps.


J
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