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latitude of the dv signal?


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#1 Delorme Jean-Marie

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Posted 06 February 2006 - 04:25 AM

Hi all
I'll be filming in dv super soon pd150 and dvx100 (2 different projects)
from your experience how many stop can the format handle between burned white and dead blacks (over and under the Key) for the pd150?
in the dvx100 it'll be different from one gamma to the other or maybe i'm wrong?
and what do you rate the pd150 at? ( for zero db) in asa
thank you verry much
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#2 Andrew Koch

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Posted 06 February 2006 - 06:49 AM

I have found that the asa of the dvx100 is about 400 at odb gain in 24p mode with cinegamma, but like you said, there are various setups that could affect the asa.

Here is how you can find out the asa of whichever video camera you decide to use. These instructions came from my cinematography instructor. You will need a waveform monitor and an incident lightmeter.

1. Set up even light across a video chip chart
2. Use the color of light appropriate to the filter (daylight, tungsten, or florescent)
3. Monitor the output of the camera to a waveform monitor. (Check the calibration/connection of the waveform monitor with color bars from the camera.)
4. Set the camera to the desired filter and gain settings.
5. White balance with auto iris on. Once white balance is set turn auto iris off.
6. Set the frame rate on your incident light meter to 24fps and 180 degrees (This is so you simply have a reference to film)
7. Adjust the t-stop on your video camera so that the whitest chip on your chip chart reads 100 IRE on the waveform monitor.
8. Measure the light on the chip chart with your incident meter.
9. Change the ASA on your meter until the stop on the meter reads the same as the stop on the camera.
10. This is the ASA of this camera setup.

I don't believe any DV cameras have a fixed ASA. Various settings such as filter and gain will alter the ASA so you will need to do this for each different filter, gain combination.

Once you have done this for a particular camera setup, you can use a reflectance lightmeter and waveform monitor to get an idea of the latitude of the particular camera.

On the waveform monitor, images higher than 100 IRE will be clipped. Images lower than 7.5 will be black (i think in some cases you might be able to go down to 0, but as far as I know, 7.5 is black in NTSC broadcast). You can take reflectance readings of a subject. If you set the camera for middle grey, you can see on the waveform monitor where things start to clip or get crushed. However many stops over and under that is will be your latitude. (if someone could explain this better, please step in). Most DV has about 6 stops of dynamic range, but don't quote me on that.

I hope this helps.
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#3 Phil Rhodes

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Posted 06 February 2006 - 07:33 AM

Hi,

Be aware that the terminology to your original question is misleading. The "DV signal" itself can represent any number of stops of dynamic range, although if there's more than 216 or so you won't actually be able to tell adjacent ones apart...

What you're talking about is the ability of the camera head to image high-range scenes, which is a different consideration to "the DV signal" itself.

Phil
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#4 Delorme Jean-Marie

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Posted 06 February 2006 - 08:38 AM

thanks
often when my terminology is wrong, it's because it's not clear for me
my point was with the pd150, from what is recorded on tape, how many stops can i expect from a small detail in the dark to a hot spot where the information is almost washed out? thats what i call the latitude i'm i wrong?
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#5 Mathis Nitschke

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Posted 20 March 2006 - 08:26 AM

I´d like to bump up this question since I think it´s very interesting and relevant. Did anybody measure it?
Probably not very complicated, thinking about it. Will do myself.
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#6 Phil Rhodes

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Posted 20 March 2006 - 09:46 AM

Hi,

Almost all consumer cameras have about six or seven really useful stops, and two or three more buried under the noise floor which can be used with care. Better, broadcast cameras often average about ten; unprocessed raw capture devices like Viper (and presumably-hopefully things like Genesis and D20) can exceed eleven or twelve.

Phil
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#7 Josh Bass

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Posted 20 March 2006 - 10:10 AM

I thought I'd heard that for these prosumer cams, it was 5 stops? Is that outdated info? Never true in the first place? Only relevant to the XL1s (as opposed to the DVX)?

This is for the SD miniDV cams, not so much the HD/HDV.

Edited by Josh Bass, 20 March 2006 - 10:11 AM.

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#8 Phil Rhodes

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Posted 20 March 2006 - 11:02 AM

Hi,

I've done tests on recent HDV cameras and they came out at about 7 each, which figures against other numbers I've heard. You'd expect HDV cameras to be slightly less good, given the smaller CCDs.

Phil
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#9 Josh Bass

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Posted 20 March 2006 - 12:20 PM

So you're saying that applies to all the SD cameras too, or no?
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#10 Phil Rhodes

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Posted 20 March 2006 - 06:44 PM

Hi,

Maybe.

I haven't checked every camera in the world. Run tests.

Phil
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#11 Simon Wyndham

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Posted 21 March 2006 - 05:54 AM

http://www.bbc.co.uk...hp/whp034.shtml

The addendums are tests of various cameras plus their settings for 'film look' and 'video look' Included in these is a break down of how many stops they can capture after the settings have been modified.
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#12 Rupe Whiteman

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Posted 22 March 2006 - 05:40 PM

http://www.bbc.co.uk...hp/whp034.shtml

The addendums are tests of various cameras plus their settings for 'film look' and 'video look' Included in these is a break down of how many stops they can capture after the settings have been modified.


simon,

I see on your 'site you own an xdcam... just wondering how you find it and how investing in one has paid off. I'm a little terrified of investing in new cameras as they seem to change and be updated so fast now. I guess it all comes down to getting the jobs in to pay for it but I wonder if you had to make clients aware of the benefits of the xdcam or did you already have producers who were like minded...

Regards,

Rupe Whiteman
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#13 Simon Wyndham

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Posted 23 March 2006 - 11:25 AM

Well, the XDCAM workflow I bought more to save my own sanity than anything else. I absolutely hate the ingest process from tape with every fibre of my being. At the time I wanted to upgrade to a 2/3" camera, so XDCAM was in the right place at the right time.

The camera is paying for itself. I never had any worries about cameras being upgraded etc. Whenever you buy new electronics equipment it will always be superceded by something better. But usually it is a microscopic improvement rather than a huge one. I stuck by my guns when everyone was telling me to get an HDV camera and I do not regret the descision for one moment. My advice is to buy what you need now (or rent if work is sporadic), and to consider what you will be doing in a year or twos time. I knew I'd be in SD land for a while because other than one or two indie projects most of my work is for third parties who won't need the footage again down the line. Plus it will be a while before any HD distribution takes off. At present I only have one project in mind that will involve recording some very rare footage and so will need HD to be of use in the future.

I am considering an XDCAM HD for the future, but will see how things pan out. I will probably wait for the 2/3" version as I will want to replace the 510 with a true equivilent upgrade. I am in no hurry.
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