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Getting the correct exposure


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#1 mmonte000

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Posted 30 September 2005 - 06:37 PM

I will be shooting with the SDX-900 all October for a feature. I was wondering if o get the right exposure you set the iris to zebras and stop down till they disappear (At least for the subject) is this right or is there a better way to get correct exposure? Also what is the range that this camera can obtain detail I've heard some people say 5 stops and others 8. Some of the shots I would like a 1:4 or 1:6 ratio.

Also, if I want slow motion or time-lapse, can I change the shutter speed like I would with film? And when it plays back will it automatically do it or will I have to change it in post?
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#2 Tim J Durham

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Posted 01 October 2005 - 12:15 AM

I will be shooting with the SDX-900 all October for a feature. I was wondering if o get the right exposure you set the iris to zebras and stop down till they disappear (At least for the subject) is this right or is there a better way to get correct exposure? Also what is the range that this camera can obtain detail I've heard some people say 5 stops and others 8. Some of the shots I would like a 1:4 or 1:6 ratio.


5-8 stops? Man, are YOU talking to the wrong people. That camera is capable of 11-12 stops if properly set-up. As far as setting exposure by zebras, it would depend on where you set your zebras. There are two sets. I set one at 70 IRE for flesh tone on white people (and I do back off just a bit, to around 68 IRE but that's subjective and situational). Then the second set, I put on wherever I want to not expose above. Sometimes it's 100 IRE, sometimes it's less. It depends. Sometimes I don't use the second set if I know I'm going to have blown out highlights (on purpose). The only REQUIREMENT is if you shoot for broadcast, the FCC mandates that luma and chroma signals not add up to more than 130 IRE. If you're not shooting for broadcast, it's up to you.

Also, if I want slow motion or time-lapse, can I change the shutter speed like I would with film? And when it plays back will it automatically do it or will I have to change it in post?

The camera has an intervalometer which you can set up to record in as little as two-second bursts at whatever interval you like. There is also an optional board you can have installed that will allow you to record 1-frame at a time at whatever interval you like.
For slo-mo, you can (if you are shooting in 24p or 30p) shoot at 60i and de-interlace, then stretch the footage in your editing sequence. There is a guy here named Sam Wells who posted an example a while back if you want to check it out.

One more thing, If you are planning to do a film-out, you should discuss your camera set-up with the people handling the film-out. They will have suggestions for your set-up to get the best results.
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#3 mmonte000

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Posted 01 October 2005 - 01:55 PM

Okay, thanks. Where on the camera am I able to change the IRE? Is it good to just go by the monitor?

Edited by mmonte000, 01 October 2005 - 02:02 PM.

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#4 Stephen Williams

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Posted 01 October 2005 - 02:12 PM

5-8 stops? Man, are YOU talking to the wrong people. That camera is capable of 11-12 stops if properly set-up.



Hi,

Are you really saying it has +/- 5.5 to 6 stops from middle grey.
The Viper is almost 10 stops , so a video camera with a contrast range of 2048 to 4098:1 would be cool ! If it were really true I would be rushing to sell my Kodak shares!

How did you calculate?

Cheers

Stephen
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#5 Dimitrios Koukas

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Posted 01 October 2005 - 02:18 PM

Okay, thanks. Where on the camera am I able to change the IRE? Is it good to just go by the monitor?


This is on the zebra's menu where u can adjust the low zebra and high zebra levels, remember to have your zebra button on .
I believe that 70-75 % for low and 100% for high is really satisfactory, if you get used to it.
Dimitrios Koukas
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#6 Gordon Highland

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Posted 01 October 2005 - 02:25 PM

Okay, thanks. Where on the camera am I able to change the IRE? Is it good to just go by the monitor?


No, you can't completely trust the monitor for overexposure, more just for for ratios. It's in the menu under VF something or other, Zebra 1 and Zebra 2. If you have a waveform monitor, that would be ideal, because it would show you the full range. On a feature I'd say it's a must-have. I tend to underexpose everything just a tad with this camera, and I use Filmlike2 gamma most of the time.
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#7 Stephen Williams

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Posted 01 October 2005 - 03:37 PM

I've heard some people say 5 stops and others 8.



Hi,

I have just had a good look at the Panasonic site. The recording is 8 bit, that would itself imply a maximiun of 7 Stops.

Stephen
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#8 Tim J Durham

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Posted 01 October 2005 - 07:18 PM

Hi,

Are you really saying it has +/- 5.5 to 6 stops from middle grey.
The Viper is almost 10 stops , so a video camera with a contrast range of 2048 to 4098:1 would be cool ! If it were really true I would be rushing to sell my Kodak shares!

How did you calculate?

Cheers

Stephen

Hi Stephen,
I can't comment on the Viper but the SDX900 has 11-12 stops of dynamic range (slightly BETTER than the F900!) if you set it up properly. The BBC, in addition to testing all available HD cams, ran tests on the SDX900 (because at the time it was the only camera offering 24p in SD) and came up with set-up parameters to achieve the maximum dynamic range while, at the same time, fixing the telltale video look.

So, because I have worked for the BBC a few times in the past, I was made privy to those set-ups and I have put them into practice and although even a high-end field monitor can only show you about 8 stops, the camera looks pretty sweet. But I haven't MEASURED the range myself. I wouldn't know how to do it in a scientific-method sort of way. Looking at the end result, I trust it's true.
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#9 mmonte000

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Posted 01 October 2005 - 08:52 PM

No, you can't completely trust the monitor for overexposure, more just for for ratios. It's in the menu under VF something or other, Zebra 1 and Zebra 2. If you have a waveform monitor, that would be ideal, because it would show you the full range. On a feature I'd say it's a must-have. I tend to underexpose everything just a tad with this camera, and I use Filmlike2 gamma most of the time.



It's a very low budget movie, and to tell you the truth I have never used one so I wouldn't know hoe to read it..
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#10 Gordon Highland

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Posted 01 October 2005 - 08:56 PM

The BBC, in addition to testing all available HD cams, ran tests on the SDX900 (because at the time it was the only camera offering 24p in SD) and came up with set-up parameters to achieve the maximum dynamic range


I have a feeling what this means is taking the camera head itself, and using the optional SDI out, running uncompressed into an external deck. The recorder, to a large degree, is what limits this camera. This technique has been recommended for composites and whatnot, although I couldn't say technically how it affects stop lattitude.
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#11 Tim J Durham

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Posted 01 October 2005 - 10:22 PM

I have a feeling what this means is taking the camera head itself, and using the optional SDI out, running uncompressed into an external deck. The recorder, to a large degree, is what limits this camera. This technique has been recommended for composites and whatnot, although I couldn't say technically how it affects stop lattitude.

Compression doesn't so much limit the dynamic range just the shades of grey (or blue or whatever).
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#12 Stephen Williams

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Posted 02 October 2005 - 07:16 AM

Hi Stephen,
I can't comment on the Viper but the SDX900 has 11-12 stops of dynamic range (slightly BETTER than the F900!) if you set it up properly. The BBC, in addition to testing all available HD cams, ran tests on the SDX900 (because at the time it was the only camera offering 24p in SD) and came up with set-up parameters to achieve the maximum dynamic range while, at the same time, fixing the telltale video look.

So, because I have worked for the BBC a few times in the past, I was made privy to those set-ups and I have put them into practice and although even a high-end field monitor can only show you about 8 stops, the camera looks pretty sweet. But I haven't MEASURED the range myself. I wouldn't know how to do it in a scientific-method sort of way. Looking at the end result, I trust it's true.



Hi,

11-12 stops is far better than a F900 recording to HDCAM. I am aware of the curves Steve Shaw of DigitalPraxis developed for the BBC. To get the most from thease curves you have to record to disc. Some LCD screens claim 2000:1 or more, when in reality they are under 450:1.
I guess they are compressing the range. The same as using a Low Contrast filter.
Don't get me wrong the SDX900 is a very GOOD camera!

Stephen
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#13 Phil Rhodes

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Posted 02 October 2005 - 08:44 AM

Hi,

> I have just had a good look at the Panasonic site. The recording is 8 bit, that would itself imply a maximiun of
> 7 Stops.

No!

Good grief, how many times...

You can have a thousand-stop range rendered as one of 256 levels. You can have a two-stop range rendered over 256 levels. Bit count implies a certain resolution not a certain range.

Dynamic range on a camera head is determined by the manufactured characteristics of the CCD (generally, larger pixels have bigger dynamic range) and the setup of the very, very analog drive electronics that control it.

CCDs are actually very old tech, but this is how they (and frequently CMOS too) works. You have a big grid (possibly a VERY big grid if you're Dalsa) of photodiodes, each of which is capable of turning one or more photons into one or more electrons. These photovoltaic electrons sit in a quantum "well" on the surface of the diode substrate. The size and charge of this substrate determines how many electrons can sit on it before it's full (peak white) or overflows (vertical streaking.) The bigger you make it, the more electrons can sit in it, but also the more cosmic rays and solar wind particles are likely to strike it, which causes noise, so it's not a linear improvement.

Once you've let your photodiode array accumulate electrons for as long as you feel is convenient (frequently 1/48s) you discharge the substrate and begin shifting the image down, row by row, so the charge eventually falls into a chain of semiconductor devices at the bottom of the array in a process called "binning." This horizontal row is then read out into an amplifier and the process repeated; what comes out is, not coincidentally, akin to a normal video signal in that it serialises an image as an array of lines.

Only after it's been through the output amplifier do you digitise it.

Phil
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#14 Tim J Durham

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Posted 02 October 2005 - 08:53 AM

Hi,

> I have just had a good look at the Panasonic site. The recording is 8 bit, that would itself imply a maximiun of
> 7 Stops.

No!

Good grief, how many times...

You can have a thousand-stop range rendered as one of 256 levels. You can have a two-stop range rendered over 256 levels. Bit count implies a certain resolution not a certain range.

Dynamic range on a camera head is determined by the manufactured characteristics of the CCD (generally, larger pixels have bigger dynamic range) and the setup of the very, very analog drive electronics that control it.
(...)
Phil

I was wondering when you were gonna jump in there. My techie credentials are somewhat lees than stellar.
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#15 Stephen Williams

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Posted 02 October 2005 - 10:17 AM

Hi,

> I have just had a good look at the Panasonic site. The recording is 8 bit, that would itself imply a maximiun of
> 7 Stops.

No!

Good grief, how many times...

You can have a thousand-stop range rendered as one of 256 levels. You can have a two-stop range rendered over 256 levels. Bit count implies a certain resolution not a certain range.

Dynamic range on a camera head is determined by the manufactured characteristics of the CCD (generally, larger pixels have bigger dynamic range) and the setup of the very, very analog drive electronics that control it.
Phil


Phil,

Do you think 11-12 stops is correct?
I may be missing something, but a large stop range with a low resoloution is not the Holy Grail we are looking for! Or is it?

Stephen
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#16 Tim J Durham

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Posted 02 October 2005 - 10:33 AM

Phil,

Do you think 11-12 stops is correct?
I may be missing something, but a large stop range with a low resoloution is not the Holy Grail we are looking for! Or is it?

Stephen

Still don't believe me? That's OK.
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#17 Stephen Williams

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Posted 02 October 2005 - 10:55 AM

Still don't believe me? That's OK.



Tim,

I have not personally ever seen 12 stops from a 2/3" CCD when I've tested myself, or seen other peoples test that showed 12 Stops.

Phil only dismissed my 8 bit theory. He did not confirm the CCD had a 12 stop range!

My understanding is that with 8 bit if you push too broad a dynamic range into the 8 bits then you can get banding when it is stretched back out. Bit depth affects the smoothness of the transitions in the tonal scale.

Stephen
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#18 Phil Rhodes

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Posted 02 October 2005 - 11:32 AM

Hi,

No, it's not the holy grail, but the point is that it's much easier to digitise something more finely than it is to develop a CCD with a big dynamic range, so really, the problem is the CCD mechanics not the digital resolution. This is why modern video cameras have high bit count DSPs - if you're going to do colour correction and other operations in a DSP, you need more information than you will eventually be recording. The problem here of course is that if you want to defer your colour correction to a manually controlled postproduction operation then you need to record that high bit depth verbatim, hence the practice of recording DI data as 10-bit log and the problem of enormous hard disk arrays on uncompressed camera systems.

To be honest a lot of these modern cameras are just quantising fuzz and jitter in any case - there's simply no way the least-significant few bits of an 18-bit video DSP are anything but noise. Now, this is somewhat good, in that noise diffuses banding, and I'd certainly rather faithfully record CCD noise than quantise the values down too much, but it's also a warning that simply increasing DSP bit depth doesn't help beyond a certain point - you may as well record it at a lower depth and add diffusion dithering in post!

Phil
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