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#1 iga wrotek

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Posted 02 September 2008 - 04:51 AM

Hi all.
I'm not such an expirienced cinematographer as some of you so I decied to ask for help.

I'm about to shoot a short commercial on a blue screen. And production demands HD camera.
Maybe someone could help me out if i'm thinking the right way.

The shot will be very simple. It's just a character walking in the frame and talking.


I'm totaly insecure about lighting.
I thougt I would use 3 spacelights for background
and chimera with dedo's for an actress
Thought also about backlighting with two 120s kinoflos.

Few words about the camera I'm thinking of choosing:
I thought I'd use HDC f900r camera with zoom fujinon lens Cine Style HAC13x4,5-m10B
I imagine it would work pretty good for what we need.
But I don't know if I should ask to go into menu of the camera and change anything on the set.
Or should I just balance it? Or go on preset?
BUt I'm not sure if it's enough, if it's good, if it would work?.If it's right direction to go?
Ofcourse I will get to know while I'm on the set.
But if anyone could comment I'd aprreaciate it.

thanks and greetings
iga
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#2 Walter Graff

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Posted 02 September 2008 - 08:58 AM

Lighting wise, I'd ask, what's in the background. The lighting you describe sounds like a good general illumination if that is what you back plate calls for. You don't have to go crazy with back light in terms of intensity unless you want it. Some think you can't do chroma key without a back light but this is mostly myth. As for camera simply set it for preset 3200 and you'll be fine. No need to fool around inside. Also, I'd consider what your talent wears and think whether green might be better. Chroma keys today also use luminance differences so if your talent is wearing dark, green will be a better choice. If lighter clothing, than blue would be a better choice. As for overall intensity, simply make the screen glow the color it looks to the eye without washing it out and you'll be fine. Some like to use some sort of ratio of talent to screen for lighting but that is really more of an urban legend, it's about contrast of talent to screen color and making sure your screen saturation is closer to reality than lit like a Christmas tree. In reality you really are lighting the screen for itself in terms of even color saturation and the talent any way you want (what works best for the backplate). Both have little if anything to do with each other on the set. The talents lighting has more to do with what goes in the back plate than what it looks like in front of the screen. In the end your talent and screen usually end up in the same range of exposure more than different in terms of intensity. On a waveform a blue screen or green screen need only be in the 30-50 unit range to do what it needs to do in post.
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#3 Daniel Pearl ASC

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Posted 02 September 2008 - 11:48 AM

I'd like to agree that back light, particularly specular or hot backlighting, is not absolutely necessary to pull good mattes. It's true that some subtle backlight can help reduce color bleed of the light bouncing off the screen yielding cleaner mattes, but if the backlight is too powerful or incongruous with the background plate, it can be telltale of a matte shot.

This hopefully will be subject of further debate here, but I have two steadfast rules: 1) Never use digital green, although it needs very little lighting, it is so luminescent that it can be more problematic with reflecton and bleed. Also, it's ugly. 2) Never color the lights used for the screen with a gel that matches or enhances that color. The technology is way better than that, and you simply don't need to run the risk of contaminating your foreground subject with the colored light that only makes the keys less good.
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#4 Saul Rodgar

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Posted 02 September 2008 - 12:41 PM

Never color the lights used for the screen with a gel that matches or enhances that color. The technology is way better than that, and you simply don't need to run the risk of contaminating your foreground subject with the colored light that only makes the keys less good.


You mean using daylight (blue) balanced or CTB-gelled tungsten (resulting in greenish hue) lights for chroma key green screen with the camera set to 5600K or daylight balanced film? I have never had any problems doing it that way, I may have been lucky.

Edited by Saul Rodgar, 02 September 2008 - 12:43 PM.

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#5 darrin p nim

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Posted 02 September 2008 - 03:08 PM

This hopefully will be subject of further debate here, but I have two steadfast rules: 1) Never use digital green, although it needs very little lighting, it is so luminescent that it can be more problematic with reflecton and bleed. Also, it's ugly. 2) Never color the lights used for the screen with a gel that matches or enhances that color. The technology is way better than that, and you simply don't need to run the risk of contaminating your foreground subject with the colored light that only makes the keys less good.


You mean using daylight (blue) balanced or CTB-gelled tungsten (resulting in greenish hue) lights for chroma key green screen with the camera set to 5600K or daylight balanced film? I have never had any problems doing it that way, I may have been lucky.


I too am a little confused by this comment. Daniel, are you also referring to NOT using Kino Flo's Greenscreen and Bluescreen globes, in the sense that they would match and enhance with the corresponding screen?

I had learned, that for digital/high definition material, to strongly avoid using blue screen. Especially with a 3:1:1 color space/sampling, which I believe the F900R has. I believe this was proven with the film, Sky Captain and the World of Tomorrow, which was shot on the F900. Blue is the noisiest channel in digital/high definition. Now if you went with the F950 to an HDCAM SR Deck I believe you'll give your self 4:4:4 color space/sampling but if that's even possible. :)
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#6 David Auner aac

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Posted 02 September 2008 - 03:08 PM

You mean using daylight (blue) balanced or CTB-gelled tungsten (resulting in greenish hue) lights for chroma key green screen with the camera set to 5600K or daylight balanced film? I have never had any problems doing it that way, I may have been lucky.


Hm, I have never done that, but I lit blue screen with CTB gelled tungsten. But I was sure not the have it spill onto my talent, which was easy because the shot was pretty close. From what I was told by a friend, a long time dp, is that with green it doesn't really help to put gels on. This is because you can't increase the saturation of the green screen that way to help you with the separation. I hope I remember this correctly...

Cheers, Dave
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#7 iga wrotek

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Posted 02 September 2008 - 03:37 PM

I had learned, that for digital/high definition material, to strongly avoid using blue screen. Especially with a 3:1:1 color space/sampling, which I believe the F900R has. I believe this was proven with the film, Sky Captain and the World of Tomorrow, which was shot on the F900. Blue is the noisiest channel in digital/high definition. Now if you went with the F950 to an HDCAM SR Deck I believe you'll give your self 4:4:4 color space/sampling but if that's even possible. :)
[/quote]

this is such an important information for me. thanx! I'm sure going with F950 and SR deck will double the costs. BUt I will try to force it in the production.


The background that they want to put in post is cartoon looking like waterfall or moving cartoon caracters (they havn't decided yet).
Does it really determine my lighting?

About backlighting - I don't want to kill the actress with it, just little smooth cutting of the background is something I thought about.


Thanks for all the replys so far.
:)
iga
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#8 Walter Graff

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Posted 02 September 2008 - 10:07 PM

You mean using daylight (blue) balanced or CTB-gelled tungsten (resulting in greenish hue) lights for chroma key green screen with the camera set to 5600K or daylight balanced film? I have never had any problems doing it that way, I may have been lucky.


That is because by using the 56k balanced lighting you are making sure the blue noise is reduced considerably. By using 3200k lights on blue you add noise to the blue channel because of how much blue is needed to make yellow look white. Blue is perfectly okay to use with formats such as HDCAM when you know this trick. With the 900 you can easily use the D5600K in the menus to change the native white of teh camera so you don't have to use the filter wheel. More importantly is what the final product will be shown on, the complexity of the mattes and the process you use to make the mattes that can affect the choice of blue so I find to say as a generality that one should never use blue is nieve. I have seen the use of blue in some films that created no problems and some films that state they did have issues but then agian it is about that process as I mentioned and also the people doing it. Often people get notions, or get frustrated during a process and assume it is something and that assumption becomes fact. But it never really was a fact. There are many ways to accomplish things, none right or wrong, but some more effective.
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#9 darrin p nim

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Posted 03 September 2008 - 09:10 PM

That is because by using the 56k balanced lighting you are making sure the blue noise is reduced considerably. By using 3200k lights on blue you add noise to the blue channel because of how much blue is needed to make yellow look white. Blue is perfectly okay to use with formats such as HDCAM when you know this trick. With the 900 you can easily use the D5600K in the menus to change the native white of teh camera so you don't have to use the filter wheel. More importantly is what the final product will be shown on, the complexity of the mattes and the process you use to make the mattes that can affect the choice of blue so I find to say as a generality that one should never use blue is nieve. I have seen the use of blue in some films that created no problems and some films that state they did have issues but then agian it is about that process as I mentioned and also the people doing it. Often people get notions, or get frustrated during a process and assume it is something and that assumption becomes fact. But it never really was a fact. There are many ways to accomplish things, none right or wrong, but some more effective.


I think Saul and I are a little confused by what Mr. Pearl said. I think for the most part, we three, You, Saul and I agree that it helps to supplement the screen with additional color.

Though Walter, as far as saying "to say as a generality that one should never use blue is nieve." is a little presumptuous. From my readings, namely the article in American Cinematographer with Cinematographer Eric Adkins, studies and accounts from more skilled 600 Cinematographers and mentors, I have come to my personal understanding that Green is a far more efficient key. Green is carried in the Luminance channel "Y" and for most digital/high definition cameras the Luminance channel carries the most information. Rendering it, in my opinion, better for keying but then again I'm no VFX artist. Just from my experience, the VFX artists that I've had a chance to ask (which are only a couple) have reluctantly said Green is preferred with digital media. So that's beyond my naivety, if that were the case.

As for Iga, I don't believe it would be in your best interest to speak to production about renting a F950 and SR Deck. As like you said would be a financial issue. I would suggest, if at all possible, to request a Green screen. It would be a more affordable and logical replacement. Just my opinion.

Edited by darrin p nim, 03 September 2008 - 09:12 PM.

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#10 Scott Fritzshall

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Posted 04 September 2008 - 12:11 AM

Green is probably used more commonly because the green channels of film and most video tend to have less grain/noise than blue. Heavy grain or noise can make pulling a good key very difficult. On the other hand, there are more considerations than that. You've also got to take into account the content you're shooting. Are your actors wearing bright green costumes? Probably not a good idea to put them in front of a greenscreen, or you're setting yourself up for a lot of roto. Same goes for blue on blue. Dark hair is easier to key off of green, blonde hair is easier to key off of blue. Also, if your scene is supposed to take place outside or is primarily lit by the sun, it might be worth considering blue, because the spill looks more naturally like sunlight and may need less treatment than green in order to match.

I definitely agree with Walter and Daniel on backlighting. The best light is that which most closely mirrors the conditions your subjects are supposed to be in. Don't screw with it beyond that or try to get too clever with your lighting. Light for the screen should be as even as possible; with a good gaffer and a few minutes, you should be able to get the whole thing even to within 1/4 of a stop. That alone makes way more difference than anything else. Don't overlight the screen; everyone's got their own rules of thumb, but I like ~1 stop under key for the screen. This could be different depending on your content; if your background is supposed to be very bright or very dark, you might want to increase or decrease it by a stop. Don't go too bright because then you're increasing spill and also losing color information.

HDCam sucks for keying. You can work with it; it's not the end of the world, and yeah there are tricks for dealing with it, etc, but I would say that it's worth looking into a superior capture format that's not going to compress and subsample your image as much. If you're able to get your hands on an SR deck, you'll be able to bypass the F900's HDCam recorder and you'll preserve more of the image. Not quite as good as just getting a better camera, but not a bad compromise if you can swing it.
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#11 Walter Graff

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Posted 04 September 2008 - 10:13 AM

"Though Walter, as far as saying "to say as a generality that one should never use blue is naive." is a little presumptuous. From my readings, namely the article in American Cinematographer with Cinematographer Eric Adkins, studies and accounts from more skilled 600 Cinematographers and mentors, I have come to my personal understanding that Green is a far more efficient key."


Green CAN be a more efficient key. The choice is both subjective AND technical. While one man expresses his desire to 'never' shoot blue, to tell folks that they should never is simply naive. It was one persons opinion, but I wanted to stress that it is just that.

I have a great deal of composite experience. I have been doing both the production and post production side of keying and matting both optically, and digitally since 1984. I even consult to some of those 600 professionals you mention. A recent article in Scientific American on how the matting process works was consulted on by me. I recently consulted on a project for a major museum that consisted of matting 65mm film for a 17x17 foot projection where the museum goers would be allowed to stand inches from the display so everything from the matte process to focus was critical. My point: While I don't carry any initials with my name, I carry a lot of practical experience with chroma key and matting. And what it has shown me is that it's not about 'always' using one color.

Today, green is used in video often as it carries the most information in terms of sampling rate of the three channels so can offer a slight advantage, and it is the easiest to light on a set. This was not the same for analog video years past as green was the reference channel and if you used it you lost some of the fine tuning ability in post and on the set with live keying methods such as Ultimatte due to the need to compare the reference channel to the chroma sub carrier. But while green might have a 'sharper' apperence in video, that alone is not a reason to always prefer it.

In film the opposite has been true for matting for years. For instance, the blue channel offers the sharpest picture. Optically it was the only choice. In general there are technical reasons for using both but each particular job may have needs and reasons to use one or the other. That may have to do with what your talent needs to wear, the format you choose to shoot with, and/or the effect you are trying to create. And in some cases, colors outside of both blue, green and red are used. I did some special effects work were we used orange fro some technical reasons.

Don't confuse one persons opinion with fact. The only fact in this thread is that the overriding theme and various technical considerations of each shot should determine what color you use, NOTHING MORE. In general, it is difficult to say one should 'always' use one color or 'never' use another. It's simply not the case.

As for this notion that there are ratios of screen to talent with lighting, it has some validity but that depends so it is personal preference rather than a rule. In the case where your talent is standing IN FRONT of a screen, you are lighting two separate and distinct sets so 'ratios' between talent and screen have little rationale.

First you are lighting the screen for even illumination and color saturation based on it's proper expose. Second you are lighting the talent for the back plate he is going to be matted into based on his proper exposure. In other words, neither the screen nor the talent have anything to do with each other at all other yhan both need to be properly exposed. So if you tell folks that you always light your screen one stop under your talent, about all you might be affecting by doing so would be reflections if anything. In other words, I would not light my talent at 100 foot candles and my screen at 500 fcs or I'd have a heck of a glow and potentially a reflection. But I could without any issues just as long as the exposure of both the talent and the screen were in proper range for their exposure.

All I am doing when lighting a blue/green screen is to get a screen to hit it's proper point on a vectorscope. That means I usually you need about 55 fcs for blue and slightly less for green. I can do it with 100 fcs too, just as long as my exposure for that screen puts it in the blue or green box on a vectorscope. Do I have to light my talent at 100 fcs? No, usually you will always light your talent in a range that when compared to the screen is really about the iris of the camera and the relationship of proper exposure of both to that, not to each other.

I always suggest a simple procedure for lighting this type of (talent standing in front of a screen) setting. For the first part you don't need your talent. Have them step out. Simply light the screen so that luminance matches the correct level of the blue hue on a wavefrom which is usually around 40 units. Then turn off the lights to the screen.
Now light your talent for proper exposure and for whatever the setting of the back plate calls for. Now turn on the screen lights and you have a perfect chromakey lighting set up.

In general, I find that anywhere from a stop under to a stop over ends up being what you are left with after all is lit and levels checked. But the only reason for that is because of the need for proper exposure of both, so realistically to say you should always light your screen a stop under is irrelevant since your talents relationship is to camera exposure and not necessarily a comparison to the screen.

In a full body scenario where you have screen behind and below talent, your lighting is now more locked between talent and screen in terms of overall exposure and the allowable ratio. Using your light, you will light the screen, but this will also affect the talent's exposure to some degree. This might be one of the technical reason I mentioned earlier as to why you might choose green. It would take less light to saturate that green for proper exposure than it could blue meaning that if your talent needed little exposure to one side of his face, that effect might be lost to the light needed to illuminate the blue screen. It takes little light to get the green to glow which might help. But then again, green makes for more shadow so you may need blue in such a case due to how you have to light your talent, yet another consideration of why blue might be a better choice.

In general, in the case of lighting a screen where talent is 'on' the screen, I find I always end up with talent and screen being far closer in exposure to the screen, due to their 'must-be-together-in-the-same-place' physical relationship. In many scenarios with added talent light, in this relationship my talent sometimes slightly brighter in exposure. But that is not a fact, as sometimes due to the backplate, they are not. I often find that I have to do considerable changes in lighitng close ups to wide shots with gren screen more than I do with blue do sometimes to shadows with particular lighitng set ups.

In general in this "on screen" scenario, it's probably better to have the screen exposure under the talents if possible to help with any glow or reflection from affecting the talent and the key since they are standing in the screen so immersed in the color. This might be were this "one stop under" thing comes from, but like anything else, it is not a rule. It's easier with blue for me than green to have exposures closer to each as I find green can cause refelctions easier than properly exposed blue. But then again, todays software has blue and green filters that allow me to remove spill far easier than in older days when I had to do it all with light. Which brings up the most important point.

The key for a cinematographer in understanding the process is to know what happens when he is done and hands over the footage. I work with people who have all sorts of notions and rules for how the shoot keys, but who have no idea of how the post production works and most of their rules and notions are based on hearsay and nothing more.

So my suggestion to all here who want to be a better cinematographer when it comes to keying is to follow a project through so you see what you did, what affect it had. That alone will improve your abilities immensely and more of the myths of keying that are so prevalent will disappear.
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#12 Scott Fritzshall

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Posted 04 September 2008 - 02:47 PM

Oh yeah, forgot I was going to post this ;)
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#13 darrin p nim

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Posted 04 September 2008 - 05:35 PM

Walter you are right. I did fail to address the purposes and differences in using the two. Although, I did state my opinion, I failed to complete the statement with the information you provided. My original thoughts were so set on the screen itself that I forgot to recognize the importance of the subject in front of the screen and the other plentiful factors involved.

But Walter, I had never stated "never", like you so previously quoted:
"While one man expresses his desire to 'never' shoot blue, to tell folks that they should never is simply naive."
I had stated that, "I had learned, that for digital/high definition material, to strongly avoid using blue screen." though i guess it depends on your interpretation of that statement. And I may be splitting hairs here but I had felt in my previous typing that "avoid" was not a definitive more so suggestive. I should be more careful when using such terms for fear of misconception. I don't believe Blue screen should be never be used. As mentioned, testing has shown blue can key out easier. I will admit that the choice is situational and everything should be taken into consideration.

Honestly, if I do come off naive, it is not purposeful. I'm still learning with the rest of us. I did, however, unfortunately put myself in a situation where I felt I had the quality resources to make a proper assertion. I apologize for misinforming or shortly informing anyone.
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#14 Saul Rodgar

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Posted 04 September 2008 - 05:55 PM

Oh yeah, forgot I was going to post this ;)
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What could go wrong? :lol:
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#15 Walter Graff

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Posted 04 September 2008 - 07:11 PM

But Walter, I had never stated "never", like you so previously quoted

Honestly, if I do come off naive, it is not purposeful. I'm still learning with the rest of us. I did, however, unfortunately put myself in a situation where I felt I had the quality resources to make a proper assertion. I apologize for misinforming or shortly informing anyone.



I wasn't even talking to you. I said "someone" here. It wasn't you. Someone said "Never use digital green, although it needs very little lighting, it is so luminescent that it can be more problematic with reflecton and bleed."

I misquoted him and changed green to blue but regardless, while it is his personal opinion, it's important to tell those less experience that "never" might be the wrong word to use. There are perfectly good reasons to use blue and green as I stated in an earlier post and to disclude one color, is not a good thing for others here to take as a rule, but rather an opinion.
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#16 Tim O'Connor

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Posted 04 September 2008 - 09:19 PM

I think Saul and I are a little confused by what Mr. Pearl said. I think for the most part, we three, You, Saul and I agree that it helps to supplement the screen with additional color.

Though Walter, as far as saying "to say as a generality that one should never use blue is nieve." is a little presumptuous. From my readings, namely the article in American Cinematographer with Cinematographer Eric Adkins, studies and accounts from more skilled 600 Cinematographers and mentors, I have come to my personal understanding that Green is a far more efficient key. Green is carried in the Luminance channel "Y" and for most digital/high definition cameras the Luminance channel carries the most information. Rendering it, in my opinion, better for keying but then again I'm no VFX artist. Just from my experience, the VFX artists that I've had a chance to ask (which are only a couple) have reluctantly said Green is preferred with digital media. So that's beyond my naivety, if that were the case.

As for Iga, I don't believe it would be in your best interest to speak to production about renting a F950 and SR Deck. As like you said would be a financial issue. I would suggest, if at all possible, to request a Green screen. It would be a more affordable and logical replacement. Just my opinion.




"Just from my experience, the VFX artists that I've had a chance to ask (which are only a couple) have reluctantly said Green is preferred with digital media."


Why "reluctantly" ? Is there something else that they'd rather do first?

Thanks.
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#17 darrin p nim

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Posted 04 September 2008 - 11:20 PM

Reluctantly, because I wasn't extremely descriptive in the language I used to discuss with them. Said conversations had taken place a couple years ago, I'm sure they wanted to get me off their backs. :D
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#18 Tim O'Connor

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Posted 05 September 2008 - 01:43 AM

Reluctantly, because I wasn't extremely descriptive in the language I used to discuss with them. Said conversations had taken place a couple years ago, I'm sure they wanted to get me off their backs. :D



Oh, I thought that maybe you meant that they had some other non screen way that they preferred but for which productions would usually never pay.

Thanks.
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#19 Andre Labous

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Posted 05 September 2008 - 02:09 PM

Another option other than SR deck is to go into a panasonic P2 mobile. It will take SDI in from F-900 and record onto P2 cards at full 1920x1080, 10bit, 4:2:2. using the AVC Intra codec.
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