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Old April 26th, 2012, 01:23 PM   #1
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F3 vs Alexa - non log?

I met with a producer yesterday who told me he compared an Alexa and an F3 in non-log formats - (Alexa shooting 709 don't know about the F3 gamma) and chose the Alexa because it had much more highlight lattitude. Is the Alexa that different in 709 from an F3 in cinegamma? I realize the F3 doesn't handle highlights too nicely in 709.

He didn't want to take the time to grade. I don't know if the smaller amount of grading necessary for cinegamma would still have been more than he wanted to bother with. (Of course looking at the Alexa footage which he said was perfect and didn't need grading I definitely would have graded every shot anyway.)
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Old April 26th, 2012, 01:44 PM   #2
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Re: F3 vs Alexa - non log?

I would have been surprised if it was the other way around.
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Old April 26th, 2012, 02:30 PM   #3
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Re: F3 vs Alexa - non log?

In theory if two cameras are both set to REC-709 then the dynamic range should be identical as the cameras response will be limited to the REC-709 specifications. True REC-709 should only exhibit about 5 stops of dynamic range from 0 to 100%. The addition of superwhites at 109% gives a little more and then the knee on top gives a bit more again. In reality the REC-709 gamma curves in most cameras don't correspond exactly to the true 709 specs as everyone would be up in arms if the camera only had a 6 stop range.

With almost any reasonably up to date cameras, anyone comparing a couple of cameras dynamic range with REC-709 and saying A has more dynamic range than B is a bit of a misnomer. Yes there will be differences in the way the knee works and perhaps A will give a more pleasing picture than B, but this is unlikely to actually be due to the dynamic range of the camera, just different ways the manufacturer has chosen to interpret the restrictions imposed by REC-709.

In my opinion, the only times you would want to use 709 is when you are shooting direct for broadcast where there won't be time for grading or if you have enough control over your lighting to stay within a 6 stop range and that 6 stop range gives you the look you want.

Otherwise, I would use one of the extended range gammas included in most cameras these days, log, cinegamma, hypergamma etc, as these extended range gammas don't try to comply to the REC-709 specifications they are not restricted to the legacy dynamic range imposed on us by REC-709. As a result they can easily accommodate much greater dynamic ranges and get closer to utilising the camera sensors full range, but at the expense of requiring some grading to restore contrast.

So back to Leonard's post, what he is seeing is just differences between the way Arri and Sony interpret the REC-709 specification, plus perhaps the F3's less than perfect knee operation. I'm sure with a good camera tech could probably have created a picture profile using a cinegamma that would have exhibited greater dynamic range than the Alexa in REC-709 and then added some negative black gamma to give it more contrast as per REC-709.
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Old April 26th, 2012, 02:46 PM   #4
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Re: F3 vs Alexa - non log?

I wasn't there for this comparison and was skeptical when told about it the other day for exactly the reasons you mention Alister.
Would love to hear from some who has actually seen them both side by side though.
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Old April 26th, 2012, 11:04 PM   #5
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Re: F3 vs Alexa - non log?

Quote:
Originally Posted by Alister Chapman View Post
In theory if two cameras are both set to REC-709 then the dynamic range should be identical as the cameras response will be limited to the REC-709 specifications.
The Rec709 color mode on the Alexa (which I've shot with) is nothing like Alister's definition. I can't rightly say what aspect of the Alexa's 709 mode is "709", but that's what they call it. It's flat, it's desaturated, it looks like S-Log.

In fact, Alexa Rec709 mode is even somewhat more flat to the naked eye than S-Log in my estimation, and I have no doubt it has the same latitude as F3/S-Log if not more so. It certainly does in Log-C mode, plus another stop or so.

Make no mistake, the Alexa is the better camera. The F3 is the closest I've seen come to it though.

Here's a Youtube video I found a while back with Alexa footage that is mostly ungraded. This is what 709 mode looks like on it. I know, because Log-C footage is so flat it looks broken almost:

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Old April 27th, 2012, 04:37 AM   #6
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Re: F3 vs Alexa - non log?

Not trying to say that the F3 is a better camera than the Alexa. But I think Sony's REC-709 implementation is possibly closer to to true 709 than Alexa's. The problem is that 709 is a viewing specification so it's wide open to interpretation when it comes to camera implementation. If all cameras were set to the same REC-709 gamma then they would all output exactly the same, sadly REC-709 is a standard that seems to have no standard, which kind of defeats the object. It's like having a standard for motorised transportation, called "car" but then when you look at different manufactures interpretation of car we see some huge variations. If you tried to compare two cars you would have to be careful as to which models you compared to ensure you were getting a true like for like comparison. Given that as Nate says, Alexa's version of REC-709 is very flat and log like, while the F3's REC-709 is much more contrasty is this really a fair comparison? A better comparison would be with the two cameras set up with matching gamma curves, as I suggested maybe the F3 would fair better in the test with a cinegamma, which may be a better choice than Alexa's ultra flat look for direct to air.
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Old April 27th, 2012, 01:13 PM   #7
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Re: F3 vs Alexa - non log?

Quote:
Originally Posted by Alister Chapman View Post
Not trying to say that the F3 is a better camera than the Alexa. But I think Sony's REC-709 implementation is possibly closer to to true 709 than Alexa's.
I didn't think you were. I think my comment was directed more at Lenny, who seemed to doubt it would have more highlight latitude? Maybe I read him wrong.

Quote:
Originally Posted by Alister Chapman View Post
The problem is that 709 is a viewing specification so it's wide open to interpretation when it comes to camera implementation. If all cameras were set to the same REC-709 gamma then they would all output exactly the same, sadly REC-709 is a standard that seems to have no standard, which kind of defeats the object.
Agreed. The Red a few years back had a Rec709 LUT you could apply during shooting and decode with in post. It was impossible to figure out what aspect of that setup was 709 as well. It was kind of 1st generation, messed up skin tones with subtle yellow patches, and eventually they dropped it.

I had a thought on Arri's intent with the 709 mode/name. I think it's probably more just to imply that it has directly viewable gamma (debatable), as opposed to Log-C, which is kind of extreme (and intended for 12bit recording, as well).

Quote:
Originally Posted by Alister Chapman View Post
Given that as Nate says, Alexa's version of REC-709 is very flat and log like, while the F3's REC-709 is much more contrasty is this really a fair comparison?
Not in the slightest. You have to have spent a few moments with the Alexa, and weeks with the F3 to kinda know that. The Alexa is VERY easy to figure out. It's like an original iPod, both in operation and setting simplicity.

Quote:
Originally Posted by Alister Chapman View Post
A better comparison would be with the two cameras set up with matching gamma curves, as I suggested maybe the F3 would fair better in the test with a cinegamma, which may be a better choice than Alexa's ultra flat look for direct to air.
Well, not possible with the Alexa, other than maybe loading LUTs into it to modify the look, but I'm pretty sure there's no option to record those LUTs internally. You get "Rec 709" mode, and you get "Log-C" mode. That's it. It's designed through and through to be colored in post. And based on that, you're right, the F3 is a better choice if you don't want to color.
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Old April 27th, 2012, 09:06 PM   #8
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Re: F3 vs Alexa - non log?

Thanks for the responses.

I spoke to someone at my favorite rental house who also responded more or less like you guys did saying well yes the Alexa has more highlight latitude in 709 but she thought it was very "milky" in 709 and needed grading while 709 on the F3 was really designed for no grading ( though I grade everything anyway.) When I saw the footage I didn't think it looked as flat as s-log but the blacks were certainly quite elevated and it all looked like it needed some snap & contrast added. Of course I wasn't there for the comparison test, and don't know how the F3 was set-up, so I can't can't speculate too much.

Nate, I would expect the Alexa to be a better camera given the price difference but am wondering how you would define the difference? I do understand that the F3 is actually sharper but the Alexa has much less moire and may just be prettier. I would expect that in log the DR would be similar.
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Old April 28th, 2012, 04:06 AM   #9
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Re: F3 vs Alexa - non log?

In log the Alexa is a little better than the F3, about a stop better.
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Old April 28th, 2012, 11:01 AM   #10
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Re: F3 vs Alexa - non log?

I'm finishing up a feature one Alexa and the images are so lovely, it's easy to see why so many noted DP's have embraced the camera as the first truly worthy successor to celluloid. I like the F3 also but I feel like the Alexa does indeed demonstrate more dynamic range and smoother transitions, but it's hard to pinpoint.

I'm glad to read about the Alexa's 709 mode being "mushier"--I've noticed this myself. We are building LUT's on set but we will use the 709 setting as a reference occasionally and it often seems low contrast to me, compared the F3.

Mostly what all of this reminds me is that the only way to say for sure is to put the cameras next to each other and evaluate the results.
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Old April 28th, 2012, 12:34 PM   #11
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Re: F3 vs Alexa - non log?

Funny, my experiences with the Alexa in REC709 don't look anything like the Alexa Testmovie that Nate has posted here. Basically, I've never shot nor seen on the Alexa anything resembling the flatness of that video that wasn't ungraded C-Log.

I have found that the REC709 LUT output is not nearly as flat as depicted in this video, it would be my guess that it was graded to have that low contrast look. Just in the past few weeks I've spent time on both Grey's Anatomy and the final episode of Desperate Housewives querrying the DP's about their transition this year from film to Alexa. Both use the Log-C with LUT's for video village, neither LUT I watched looked anything like the Alexa Testvideo, but rather displayed rich colors and high contrast shadow areas. LUT #8 was used on DH.

I have been using on various F3 shots the S-Log for highlight suppression and recording simultaneously the HyperGamma LUTs for immediate dailies. The LUT on the F3 seems substantially less saturated than on the Alexa, but well within range for post to goose up.

Alister is correct when he says that REC709 is a viewing specification as it was developed for CRT monitors. I can remember clearly that an Ikegami HL79 vs Sony 300 tube camera would look very different on the same monitor and that was always explained as a manufacturer's color matrix difference. The same held true when the switch to CCD cameras came along. Perhaps that is what Leonard's producer friend was witnessing when comparing the Alexa to the F3, they are two very different color matrix systems.
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Old April 28th, 2012, 12:41 PM   #12
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Re: F3 vs Alexa - non log?

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Originally Posted by Bruce Schultz View Post

I have found that the REC709 LUT output is not nearly as flat as depicted in this video,
Bruce, are you talking about Alexa in 709 mode with a LUT applied on top of that? Or without a LUT?

Just clarifying because Alexa's 709 mode, as far as I could tell when I had the camera in my hands, not a LUT. Of course you can apply one after @video village, but I was meaning it's clean 709 mode output.
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Old April 28th, 2012, 12:50 PM   #13
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Re: F3 vs Alexa - non log?

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Originally Posted by Leonard Levy View Post
Nate, I would expect the Alexa to be a better camera given the price difference but am wondering how you would define the difference? I do understand that the F3 is actually sharper but the Alexa has much less moire and may just be prettier. I would expect that in log the DR would be similar.
I knew that question was coming as soon as I said "better" without qualifying it.

-The camera appears to oversample more, which makes for nicer fine details. I wouldn't call the F3 sharper at all. But you really need a full raster, 1080p broadcast monitor to really see the difference easily. Even then it's not a runaway win, in my opinion.

-It has at least the latitude of the F3 in S-Log in Rec709 mode, and 14.3 (ish?) stops in Log-C mode. That's a stop better than any tested or published F3 numbers I've seen.

-ProRes HQ recording at low end, ProRes 444 in 12bit in camera, and RAW at high end recording options.

IQ-wise, the only thing I can think the F3 has on the Alexa is it might be a tiny bit cleaner as the ISOs go up. Probably not enough though to choose the F3 over the Alexa on that alone, though.
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Old April 28th, 2012, 01:40 PM   #14
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Re: F3 vs Alexa - non log?

I have shot both Log C with LUT applied and straight REC709 on the Alexa, and neither looked like that video. Granted there is some saturation and contrast loss on the straight REC709, but not enough to make it unusable and clearly it is usable as is and ungraded. The newest Alexa firmware makes the REC709 vastly improved too.

(BTW, I meant Private Practice, and not Grey's Anatomy on my earlier post)
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Old April 30th, 2012, 07:19 AM   #15
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Re: F3 vs Alexa - non log?

Question to Bruce ,

Since you commented on the film to Alexa transition in LA, I watched Desperate Housewives last nite for the first time this year. An that once beautifully shot show was a complete mess last nite-green shadow cast and very crushed blacks. Lighting and scene grading all went to hell. Are they taking the low road for the last season? ABC usually delivers such high standards in it's ABC Studio series.
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