FS7: Rec-709 (800%) as an Exposure MLUT

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karma17

Well-known member
I have been reading with some interest Chapman's 2017 ebook on the FS7.
https://s3.amazonaws.com/ngp-prd-live-protein-upload-cfn/cms-static-content/uploadfile/28/1237495128028.pdf

On page 57:
"When the LUT [meaning the REC-709 (800%) MLUT] is correctly exposed, so too is the S-Log2 or S-Log3 recording."

Later on the same page, he states that if you wish to use zebras for exposure assessment (when using the REC-709 (800%)) that you should "use the zebra function exactly as you would for normal gamma curves."

My question/confusion is this:

Isn't the REC-709 (800%) MLUT closer to a hypergamma curve than a normal gamma curve? By the MLUT being 800%, doesn't that mean that it has 3 stops more of DR than a normal curve?

If I were to expose the MLUT REC-709 (800%) as a normal gamma curve, then I would put 18% gray at 44 IRE and 90% white at 89 IRE (source: Lutcalc.com). Is that correct?

And finally, doesn't Rec-709 (800%) clip at 109 instead of the usual 100?

The documentation online that refers to exposure values for standard or normal curves is from Chapman's site, and there he provides more of range of values.

http://www.xdcam-user.com/2014/08/exposing-and-using-slog2-on-the-sony-a7s-part-one-gamma-and-exposure/

I'm still a struggling student of the FS7, so I sincerely appreciate any thoughts or further clarification.

Thanks!
 
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Exposing using LUTs can work quite well, I sometimes do it as in reality if you apply the same LUT in post you will end up with the same look/exposure as you had seen in camera.

But regarding actual IRE levels, well LUTS can map proper slog values (40% for grey / 60% for white) to whatever new values they like and so there is no such thing as using traditional exposure values such as 45% for grey / 90% for white.

Instead you need to know how specific LUTs are mapped and you can do this yourself by simply shooting a grey and white card in slog and flipping over to respective 3D LUTs and observing the mapped values.

This was my result,

LUT-exposure-levels.png
 
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starcentral said:
Exposing using LUTs can work quite well, I sometimes do it as in reality if you apply the same LUT in post you will end up with the same look/exposure as you had seen in camera.
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When I have to shoot log on my 55, I shoot and expose to the regular REC 709 LUT.
 
+1

Yep agreed. I switched over to 709(800%) a while back, just a real nice basic overall plain look. The LC709 and LC709A too much funny business, not for me.
 
LennyLevy said:
what do you mean by funny business?
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How I would see it.. if its only your monitor LUT.. why not go with the plain vanilla 709 levels ,that alot of people know for many years.. why go for a "look" LUT as your monitor LUT.. unless you are sure thats the LUT you will base your grade on of course ..
 
Biggest problem with the 709 LUT is it looks too contrasty with the VF on the FS7, whites look blown and blacks look crushed which can lead to poor decision making. Certainly, it's not a good way to judge exposure.
 
about funny business, I just found blacks too high on LC709A and colours a bit too nuclear/saturated on LC709 (at least on F55).

709(800) just seems more natural for me to look at.

:Drogar-Smoke(DBG):
 
No MLUTS at all for me. After 5 years of shooting nothing but S-LOG/RAW I still love the look of the pure, clean, natural, unadulterated LOG images in my viewfinder. And as an added bonus I don't have to worry about MLUTs coming and going in certain shooting modes.
 
Doug Jensen said:
No MLUTS at all for me. After 5 years of shooting nothing but S-LOG/RAW I still love the look of the pure, clean, natural, unadulterated LOG images in my viewfinder. And as an added bonus I don't have to worry about MLUTs coming and going in certain shooting modes.
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What works for you works for you. But put it this way, of all the feature film sets I have been on where they were shooting sLog or RAW, the 1st AC's have never been pulling focus looking at the sLog or RAW image. And for good reason.


Check out the Panny DXL2 that was on a set last week, complete with a vintage 70mm format Primo lens in the nude:

IMG_3269 copy.jpg
 
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The MLUTs don't make a damn bit of difference for focus, nor is the focus puller concerned with exposure so I don't see how your comments pertain to the subject line of this thread. I'll also bet that exposure on those feature films was being set by the DP using a light meter or some other tool that was completely independent of the MLUT or lack of MLUT being displayed on those monitors.

Sure, I'll put spit out an MLUT on my external monitors to give everyone else a prettier picture look at, why not? But I'm certainly not going to be setting exposure based on those external monitors -- whether they have an MLUT applied or not. As I said, I prefer to keep my viewfinder clean and to me that makes exposure 100% fool proof and I never have to wonder what MLUT I'm using and how it may or may not affect my interpretation of the exposure. I'm not saying that exposure can't be set fast and accurately with an MLUT if you choose to, I'm just saying I think it is a hell of a lot easier without it.

Everyone needs to find what works best for them, but I'm just suggesting that if someone hasn't already tried working without an MLUT in the viewfinder then they should at least give it a try.
 
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Doug Jensen said:
The MLUTs don't make a damn bit of difference for focus
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I find it more difficult to find focus when viewing sLog than with an MLUT applied to the VF or monitor. I know that others do as well. Maybe, as your claim suggests, that is all in our imagination and in fact it is no more difficult to focus when viewing the sLog image than it is with a MLUT applied to the viewed image.
 
I mostly do studio work where there are many others present so they will always get a LUT'd image to view. For myself I will flip back to log view periodically to see what levels are doing, but for operating/viewing/recording I like to look at a LUT'd image. Many times in nice rich color and proper contrast it becomes easier to spot issues that might be going on in the frame and correct which might otherwise go unnoticed.
 
No, I don't have one but work with the FS7 a lot. All my multi-camera shoots so far have been F55 and FS7.. on some projects the FS7 is "b-cam" but to be honest the FS7 can end up being 50% of the footage in the final piece and it's very hard to tell any difference over the F55.

These LUTs really act the same way on both cameras from what I've seen, I just prefer 709(800) for basic look on top of slog.
 
I've made some simple LUTs in LUT Calc (using Art Adams suggestion) with the Varicam gamma for a slightly punchier look than 709A and then I lower the blacks a touch and boost the saturation , so its not as flat as 709A. Even Art who developed 709A thought it looked too flat. These seem to look pretty good to me and frankly I have had good luck just lighting to the monitor as long as I check my waveform to make sure I've got a solid and consistent exposure . No complaints so far.
 
starcentral said:
No, I don't have one but work with the FS7 a lot. All my multi-camera shoots so far have been F55 and FS7.. on some projects the FS7 is "b-cam" but to be honest the FS7 can end up being 50% of the footage in the final piece and it's very hard to tell any difference over the F55.

These LUTs really act the same way on both cameras from what I've seen, I just prefer 709(800) for basic look on top of slog.
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I can see in a controlled environment the contrasty 709 LUT will help you find mid-grey easily enough. My main issue though, is out on location, where I like to see those extra levels - particularly in the highlights, that the lower contrast LUTs deliver.

We all work differently, I directed a shoot on Red the other day and I couldn't make head nor tail of how my DoP set-up his monitor, I actually thought it was broken. But it was exactly how he likes it, and that's all that matters.
 
I know this topic has been covered & recovered.... will only add that I prefer plain slog in my viewfinder of my fs7 (but I also cut my teeth in the b/w viewfinder days of ENG, so this makes me feel young again. :Drogar-BigGrin(DBG)) , But, when shooting under mixed lighting situations - will use either the built-in 709 LUT or preferably on jobs I'll be grading - use my go to user LUT. (Usually have small LUt monitor with me on every job anyway.)
Lastly - I very highly recommend setting user button to Hi/Low Key if you are using a LUT in the VF - so you can really see where your shadows & highlights "can" be.
 
Liam Hall said:
Biggest problem with the 709 LUT is it looks too contrasty with the VF on the FS7, whites look blown and blacks look crushed which can lead to poor decision making. Certainly, it's not a good way to judge exposure.
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Liam I think that's why Sony gave us the assignable HIGH/LOW KEY option so that you can quickly cycle through high, low key and normal exposure ranges to ensure that you are happy with the exposures at the top and bottom of the dynamic range as obviously the little camera monitor can't cope with the dynamic range the camera outputs. Explained fairly clearly by Alistair C. here:

http://www.xdcam-user.com/2015/02/using-the-highlow-key-function-on-the-pxw-fs7-pmw-f55-and-pmw-f5/

Chris Young
 
Doug Jensen said:
No MLUTS at all for me. After 5 years of shooting nothing but S-LOG/RAW I still love the look of the pure, clean, natural, unadulterated LOG images in my viewfinder. And as an added bonus I don't have to worry about MLUTs coming and going in certain shooting modes.
Click to expand...

+1 as Doug says.

Yes I find I can work pretty accurately with the LOG image plus the assistance of the Zebras. I find once you have a reasonable amount of experience working with the LOG image in the VF it becomes another judgement skill set as was learning to judge focus distance and exposure pretty accurately by eye when shooting film. I always output a LUT to others on the set as it stops the interminable questions of "Why doe it look like that? Not much color?" Also frequently record externally with a LUT so rushes and TC burn-ins can be supplied pretty quickly.

Chris Young
 
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