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Tuesday, May 19, 2015

••◊ Using S-log3 with the Sony FS-7

This last Thursday I received a call from the rental shop I do video blog work for.  Dominique tells me that the brand new FS-7 is suddenly free Saturday and I can shoot with it.  Woohoo!  Breaking in a new camera is a challenge that I readily accept.  The problem is that I get to spend zero time with the camera before the shoot.  So that night I read through (the important parts) of the user manual and study up online.  Lucky for me, there's lots of great user advice out there.

Then in the middle of the night (yes, I know that's weird...I'm a camera guy) I get the idea that I should try out S-log3.  I'm not really a log shooter for blog videos.  I'd rather just shoot with the final look baked in for these short projects that go straight to Vimeo/YouTube.  However, S-log3 is it's own work flow and I figured I'd better learn it sometime.  This was going to be a glorious success or an absolute A-bomb disaster.  What the hell...you only live once.  What could go wrong?

So I got to the shop about 10am on Saturday and had about 30 minutes to do camera prep, which involved setting at least 20 parameters in the camera.  I'm trying to read the PDF of the manual and figure out the menu system at the same time.  Cameras pretty much all do the same fundamental stuff.  It's usually a case of where did the engineers hide it?!

The first problem I needed to resolve is with exposure.  The battery on my Sekonic meter died the morning of the shoot, however I had a DSC ChromaMatch Lt. chart that the kind folks at DSC gave to me during NAB.  As far as I can tell, the chart has an 18% neutral gray background.  S-log3 needs middle gray be exposed at 41 IRE for proper exposure.  So I was in luck.  You can't exposure S-log3 by eye since it will look too dark while recording in camera - see the picture below.  Even while using the rec.709 monitor LUT, the exposure was a bit touchy for "eyeballing-it."  On the Atomos Samurai I had connected I looked at the gray surround and exposed it at exactly 41 IRE using their luma scope.  In the second picture below I cropped the first picture to just the right edge of the card so you can clearly see the exposure level.  The other advantage I had here is that the card has a number of neutral patches, any of which could act as a white balance reference in post.



This brings me to my second point...In S-log3 you only get three white balances: 5600K, 3200K, and 4300K (I think).  So if you need another white balance for a tricky lighting situation or effect, then you'll need to take a few seconds of video with a white balance chart.  The plasma lights I was using were pretty close to 5600K and a good CRI rating, so I chose 5600K and didn't have to do any re-balancing in post.  Even when I tried to white balance using the DSC chart in post, the color wheel barely moved - not enough to bother.

What I still don't completely understand are the SGamut3 and SGamut3.Cine color gamuts.  Did I mention that I only got 30 minutes of camera prep?  Sony has an excellent tutorial posted on their web site.  Essentially SGamut3 is a super wide gamut meant for ultra-HD TV (i.e. UHD rec.2020), and ACES work flows.  SGamut3.Cine is meant for film print emulation and DCI-P3 work flows.  Which works better for rec.709/sRGB displays?  I'm not that far yet.  Sony says they have a .cube file to convert SGamut3.Cine to 709, so that might be the way to go until I learn more.  The Sony Community Forum posts also suggest this from a few users.

So...how about the color grade.  Well, let me tell you - it's a whole different world having a professional 10-bit codec.  No more suffering the limitations of 8-bit banding and artifacts.  You don't have to be gentle during color correction.  The first picture below is of the uncorrected image.  In the second picture I started by raising the recorded middle gray (41 IRE) to 55 IRE for rec.709/sRGB displays,  then I applied the toe and knee to the curve to add back in highlights and shadows.  The third picture below shows that I added about 40% saturation to the image, which is what Sony seems to recommend for S-Gamut3.Cine.  This make the skin tones about perfect for Dominique.


 

You can use S-log3 in "Custom" or "Cine EI" modes on the Sony FS-7.  In custom mode you can tweak the image parameters, but in Cine EI mode the list of parameters you can change decreases, more like a film stock.  Most notably, in Cine EI mode there is no in-camera noise reduction.  For those used to standard video cameras that do noise reduction, having no noise reduction by default can be a bit discerning at first.  Cine-EI is meant for people that will have a definite post production work flow and treats the image more like a digital negative than image processed video.

One thing I noticed is very slight red noise in Dominique's black shirt.  However the noise was so minor that it didn't really warrant any post noise reduction.  Members of the Sony Community forms suggested that you're OK up to about ISO4000 with noise, but until I can test it for myself I won't know for certain.  If you can't see it in the picture below, then it's probably not going to be an issue.  Other members suggested recording at a lower ISO sensitivity to reduce noise further.  At a native ISO of ISO2000 there's certainly room to do so.


Which brings me to my last topic: ISO sensitivity in Cine-EI mode.  By design, S-log3 has six stops above middle gray when you use the native ISO rating.  If you reduce the ISO sensitivity in Cine-EI mode you lose 1 stop of highlight range for every 1 stop decrease in sensitivity.  For instance, if you were wanting to record at ISO1000 to reduce noise in a dark scene you would only have five stops of highlight range.  Conversely, if you increased the sensitivity to ISO4000 you would have seven stops of highlight range, but a hella-ND filter to put in the matte box! 

The sensitivity in Cine-EI mode is just like push and pull processing with film.  The digital negative has a set sensitivity that does not change in Cine-EI mode; in this case ISO2000.  If you set the ISO setting one stop lower in Cine-EI mode (i.e. ISO1000) and expose properly for that, your digital negative will be one stop over-exposed and you'll have to effectively do pull processing in post production.  The good thing about this feature with a digital camera is that the monitors can be compensated look like the ISO sensitivity you choose, which gives you immediate feedback on what you're about to record.  Also, in Cine-EI your dynamic range doesn't change.  It's always 14-stops with S-log3.  You only trade off highlights for shadows and vice versa if you diverge from the camera's native ISO2000.

I personally found that the full six stops of highlight range was more than enough.  When I viewed the white walls at the left of the frame with a rec.709 monitor LUT I was worried that they were going to be greatly over-exposed - and even went to the extent of flagging some light off of them.  However, when I got in post I saw that the walls were nowhere near over-exposed - not even close to nowhere near.

It's been a wonderful camera so far and I look forward to using it again.  Now if only I could afford one!

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