Can't reproduce good colors with S-Log2 footage

I've never worked with Sony cameras, but when shooting LOG with the BMPCC, my first step in color work is to apply the BMD supplied LOG to Rec. 709 LUT.

My first recommendation would be to do the same here.  Find a Sony developed LOG to Rec 709 LUT and start there.

"... but the final result is always unusable."

It would be most useful for you to both tell us and show with a screen-grab your process and that final result.

But when you say final result, are you meaning looking at it within PrPro or after exporting in say ... the QuickTime player? If say on re-import it looks fine in PrPro, but that export doesn't look as "deep" in QT, well ... that's QT, not the media.

There are two separate parts to correcting a LOG encoded clip ... first, inverting the curve that was used in-camera to make this back to a "normal" or normalized clip ... for this, you need a curve adjustment that you can simply apply ZAP to nearly all clips from the camera.

Second, you need to adjust each clip's black/white points, shadows, mids & highlights, plus saturation ... the same as any other clip. But this must be done before that curve adjustment, through that curve in the scopes and display, or the inverted curve will possibly clip data that your camera worked pretty hard to record. This is all basic Log normalization as taught by Alexis Van Hurkman, and done daily in Avid, Resolve, Baselight, wherever. In Resolve, for instance (the most used grading app in professional suites), LUTs are always applied to the output processing side of a 'node' (layer, in Adobe terms) ... so you apply a corrective LUT to the first node, then go into the node and adjust the clip. The adjustments are processed before the LUT, and you see the clip in scopes & viewer after the LUT.

What's the starting point?

First, you need to have a good sense of when you've got a properly inverted curve shape for the Log. This is why a lot of people do like to start with the manufacturer's LOG corrective LUT for that camera. As one builds skills, most of the colorists I know end up creating their own corrective LUTs for the cameras they work with most often. I could add more detail about how to create your own if you want, but for now, just say ... if you shoot a standard medium contrast scene with a bit of real white and real black with that camera set in LOG, and when loading the uncorrected clip into PrPro, the top of the data in the Waveform scope is about 65-70 on the left-hand scale, you've got the exposure pretty close.

• In the Lumetri Curves tab, grab the black point and drag it to the right so the bottom of the scale in the Waveform scope drops to maybe 8-10. Then the white point to the left so it gets your whites to maybe 95 max. Then click about a quarter of the way up from the bottom of that line and drag to the right just a small amount, to pull some more of the mids down a bit lower ... that's a basic crash course on inverted LOG curves.
• Now, right-click on the clip, Copy, and choose the next clip ... then "Paste Attributes" and only select the Lumetri effect. Do this with several different clips. Does this curve work pretty well for most of them? Not perfectly ... just makes them look 'real' again. When you've got that, you're good to go.

Now, at the top of the Lumetri tab, there's a little three-bar menu panel. You can save this Lumetri effect with only that curve set as a preset, saving it with the name of the camera it's built for, or save by choosing "Export .cube." Either works, you just apply them a bit different.  

• Exporting as a preset, you go to the Effects panel lower-left, User Presets, and drag/drop your Log corrective preset onto a clip. You now have a full Lumetri effect on that clip, with only the curves panel adjusted setting in your log corrections, and you'd start at the beginning in the Basic tab adjusting the shadows, highlights, and whites to fit that clip best into the Log correction. Then go into the later tabs for further work.
• Exporting as a .cube LUT, you would go into the Lumetri workspace panel, the Creative tab, and use the navigation features to find & select that .cube you exported. Then as above, go to the Basic tab to fit the clip into the LUT, and the rest of the controls are available for further corrections & grading.

The second is the method I use.

Neil

You need to see somebody do it in a tutorial - like this one:

Grading Log Footage in Premiere Pro CC - YouTube

Go to 2:35 in to the start of the tutorial.

There are lots of others - do a Google search.

MtD