Recently I needed to familiarize myself with the Sony A7S camera’s core features fast, quick enough to duck out during a rare, relative lull in Sydney’s freezing winter rainstorms. Key to the A7S is its ability to shoot movies in the Sony S-Log2 picture profile. But what, precisely, does that mean? And even more crucial, how do you get the best out of it?
I had read a few articles that touched on what S-Log2 is but they didn’t cover everything I needed to know to best understand it and use it well. Googling quickly got me to Alister Chapman’s article title ‘Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.’
Chapman is a 30-year broadcast industry veteran and freelance videographer since 1990. He knows Sony pro video gear so well that he appears on the Sony stand at major trade shows. If anyone can fully explain Sony S-Log2, it is Alister Chapman.
That is exactly what he does by using a series of screen grabs, color charts, grey scales, tables and graphs. As a longtime some system user in stills and filmmaking I appreciate Chapman’s reference to grey scales and middle grey, helping greatly in understanding the ins and outs of best exposing for S-Log.
This article will be followed by a second one according to Mr Chapman and, hopefully, more. He promises that part two will cover grading and getting the very best out of S-Log2 by using Look Up Tables – LUTs. Publication of the next installment has been interrupted by Chapman’s attendance at IBC in Amsterdam. Let’s hope he gets back into it now that IBC is over!
Meanwhile I cannot recommend part one of “Exposing and Using S-Log2 on the Sony A7s’ highly enough.
Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure
One of the really nice features of the Sony A7s is the ability to use different gamma curves and in particular the Sony S-Log2 gamma curve.
What are gamma curves?
All conventional cameras use gamma curves. The gamma curve is there to make the images captured easier to manage by making the file size smaller than it would be without a gamma curve. When TV was first developed the gamma curve in the camera made the signal small enough to be broadcast by a transmitter and then the gamma curve in the TV set (which is the inverse of the one in the camera) expanded the signal back to a normal viewing range. The current standard for broadcast TV is called “Recommendation BT-709″, often shortened to Rec-709. This gamma curve is based on standards developed over 60 years ago and camera technology has advanced a lot since then! Even so, almost every TV and monitor made today is made to the Rec-709 standard or something very similar. Many modern cameras can capture a brightness range, also known as dynamic range, that far exceed the Rec-709 standard.
The limitations of standard gammas.
As gamma effects the dark to light range of the image, it also effects the contrast of the image. Normal television gamma has a limited dynamic range (about 6 to 7 stops) and as a result also has a limited contrast range.
When shooting a high contrast scene with conventional gamma the brightest highlights and the darkest shadows cannot be recorded. The contrast on the TV or monitor will however be correct as the camera captures the same contrast range as the monitor is able to display.
Read full article from Alister Chapman “Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure”
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(cover photo credit: snap from XDCAM-USER)
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