Science of Exposure Lectures...

[fcotterill]

....Dynamic Range, ISO, ISO Invariance.... Dual Gain Sensors
I know I'm not alone in struggling to find a fully detailed, and above all accurate, explanation of the science of exposure, which in particular explains Dynamic Range and ISO Sensitivity. These lectures by John Hess take some stamina and concentration. They are pitched in a series that explores many aspects of Cinematography, including the history of this applied science and its role in the industry. They're well worth the time spent. Although I've shared these links are in a recent thread, they're less obvious there.

This guy presents a different way of thinking about Exposure, which he admits he found very challenging to compile and distill into the explanatory principles and graphics. For one thing, this deeper dive requires one unlearn the notion of the Exposure Triangle (a timeworn concept broadcast far and wide across the cottage industry of photography eduction blogs and youtube videos). The Pathway of Light is more accurate metaphor of the mechanics of exposure.

 

[fcotterill]

Our modern cameras have introduced new factors that influence optimal exposure. Dual - Gain sensors underscore what is the (almost) the new normal, given their prevalence. For example, the dual gain sensor in the Nikon Z9 is basically ISO-invariant up to ISO 400, then the gain shifts to reset ISO invariance from ISO 500 upwards to 12800. Sensors vary, as in Z6 II, in which dual gain changes at ISO 800 - which changes the context to set optimal exposure to maximize dynamic range in relation to ISO Sensitivity. This derived essay helps to set up the context (well, apart from citing his older exposure triangle video!):

The Best Explanation of Dual (Native) ISO We've Seen Yet

The Dual ISO sensor is on the rise, and every major camera manufacturer has made one (or will very soon). What is it, though, and what does it mean?

www.premiumbeat.com

 

[Nimi]

There is a distinction between Dual Native ISO that's found in many modern cameras and Dual Gain Sensors that are found in Reds, Arri, and some Canons. My understanding: Dual ISO optimized noise (and subsequently DR) at two points along the ISO continuum and as a side effect produce some invariance. Dual gain sensors produce a high dynamic range (16 stops) by treating different parts of the sensors differently depending on the amount of light hitting them.

 

[fcotterill]

There is a distinction between Dual Native ISO that's found in many modern cameras and Dual Gain Sensors that are found in Reds, Arri, and some Canons. My understanding: Dual ISO optimized noise (and subsequently DR) at two points along the ISO continuum and as a side effect produce some invariance. Dual gain sensors produce a high dynamic range (16 stops) by treating different parts of the sensors differently depending on the amount of light hitting them.

Then the terminology is conflicting, about the different ways by which sensor designs have modified their respective data processing. Apparently, the design implemented in many of the Sony designs in still ILCs was invented by Aptina and this was first used in Nikon 1 sensors. This technology was licenced to Sony, who have presumably used it in what are being called Dual Gain Sensors.

This is presumably what Thom Hogan's describing here and in discussions about optimal exposure in the Nikon Z9 and other current ILCs in his eBooks. So the dynamic range recorded in the RAW file is specific to the ISO settings by a dedicated amplification circuit.

Dual Gain Becoming the Norm | Sans Mirror | Thom Hogan

Dual gain on new mirrorless cameras

www.sansmirror.com

What is dual gain and how does it work?

The Panasonic GH6's 'DR Boost' mode is based on an interesting sensor design, but it's not the same as the 'dual gain' chips we've become accustomed to. We look at the differences and why you use gain at all.

www.dpreview.com

According to this article in dpr, the Panasonic mechanism is combining data off two different amplification circuits ie 2 sets of exposure values off the sensor. It processes shadows and highlights differently, which are combined into a 16 bit RAW file.

The Dual Gain lecture above explains the exposure performance of a Blackmagic sensor using a Dual Native ISO design that's cross referenced as similar to the ISO Invariant sensors in still cameras;

Indeed, the dual amplification circuitry sounds like a version of the Aptina technology. The readjusted gain threshold at ISO 1250 resets the Middle Gray sensitivity point to capture more information in the shadows.

 

[Nimi]

Then the terminology is conflicting, about the different ways by which sensor designs have modified their respective data processing. Apparently, the design implemented in many of the Sony designs in still ILCs was invented by Aptina and this was first used in Nikon 1 sensors. This technology was licenced to Sony, who have presumably used it in what are being called Dual Gain Sensors.

This is presumably what Thom Hogan's describing here and in discussions about optimal exposure in the Nikon Z9 and other current ILCs in his eBooks. So the dynamic range recorded in the RAW file is specific to the ISO settings by a dedicated amplification circuit.

Dual Gain Becoming the Norm | Sans Mirror | Thom Hogan

Dual gain on new mirrorless cameras

www.sansmirror.com

What is dual gain and how does it work?

The Panasonic GH6's 'DR Boost' mode is based on an interesting sensor design, but it's not the same as the 'dual gain' chips we've become accustomed to. We look at the differences and why you use gain at all.

www.dpreview.com

According to this article in dpr, the Panasonic mechanism is combining data off two different amplification circuits ie 2 sets of exposure values off the sensor. It processes shadows and highlights differently, which are combined into a 16 bit RAW file.

The Dual Gain lecture above explains the exposure performance of a Blackmagic sensor using a Dual Native ISO design that's cross referenced as similar to the ISO Invariant sensors in still cameras;

Indeed, the dual amplification circuitry sounds like a version of the Aptina technology. The readjusted gain threshold at ISO 1250 resets the Middle Gray sensitivity point to capture more information in the shadows.

I believe Arri preceeded Aptina and I recall reading an article about the difference. Canon's sensors on the C300 and C70 use something similar to Arri, Sony is different and produces less DR at the native ISO(s). The Arri Alexa has a native ISO of 800 but 15 stops DR. The Sony Venice has dual ISO sensor, do DR is highest at two native ISOs. I am not aware of any hybrid camera that uses "true" dual gain sensors, although some suggest that Lumix does (and that's practically a cinema camera in a stills body). I believe heat management is a gating issue which why we aren't seeing high MP sensors with Arri-like technology.

You peaked my curiosity, I'll read up further! I've always strive for the highest DR over everything else as I can control it better in post.

 

[fcotterill]

Well thanks. Very interesting, and this is all new to me, as Stills and Cinematography are largely separate universes, but it's stimulating that MILC technology is forcing some of us out of the shadows!

 

[Winston Churchill (Sir)]

Interesting videos - reminds of of what I have forgotten from years ago!