As more cameras hit the market with dual native ISO functions, it is important to understand how and why this works.
It may not be as easy as you think.
Blackmagic design has ditched camera after camera with the features we all want – features that are useful to any filmmaker. In my opinion, one of the most important tools a filmmaker can have is the ability to shoot in almost any setting with extreme control of the image regardless of the lighting conditions.
With her most recent publications in Pocket Cinema Camera Line has included Blackmagic Dual native (or Dual Gain) ISO as part of the feature set. For my purposes, this incorporated this camera line into my equipment as my ultimate cinema camera for documentary and / or guerrilla films. It opens up a number of possibilities that were never available to the average filmmaker just a few years ago.
As with most breakthrough developments in camera technology, however, it’s not just a magic button for seeing in the dark. There are a few things you need to know in order to get the most out of dual native ISO.
In order to achieve the greatest possible dynamic range with the cleanest possible image, it takes a lot more than just turning the ISO slider as high as possible.
How does it work?
I’ll be honest with you, you should probably check out the video below where John P. Hess of Filmmaker IQ gives a definitive explanation of the whole concept at the microphone drop level. It’s worth a look (or four) in my opinion.
First, let’s dive into how a digital sensor works. When creating a sensor, the actual sensitivity of the sensor is more or less burned into the hardware itself. The hardware sensor is a tiny little square with thousands of tiny “photosites” that collect light and convert it into energy. This energy is then perceived and converted by a so-called ADC (Analog to Digital Converter). This is the part of the signal chain that converts physical light into what are essentially the zeros and ones that make up your image.
In some fairly simplified terms, ISO is essentially like changing the “gain” knob on a guitar amplifier. The signal coming from the guitar is always the same level, but the amplifier amplifies that signal, and the more you turn up that signal, the more distorted or noisy it gets. In your camera, the signal is literally passed through digital or analog amplification when you change the ISO.
If a camera has two native ISOs, it means that the signal can pass through two amplifiers. Two amplifiers in which the signal is boosted much more in one than in the other.
For this reason, dual native ISO is almost a misnomer, as it is more of a dual gain system. The native ISO of the sensor itself is always the same (like the pickups on a guitar to reflect the same analogy).
How to make the most of it
Every camera is different when it comes to dynamic range and how your ISO choice affects it.
Obviously, when shooting RAW, most of these choices are stored in the metadata and can be more of a post-production decision. However, an important clue is that as you move from one level of the ISO spectrum (the lower one) to the other (the higher one) you will stick to that range of ISO settings in post-processing (i.e. 100-1200 or 1250-25600). That decision will burned into the RAW files at the time of recording. So make sure you are using the best “native” ISO for the situation.
With dual native (gain) ISO systems, however, it is important to know what is happening to your footage when you change the settings, be it in production or in post-production. When you change your ISO, you change what you want your camera to see as “medium gray”.
In the case of Blackmagic cameras (which have a dual native ISO starting at ISO1250), there are a few somewhat counter-intuitive things about how to expose your images. When looking at the table above, pay close attention to the ISO 1000 representation. You will see that this particular ISO has the greatest possible margin over the middle gray.
That said, if you have an image with particularly bright areas, consider this ISO.
“Wait, I want a higher ISO in a bright place?” Yes. Like I said, it’s a bit counter-intuitive.
As you can see in the image above from John’s video, the ISO set to 1000 has 1000 metric tons more dynamic range than recording at ISO 125.
That single tip from this video absolutely changed the way I shoot mine BMPCC. When I roll to a bright daylight scene, I always drive my ISO value up to 1000 (thanks to ND filters that save me from a completely blown out image).
I am always amazed at how much more dynamic you get with this method.
Alternatively, if you’re shooting in a dimly lit environment (especially one with lots of slightly textured darker areas below mid-gray), you’ll want to shoot at the lowest ISO possible for the cleanest image. This is unless You’re at the high end of the lower native ISO – meaning don’t shoot ISO1000 when you’re in the dark. Go ahead and enable the higher gain ISO setting.
If you can, However, shoot at the lower side of the lower gain setting.
Confused? Well, look again at the picture above. It explains it pretty well. The middle image (at ISO1000) is by far the noisiest.
So if you are in a bright point with the BMPCC line then maybe try ISO1000 (without going to 1250) and if you are in a dark point you are photographing so low on either end of the “gain” as possible. Spectrum. It really helps to keep this in mind. That way I was able to keep some really bright highlights and clean sharp shadows.
Do you have any other tips? Share them in the comments.