A topic that is picking up a lot of traffic right now is ISO invariance. I’ve had a lot of questions come up on it, and photographers are wondering what my recommendation is about it. Should I change my shooting habits? Does it really affect my images? Can’t new cameras just get it right without knowing all this ‘techy stuff’? Great questions!
Photography has always been a mix of technical skills and creative vision. We need to know how to operate the camera and use the right settings to create the image we have in our mind. But is there a point the technical inhibits the creative process? I’ve always been interested in the technical aspects of photography, and was curious about ISO invariance when I first started reading about it. I will do my best to explain what ISO invariance is, and how you might use it in your photography.
First up, what is ISO invariance? Invariance means something that doesn’t change…ISO invariance implies changing the ISO doesn’t really affect anything. In the most basic terms, ISO invariance refers to the concept that your image sensor signal is constant, and the only thing that changes is how the signal is amplified. In other words, if I take an image at ISO 6400 at the correct exposure, and take the same shot at ISO 200, five stops underexposed, but then add five stop of exposure in Lightroom or Adobe Camera RAW…guess what happens? The image at ISO 200, the one I opened up five stops in Lightroom, looks almost exactly like the one I shot at ISO 6400. ISO performance looks almost identical using this approach. But the image I took at ISO 200 has better dynamic range and any highlights are fully protected. I can create a better image using the five stop underexposed version than the correct in-camera exposure at ISO 6400. So does that mean we all have to underexposure all our images to get the best quality?
Before we answer that question there is one more aspect that gets mixed into this conversation…dual gain sensors. I know, some of you just stopped reading, this is getting way too technical. Can’t I just turn on my camera and take the photo? (spoiler alert…yes!). Dual gain sensor processing is a way for your camera to improve dynamic range and noise levels in sensor processing. The question is when does this dual gain processing kick in? On the Z9, dual gain sensor processing starts at ISO 500. So the idea goes then if I am shooting at ISO 300 or ISO 400 shouldn’t I switch to ISO 500 for a better image?
With many of today’s cameras being almost perfectly ISO invariant, the theory is you can get better results shooting at lower ISOs and opening exposure up in the computer rather than taking the correct exposure in-camera at a higher ISO with less dynamic range.
Here is my read on this. First, ISO variance is a tried and true concept. If you are worried about clipping your highlights in an image, then underexposing the photograph and opening up shadows will give you good results (if you shoot in RAW). For night photographers who photograph bright objects like the moon in darkness…. underexposing the image and opening up later might be something you want to do. For wildlife photographers who are worried about clipping a highlight (like a bald eagle head) maybe you underexpose to protect the highlight and open shadows later in LR or ACR (Adobe Camera Raw).
Consider a few other things. First, if you are underexposing everything in the field you will be committing yourself to having to edit more later. Underexposing an image can make it harder to compose a shot and for autofocus to work. And you aren’t really gaining a whole lot in terms of better image quality (maybe a little better dynamic range, ISO pretty close). Is that benefit going to even show up on your computer monitor or in the final print?
If you are way into the technical side of photography, then maybe you jump all over ISO invariance. I have some colleagues who love the technical side of photography. Enjoy exploring the technical side of things, and see how much you can improve your images using ISO invariance principles.
ISO invariance hasn’t changed the way I shoot. I get the exposure correct in the camera, which means I expose for the subject. Sometimes my subject has highlights, and I underexpose to protect those highlights. Other times my subject is mid tone like a grizzly bear and I exposure for the bear….I’m not worried about highlights. For my night shooting I still use high ISOs, I’m happy with results. The new Adobe Noise Reduction works great. With Northern lights I just watch the aurora highlights (generally green) and make sure they aren’t overexposed. I never worry about using ISO 200-400 and changing it to ISO 500 for a slight bump in quality.
ISO invariance is an important topic, and one I’m sure we will hear more about in the future. Some photographers are using these principles in their photography, and others are not. Understand the concept, do what works for you, enjoy your photography, and explore creativity with your camera. “Think less, feel more…,”