Wildlife photographer and YouTuber, Steve Perry, has released a video called 'The TRUTH About ETTR: Let It Go And Do THIS Instead', debunking modern usage of the expose-to-the-right (ETTR) technique. ETTR is performed by pushing the exposure on your histogram as far right as possible, without clipping the highlights. The theory behind this is that you can capture an image with less noise and more dynamic range.
By lowering the exposure in post-production, you’re essentially lowering the ISO which – in theory – should produce less noise and better image quality. But Steve isn’t convinced – at least not when it comes to modern sensors.
He explains that modern sensor noise is almost exclusively photon noise, but older digital cameras would produce both photon and electronic noise. And while ETTR can work to reduce electronic noise, it doesn’t reduce photon noise. Check out the video:
ABOVE: Watch the ETTR principle debunked
You see, the more photons collected by the camera, the less noise. The basis of Steve’s theory is that ISO does not affect the number of photons that reach the sensor, since it doesn’t actually gather light – like aperture and shutter speed – it amplifies it. So, this means that ISO doesn’t create noise.
This is hard to get your head around. And I’ll admit, it confused me at first. Steve says: “I realize, we often use ISO as a rough gauge when talking about how ‘noisy’ a photo is but that’s only because we’re generally talking about images with a proper exposure at a given ISO.” He uses the example of a properly exposed ISO3200 image providing similar noise to another ISO3200 image, but with different aperture and shutter speed settings.
I think the biggest confusion here is that we often say we’re using a wider aperture and longer shutter speed to gather more light, or we’re using a narrow aperture and shorter shutter speed to gather less light. But when it comes to achieving the correct exposure using the same ISO, we’re altering the aperture and shutter speed to gather the necessary amount of light to properly expose the image.
So, if you can shoot at ISO3200 and achieve a balanced exposure, it doesn’t matter whether you’re shooting in low light with a wide aperture and long shutter speed or bright light with a narrow aperture and fast shutter speed, you’re gathering a similar amount of photons and thus, creating a similar amount of noise. But move that ISO down to ISO1600 and you’re going to be gathering more photons and therefore less noise.
Steve uses a few examples in his video so you can see this concept in action. It might take a couple of viewings to get your head around it though. He also goes into much more detail, considering the effects of dual-gain ISO and base ISO. So make sure you give the full video a watch!
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