I am a traditional photographer and by that, I simply mean that I learned my craft through working with film and developing prints in the darkroom. Working this way instills a strong belief in the importance of engaging with your subject and getting as much right in camera as possible.
I fully understand that digital photography has introduced significant new ways of thinking, particularity with regards to the equipment and tools we use and the way we process our images. Yet the majority of the craft & skill needed to produce good images is still very much grounded in the methods of image capture that can be traced right back to photography's very beginning. Despite this, many of today's amateur photographers seem more willing to follow the marketing and commercial hype that surrounds digital photography with a significant number of today's newbie photographers unfortunately willing to believe anything they are told, particularly when it is regurgitated at infinitum on social media platforms.
Nowhere is this more apparent than with the so-called exposure triangle. I am not too sure where this concept as a means of explaining exposure came from and whilst the principles behind it are sound, it has one major flaw. The exposure triangle gives equal parity to using ISO to control exposure alongside shutter speed and aperture. ISO is not used to control exposure, that is achieved by altering the shutter speed and/or aperture settings. Whilst changing ISO can be used to effect exposure, there are very few situations in which you really need to use ISO in this way. More importantly, the exposure triangle goes a long way to causing confusion amongst those who are struggling to get to grips with exposure for the first time. Why struggle to work with three variables and when you only need to work with two?
ISO comes from film photography and is simply a measure of how sensitive the film is to light. The name was carried over into digital simply because its effects are similar in that it appears to make the sensor more “sensitive” to light. In fact, increasing ISO simply amplifies the signal from the sensor, which has the downside of introducing of “noise” which can degrade the quality of the image. So basically the best image quality will be achieved by keeping your ISO at it lowest, or base setting. When first learning photography it is probably best to simply set and forget ISO and come back to it when you are a little more comfortable in understanding basic exposure control using shutter speed and aperture.
These two setting, shutter speed and aperture, work in combination in allowing the required amount of light into the camera for the image you are trying to capture. The only time that you really need to change your ISO is if you are shooting handheld in low light and cannot get a fast enough shutter speed to hold the camera steady. There are possibly some situations where you want to have a specific shutter speed and aperture combination which can only be achieved by changing the ISO setting or switching to Auto ISO and letting the camera decide the setting, although in over thirty years of photography I have never come across a situation where I have needed to do this.
When digital cameras first started to become popular, ISO was there but increasing ISO led to serious image quality issues. Over the years image quality at high ISO settings has significantly improved to the point where quality issues are almost a thing of the past. This increased performance though has been used to sell cameras, often being hailed as some sort of major technological advancement. I believe that it is this hyped-up commercial marketing that has led to the advancement of ISO being used to control exposure which is simply nothing more than an over complication of what is, in fact, a quite simple concept.