Article: Camera Trivia 🦍 《ISO》
Camera Trivia 🦍 《ISO》
We always talk about the exposure triangle - ISO, aperture, and shutter speed. ISO is always at the top, which shows how important it is! The main reason is that the ISO level actually represents the inherent sensitivity of the film/sensor [CCD/CMOS]. Besides controlling the brightness of the photo, it also affects the image quality.
Although there are many ISO numbers, it's actually simple to differentiate them. Just remember that the smaller the number, the slower the sensitivity, and the larger the number, the more suitable it is for low-light conditions. Commonly available film ranges from approximately 100-3200.
ISO is usually marked in doubles, such as 100, 200, 400, 800, 1600, 3200, 6400, etc. You can imagine 100 as the starting point. For every doubling, the exposure will be twice as bright under the same aperture and shutter speed. For example, if you need 1/50th of a second with f/4 at ISO 100, then with ISO 400, you can increase it to 1/200th of a second, and ISO 1600 would become 1/800th, and so on. Each doubling of ISO is called "one stop higher ISO." So, under what circumstances should you use which ISO?
There's no definitive answer, as everyone uses different lenses, and the lighting conditions of each scene also have an impact, so the combination of the exposure triangle can be completely different! However, to take a normal, shake-free photo, you can use a higher ISO to increase the shutter speed. I'll explain what "safe shutter speed" is once I've covered all the basic information.
So, from the perspective of film photography, what are the drawbacks of high ISO?
Although high ISO can result in faster shutter speeds, the grain will be coarser, and the image will appear "sandy," sacrificing detail. This is what we commonly refer to as "noise" today. If you're interested in why, I'll explain it in more detail below. Also, in certain situations, the dark areas of the photo might appear brighter, making the photo seem to have lower contrast and an overall grayish tone.
Is the ISO for film and digital cameras the same?
You need to know that ISO is actually divided into two main categories:
1) ISO - This is equivalent to the ISO marked on film and is its inherent physical property. Taking traditional black and white film as an example, one layer of the film contains silver halide crystals. They are transparent when unexposed, but when exposed to light, they transform into colored metallic grains. So, each piece of film is actually composed of countless silver halide grains. If you understand this principle, you'll know that films with different ISOs actually use different silver halide formulas. The most common practice is to use larger silver halide grains for higher ISO films, because larger particles have a greater surface area, which allows for greater and faster exposure. However, because of this, you will see that high ISO films have coarser grain.
2) Base ISO - The ISO of digital cameras is somewhat different from film. They use different electronic components to convert light into electrical signals, which are then stored on a memory card. So, in this situation, a single camera only has one sensor, and therefore only one native ISO, which is its Base ISO. You might think I'm lying, as you use your camera daily and have used ISO 50 and even 51200, so how can there be only one base? In reality, digital cameras indeed have only one native ISO, but because digital cameras can process data, all other ISOs are actually simulations created by taking photos at the Base ISO and then applying the camera's own processing. Since it's a simulation, you know it won't be as good. So, when using a digital camera, the closer you are to its Base ISO setting, the cleaner the image will be and the greater the dynamic range. However, it's important to note that BASE ISO does not equal 100, and manufacturers won't tell you what it is! But there are ways to calculate it, and I'll explain what these are if I get the chance. Those who understand, understand; those who don't, just ignore it 🐹
That's all for this week. See you next week, bye!
Although there are many ISO numbers, it's actually simple to differentiate them. Just remember that the smaller the number, the slower the sensitivity, and the larger the number, the more suitable it is for low-light conditions. Commonly available film ranges from approximately 100-3200.
ISO is usually marked in doubles, such as 100, 200, 400, 800, 1600, 3200, 6400, etc. You can imagine 100 as the starting point. For every doubling, the exposure will be twice as bright under the same aperture and shutter speed. For example, if you need 1/50th of a second with f/4 at ISO 100, then with ISO 400, you can increase it to 1/200th of a second, and ISO 1600 would become 1/800th, and so on. Each doubling of ISO is called "one stop higher ISO." So, under what circumstances should you use which ISO?
There's no definitive answer, as everyone uses different lenses, and the lighting conditions of each scene also have an impact, so the combination of the exposure triangle can be completely different! However, to take a normal, shake-free photo, you can use a higher ISO to increase the shutter speed. I'll explain what "safe shutter speed" is once I've covered all the basic information.
So, from the perspective of film photography, what are the drawbacks of high ISO?
Although high ISO can result in faster shutter speeds, the grain will be coarser, and the image will appear "sandy," sacrificing detail. This is what we commonly refer to as "noise" today. If you're interested in why, I'll explain it in more detail below. Also, in certain situations, the dark areas of the photo might appear brighter, making the photo seem to have lower contrast and an overall grayish tone.
Is the ISO for film and digital cameras the same?
You need to know that ISO is actually divided into two main categories:
1) ISO - This is equivalent to the ISO marked on film and is its inherent physical property. Taking traditional black and white film as an example, one layer of the film contains silver halide crystals. They are transparent when unexposed, but when exposed to light, they transform into colored metallic grains. So, each piece of film is actually composed of countless silver halide grains. If you understand this principle, you'll know that films with different ISOs actually use different silver halide formulas. The most common practice is to use larger silver halide grains for higher ISO films, because larger particles have a greater surface area, which allows for greater and faster exposure. However, because of this, you will see that high ISO films have coarser grain.
2) Base ISO - The ISO of digital cameras is somewhat different from film. They use different electronic components to convert light into electrical signals, which are then stored on a memory card. So, in this situation, a single camera only has one sensor, and therefore only one native ISO, which is its Base ISO. You might think I'm lying, as you use your camera daily and have used ISO 50 and even 51200, so how can there be only one base? In reality, digital cameras indeed have only one native ISO, but because digital cameras can process data, all other ISOs are actually simulations created by taking photos at the Base ISO and then applying the camera's own processing. Since it's a simulation, you know it won't be as good. So, when using a digital camera, the closer you are to its Base ISO setting, the cleaner the image will be and the greater the dynamic range. However, it's important to note that BASE ISO does not equal 100, and manufacturers won't tell you what it is! But there are ways to calculate it, and I'll explain what these are if I get the chance. Those who understand, understand; those who don't, just ignore it 🐹
That's all for this week. See you next week, bye!