Let’s take the clichés out first. ISO is not an International Standards Organization. ISO may be considered a part of the exposure triangle in photography, but it wasn’t meant to be, especially not in the film.
And ISO is just a simple thing – it controls the brightness of the image, while other factors such as dynamic range, sharpness, colour reproduction, are indirectly proportional to the value of ISO in general terms.
With the clichés out, let’s talk about what is ISO, actually?
Have you heard about the sieves? The one which is used to filter our larger pieces while smaller pieces pass through? ISO is simply like them. The higher the ISO or the pores of the sieve, the bigger the pieces that pass through or, the lighter is recorded, while the smaller the pores of the sieve, the lesser number of pieces pass through, but they are also finer pieces.
So less in number but finer light enters. ISO is basically about allowing the amount of light to be recorded irrespective of the other settings of the camera. And this is why ISO isn’t remotely related to Exposure Triangle.
ISO in Films: Film Speed
ISO in films used to be dependent on the film roll. Once you load a particular roll in the camera, you can’t change the settings. Therefore, ISO used to be fixed and only shutter speed and aperture controlled the exposure. It was originally called Film Speed, and it was a measure of the film’s sensitivity to light.
A lower film speed will require more exposure to produce the same image density photo as one which is recorded on higher film speed. This needs to be compensated via slowing shutter speed or opening up the aperture.
The ISO is actually the most recent numerical scale to measure the sensitometry of the photographic film, and there have been many before that. The first practical sensitometer – Warnerke – was invented by Polish engineer Leon Warnerke.
The present-day system of ISO has been combined from ASA and DIN systems and is considered a standard since 1974. The current systems for ISO are:
Colour negative film: ISO 5800:2001
Black and white negative film: ISO 6:1993
Colour reversal film: ISO 2240:2003
Digital still-cameras: ISO 12232:2006
ISO in Digital: The Film Speed Standard
ISO is an International Organization of Standards, and in August 1998, it was designated for Digital still-cameras (ISO 12232:2006) and has been revised several times since, especially with each new technology. The origin of the word ISO in photography actually comes from:
“word-forming element meaning “equal, similar, identical; isometric,” from comb. form of Greek isos “equal to, the same as” (e.g. isometor “like one’s mother”).“
The method remains the same, although, in digital, sensitivity is a feature of the sensor and not film. Because it is a digital sensor, the settings can vary by the click of a button or by turning the dial, and it makes photography a lot easier than it was, ever.
ETTL refers to Expose to the Left. In film photography, all the grains are a feature of the highlights. Hence to cut out the grains, the exposure used to be slightly underexposed to the ideal one, which also could bring out more details on the subject. It is also a common knowledge that a -1/2 exposure will get much higher details while a +1/2 image will get lesser details.
ETTR: The Digital Version
ETTR refers to Expose to the Right. In digital photography, there aren’t grains but noise. Noise is usually seen in the shadows and not highlights. Therefore in digital, expose to the right is the right way to go to get cleaner and better shots. Also, because of post-processing, if there’s a need then we can add noise later in the editing.
Another thought, however, says, that with modern-day post-processing tools, one need not worry much about ETTR because if there’s a bit of high ISO noise, it can be cleared up in a post. But if we try ETTR, we may push the noise further by raising the ISO further. That can be detrimental.
We talked earlier about films and how film speed used to be fixed. Therefore, there was no possibility of changing ISO mid-way through the roll. You had to finish the roll to move to the next one.
In digital, however, we can change the ISO with each different image, giving us more flexibility, and fewer worries of carrying a different set of rolls for different conditions.
The real boon, however, is Auto ISO. When shooting in changing light conditions, especially during times when you can’t repeat the action, it is important to get the exposure right.
With fixed ISO, sometimes the shutter could go too slow or the aperture could be wide open and yet the exposure isn’t correct if the light conditions vary slightly. For such conditions, Auto ISO is the answer.
Yes, we discussed that ISO isn’t part of the exposure triangle. In fact, while shutter speed determines the duration of time when light hits the sensor and aperture determines the volume of light, ISO is merely the sensitivity. Yet, in such severe conditions, for example in bird photography, you can’t miss the perfect shot because you have the modern-day tools at hand, especially with exceptional low-light and high-ISO performances of some of the DSLRs of this age.
Another feature of the modern-day cameras is limiting the maximum ISO. This way, you can ensure that the noise level doesn’t reach beyond what you would like to have, and you can leave the worries of exposure to the camera.
One important factor, here, is that the metering needs to be precise. The knowledge of how a meter works, and which meter to use, is what will determine whether you can nail the exposure or not.
ISO, Dynamic Range, Sharpness, and Color Reproduction
While there definitely an upswing in the high ISO performance with regards to lesser noise, or more manageable noise, there is also the downside. As we move the ISO up, the sensor loses details, sharpness, and dynamic range. Some of the Canon cameras produce higher colour reproduction at higher ISOs, but generally, the ideal range of ISOs is between 100-3200 for full-frame cameras.
Pushing the values upwards or downloads have their effect. It is only with practice and knowledge of the equipment that we can determine what works the best for us, and how much we are able to compromise on the dynamic range to get better exposure, especially when we don’t have many alternatives.
ISO: As Stops of Light
All this while, we have talked about ISO not being part of the exposure. Now, we will be talking about ISO stops. Here again, we are talking about sensitivity and how it affects the brightness of the picture. So considering if we have an exposure coming correctly at 1/1000, f4, ISO 800, and we want to go faster but the lens is already widest open, what do we do?
We double the shutter speed, and to compensate for the lesser amount of light; we double the ISO. In effect, we will get the same brightness or exposure of the image.
*Image By The Tripod Diaries
The various stops of ISO can be covered as:
501002004008001600320064001280025600 and so on.
Moving from left to right, the brightness of the image gets doubled, although digitally, as a result of an increased sensitivity of the digital sensor. Also, the picture gets noisier as we go right, and depending on the camera body, a point comes after which noise isn’t manageable.
ISO and Sensor Size
Another important factor that determines ISO sensitivity is the sensor size. The larger the size, the better the sensitivity and performance at higher ISOs. Therefore, full-frame DSLRs are best when handling high ISO, and then APS-C cameras, and so on. The reason for this is attributed to the pixel size.
When more pixels are accommodated in a smaller sensor, the pixel pitch often comes lesser than 2 microns, as in the case of mobile cameras and compact cameras. This results in a non-acceptable performance even at slightly higher ISO.
As the sensor size grows, the pixel pitch improves, thereby allowing better reception of light on individual pixels and better ISO performance. As an idea, the following are the maximum ranges of ISO based on sensor sizes. They obviously have been improving as the technology has improved.
Full-frame DSLR3200 (or even more)
Compact Camera/Advanced Phones 200-400
Although ISO isn’t part of the exposure triangle, modern-day cameras have this advantage of using ISO almost as the third wheel in the vital cog of exposure. It is a boon to have changeable ISO from within camera and also auto-ISO with maximum ISO settings. The only thing that holds you back in modern-day photography is your creativity.
What is ISO?
Learn how, why and when to use your DSLR ISO settings to tackle low light conditions
Photography is all about light. However, there will be times when you’ll find yourself in a situation where you simply don’t have enough of it to make a good exposure.
There are several ways of dealing with this: You could simply adjust your exposure to let more light in or use flashlights, but these don’t always solve the problem. You may not have a flashgun, and adjusting the exposure might require the use of a tripod, which isn’t always practical.
The other way to deal with a low light situation is to use your camera ISO. ISO indicates the sensitivity of your camera sensor to light. The higher the number, the more sensitive it is. Typically, the range is from ISO 100 to 200, 400, 800, 1600, 3200, 6400, 12500, 25600, 51200, 102400 etc.
Like all good things, there’s a downside to using ISO to getting yourself out of a low light situation. The higher the ISO number you use such as 6400, the more digital noise you’ll see in your pictures. This noise looks a little like grain.
When you change the ISO to a higher number, the other settings on your camera change, for example, your shutter speed can become faster. So it can be useful in low light to make your camera sensor more sensitive to the light but remember you start to compromise on image quality the higher the settings get.
Some DSLR has an ISO button on the main body. With others, you’ll need to access the ISO through the camera settings menu. If you’re unsure on how to use yours refer to your manual. If you want your image quality to be high you’ll need to select a setting around 100, 400, 600, 800.
However, remember you’ll need more light when using these settings. At the other end of the scales, if you’re shooting in less light, select a higher number such as 6400, 12500. But remember you’ll get digital noise with these settings.
I started the road of photography, repairing some film cameras. But soon I've realised that I need some knowledge on how the photos are formed inside the camera. This road is tougher than I thought, but life is always a learning experience, and I am hoping that you could join me in this wonderful world of photography.
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