ISO Learning with MUNNS - October 2018

Part 1 – What is ISO?

We’ve covered Aperture and Shutter Speed; ISO is the third part of mastering your exposure and plays a key role in allowing you complete creative control of your image.

I like to think of ISO as “InStead Of light” but it actually stands for International Standards Organisation of whom the real name is the International Organisation for Standardisation but was renamed to make it internationally understood.

Confused... no problem, that bit really isn’t important.

For now, I will just say that increasing or decreasing the ISO will make the final image brighter (higher ISO), or darker (lower ISO).

Like with everything in photography, it’s not quite as straight forward as that, but we’ll cover everything a bit later.

Part 2 – Measurements and Adjustments

Every camera has a different range of ISO values (speeds) and a different ‘base’ ISO (native or optimised).

The base ISO is the setting from which the camera is optimised to provide the best quality image.

For example a Full Frame camera (35mm) may use a base ISO of 100, whereas the Micro Four-Third systems use mostly ISO200 as their native ISO.

Like the shutter speed, the ISO values use stops that are proportionate to the amount of light required by the sensor.

1/1000sec @f/2.8 & ISO200 is the same as 1/2000sec @f/2.8 & ISO400

You may also hear about ‘Extended ISO’s’.

A Standard ISO range will depend upon the camera and sensor, but I will use Olympus OM-D’s as an example for this.

The standard ISO range on an Olympus OM-D is ISO200 to ISO6400.

The available ISO in the camera runs from low (ISO50-ISO100) all the way through to ISO25600

The ISO values above 6400 and less than 200 are the extended values and not really used in every-day photography. They are therefore normally excluded from any ‘Auto ISO’ settings.

Part 3 – ISO and Exposure

As stated previously, ISO plays a vital role in how we set up the camera for a shot.

You can see in the image above that raising the ISO doesn’t just make the image brighter, it also starts to introduce ‘Noise’ (or grain).

Because Noise plays a large role in the clarity and quality of an image, we (the photographers) must balance the options carefully before taking a shot.

If the shutter speed is too slow, we risk movement or shake, if the ISO is too high, we risk losing detail and creating a noisy image. An aperture too wide can lose sharpness at the edges and create an unnecessarily shallow depth of field.

For these reasons, ISO is normally the first setting on the exposure triangle we will adjust, either because we want a high quality image, or because it’s set to auto making exposure slightly easier.

Why do we get Noise (or grain) with higher ISO?

The noise is caused by amplification of the signal from the sensor or fluctuations in the electronic signal provided by the camera. A picture is just light and if there isn’t enough light to build a picture, the camera must ‘fill-in the gaps’. It does this in many ways from duplicating pixels to averaging the available light across the image. If there isn’t enough light to use, it simply fills it with whatever is available (not always correctly) and this provides the various forms of noise.

Here we can see a very simple explanation of what happens when there is not enough light to fill the pixels with light.

You see the camera amplifies or duplicates what it can, filling in the rest with what it knows.

Not necessarily the same as what is correct.

Part 4 – Types of ISO

Reading through this and other people talking, you’ll hear a lot of different terminology for ISO most of which comes from the film days when ISO referred to the sensitivity of the film (the size of the silver halide in the emulsion).

You may be familiar with ‘Speed’, ‘ASA’, ‘DIN’, ‘Sensitivity’ or ‘High’ and ‘Low’; all of which relate to the ISO Values.

Now with digital photography, we have two types of ISO; ‘Native’ or ‘Base’ and ‘Extended’.

Native ISO:

A Native ISO scale is a range of ISO values used and tested for acceptable use in most (if not all) camera functions. This scale will be dependent on the manufacturer and the technology use in camera.

Most camera makers will limit any ‘Auto ISO’ settings to this ‘Native’ range.

Extended ISO:

This is a range of ISO used in more extreme conditions and/or in specific circumstances.

Extended ISO shots will almost always lose detail, effect the true colour representation and add a vintage style gritty look to your image.

High and Low ISO:

High and Low ISO will not always mean Native and Extended.

When someone is shooting a low ISO, it will generally mean shooting at between ISO50 and ISO400.

Anything above ISO800 is generally considered high, or at least a higher ‘speed’.

ASA and DIN:

ASA is an old standard for ISO. The American Standards Association became ISO in 1987 and ASA is no longer really used ASA100 is equal to ISO100.

DIN is also no longer used in photography since the understanding of ISO is far easier to grasp. DIN is a German logarithmic system defined by the Deutsches Institut für Normung in 1961. An increase of 3 in DIN is doubling the ISO value (DIN21 = ISO100, DIN24 = ISO200 and DIN27 = ISO400).

There are many others I won’t go into such as the BS, GOST (ГОСТ), H&D, Weston, Scheiner, Ilford and Wellcome scales.

Part 5 – Why is ISO important?

As you can see below, there isn’t much difference when shooting small JPG’s with the in-camera Noise Reduction.

For this reason shooting in high or even extended ISO means there is no real issue when posting to places like Instagram or Facebook.

On closer inspection you can see why using ISO correctly is necessary if you’re going to shoot for large websites, professional prints or client shoots.

Basically put, ISO doesn’t really hold any creative control itself; it will only ever have a negative effect on the final image if moved from its base setting.

ISO does however allow you full creative control of both the Aperture and Shutter providing the ability to get the exact shot you require.

ISO is the third point of the exposure triangle and plays an equal part of ensuring the correct exposure of your images.

These are only guidelines. Now that you know why and how to use ISO, you can experiment and have some fun!

Look out for more tutorials coming soon and let me know if there’s anything specific you’d like to cover.

Created By
David Munns

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