What is ISO in Photography?

A guide to understanding what ISO means and the ideal ISO settings for your photos.

ISO is one of the most essential photography terms to understand, but it can be very confusing to figure out! What does ISO stand for? How do you know what to set your ISO to? How does ISO work and how does your ISO setting affect the quality of your photo?

In this tutorial we’ll walk through what ISO means, why its called ISO in the first place, and how to set your ISO properly in different lighting conditions.

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What does ISO actually mean?

ISO is a photography term originally dating back to film cameras. Different types of film possess different levels of sensitivity to light. Companies had different systems for measuring this sensitivity. ISO was one such system, and eventually became the golden standard photographers used. In today’s modern digital cameras, ISO changes the sensitivity of a cameras sensor to light. Increasing the ISO brightens the image but also increases digital grain, loss of detail and lowered color accuracy. A good rule of thumb is to always shoot at the minimum ISO required for your situation. 

This is the short definition of what ISO means and where it all comes from. We won’t spend much more time focusing on the history of ISO and where the term ISO came from – Just suffice it to say that it isn’t a clever abbreviation, its simply a standardized system that measures light sensitivity.

Now that we have a basic understanding of where the term ISO came from, lets take a look at the practical applications of using ISO and what is actually happening when you adjust the ISO in your camera.

What does changing my camera’s ISO do?

On a digital camera, when you adjust your ISO, you are adjusting the relative sensitivity of your camera’s sensor to light.

This sounds complicated, but it’s basically a fancy way of saying it makes your camera see better in the dark.

This is not too different from turning up the volume on your headphones when something is too quiet. You can increase the ISO on your camera to make the light “louder”

But this all comes at a price.

Just like turning the volume up too loud on your headphones can create distortion or feedback, turning up the ISO on your camera can create digital distortion (which photographers call “noise”) and loss of detail and color in the photo.

The higher your ISO, the more image quality decreases.

So when trying to figure out the best iso setting for your photo, the basic rule is this: Only increase your ISO the minimum amount necessary.

This video tutorial on ISO visually covers the basic fundamentals:

For a more in depth guide, keep reading.

The Full frame ISO advantage

Interestingly enough, the bigger your camera’s sensor, the better it will perform in low light with high ISO settings. This is because full frame cameras have more pixels vs aps-c vs crop sensor cameras. Without getting too technical, this winds up making the digital noise & loss of quality less noticeable on a full frame camera vs a crop sensor camera, because the pixels on a full frame camera are smaller than the pixels in an aps-c, m43 or crop sensor camera.

If you shoot a lot of photos in the dark or in challenging lighting situations, then having a camera with better ISO performance is going to make a big difference and improve your photography. Full frame cameras with the current best ISO performance are the Sony a7 series, Nikon Z7 and Panasonic S1 lineup.

Its important to not that you don’t HAVE to have a full frame camera to take great photos! Many professionals (Myself included) use crop sensor cameras. Full frame vs crop cameras have different strengths and weaknesses. All that matters is you know that when using a crop sensor, aps-c or micro 4/3 sensor, that you will need to be more careful with using high ISO settings than on a full frame camera.

Now that we’ve talked about the differences between ISO performance on full frame and crop sensor cameras, it’s time to discuss how to find the ideal ISO setting for different lighting situations.

Finding the best ISO settings

As we mentioned in our introduction, ideally you would set your ISO to the lowest possible setting in every photo. This will give you maximum image quality. That said, in real life sometimes there just isn’t enough light to do this, and so you’ll need to find the right ISO setting based on your situation.

There are 3 ways to change the brightness of a photo:

• Exposure (Known as shutter speed)
• Aperture (Sometimes called “f stop”
• ISO

As a general rule, it is best to leave your ISO at the lowest number, and adjust your shutter speed and aperture until your photo looks good.

Sometimes you run into problems though. There are situations where you can’t adjust your shutter speed or aperture any further, because:

1. If you shutter speed is too low, your photo might have motion blur. With moving subject, you generally want to have a higher shutter speed so that everything captured is crystal clear.
2. If its simply too dark and your aperture / f-stop is already maxed out, you’re out of options!

If you run into any of these challenges, its time to increase your ISO.

Here are 5 factors that will help you decide on what ISO setting to use:

Figuring out the ideal iso settings for different situations can be tricky. Start by asking these 5 questions:

1. Light – Is the scene well lit, or dark?
2. Depth of Field – How much of my image needs to be in focus?
3. Tripod – Can I use a tripod?
4. Movement – Is my subject moving or stationary?
5. Focal Length – Different zooms require different setting

LIGHT & ISO

When your scene is bright enough, set your ISO to its minimum setting.

If your scene is too dark, if possible add light or move locations before cranking up your ISO. Improving your lighting is often much better than increasing ISO to compensate.

DEPTH OF FIELD & ISO

Depth of field is a fancy photography term for how much of the photo is in focus (The focus plane) and how blurry your background is. Sometimes you’ll want more of your photo in focus and will need to keep your aperture higher + use higher ISO. One such situation is when photographing a live event. A higher aperture will make it more likely your photos are in focus and you don’t miss important moments. In this case, you may need to raise your ISO to compensate.

TRIPODS & ISO

Using a tripod gets rid of camera shake and allows you to set your shutter speed to very long exposures. With night photography a tripod is essential because you can shoot in very dark environments while keeping the ISO at its lowest setting.

MOVEMENT & ISO

As discussed earlier, if your shutter speed is too low when photographing movement, moving subjects will appear blurry in your photos. The faster the movement, the faster you need to set your shutter speed, which will require you to compensate for this loss of light with a higher ISO.

FOCAL LENGTH & ISO

Longer, more zoomed in lenses exaggerate depth of field & motion blur. Because of this, the more zoomed in your lens, the higher you’ll often need to set your shutter speed and aperture to ensure your photos are in focus. For instance, a bird photographer using a 800mm zoom lens might use an aperture of f5.6 and shutter speed of 1/1600th. This will make the photos much darker than a 35mm lens with an aperture of f2.0 and shutter of 1/200, and so you’ll need to compensate with higher ISO.

As you can see, anything that affects shutter speed and aperture simultaneously affects ISO. The less light you let into your camera, the higher you’ll need to set your camera’s ISO.

This handy ISO Photography infographic summarizes what we’ve covered so far:

Here are a few specific examples of the best iso settings for photography:

Best ISO setting for night photography

Taking photos at night? The best iso for night photography is to use the lowest available setting on your camera, and place it on a tripod while using a very slow shutter speed + bright lens. If using a tripod isn’t an option, then consider adding lights or using a flash, while keeping your ISO low. With night photography a low ISO is especially important as all cameras tend to have a harder time capturing good colors at night.

Best ISO setting for stars

Similar to the best iso for night photography, taking photos of the stars is best done with your iso set all the way down to iso 100, 200, or whatever your lowest setting happens to be. To do this you’ll need a tripod and a reasonably bright lens (f1.4, f1.8 etc – the lower the number, the brighter the lens!)

Best ISO setting for portraits

The best ISO setting for portraits is somewhat debated. In general, the best quality portraits will come from using the lowest possible ISO for your lighting situation. But some famous photographers like Sue Bryce used to say they preferred to shoot at a slightly higher iso as she felt it gives the photos a more dreamlike, filmy vibe. In current years however she no longer instructs photographers this way.

Almost ALL professional portrait photographers use the minimum possible ISO when photographing portraits.

Best ISO setting for outdoors

The best iso setting to use outdoors is going to depend on the unique location and lighting for your scene. Is the shoot taking place at sunrise, during the middle of the day, or in the middle of the night?

Generally speaking, outdoor scenes are much brighter than indoor and so you can easily set your ISO to its minimum possible setting, which is going to be the best setting across the board for everything including outdoor photos.

Best ISO setting for indoors

Photos taken indoors often require higher ISO settings in order to properly expose the photo. When possible the best setting is always the lowest one available, so do what you can to maximize the available light in the room by opening windows, adding lights or using flash in order to minimize ISO.

IMPORTANT: Note that more light does not always equal better light. It is far better to take a photo with great light and high iso than to fill the scene with bad lighting + minimum iso. Not all light is created equal!

Best ISO setting for food & product photography

Photographing food or products? Because food and product photograph typically takes place in a studio, you can usually accomplish this by increasing the amount of light and using a tripod. Set your camera on a tripod, use a fast lens and maximize your lighting to lower your iso to the ideal setting. The ideal ISO setting for product & food photography will be the lowest possible on your camera.

Best ISO setting for weddings

We’ve said it several times: The best ISO setting is always the lowest you can get away with for that situation. So the best ISO setting for weddings would ideally be ISO 100, but often this isn’t practical.

When photographing weddings, I will start by setting my shutter speed and aperture as low as I can get away with, then adjust the ISO up as necessary. In general this will be anywhere from ISO 100 during the photoshoot to ISO 6400 for the first dance inside at night. When possible during the reception you are better off using a flash + ISO 100 than going ISO 6400 with natural light, but sometimes you don’t have time to do this and you’re better off capturing the photo at the right exposure than shooting with a lower ISO and underexposing – You’ll lose a lot more detail doing this.

Often I will favor a higher aperture + fast shutter speed for the ceremony in order to make sure I get everyone in focus as they walk down the aisle. This might mean I need to bump my ISO up to compensate accordingly. I’m okay with the slight loss in quality because I’d rather have the photo a little grainer and in focus than a little cleaner and out of focus!

On different cameras you can get away with different ISO settings for weddings. On my Canon 5D mark iii, I could only photograph up to around ISO 3200 comfortably. My Panasonic GH5 I would NEVER photograph above ISO 1600 unless totally desperate. My new Panasonic S1 however can shoot ISO 12,800 totally clean and makes photographing a wedding reception SO much easier – I love it!

There is a lot of nuance to finding the right ISO for wedding photography, but the best tip I can give you is to practice by taking your photo around different parts of your house + yard, and practicing switching exposures + dialing in your ISO between scenes. Go to the living room, the kitchen, the basement, the bathroom, the front yard, back yard etc and see how quickly you can get settings correct.

Best ISO setting for birds

Determining the best ISO setting for birds starts by dialing in the right shutter speed and aperture. The general rule is your shutter speed should be MINIMUM double the focal length of your lens (I’d go for slightly higher though) This would mean that a 400mm lens should have a minimum shutter speed of 1/800th. Your aperture generally should be at least slightly less than the maximum, so an f4 lens would be sharpest around f5.6.

After you dial in shutter speed and aperture, the best ISO for your bird photography is whatever setting is necessary to properly expose for your photo.

Conclusion

In this tutorial you’ve thoroughly covered the basics of ISO. You know where the term ISO came from and what ISO stands for, what ISO is used for in digital photography, and how to set your iso to the ideal settings for different situations. You’ve also learned the benefits and weaknesses of raising your ISO, and how the best photo quality is always achieved from the minimum ISO you can get away with in your scene.

Hopefully this guide has made ISO a little less confusing and you now feel confident to go out and figure out what ISO you should use in any situation.

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Go make something awesome,

Ryan