Understanding ISO – A Beginner's Guide
It is extremely hard to take good pictures without a good understanding of how ISO works and what it does. Camera ISO is one of the three pillars of photography (the other two being Aperture and Shutter Speed) and every photographer should thoroughly understand it, to get the most out of their equipment. Since this article is for beginners in photography, I will try to explain ISO as simple as I can.
Before we go any further, you should first understand how DSLR cameras work.
1) What is ISO?
In very basic terms, ISO is the level of sensitivity of your camera to available light. The lower the ISO number, the less sensitive it is to the light, while a higher ISO number increases the sensitivity of your camera. The component within your camera that can change sensitivity is called "image sensor" or simply "sensor". It is the most important (and most expensive) part of a camera and it is responsible for gathering light and transforming it into an image. With increased sensitivity, your camera sensor can capture images in low-light environments without having to use a flash. But higher sensitivity comes at an expense - it adds grain or "noise" to the pictures.
Take a look at the following picture (click to open a larger version):
ISO 200 and ISO 3200 Comparison
The difference is clear - the image on the right hand side at ISO 3200 has a lot more noise in it, than the one on the left at ISO 200.
Every camera has something called "Base ISO", which is typically the lowest ISO number of the sensor that can produce the highest image quality, without adding noise to the picture. On most of the new Nikon cameras such as Nikon D5000, the base ISO is typically 200, while most Canon digital cameras have the base ISO of 100. So, optimally, you should always try to stick to the base ISO to get the highest image quality. However, it is not always possible to do so, especially when working in low-light conditions.
Typically, ISO numbers start from 100-200 (Base ISO) and increment in value in geometric progression (power of two). So, the ISO sequence is: 100, 200, 400, 800, 1600, 3200, 6400 and etc. The important thing to understand, is that each step between the numbers effectively doubles the sensitivity of the sensor. So, ISO 200 is twice more sensitive than ISO 100, while ISO 400 is twice more sensitive than ISO 200. This makes ISO 400 four times more sensitive to light than ISO 100, and ISO 1600 sixteen times more sensitive to light than ISO 100, so on and so forth. What does it mean when a sensor is sixteen times more sensitive to light? It means that it needs sixteen times less time to capture an image!
ISO Speed Example:
ISO 100 - 1 second
ISO 200 - 1/2 of a second
ISO 400 - 1/4 of a second
ISO 800 - 1/8 of a second
ISO 1600 - 1/16 of a second
ISO 3200 - 1/32 of a second
In the above ISO Speed Example, if your camera sensor needed exactly 1 second to capture a scene at ISO 100, simply by switching to ISO 800, you can capture the same scene at 1/8th of a second or at 125 milliseconds! That can mean a world of difference in photography, since it can help to freeze motion.
Take a look at this picture:
Black Skimmers, 1/2000th of a second at ISO 800
I captured these Black Skimmers at 1/2000th of a second at ISO 800. My camera sensor only needed 1/2000th of a second to fully capture this photograph. Now what would have happened if I had ISO 100 on my camera instead? My sensor would have needed 8 times more time to capture the same scene, which is 1/250th of a second. At that speed, I would have introduced motion blur into my picture, because the birds were moving faster than that. In short, I would have ruined the picture.
2) When to use low ISO
As I've said above, you should always try to stick to the lowest ISO (base ISO) of your camera, which is typically ISO 100 or 200, whenever possible. When there is plenty of light, you should always use the lowest ISO, to retain the most detail and to have the highest image quality. There are some cases where you might want to use low ISO in dim or dark environments - for example, if you have your camera mounted on a tripod or sitting on a flat surface. In that case, bear in mind that your camera will most likely need more time to capture the scene and anything that is moving is probably going to look like a ghost.
Oh No! It's a GHOST ATTACK!
Just kidding, of course! That's my lovely nephew Bahtiyor being the subject of my long exposure test. I set the camera to the lowest ISO to retain the detail, which also resulted in a long exposure of 5 seconds. My nephew sat still, while our friend Max stepped in for a brief moment to introduce the ghost :)
3) When to increase ISO
You should increase the ISO when there is not enough light for the camera to be able to quickly capture an image. Anytime I shoot indoors without a flash, I set my ISO to a higher number to be able to freeze motion. Other cases where you might want to increase ISO are when you need to get ultra-fast shots, like the bird picture I posted above. But before increasing the ISO, you should think if it is OK for you to introduce noise to the image.
On many of the newer DSLRs, there is a setting for "Auto ISO", which works great in low-light environments. The beauty of this setting, is that you can set the maximum ISO to a certain number, so when the ISO is automatically increased based on the amount of light, it does not cross the set barrier. So, if I want to limit the amount of grain in my pictures, I typically set the maximum ISO to 800.
If you have any questions, comments or feedback, please post them in the comments section below.
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12/17/2009 - 06:26
This is an excellent explanation for beginners like me!
Now I understand the ISO speed by your very detailed example.
I will be looking forward for your further explanations on photography :)
Thank you.
12/17/2009 - 14:18
Thank you Dilorom, glad you liked the article. I will be posting more tips and tricks for beginners in photography very soon.
12/17/2009 - 18:07
Got here by a link on dpreview. Excellent stuff. Very good explanation. Your site is bookmarked now. ;)
12/17/2009 - 18:26
JD, thank you for visiting us! I will be posting more info and pictures later this week, so stay tuned! :)
01/09/2010 - 02:20
Nasim, thanks for your knowledge! Why can’t you just increase shutter speed in low light, and make the aperture large? And, does increasing SS automatically increase the ISO? I wasn’t sure if it was a two-way thing.
01/10/2010 - 13:08
Cece, you are welcome!
In low-light situations, if you max out on aperture (every lens has a specific limit on maximum aperture), you can only go so far on shutter speed before the image gets darker (depending on the amount light). For example, let’s say you are shooting in aperture priority mode and set your aperture to f/1.4 on your 50mm f/1.4 lens. Let’s say the camera meters and wants to use 1/25th of a second shutter speed at ISO 100 to expose the image properly. At 1/25th of a second, you have a chance of introducing camera shake, because the shutter speed is too low and if your subject moves, you can also cause motion blur. By increasing ISO to 200, you essentially make the camera double the shutter speed, so this time it would need 1/50th of a second to correctly expose the image. Increasing ISO to 400 would make it 1/100th of a second and increasing ISO to 800 would make it 1/200th of a second. So as you can see, by increasing the ISO from 100 to 800, you can essentially increase the shutter speed from 1/25th of a second to 1/200th of a second, which is sufficient to freeze normal motion.
As far as the second part of your question “does increasing SS automatically increase the ISO?”, it depends on the camera mode you are using (in auto mode most cameras have “Auto ISO” turned on, which causes ISO to automatically increase/decrease depending on light conditions). If you are shooting in other modes, then the camera might not have “Auto ISO” turned on. In that case, just go to your camera settings and set it to on yourself.
For more information, please read my article on camera modes here.
Please let me know if you have any other questions.
12/22/2009 - 18:39
Thank you,
very informative.
I like your series of “A Beginner’s Guide” articles.
So in low light condition using high ISO one can take sharp (of course with noise) images without a flash and a tripod?
Just curios, why they call it ISO speed, when ISO refers to the sensor sensitivity?
12/23/2009 - 02:11
NanOnaN, you are welcome!
That’s correct, as long as it is not too dark. Increasing ISO to a higher number allows you to shoot at higher shutter speeds. In low-light conditions, even a slight increase in shutter speed can help to get a sharp photograph. There is a huge difference between 1/25th and 1/50th of a second shutter speed, while there is only one stop of ISO increase in between. For example, if in a low-light condition your camera is set to ISO 100 and your shutter speed is 1/25, simply increasing ISO to 200 gives you 1/50 shutter speed, while increasing ISO to 800 gives you 1/200 of a second!
I will write more about this in my next article where I’ll mix shutter speed, ISO and aperture altogether.
As far as why photographers sometimes say “ISO Speed”, it is because back in the film days, photographers used to say “Film Speed” when they referred to films with different sensitivities. ISO does increase the speed of the camera by increasing the sensitivity of the sensor, which in turn, increases shutter speed.
12/24/2009 - 01:47
I am really enjoying the articles on your website. I have been doing a lot of photography reading on the internet and i must be honest your articles are among the best for their clear and simple explanations, especially to beginners like me! Keep it up.
12/24/2009 - 23:14
Donald, thanks so much for your feedback! I’m glad that you like the articles – I wish I spent more time on these, because I know I can do better :) I’m hoping to go back and update these later with more information and write some more new guides for beginners.
If you have a hard time understanding what I write, please let me know and I will be more than happy to explain it in more detail.
01/12/2010 - 05:53
Thank you. Very well done for beginners. Concise and clear.
01/12/2010 - 15:17
Thank you for your feedback, you are most welcome! :)
02/22/2010 - 18:49
i go through all your articles on aperture, shutter speed and ISO, still not really understand even you describe in a simple words, but better than before reading your articles. thank you, really good for beginner like me. i just bought a NIKON SLR D5000, still learn how to use, will continue trying and read your article.
02/23/2010 - 18:41
Huang, what exactly are you having a hard time understanding? Let me know and I will do my best to help you out.
02/24/2010 - 06:45
thanks again for your kind offer. first- facing problem to apply all this in real condition especially in manual mode, combination of shutter speed, aperture and ISO to get the desired result, like freeze motion, flying bird, night scenery etc. second-facing problem understanding the camera user’s manual(nikon D5000). this 2 combine together confuse me a lots, will spend more time to understand all this.
02/24/2010 - 12:13
Huang, I recommend using Aperture Priority mode instead of Manual mode. You should shoot manual only when the camera cannot properly meter the light and when you have special situations (like shooting panoramas).
Try reading my “understanding shutter speed, ISO and aperture” article where I talk about how you can combine the three to create an exposure.
The best you can do right now is to photograph more. Take lots of pictures outside and experiment with camera settings. That’s how most photographers learn…so for the start, set your camera on aperture priority and take plenty of pictures. Understand what depth of field is and how you can control it with your camera. Within a week or two, you will start to understand how shutter speed works in different lighting conditions and once you have a good grasp of shutter speed, aperture and ISO, then you can experiment with Manual mode.
Hope this helps. Let me know if you have any questions.
02/25/2010 - 05:19
thanks and i will definitely follow your suggestion – set on aperture priority and take lots of photo in different situation.
02/23/2010 - 19:46
on a d700 would you go up to 6400 iso in dark conditions, or would that be to grainy? Specifically on the auto iso feature, should I do 200-3200 or 200-6400. The reason I ask is because I had it on 200-6400 and I was taking some pictures in my house without the flash in a room lit by lamps and the auto iso was going all the way up to 6400. I was thinking going up to 6400 would be in almost pitch black conditions.
02/24/2010 - 12:18
Monty, it really depends on what noise levels are “acceptable” to you. I personally set my Auto ISO to 200-1600, but in some situations increase it to 3200 (if my shutter speed is too low). I rarely increase it to 6400, because the noise starts affecting the sharpness of the image and I do not like it.
Hope this helps :)