What is ISO?
Posted on | February 14, 2007 | 37 Comments
ISO is actually a common short name for the International Organisation for Standardization.
The ISO setting on your camera is something that has carried over from film. Remember back in the ‘old days’ when you used to go and buy your rolls of film and you would buy film rated at 100, 200 or 400, maybe even 800 or 1600? Well that number refers to the film’s sensitivity to light. The higher the number, the more sensitive to light the film is. The ISO bit is from the standards for film sensitivity, and the number refers to it’s rating.
So what does sensitivity mean? Well a low sensitivity means that the film has to be exposed to light for a longer period of time than a film with a high sensitivity in order to properly expose the image. With a lower sensitivity you also get a better quality image too which is why you should always try and use the lowest sensitivity you can get away with. Let’s not get ahead of ourselves though, a little more explanation is required.
You might remember buying film for a sunny holiday and the shop assistant would recommend using a film rated at 100 or 200. If, on the other hand, you were going to be taking pictures indoors, then you might be recommended a higher sensitivity like 400 or maybe 800. If you used ISO100 film and decided to take some pictures indoors, chances are you would need to use the flash, or your pictures would come out quite dark. This is because the film’s sensitivity is so low that the shutter would need to be open for a long time to let enough light in. Your camera may not have had the features to allow it to keep the shutter open for long enough, which is why you ended up with dark pictures.
This was one of the problems with film. Once you’d loaded it into your camera, you were pretty much stuck with that film sensitivity for 24 or 36 shots.
Bring on digital cameras and you can now change the ISO setting for each shot you take. That is one of the big advantages of digital photography.
So why do you only get choices like 100, 200, 400, 800, 1600 and maybe 3200 when it’s digital, surely you could set 154 or 958 if you wanted it? It’s only electrical currents and circuits after all, not a piece of film. Well, in theory you could choose any setting you wanted, but imagine how tricky that would be. There are three settings which combine to give you the exposure, these are Aperture, Shutter Speed and ISO. Each one can be changed individually to allow you to set then to what you think will give you the perfect exposure, or you can let the camera set them for you to what it thinks is the perfect exposure for the conditions it can detect. Already with three different options, each having several settings themselves, the combinations are numerous, so keeping ISO to set values, which people will understand makes it a little less confusing.
Now, I mentioned quality too, and that better quality images are achieved with a lower ISO number. If, again, you go back to film days you may remember the sort of grainy effect some images had. Well this grain effect is what is introduced with a higher sensitivity film. Digital has it’s own grain effect with higher sensitivity and is known as Noise. Digital noise can be seen a sort of speckley effect in areas of similar colour, like skies or dark shadow areas. It is a subject of much discussion and the camera is often judged on the amount of noise it produces at these higher sensitivities. This is why you should always try and keep your ISO set to the lowest number, and use aperture and shutter speed to get the right exposure. If you can’t do that with aperture or shutter speed, move up to the next ISO setting and try again. One of the big selling points about digital cameras is how they handle the digital noise at higher ISO settings. The top pro level cameras from Nikon or Canon will have better control over noise than the cheaper models and this allows the pros (or anyone that can afford a Nikon D3 or Canon 1Ds for example) to get away with using a higher ISO and still getting good enough quality for print.
Why is a high ISO setting needed? Well for indoor work, where flash isn’t allowed and the light levels are fairly low. Or you can use it deliberately to get the grainy gritty feel to the image (although I would prefer to add this later on the computer).
It’s well worth experimenting with ISO settings so you can see just how your camera performs at the various levels. Once you have got to grips with how changing Aperture, Shutter Speed and ISO effect your image, you’ve pretty much got all the technical fundamentals nailed.
Over at the Digital Photography School Blog there is a nice post on how to choose the right ISO setting which is worth checking out. My rule of thumb is to keep the setting as low as possible until you absolutely need to increase it in order to get the shutter speed you need. Just remember to turn it back down low again when conditions get better.
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37 Responses to “What is ISO?”
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February 15th, 2007 @ 2:00 am
Can I change ISO settings on a digital camera, or only DSLR?
February 15th, 2007 @ 8:42 am
It depends what type of digital camera you have. Some of the smaller point and shoot cameras may not have an ISO setting, others may have a limited choice, but you should get some options in the menus if it’s not on a dial on the camera body.
April 2nd, 2007 @ 10:20 am
[...] another of my posts called What is ISO I talked about something called noise. This is the grainy effect you can see on your images in [...]
July 13th, 2008 @ 5:38 am
[...] photography basics [...]
March 1st, 2009 @ 3:18 pm
This is a great site.
August 27th, 2009 @ 8:46 am
nice site very informative… Is there any gadget aside from flush that will help the ISO?
October 5th, 2010 @ 6:11 am
cool sharing..much easier for beginner with dslr..thanks!
November 5th, 2010 @ 11:00 am
For the question at the top, yes you can with most cameras if they are not dslr’s, go into the settings and look for ISO or light sensitivity.
This site was a good help for my photography work, thanks
December 6th, 2010 @ 10:01 am
Dear its very informative and understandable, if you add some pictures as an example this would give a very sure understanding. This article is quite good and i have learnt what i want to..
December 30th, 2010 @ 9:41 am
It’s very use full Site ………..
March 20th, 2011 @ 8:34 am
Thank you Garry, these shared information is very usefull for DSLR beginners like me, cheers.
April 14th, 2011 @ 5:52 am
I found it really very informative.
Thanx Garry for sharing this with all.
April 15th, 2011 @ 2:23 am
Thank you for providing your explanation in plain English as opposed to “Camerageekese”
April 26th, 2011 @ 6:07 pm
Quite informative. It’d definitely help beginners like me. Thanks a lot.
April 29th, 2011 @ 4:26 pm
very usefull, really, u saved my money brother, well explained, even a man with a low english knowledge can understand
May 22nd, 2011 @ 9:14 pm
Giving you million of thanks for such a simple (best ever) explanation on ISO. This holds good for articles on Shutter speed & Aperture which I followed from this page. Heartfelt thanks from a budding photographer !!!
May 31st, 2011 @ 5:21 pm
[...] see both lion and brave child posing together in a more natural light. All I did was increase the ISO (the light sensitivity of your camera) from 100 to [...]
June 18th, 2011 @ 6:49 pm
Just wanted to thank you for this info and a few other articles I’ve read on your site. I just bought my first SLR (Eos 550d) and I’ve been quite confused about the different settings. I think I now understand the basics after reading your posts… Cheers!
June 21st, 2011 @ 10:14 pm
very understandable explanation. thank you
July 7th, 2011 @ 5:33 am
How can I use ISO in my new camera Canon EOS 1100D. I m a new user.Inform me plz
July 22nd, 2011 @ 4:28 pm
thnx…
July 25th, 2011 @ 5:33 pm
very good,informative site…
lots of thanks for the people behind this….
August 12th, 2011 @ 6:24 pm
I’m afraid I don’t the details of each and every camera model out there but there should be a button on the camera or a setting in your menu system to alter the ISO. It should be clear in your manual.
August 15th, 2011 @ 4:17 am
brief and understandable!!! thanks
August 21st, 2011 @ 4:25 pm
its good. very helpful & practical..
August 25th, 2011 @ 5:44 am
[...] If you can’t do that, for heaven’s sake, turn it off and learn how to fiddle with your camera’s ISO. [...]
August 25th, 2011 @ 10:28 am
Which is the best Bridge camera available now?
September 3rd, 2011 @ 1:26 pm
fantastic info for beginers like me. now i can understand what iso stands for and the importance for a good result. thank you
September 6th, 2011 @ 10:49 pm
[...] my ‘ISO’ will give me sharper pictures and loss [...]
September 23rd, 2011 @ 8:03 am
Good explanation
October 17th, 2011 @ 10:10 am
Could you tell me what is the modus operandi of ISO??
I mean,what changes inside the camera when i change the iso from say 100 to 200??
November 9th, 2011 @ 4:20 am
This was a fantastic article. Gave the inputs re. ISO setting. I was always under impression that the Higher ISO rating is better. I am sure this will help me a lot.
December 3rd, 2011 @ 2:45 pm
well explained
December 15th, 2011 @ 11:01 am
Your Article is really Informative for Begginers, Awesome Explaination about ISO..
January 1st, 2012 @ 7:21 pm
well explained
January 7th, 2012 @ 3:43 pm
good comments on iso
January 15th, 2012 @ 12:44 pm
[...] Paulissen gave a great talk and review of the article What is ISO? from the Photography Basics [...]