Written by: Derek Watterson

A recent post on our Exposure Control Lesson posed the question, What is ISO? Here’s a more in depth explanation.

Photography ISO

What is ISO?

What is the ISO standard and what it means to Photographers

ISO is short for International Organizational Standard.  In the photographic world, ISO is most commonly referred to as a film rating system.  Think film photography, not the movies :)  In terms of film, ISO is used as a rating system to tell you how sensitive the film is to light, or how fast the film is.  The lower the ISO number (ie 50) the more time the film needs to be exposed.  The faster the ISO film speed, less light is required to take a picture.

What is the Best ISO?

In many situations it is not possible to have a film with low sensitivity.  Such situations include those where there is low light and no tripod, or where the motion is very quick such; as in sports photography.

Film ISO vs Digital ISO

If you are using a film camera there is a much better chance that you are already familiar with ISO.  When you choose your film you select the ISO.

Digital photographers are not so constrained by a roll of film having one set ISO sensitivity, and can change the ISO sensitivity rather easily.  That isn’t to say digital cameras can escape the adverse effects of shooting with higher ISO.

In film, when the ISO is too high, photos tend to appear grainy.  The same is true with Digital Cameras instead of being called grainy it’s called noise.   The higher the ISO, the the more noisy digital photos appear.

Whether your using film, or a digital camera, ISO speed affects the aperture and shutter speed combinations you can use.

So What is ISO?

ISO is a standard telling you how sensitive your film/digital sensor is to light.

  • Higher the ISO, the more sensitive the film/sensor is to light.
  • ISO speed affects allowed aperture and shutter speed combinations.
  • Higher the ISO, the more grainy or noisy pictures may appear.

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37 Responses to “What is ISO?”

  1. Margaret Ann Ward on September 12th, 2009 at 8:42 pm

    This lesson sums it up just fine so that I understood it exactly with a few precise words- rather than a lot of long paragraphs. I will play around in your site more. This was my first spot on the website.

    Thanks for the information and for taking your time to post it.

    Margaret

  2. Your welcome. I hope you enjoy the rest of the lessons. If there’s anything you think we’re missing let us know. We’re always looking for new lesson material.

  3. Enjoyed the review on ISO. I now use a digital camera most of the time. If I set it to “No Flash” Does this force the camera to automatically increase the exposure time in a low light setting? I like to use a tripod and often do not want the glare of a flash.

  4. If your camera is set to automatic then it will automatically update the exposure. If it’s set to manual you will have to compensate for not having a flash. It’s great that you use a tripod in such cases and I agree that a flash can ruin any great composition.

  5. Thanks a lot always wondered how it worked. Still have a lot to learn but your site helps a lot. Thanks again

  6. Hello,

    From the lesson I have understood what ISO is, but i still have not figured as to when one could use higher ISO’s or lower ISO’s. Could you give an example. In the sense, if you are capturing a bright object, is the ISO to be set to at a relatively high number and vice versa?

    Awaiting your response!

    Thanks in advance,

    Nutts

  7. Because lower ISO provides higher quality photography it’s recommended that you use low ISO sensitivity as often as possible. High sensitivity ISO, around 1600, results in grainy photography. High Sensitivity is typically used when you want to capture very quick motion such as in Sports Photography, or when you cannot make the shutter speed any slower or open the aperture any larger in low lighting conditions.

  8. Thanks a lot for the brief and to the point explaination. I understand ISO a lot better now.

  9. Thanks a lot, it is what we say less words more knowledge. i am beginner in photography and i am gaining a lot of information from this site. ENJOYING PHOTOGRAPHY WITH MY NOKIA N86 8MP Camera. KEEP GONING DUDE

  10. u wounder how ISO is short for International Organizational Standard, which intials IOS instaed of ISO

  11. I’m a beginner in photography and I need to learn everything I can. Thanks for the explanation of ISO.

  12. Thank you for this wonderful lesson very straight forward and easy to understand! i’m a beginner and I’m trying to learn everything i can! congratulations to the admins for the good work!

    David

  13. NOW I understand why I’m getting grainy photos in certain low-light conditions. I need to use the ISO setting! A simple discover that will make a huge difference in my low-light photos.

  14. Hi,
    Thanks a lot for understanding on ISO..I’m new to photography and want to learn it badly, I first thought ISO was just to improve the light factor? but never heard the term aperture before? not sure what that is, I have a Canon Rebel XT.. I was planning on buying Nikon D90(felt really comfortable with it)not sure to ask but do you favour Canon and why ?
    Kindly let me know.

  15. Nice description of the photographic term ISO .I am a beginner I learned and want to learn more thanks admin

  16. Dheeraj,

    We’ve got an article on Aperture and many others on the effects of aperture on your photographs. If you search for aperture in the sidebar on the site you’ll find them. The wedding photographer on staff prefers canon. The designer on staff and I prefer Nikon although for entry level cameras Olympus offers a good deal on their Digital SLR and we compare those three brands on our Digital SLR Comparison article. The staff wedding photographer loves Canon because she loves canon lenses.

  17. Oh! at last i got the answer,(what is ISO?)…
    I m a beginner and very confused about ISO & Aperture.Now i get it.Thanks a lot……I also want to learn more from u…I know u help me to be a professional…

  18. WOW. It is nice. Straight & to point. Now I have a question, somehow I think maybe it has to do with ISO but not sure. I have a basic Nikon CoolPix S570 with wide 5x zoom & no clue what that means either lol. BUT, I want to know how to blur the background in a photograph. Maybe what the wide 5x zoom means Thanks in advance!
    Tammy

  19. What you’re referring too is the depth of field. To get the effect you’re talking about you need a wide open Aperture. And a long focal length (Zoomed all the way in). You’ll have to use manual mode to change the settings, even then your camera may not have a long enough focal length or an open enough aperture to make the effect you’re looking for.

  20. Your ISO really help me lot to make my photography better. Thank once again for the details you provided about the difference between Film ISO and Digital ISO.

  21. I love to do photography but i am little slow in english thats why sometimes I don’t understand but this time it was very easy and quick to learn photography. I tried this at my own I got wonderful pictures
    Thanks to this website who teaches a free photography course very easy and quick
    Aditya

  22. Cinclair Chucks on May 13th, 2010 at 6:00 am

    Want to know more about being a professional photographer. Any useful training guide and resource will be appreciated.

    Thanks.

  23. Here’s where we keep our articles by professional photographers for aspiring photographers.

  24. Thanks,now I understand better about digital ISO.I use to take my pictures, the Nikon D50 and Nikon D80.Thanks again.

  25. Its really simple and superb. I will start my photography from today onwards with my Canon PowerShot A590 IS.

  26. I have had my Nikon D80 for 2 years and don’t know how to use it properly. I have now learned about ISO. Will practice tomorrow at day light. Any tip on how to get great pictures with the Nikon D80 will be appreciated. I love photography. Thanks to all who reply.

  27. um…
    thanx 4 all u ppl who do give some tips

  28. The lecture was great but I wanted to know if zooming has any thing to do with ISO because whenever I zoom the picture appears darker.

  29. ISO isn’t effected by zooming but the aperture is. The more you zoom in or the longer the focal length: the less the aperture can open and that’s why you are getting darker pictures when you zoom in. After you zoom you have to re-evaluate your exposure.

  30. I have a cannon 5d and am still learning. My photos have been selling well but I am concerned that they don’t have that real sharp clear look to them. Can you give me any tips. Also if the iso should be lower and it isn’t a really bright room would I just have to change other settings to let more light in instead of going higher in iso. The last practice I did was in a bedroom and the photos were very noisy.
    This is the best site I have come across by the way. IT’s fantastic for us beginners !!

  31. If you want to get rid of the grainy look you’ll have to lower your ISO. That might require a tripod. If there is motion you’ll have to add more light in order to keep your iso low and still freeze the motion.

  32. Just found this site…I’m a beginner myself and I really want to learn Photography and hopefully get a degree. I actually learned a lot with not so much of reading long paragraphs. I like how its straight to the point and understandable at the same time.

  33. God bless you all for all the information on this site, I’m just about to buy my first dslr and I’ve always loved photography and wanted to be a pro. I’m excited and eager to learn, I’ll update you as I get along.

  34. Great class, is there worksheet that I can use as a guide for which ISO to use.

  35. Lowest is always best, but it depends on if you can use a tripod or if your subject is in motion. If they are moving and there isn’t much light you’ll have to increase the ISO. It’s kind of a last resort setting.

  36. This is great! I´ve heard all this concepts before but had no clue what they meant. I love it how you “tranlate” them into examples. Now I know what to do with ISO! It´s not chinese anymore. This is exactly the type of site I was looking for to learn about photography in simple words. Thanks again!

  37. love the site! have a question on ISO: when I’m on manual mode I currently have ISO on auto. But having read the above I understand that the lower the ISO the better. so if I’m setting aperture and shutter speed I’m assuming that the ISO will automatically adjust to get the best exposure? which may mean the ISO goes higher than it needs. So it would be better to set this manually too?
    also when you’re in fully manual, which do you set first? aperture or shutter speed and ISO? I know it’ll differ if the subject is moving or not – if moving you want to reduce shutter speed. and then for static pictures would you always set aperture first to control the depth of field?
    so far I’ve been trying to get my head around the technical side of things, but when it actually comes to taking a photo on manual mode I feel completely at a loss!!! Are there any good starting points? I liked the guidelines for aperture dependent on how much natural light there is but not sure where you would start on shutter speed….
    Looking forward to your response
    Thanks

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