What Is ISO And How It Effects Your Images

posted on 9th of november, 2009


The ISO (International Standard Organisation) or the ASA (American Standard Association) as it was formly called, is the standard for expressing the sensitivity of the sensor or the film to light. For a point and shoot camera this is normally 50 – 100. Digital cameras are more sensitive to light then film or fixed lens cameras, so normally the slowest ISO is often 200 or 100.

The ISO is expressed as film speed. The higher the number, the more sensitive or faster the film. Film with lower sensitivity to light, (a lower ISO) requires a longer exposure and is called a slow film. A film with hight sensitivity (a higher ISO) can shoot the same scene with a shorter exposure, or shutter speed and is called a fast film. Now, of course if you are shooting with a digital camera, you have that advantage that you can change the ISO for each image. With film photography, the whole film is the same ISO!

When shooting with shutter priority, the camera chooses the shutter speed for proper exposure and this will depend on the lighting, the film speed (ISO) and the aperture. A higher ISO, allows it to be exposed faster, so the shutter does not have to stay open as long for the same size aperture.

With a digital camera, when the ISO is increased, it amplifies the signal from the sensor. Each time the ISO is doubled, the camera can use a shutter speed twice as fast for proper exposure in the same lighting, at the same aperture. This I think is amazing! It was all so confusing to me at the start, but when I look at it now, it somewhat makes sense! I control the amount of light entering the sensor and I have 4 things at my disposal to use to alter the lighting.

Anyways, getting back to ISO….. the only down side of using a faster ISO is that this amplification can cause noise, or film grain so the photo will turn out bad quality. Again, this is an effect that the photographer may be wanting to create on purpose!

But for good quality photographs that can be enlarged and still clear and sharp, it is better to keep the ISO speeds set lower for a cleaner image. My camera ISO starts at 200 and goes to 1600.

You may not see the need to alter your ISO, but it is good to know the effect it will have on your images. A perfect example of needing my ISO altered, happened to me a few weeks ago. I was shooting a wedding. It was a beautiful day, the photos outside i could shoot away at an ISO of 200. But inside the church, was a different story. It was dark, and dimly lit! I wanted clear sharp images. I had a tripod, but didnt want to be using my flash during the ceremony. I needed to increase my ISO to 1600 to get clear bright images in this dark environment. Increasing your ISO increases your cameras sensitivity to light. So you can get the image you want, even if you only have a little available light.

I hope that has explained ISO to you clearly! Now get out and experiment!!

Good luck - Rebecca!

Comments (21)

Posted by Litifeta on December 07, 2009
Mine is locked on 100 on my Canon 5D. The only time I change it is in the middle of summer during the day, I drop it to 50.
Posted by Linqong on November 24, 2009
Hi Rebecca:)
A useful articles.
I am very pleased to see my image here.
Posted by Tan510jomast on November 15, 2009
very informative Rebecca, well done.
i like to add too, that with some digital SLR it seems that even their AUTO mode can give you the best noise free image. this is especially useful for those who are just starting out using their new digital camera.
i noticed this by chance with my old and first digital SLR Olympus e300.
i guess you can say that some "AUTO mode computer chip" have artificial intelligence literally, as it know which ISO will give you the best results. as i said, some cameras, this may not be so with all digital cameras.
Posted by Kenhurst on November 12, 2009
Well written article Rebecca! And nice use of DT images in it.

Posted by Yuritz on November 11, 2009
thanks for sharing those informations,useful
Posted by Svecchiotti on November 10, 2009
Good article and everything included in it is very true.
Posted by Irisangel on November 10, 2009
Great information! You have learned well since you wrote in one of your early blogs,"So.... I am stepping out and going back to college in September to do a diploma in photography, so that I can learn more and be better at what I love." Congratulations!
Posted by Gilmourbto2001 on November 10, 2009
Thanks so much. Great article. Shooting in Manual mode, I try and keep the ISO as low as possible, but always consider dialing it up if necessary to achieve the right artistic mix of Aperture and Shutter Speed. Today's digital cameras are actually quite impressive with their high ISO performance.
Posted by Conde on November 10, 2009
Thanks for the article!
Posted by Conceptualcreations on November 10, 2009
Great article...Thank you Rebecca!
Posted by Rebeccaosborn on November 10, 2009
hey Elianehaykal, i had not heard that.. but you could be right!!

To everyone else, thanks for the comments, glad the blogs are of a help to you all!! xx xx
Posted by Creativei on November 10, 2009
Thanks for this beautiful series of blogs, was waiting for your blog, Thanks Rebecca for all the time and effort to educate fellow contributors.
Posted by Justmeyo on November 10, 2009
Useful blog:)
Posted by smartview27 on November 10, 2009
Very useful informations, Rebecca. Thanks.
Posted by Fultonsphoto on November 09, 2009
Good advice, thanks.
Posted by Mani33 on November 09, 2009
Thank you! Cheers :)
Posted by Wildmac on November 09, 2009
Another great blog! Cheers :0)
Posted by Elianehaykal on November 09, 2009
Nice blog :) just one thing: I've read elsewhere that ISO is not an acronym, it's Greek & means equal.
Posted by Jonvitalija on November 09, 2009
thanks,Nice blog Rebecca!!
Posted by Bradcalkins on November 09, 2009
Another reason to bump up ISO is to use a smaller aperture for increased depth of field, and the same shutter speed.
Posted by Keki on November 09, 2009
thanks for this :) always great to refresh!

Comments (21)

This article has been read 4115 times. 8 readers have found this article useful.
Photo credits: Quentin Bargate, Linqong, Tracy Hebden.

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