ISO – what does it do to your photo?

ISO is, as earlier mentioned, a setting that decides how light-sensitive your camera is. How good nightvision it has, if you will. Low ISO, 100-200, require that more light enters through the lens. You can achieve this with a large aperture and/or a slow shutterspeed.

With high ISO the camera has “better nightvision”, and can take photos with less light. If you want to use a fast shutterspeed combined with a small aperture, for example. Or if it’s dark where you photograph.

So why not use high ISO all of the time, and not worry about shutterspeed and aperture letting in enough light? Because of quality of the photo. High ISO has a few problems called NOISE and LESS DETAIL.


Look closely at this photo. See how the fur lacks detail? See how it looks a bit grainy and spotted, and a bit smeared at places? This photo is taken at 00.01 on newyears morning, and it’s dark. ISO 2400 (that was a lot for that camera) was needed to get a photo at all.

The grainy dots you see is noise. It can be in colour, or just variation in contrast. The smeared parts is what happens when you use noise-reduction in photoshop (a bit too much). It smears the details to get rid of the noise.

And further more, with high ISO the small details get lost. Your photo does not look as crisp and sharp as it would have with low ISO.


This is another try, with another lens (you can see that the first one is taken with a smaller aperture and shorter lens, 24mm I think, because the head is bigger comparing to the body and the floor is sharper in the first photo). This is a little bit better, but you can still see the problems in the texture.

Different cameras handle high ISO differently. My first camera took useless photos after ISO 400, my present is really good up to ISO 2400 and useful up to ISO 5000. A HUGE difference! Of course, ten years and 15.000 swedish kronas plays a big part 😉

Still: a noisy photo is sometimes better than no photo at all! How do you handle low light and high ISO the best? Here is my best advice:

  1. Make the photo black and white, it almost always look better.
  2. Use noise reduction to a point! A little noise often looks better than a smeared photo.
  3. Noise shows the most in dark areas. Make sure you get the exposure right from the start.
  4. Be careful not to brighten the photo too much in photoshop, always look at the dark parts – how do they look? Zoom in to 100% and then out again to see the big picture.
  5. Use noisereduction only where you need it, not all over the photo.


As a sometimes-wedding photographer, I have had my share of really dark churchs, so I have learned a bit…You can see the noise on her necklace, her hair, and a little on her skin. I have tried to find the balance between texture and noise, and I also chose to keep the photo in a darker style. This is actually one of my all time favourite portraits (says a bit about how I portrait people, I guess…)


This is still dark, but I used a tripod to be able to use a slower shutterspeed, a really large aperture (f/1,4), and was able to keep ISO at 400 and still get a good exposure. A bit of luck – the kitten did not move a muscle. See the difference? Of course you do – I don’t even have to ask 🙂

Coming up: Feeling confused? A beginners guide to settings in different situations.

3 thoughts on “ISO – what does it do to your photo?

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