Opera House Paris Interior ISO 2500

All You Need to Know About ISO

What is ISO in photography? Do I still have to worry about ISO? Wasn’t that just in the film days? I know it can be a little confusing, but I will try to simplify it a bit. Here are to 3 things you should know about ISO. Hopefully you’ll understand why it’s still important in digital photography.

1. What does ISO measure?

In film photography ISO indicated how sensitive the film was to light. It’s been such a long time since I’ve used film. If I remember correctly, we used to buy film with ISOs that ranged from 50 to 1600. Shooting in bright daylight? We had to be sure that the film in the camera had an ISO of 100 or 200. Dark shooting conditions? Had to change the film quickly to an 800 ISO.

How about today? ISO works pretty much the same way. The only difference is that now we are talking about the sensitivity of the camera sensor to the light. As I mentioned in one of my older blogs, there are different sensor types; from small sensors used by compact cameras, to full frame cameras, which are far more performant in low light. My Canon 5D Mark II does a great job in low light shooting conditions.  This camera has a calibrated range ISO from 100 to 6400, but it can also get expanded to 25600. Pretty impressive isn’t it? In fact I took the cover photo of this post at 2500 ISO and the one below at 25600 ISO, since it was a pitch-black night.

Lighted boats ISO 25600

2. About noise

I am sure you know that noise in digital photography means loss of clarity. If you shoot at very high ISOs you will start noticing big dots on your pictures. Read more about noise in photography here. As you increase the ISO, the noise also increases. As I mentioned above, compact cameras tend to have more prevalent noise due to the size of the sensor. Better quality cameras, especially the ones with full frame sensors, do perform much better, however they are not immune to digital noise either. Keep in mind that higher ISO means more noise.

3. Setting the ISO

Most of the time I keep the ISO at 100 or 200 in my camera. Sometimes I increase it to 400 or 800 if I want to capture motion for example. I prefer to adjust the aperture and speed most of time. One thing I want to point out: the difference between ISO 100 and ISO 200 may not seem a big deal but it is. Going from one number to another one doubles the sensitivity of the sensor to the light. So, at ISO 400 the sensor is two times more sensitive than ISO 200 and four times more than ISO 100. This means that at ISO 200 the sensor can capture an image in half the time it captures it at ISO 100. If the sensor needs let’s say 1 second to capture an image at ISO 100, imagine what happens if you increase the ISO to 1600. Your sensor only needs 1/16 of a second to capture the shot. Now you understand what a difference this can make. You can now even freeze the motion.

As you see, ISO is really not that complicated. If you want to learn more, you can read a great article here. Also keep in mind that ISO is not the only control for adjusting the amount of light in your photos. It works with the shutter speed and aperture.

One more thing. Don’t get scared of digital noise. Usually good post processing software like Lightroom 5 can really help reduce digital noise. Anyway, my suggestion is to always use the lowest possible ISO.

 Happy noise free shooting!

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