Exposure Made Easy PART 3: ISO

by melissa

In the first segment of the DSLR Exposure Series, I briefly discussed the exposure triangle, and one of the three settings in the Exposure Triangle, aperture. In Part 2 we covered shutter speed, and now in Part 3 we're finally moving onto the mysterious remaining setting: ISO.

I say mysterious because when Jon and I first heard the term ISO (and for a year or two later), it sounded familiar, but we had absolutely no idea what it was. When the time came for us to bite the bullet and learn how to shoot on manual, we of course turned to the trusty (yet not always trustworthy) Wikipedia. And believe you me, you don't want to go there for ISO. It looks like a calculus class on steroids, and it sailed right over our heads in 10 seconds flat. It's math, it's logarithms, and if you're like me, it's torture. Very complicated, very overwhelming, and definitely not our thing.

So we read elsewhere and took a more 'average person' approach to ISO, leading us to an 'average person' understanding of it.


What is ISO?
Once we finally figured it out (which took some time...), the way I remembered it was to think of ISO as fake light—a last resort to lighten the shot when my aperture and shutter speed were maxed out.

For the more engineer-minded of you, here's the watered down version that we can *almost* wrap our brains around. In film, ISO is the indication of how sensitive the film is to light. If we understand this correctly, in digital photography, ISO digitally simulates sensitivity of the image sensor to light. Remember, film changes in sensitivity to light, not the camera—but since there is no film in the digital world, the camera has to mimic that sensitivity without the film (since we know it's not the memory card affecting it :)

If you can take yourself back to the pre-digital version of you in the 90's, looking for film for your sweet 110mm camera (at least that's what I had, the flat-ish, plastic rectangle that came in all colors of dreamy neon, but feel free to insert your own 90's camera model from your memory here), you may have a flashback of some film speed numbers, like 100 for outdoors, 400 for sports, 800 for indoors...or something like that. Those are basically the equivalent of ISO numbers now.

The same basic number principles apply here as in film photography—higher ISO numbers mean the sensor is "more sensitive" to light, while lower ISO numbers mean the sensor will be "less sensitive" to light. Higher ISO settings are preferred in darker situations to get faster shutter speeds (i.e., indoors, dimly-lit receptions, outside at dusk/night)—however, the cost is noisier shots. Noise is the digital version of film grain, which is basically specks that take away from the quality of the image.

Since a lower ISO will create a clearer shot, a low ISO is ideal more often than not. However, a grainy shot is better than no shot, so if you’re choosing between a high ISO or no picture at all, crank the ISO and go for it.

(please keep in mind I use high ISOs in desperation when dealing with bad lighting, so in order to show grainy examples, I had to create bad lighting, and take less-than-ideal photos. All in the name of information sharing :)

Here's your takeaway.

1. ISO is like a simulated lightening of your shot. (not to be confused with simulated lightning, which would hurt)
   Use it as a last resort to lighten your exposure when you've maxed out your aperture and shutter speed.
2. Higher ISOs will make lighter shots and a grainier/noisier shot, which also decreases image and color quality.
3. Stay on ISO 100 whenever possible, but know when and how much to bump up your ISO settings.
   For example, you could memorize some basic ISO settings, like...Sunny: ISO 100, Shade: ISO 400, Indoors: ISO 400, Indoors at night: ISO 800. Those are just basic guidelines that could obviously fluctuate depending on how sunny, shady, or dim your lighting is. But having the numbers in your head will allow you to think less and shoot more in each lighting situation.
4. A noisy shot is better than no shot!
   ISO is there for a reason, so when you're hurting for light, don't hesitate to crank that ISO! And I have to put a plug in for modern technology...we've found that newer models are seriously killing it with ISO! There are sometimes when we're fighting to find any grain in our photos shot with ISO 6400—that's pretty phenomenal.

   

   Shots I would have missed out on last November if I hadn't shot up my ISO! Left: 50mm, f/1.8, 1/200, ISO:6400. Middle: 50mm, f/1.8, 1/400, ISO:6400. Right: 50mm, f/1.8, 1/500, ISO:6400.

   
   
5.  If you've maxed out all three exposure settings and you still can't get enough light...
   ...you either need a better lens (you can read up on my lens post for ideas), or you need to find more light. (get out of the shade, turn on more lights, add more lights/lamps into your home, or you go the flash route and learn to use it without looking like you used it) Or wait until the sun comes up :)

Some little FYI nuggets about noise/grain...
(you should be able to click on the images below to see them larger and see the noise better if you want to) 

 I think it's definitely better to have ISO noise than shutter-speed blur, so don't feel bad if you have to up your ISO to lose the blur. Do it.

50mm, f/1.4, 0.4s, ISO:100

Long exposure (slow shutter speed) and a tripod will allow more light in without a high ISO, but that's typically best for still-life or capturing time-lapses (not people).

50mm, f/22, 4.0s, ISO:6400.

Noise typically shows up most in the shadows in your shot, and in the portion of your image that is not in focus, but even then it probably won't show up much until you're using a very high ISO in poor light.

haha...I just realized I was talking about "noise" and pointing to different keys on a piano...all the sudden this photo looks like a strange piano lesson illustration when taken out of context. Whoops! 50mm, f/1.4, 1/500s, ISO:1600

Probably no one will even notice the noise except you or a professional photographer.

50mm, f/1.4, 1/80s, ISO:1600

Using a high ISO in a dark place will mess up the colors of your image. Check out how different the color is in this shot!! And when color gets messed up like that in a JPG file, it's pretty much impossible to post-edit it in a way that will make it look the color it should have.

50mm, f/1.4, 1/500s, ISO:1600

BUT...noisy shots can look pretty awesome in black and white when the colors of your image are messed up :) It's a good plan B. It makes them feel a little old and newspaper-y, and what's not to love about that?

50mm, f/1.8, 1/400s, ISO:6400.

50mm, f/1.4, 1/200s, ISO:400.

Photo challenge of the week!
Gear yourself up to go full-manual mode! You can try one day a week, or even 10 minutes a week, but challenge yourself to start braving the learning curve and give it a shot! (More on how to make this process easier coming up next :)

Good luck as always! Hopefully it was clearer than mud and definitely less painful *hopefully* than looking it up on Wikipedia :)

Have a fabulous weekend...rock on, party people.