Focus: ISO. My Take On The "Exposure Triangle" Part III

Focus: ISO.  My Take On The "Exposure Triangle" Part III


So, first I will recap.  Part I covered aperture and how it effects exposure as well as shutter speed in part II. Now in Part III I will cover the third and final part of the triangle, ISO.  Once I am done with ISO, I will put them all together.


Now last but not least, ISO.  To be honest I have no idea what ISO stands for but do not fear, I know what it does.  So ISO is from the film days (not that they are gone but..) where ISO was the sensitivity or "speed" of the film.  So different film had different sensitivity to light which means different film would be better for different lighting situations.  ISO numbers that are low (100, 200) are not very sensitive to light so they would be used for a bright sunny day because it would take a lot of light to effect the film.  ISO speeds of 1600 and around there are very sensitive to light, so they would be good for dark situations because it does not take a lot of light to effect the film.


Now I am guessing for most of you reading this post are probably using a digital camera, so how does this effect you?  Well it is the same thing but a little more artificial since digital cameras have a sensor, not film. So ISO for the digital age is the same but you don't need to buy different film for different light now.  You can just go into your settings and turn up or down your ISO which increases and decreases the sensitivity to light.


So if you have your camera's ISO on 200, it will allow you to take well exposed photos during bright sunny days.  If you use ISO that is high like 1000-1600, you will have a very sensitive camera sensor that will be good for very dark situations.


Now before I put these all together... how does ISO effect you photos?  Just like aperture and shutter speed, ISO also has an effect on your photos.  Depending on your camera/film, the higher you crank your ISO, the more grain there is into your photos.  This grain is called "noise" because you can see all the pixels and it usually makes your photos not turn out so well.  To demonstrate noise I will bust out a old photo from a Weatherthans (Amazing band by the way) concert I was at when I had my old Point and Shoot camera:

The Weakerthans - Noisy Image Exmaple - P&S

So yes, that is a bad photo.  But I am posting it to demonstrate grain.  You can see all the pixels and it just isn't a great photo because of it.  This is what happens when there is not enough light so what my camera did was it automatically cranked up the ISO.  It was high enough that the photo had a lot of noise.  But it was a good concert!

Digital cameras these days are getting better and better at having minimal noise at higher ISO's.  My Nikon D90 is decent, but the D700 is known very well to be one of the best cameras in low light.  The new D3s can "shoot in the dark" or whatever the slogan was.  But they can, they can pick up light without noise from the environment that your naked eye would be hard pressed to see.  So depending on how current your camera's sensor is and the quality of it, you can have noise in your photos near ISO 1000 to 6400 haha, or never if you have a D3s.  But I am guessing if you have a D3s, you may not need to take advice from myself but if you are, I am honoured. 

So with ISO and noise, you just have to take photos at different ISO's and figure out what ISO your camera starts getting grainy.  I will quickly go over how it can be used.  So you increase your ISO if you need to keep your shutter speed and aperture fixed (or is you are already as wide as your lens can get).  So if it is dark and you need a fast shutter speed to capture action but also need a large DoF with a small aperture, then you are left with ISO to change to get a well exposed photo.  If you use a fast shutter speed and need a large DoF in a dark situation, you need to have a higher ISO to have a properly exposed photo usually.

So if you are doing star trails, or long exposure photography, having a low ISO is what to do so that your sensor is not sensitive to light which allows you to have longer shutter speeds.  If your shutter needs to be open to for a long time, you do not want your sensor to be sensitive to light or else it will look like you are being summoned to heaven again.  Also having some grain in your photos and some good post-processing (editing after) you can get a photo that looks like it was film.  This can be a desired look for some.  

Now to put it all together.  As I covered with the concert example, ISO can be used to brighten or darken a photo if you cannot use aperture of shutter speed.  So these three things are used to get the proper exposure of a photo.  So if your photos are too bright or too dark, these three things can help you depending on how you want your photo to look.  Personally I always leave my ISO at 200.  That is the lowest ISO my camera can do.  This allows me to not have any noise in any of my photos.  I rarely up my ISO because I do not want to risk noise in my photos.  But as I mentioned, if I cannot change my aperture or shutter speed more to get the right exposure, I will play with my ISO.

So depending on what you want to control in your photo, you use ISO, aperture or shutter speed to compensate for proper exposure to get the look you want in your photos.  I can't tell you how to have your camera settings for everything shot because each camera has different sensors and each lens has different apertures and every shot is different.  What I can tell you is to keep those three things in your head as you shoot.  If you are always practicing those things and actively thinking about how to control the light you will probably get better at taking photos.  

I hope my take on the exposure triangle helped in some way.  Sure you can read all of the basic foundation information for photography but you can't stop there.  You have to go out and practice.  Sometimes you only have a small amount of time to capture a great shot and you have to know your stuff to get the photo.  Sure sometimes you can take a couple of test shots before you get the one you are looking for but usually life goes easier if you can get it right the first or second time.  Saves you from taking a bunch of photos you know you are going to have to delete later.  Anywho, practice, practice and practice is what I am trying to say.

Hope that helps!  I will keep thinking up more helpful things to blog about.  I decided for me to help you better I will open up my e-mail for questions and ideas.  So you can e-mail me at tomhouston7@gmail.com if you have any questions for me on photography or an idea you want me to write a post about.  I will start checking that e-mail now to see if anyone has any questions or ideas they want me to cover.  Please don't hesitate to ask questions.  I was always asking questions on gear and photography knowledge and I still am to this day asking other photographers questions.  So thank you again for reading and I hope to hear from people now with photography questions, I hope I can help!

Thanks again,

Tom

P.S. Just made videos for understanding the exposure triangle and here is the one on ISO: http://youtu.be/h0V4SqBi6HU