Tag: exposure triangle

And Then, ISO – Photography Basics

Shutter Speed and Aperture. Check!

ISO, The Sensitive Side of Exposure

When it comes to the last side of the Exposure Triangle; you need to be nice, because it’s sensitive. ISO is sensitive. REAL sensitive.

As a matter of fact, it is the only thing in your camera that handles the sensor’s sensitivity to light.

It works like this: Low ISO (50 or 100) is less sensitive to light and thus, needs more of it to make an exposure. As you move up the scale to 200, 400, 800, the sensor on your camera becomes more sensitive to light and needs less of it.

You might think this is awesome. Just jack up the ISO to 128,000 and shoot in the dark! Wahoo!

Your Camera’s Sensor, Up Close

Look, you’re camera is not a bunny and does not eat carrots (needed to get a bunny reference in). There is a consequence for being more sensitive to light; your sensor is more sensitive to noise as well. Let’s take a look at how a typical camera sensor collects light. I’ll try to make this easy.

Pretty, isn’t it? That’s the sensor in your camera, be it DSLR, smartphone, etc…. It is made up of all these dots. MILLIONS of them (that’s the Mega in Megapixel). This image is looking straight at the sensor and there are various patterns to these dots, it’s ever evolving. Let’s turn it on its side.

This is looking at the side a row. Over each actual light sensor is a color filter to only let in red, green or blue. Above that is a microlens to focus the light. Look at your keyboard and pick four keys in a box shape, 2×2. Now imagine 10-30+ million of these sensors in that space. Amazing, simply amazing.

How Does ISO Work on a Sensor?

Storm clouds churned up by Hurricane Irene unleash their power over Zihuatanejo Bay in Mexico.

Each sensor is energized with electricity to accept light and record when it is struck (when the shutter opens to let light hit it on a DSLR, or all the time on other devices). All of those sensors are energized. And that’s where the limits come in.

When set to a low sensitivity (ISO 100), there isn’t much current passing through the sensor area. This lack of sensitivity is overcome by letting in more light, either by a longer Shutter Speed or a fully open Aperture.

But when you adjust the ISO to around 400 or 800 something else starts to happen. That sensor area needs to become more energized to detect the lower level of light. As it becomes more and more energized, with electricity, every sensor gets so energized that little bits of electrical current get lose and starts to bug their neighbor.

Not only are the sensors sensitive to light, they are are sensitive to electrical current (as that is how they measure and transfer the light information). Think of this neighbor pestering as akin to static on a radio. If you run a blender while the radio is going (humor me and pretend you have an actual radio that still gets an analog signal) that electrical current can cause static on the radio. And a mean margarita.

Noise is Not Good

That ‘static’ causes noise when the camera computer gets all the info from every sensor and things aren’t 100% as they should be. There are a couple of types of noise and I’m not going to get into all of them.

Noise (not grain, like in the film days) is ugly, should be shunned and possible fed to wolves. Noise is caused be the increased sensitivity required to capture lower levels of light. And it captures the electrical interference from neighbor sensor. Remember your keyboard? 10-30+ MILLION of these suckers in that space. Not a lot of elbow room.

If you want an exhaustive study of noise, Leica has a great explanation and better diagrams.

Revenge of the Stops

Guess what we call the 50, 100, 200, 400, 800, 1600, 3200, 6400, etc… of the ISO scale? Stops. If you guessed it right you get a +50 bonus (oh yes, you get to keep score).

100 is twice as sensitive as 50. 200 is twice as sensitive as 100. Finally the math gets easy! This means 100 needs half as much light as 50 for the same exposure. Ha ha ha ha….you walked right into that one.

I know, 50 to 100 is twice as much, but it needs half as much light? That’s the way it goes. Here’s the last piece of the puzzle.

At ISO 3200 the images will be brighter than at ISO 100 (if you leave shutter speed and aperture the same). High ISOs are great for fast objects and capturing action. Lower ISOs are ideal for scenic shots as they will have less noise (and typically aren’t moving fast or at all).

How Much Is Too Much?

How much noise is ok for you is something you need to discover yourself. For me and my Canon 7D Mark II I’m ok with 1200 at times, but the lower the better. It also matters on the subject as dark solids can tend to show noise more readily than mixed light color areas. Try to use the lowest ISO you can for the most noise free images.

Let’s put them all together on one card.

You are welcome to download the image as long as it is only used for personal information. You may not do commercial things with it, post it on the internet without a link back here or do other things I do not like. Or print it to keep with you for reference sake. You may print an extra copy to send to your Mom. She called today and is wondering why you never write letters any more.

Some High ISO Noise Examples

Click on an example below to view them nice and large with all the ugly noise you would want.

Costa Rica – ISO 10,000

Phobjeka Valley – Bhutan – ISO 12,800

Smithsonian Museum – Washington, D.C. – ISO 51,200

Utah – Mesa Arch – Canyonlands National Park – ISO 12,800

What is your ISO limit? Is it 1600 or 6400 or what?

Here’s an experiment to help you learn your own limit from the comfort of your home: ISO Limits Of Your Camera

Wahoo! We’re Done With The Exposure Triangle!

And that is the end of the Exposure Triangle. Shutter Speed affects blur. Aperture affects Depth Of Field. ISO controls the overall sensor sensitivity to light. They all need to be in balance to make a proper exposure.

But not before a Pop Quiz!! How many stops of light difference is there between 1/60 f/8 ISO 400 and 1/15 f/8 ISO 100? And how many difference between 1/60 f/8 ISO 400 and 1/15 f/8 ISO 3200?

The answer will be revealed tomorrow.

Up Next: Photography Jargon

Questions? Pop ’em like Pez in the comments section below. or email me at peter@peterwestcarey.com.

Photography Basics – A 43 Day Adventure, and its companion 40 Photography Experiments, are series written by professional photographer Peter West Carey. The series are designed to unravel the mysteries of photography, helping you can take better pictures. Subscribe here to receive all the updates and bonus material. Your comments are always welcome.

If you enjoy the series, consider learning photography first-hand on a professionally led international photo tour in Nepal or Bhutan. More information can be found at Far Horizon Photo Tours.

October 9, 2018
The Exposure Triangle – Photography Basics
With our law and rules finished, let’s jump into how to make a photo.

The Exposure Triangle

First, there is The Exposure Triangle. It balances all things. Makes things right in the Universe. Or maybe it is just a handy metaphor.

To be honest, the Exposure Triangle, to me, is better explained as two Teeter-Totters, which isn’t nearly as sexy as a triangle. What the Exposure Triangle is trying to tell you, is there are three things which have an impact on proper exposure of an image on film or on a camera sensor:
- Shutter Speed
- Aperture
- ISO
We’ll be going over each of those in more detail in the following days.

Shutter Speed

Tree Amongst Rock Formations, Bryce Canyon National Park, Utah, USA, North America

Essentially, this is how fast your camera blinks. Remember the days of film and how you were never, ever, ever, ever supposed to open the back of the camera while the film was loaded? That’s because film reacts to light and if you don’t control how much light hits it, it freaks out and exposes EVERYTHING. Much cursing typically ensued.

So the shutter does the blinking of the camera (from closed to open and back to closed). Everything is dark inside the camera and then “BLINK”, the shutter lets in how ever much light it is told to. More on this tomorrow.

Aperture

The Aperture is analogous to the pupil in your eye. It’s a hole that lets in light and can be changed in most cameras and even some smartphones.

Let’s use an analogy. It’s pitch-black inside this room the is 20′ x 20′ and you are standing in the center. Outside the room is daylight. Are you with me?

Next to you is a 40 ton, 8′ wide wrecking ball. You’ve been working out and are feeling destructive so you swing the ball forward and BAM! 8′ wide hole in your wall. How much light do you think is coming in right now? Tons.

Now back up and let’s do this again. Instead of a wrecking ball, let’s use a 1” wide drill bit on that wall. POP! Hole is in and, if you are standing back 10′, how brightly lit is the room now?

Can you see now how Aperture affects how much light comes into the room? More on how the aperture does other cool stuff on Friday.

ISO

The ferry boat Kittitas approaches a dock in a high key photograph

People often ask what ISO stands for; International Standards Organization. I get blank looks after that answer or “Oh, ok” looks followed by, “Huh?”. Wikipedia has thousands of words on ISO as it relates to photography, but in short, we’re talking about sensitivity here.

It’s the exact same sensitivity as if I punch you. If you’re a body builder, you’re not that sensitive to a punch. But if you’re….oh jeeze, now I need to come up with an example where I punch something sensitive…a cute, fluffy bunny. Sorry bunnies. Chances are, with the same punch the bunnies would yelp and jump a mile because of the guns I’m packing on this 6’1” frame. (sorry, obscure, and sometimes old, pop culture internet references may come up this month)

Better yet, let’s go back to the wrecking ball analogy. You’re in the pitch black room before the ball smashes an 8′ hole in the wall. If you’ve been in the pitch black room for an hour, your eyes are far more sensitive to light, aren’t they? Your pupils are open wide, trying to gather as much light as they can.

BAM! The ball smashes a hole and ARGGHHH!! You sensitive eyes don’t like all that light.

Same scenario but this time, before the ball strikes, we’ve been holding a flashlight pointed into your eyes for 10 minutes. By ‘we’ I mean me and the bunny you made me punch. Your eyes are now constricted and not so sensitive, are they?

BAM! Hole in the wall and you think, “Eh, not so bright”. Your eyes were less sensitive.

ISO will be covered on next Monday.

Got all that? Shutter speed = how long light hits your camera sensor. Aperture = how wide is the hole letting in light. ISO = how sensitive the sensor is to light.

Visualize

Here’s where the triangle comes in. Visualize it like this:

Except for the bunny, it’s a nice balanced triangle. However, the moment one of those corners changes, let’s say you change the ISO from 100 to 400, then the triangle gets all fuddled up and is not in balance any more.

If one, or both, of the other variables aren’t moved as well, the bunny picture won’t come out properly exposed. And by properly exposed I’m talking about an ideal here. After you learn the rules through these 43 days, you’re welcome to break them as mentioned yesterday. But until then, we’re shooting for properly exposed images.

Revisualize

Another way to think of it is:

With the Exposure Teeter Totters Of Doom, if ISO wants to move up or down, one of his buddies (or possibly both) needs to go in the opposite direction to make all things even. This is all in regards to the amount of light hitting the camera sensor. Any of the three could be in the middle and if it is changed, one or both of the other two needs to change to keep exposure proper and level.

Silhouette of mountain with trees at sunset – East Africa – Tanzania

Currently a lot of smartphones, action cameras and drones have a fixed Aperture, so you only have two settings to play with; ISO and Shutter Speed. Most DSLRs and point-and-shoot cameras can adjust all three.

That’s it!! That’s the Exposure Triangle. It’s not a huge mystery, really. It is simply an attempt to keep all things in balance for a proper exposure. Those three things, explained more fully over the coming days, are what determine a proper exposure. ISO, Shutter Speed and Aperture.

Experiment With It

Here are a few practical experiments you can try at home to help the concepts take form:
- ISO Limits Of Your Camera
- Depth Of Field – Changing Aperture
- Look At The Light
Tomorrow we will cover How Your Camera Works.

Questions? Pop ’em like Pez in the comments section below. or email me at peter@peterwestcarey.com.

Photography Basics – A 43 Day Adventure, and its companion 40 Photography Experiments, are series written by professional photographer Peter West Carey. The series are designed to unravel the mysteries of photography, helping you can take better pictures. Subscribe here to receive all the updates and bonus material. Your comments are always welcome.

If you enjoy the series, consider learning photography first-hand on a professionally led international photo tour in Nepal or Bhutan. More information can be found at Far Horizon Photo Tours.
October 3, 2018