Finally got to write the next part of the beginners tips. Complicated specially in the summer break, where you have to double for the colleagues on vacation, but here we are.
The next part is exposure. I actually started to write that two years ago, when I started this blog (“How does a camera works?” and “Exposure … more details – Shutter speed“), but I’ll re-write it. Also my understanding of the whole thing has changed in time.
I’ll break it in more than one post also, otherwise it gets too long and with the mean attention span of today (I talk for myself) long posts are rarely fully read.
Exposure is the amount of light that is registered in your sensor. The perfect exposure would be a 18% gray frame. Modern cameras have an internal photometer that measures the amount of light in the metering region and control the exposure automatically (or advise you about it in fully manual mode), so getting the right exposure is no longer a complex skill as it was before.
There are tricky situations like very bright or very dark subjects or environment that can fool the metering, like a bright sandy beach, or shooting a black car … the camera will under or over expose the scene thinking it’s not right and exposure compensation will be needed. For the rest the system is good and reliable.
This is controlled by the so called “exposure triangle”: shutter speed, the aperture (f-stop) and the sensibility (the ISO).
Back in the days of film it would be the “pair” shutter speed and aperture that would define your exposure, since you had little control over the ISO. The ISO, the film speed, was fixed by the film you used and you would not change the roll before the end of it. Or you would just ditch the remaining film for a different ISO. OK, Advantix (APS – Advanced Photo System) film would allow you to rewind it, take it out, change the roll and latter put it back. But very few cameras had the time to adopt it before digital came along.
To put the exposure triangle simply. The ISO controls how willing to record light is your sensor, shutter speed controls how long is your sensor recording light and aperture controls how much light goes into your sensor.
An analogy (very rough) is a pipe. Shutter speed is how long you let water flow, aperture is the diameter of pipe and ISO is the pressure put on the water. Or so 🙂
Actually all this information is available in your viewfinder!!!
Combinations of the triangle will provide you the same exposure, but not the same picture. Together with exposure each of the three parameters control other effects. Kind of, each comes with a price!
Shutter speed controls how much movement you have from your subject, or around it. It’s not the same to shoot a water fall with 1/500s and with 2 seconds. The first will give you a crisp “droppy” water, while the second will give you a silky water fall. There are situation you want one case, situations you want another thing.
Aperture controls the depth of field, i.e. how much of your image is in focus. A big aperture (small number, like f/1.8), will give you a subject in focus with a nicely blurred background (a Bokeh), bringing the attention to the main subject, while a small aperture (large number, like f/22), will give you mostly everything in focus, like for a landscape shot where the foreground and the background are important.
The ISO gives you the “scale” for light capture. The higher the ISO the more light your camera will capture, so you’re able to shoot in lower light, but also the higher the noise in your image.
I’ll talk a bit about the ISO here (there’s not much to say actually, is electronics) and make more detailed posts about shutter speed and aperture.
The sensitivity of your detector is given by the ISO number (ISO 100, ISO 200 …). For those who used film, the ISO or ASA was the sensitivity of the film (there was 100, 200, 400 and sometimes 800). Todays cameras get easily to ISO 6400 and high end models will go up to 256,000.
The ISO goes linearly with light. So ISO 200 will capture twice as much light as ISO 100, the same for ISO 400 and and ISO 200. You double the ISO, you double the amount of light, so you add “one stop of light” (very important concept in photography “a stop”). You half the ISO, you half the amount of light, so you subtract “one stop of light”.
Stops of light. This is an important part and an important jargon. So, you add a stop of light, you double the light. You add two stops of light you have four times more light: you double it, and the you double it again (2×2 = 4). You add three stops of light, you have eight times more light: you double it, and the you double it again, and the you double it again (2x2x2 = 8), and so on. The same downwards.
As said, ISO brings nice associated to it. What is noise? You have luminosity noise and color noise. The first is a random variation in luminosity from pixel to pixel and the color noise is the random variation in color from pixel to pixel.
As you can see in the shots below. A clean ISO 100 shot and a noise ISO 12,800 shot from a Canon EOS 60D.
There’s an “normally” usable range for each camera. Like the 60D will have great shots up to ISO 1600, usable shots up to ISO 3200 and you can survive with an ISO 6400 (the ISO 12,800 is a mega-boost mode for emergency). A Canon 5D Mark III is said to have very good shots down to ISO 25,600!
Two quotes I really like about noise. The first one is from Jay Maisel “Better a noisy picture than no picture”. In the sense of with high ISO you get noise, but with low ISO you shutter speed will be low and the scene, specially people, will be blurry and you’ll have no picture. The other one is from Rick Sammon “If someone can notice the noise in the picture, you have a boring picture”. You should have interesting pictures, where a possible noise is just an “oh well!”.
Today Lightroom and other softwares have great de-noising modules and plugins, that really do a lot for a noise shot! Don’t push them to hard, otherwise the shot will go bad, but use them!
Though my 60D doesn’t give me much leverage for that, I don’t hesitate in increasing the ISO and getting my shots!