Understanding when and how to manipulate your exposure might be a little tricky to fathom at first, but I’m hoping that after this series, you’ll have a very good grasp on how these three factors can be used to capture an image in any situation.
We’ll look not only at ISO specifically, but we’ll tie in all three and explain how, why and when to adjust them in concert to achieve proper exposure. C’mon in…
FREEBIE PHOTOGRAPHY 101 – THE EXPOSURE TRIFECTA PART 3 – ISO
ISO stands for the International Organization for Standardization (I know, I know, that’s technically IOS, but it has been referred to since its beginning as ISO, … I digress). In terms of photography, the standardization of film sensitivity was created and referred to as either ISO or ASA (American Standards Association) wherein these bodies were used to develop a universal standard, in our case, for photographic film sensitivity. With the move to digital, ISO has kept the same relative exposure based on these original standards from the film era. If you were to shoot a roll of ISO/ASA 100 film, and had a digital camera on hand, and also shot that camera set to ISO 100, you’d be working with the same relative exposure values for the given amount of light.
With digital, we are seeing the ability to adjust our cameras to sensitivities that would have been unthinkable a handful of years ago. While there are drawbacks to increasing the sensitivity which we’ll discuss a little bit later, and not all cameras will allow us to push up to some of these astronomical levels, the ability to achieve usable hand held shutter speeds in lower light by increasing this sensitivity is becoming much more common, with much better results than we’ve seen in the past.
Full ISO stops are as follows:
ISO 50 – 100 – 200 – 400 – 800 – 1600 – 3200 – 6400 – 12,800 – 25,600 – 51,200 – 102,400 – 204,800 – 409,600
Just as a full shutter speed stop, or a full aperture stop will halve or double the total light allowed for the exposure, so too does a full stop of ISO sensitivity.
A stop, whether that is by way of light transmission via the aperture, doubling or halving the shutter speed, or increasing or decreasing the ISO by a stop will all uniformly adjust the exposure value. Each of the three will affect the image in different ways, which is where it can be fun to manipulate a particular scene to suit (and we’ll sum that up shortly), but as far as how the image is exposed for the available light, it will be affected congruously.
I’ve been referring to “Fast” or “Slow” in regard to ISO, shutter speed and aperture settings throughout these articles. Let’s discuss this.
- The reason an ISO setting would be considered fast, is because it provides a higher sensitivity to light. The higher the ISO sensitivity, the faster the ISO is considered.
- A “fast” lens is one that has a large maximum aperture, allowing more light to pass through the lens which gives more exposure latitude, especially handy in lower light scenarios. Not all lenses enable the same aperture adjustment, and lenses are dictated and labeled by the maximum aperture.
- A “fast” shutter speed is pretty self explanatory, and I’d say any shutter speed that allows a fast enough fraction of time to be captured to freeze movement by either the photographer and/or subject would be “fast enough” essentially.
Why and when is this speed important? Well, have you ever tried taking a picture in a dimly lit room and everything came out blurry? This is because your shutter speed wasn’t fast enough to freeze your, and/or your subject’s movement due to less light being available from which to properly capture an exposure. To get a faster shutter speed, you need to either let more light in through the lens, or increase the sensitivity to the light available. Conversely, if out in bright sunlight, if using a slow shutter speed, large aperture setting or high ISO sensitivity (or all three) you may severely overexpose your scene producing a washed out image. This juggling of exposure adjustment is what I’ve come to call, the Exposure Trifecta.
We discussed in part 1 (HERE), that our aperture is a light valve essentially with the larger the aperture, the more light it lets through allowing for a shorter period of time that the shutter needs to stay open (faster shutter speed) for a proper exposure.
Our shutter speed, which we discussed in part 2 (HERE), is the amount of time that the shutter stays open, exposing the film or sensor to whatever light is able to come through the lens. A fast shutter speed will require more light for proper exposure relative to a slower shutter speed which will more often be required for proper exposure with less light. If you’re aperture is as wide open (large) as it can be set to, and you’re still not getting a fast enough shutter speed for your needs, or with as fast a shutter speed setting you’re able to achieve with the smallest aperture setting while still overexposing your scene, this my friends, is where ISO shines, and is the third and final part of our Exposure Trifecta.
The largest drawback to increasing the ISO sensitivity, is noise (digital grain), followed next by color shifts, both of which are shown in the image above. Noise is the signal amplification created in the analog to digital conversion while color fidelity may also struggle with the higher and higher sensitivity settings through that same conversion.
Let’s jump back to film for just a second. For those of us who didn’t grow up shooting film, or haven’t since shot a roll of film, please excuse my old timing you here. Film, at the local corner store, most commonly would be found in rolls of ISO 100, ISO 200 or ISO 400. If you knew where to go, you could find ISO 32, ISO 50, ISO 64 film for your brighter applications, or on the other end, ISO 800, ISO 1600 or 3200 if you were going to be shooting in low light. I don’t remember ever seeing a faster film personally, and only remember shooting ISO 3200 once myself in the flavor of Ilford Delta I believe. Now there may have been even faster films, but if so, I wasn’t aware of them and I doubt they’d have been commercially popular, as one of the inherent drawbacks to the “faster” films were that you’d get much grainier with each stop, and the ISO 1600 or ISO 3200 films were, um, artistic so to speak producing a pretty harsh, granular image which more or less destroyed fine detail. Still, a grainy shot is better than no shot, and that still rings true today in my opinion.
Lucky for us today though, that isn’t quite the case, not as horribly anyway. Most modern cameras, from compacts up, can provide a decently usable file at ISO 1600, and newer sensors and processors are capable of providing detail, noise suppression and resolution retention at ISO 1600 that would have been celebrated at ISO 400 a mere decade ago. This is one major upside to modern digital image making. Combine that with the ability to switch your ISO from one shot to the next (where with film you’d be stuck with one ISO setting for however many exposures you had on your roll of film), and the digital reality shows how it has spoiled us.
Enough talk. Brass tacks time. Grab your camera and set it to Manual (normally denoted by the “M” on your mode dial). Manual allows us to control both our Aperture and Shutter Speed at the same time, and for this exercise, it will be important to do so. Many cameras will have two dials/wheels to allow you to adjust both Aperture and Shutter Speed, or a singular dial or wheel that adjust both by toggling between one or the other. If you don’t know how to adjust both your Aperture and Shutter Speed in manual mode, now would be an awesome time to track down your camera manual and look for “shooting in Manual Mode” for your camera. A quick Google search may also steer you right.
We are going to manually measure the amount of light in two different scenes using the exposure trifecta, aided by our camera’s light meter.
Your light meter will show you how your scene is exposed, as the sensor is reading it, before firing off a shot. While the practice of “metering” is an article in and of itself, the basic rundown is that if you line up your light meter right in the middle, normally and in my case denoted by a “0” your scene is metered at midtone, or averaged for midtone. Basically, this means it’s properly exposed. In the example above, it is showing my scene metering at +1/3 stop (that little line to the right of the “0”) for example. Not to worry about at this point, but for this, and for most things you’ll come across, by metering in the middle, getting that little line to the mid or “0” will not do you wrong.
Let’s start indoors because, let’s face it, we’re probably indoors right now. If not, feel free to do this exercise backward.
Indoors, move to a room that has little outdoor light coming in. The less light, the better. We want to be able to see obviously, and allow our camera to focus on something, but we are aiming to have two pretty extreme, opposing exposure scenarios.
- Set your ISO to the lowest it will go (ISO 100 or 200 is pretty standard as a base ISO, anywhere around here will do)
- With your camera set to manual, open up your Aperture as far as it will go (the lower the f number, the larger your aperture setting)
- Adjust your Shutter Speed until your light meter reads directly in the middle (you’ll probably need a pretty slow shutter speed)
- Take a picture of something static/non moving (handheld, let’s not cheat and use tripods here) and take note of your shutter speed and aperture settings
How’d it turn out? If you’re anything like me, it was blurry…
Now, try adjusting your ISO up to 3200 and try this:
- Adjust your Shutter Speed an equal amount of stops as you adjusted your ISO (100-3200 = 5 stops / 200-3200 = 4 stops)
- To adjust your Shutter Speed, remember that you will halve your shutter speed for each full stop (1sec – 1/2 sec = 1 stop, 1/2 sec – 1/4 sec = 1 stop… 1/30 sec – 1/60 sec = 1 stop, etc)
- If your first shot was captured at say, a 1/15 second shutter speed, and your base ISO was 100, adjusting your shutter speed 5 stops would look like this: 1/15 > 1/30 > 1/60 > 1/125 > 1/250 > 1/500
- Now, take a second shot of the same subject
Two identical exposures with vastly different settings and results.
By adjusting our ISO to a higher sensitivity, it allowed (and required) us to increase our Shutter Speed to capture a shorter duration of time because the ISO setting was that much more sensitive to the light coming through the lens and hitting our sensor. It allowed us to adjust to a fast enough Shutter Speed to overcome our handshake. This is, in a nutshell, the power of ISO. In lower light, it can enable us to use fast enough Shutter Speeds, and/or a smaller Aperture setting to get the look or effect we’re aiming for.
Alright, now, keeping our camera on Manual, and without changing anything, let’s take the camera outside. Okay, read this first, then take the camera outside. Assuming we’re doing this in the daytime with a decent amount of daylight… If not, move to the brightest spot you can, turn on a bunch of lights or something, you get the idea.
- Take a shot with your camera set at the same exact settings as were used for the second shot as we did above
Blown out? More than likely, your shot will have little detail and look like a white cat in a snowstorm. This is overexposure. Because we had our ISO set to allow a fast enough Shutter Speed in low light, this same amount of exposure value by way of our settings will have allowed far too much light to be recorded for this exposure.
After your first, overexposed shot, to correct for the amount of light available, let’s keep our Shutter Speed as our constant now and adjust our Aperture and ISO as follows.
- Adjust your ISO setting back down to the base (ISO 100 or 200, or whatever your lowest setting is)
- Now, adjust your Aperture to a higher number (smaller aperture) until your light meter reads directly in the middle again
- Take a second shot
Here are mine:
Shot 1, with the same settings as were used for the properly exposed bottle shot above:
And, shot 2 after I reset my ISO to its base setting and adjusted my aperture so that my light meter read directly in the middle.
What aperture setting did you need to adjust to? You can go back and forth between different rooms, inside/outside or whatever to practice this. Once you start to use manual exposure, it starts to become second nature, and having mentioned our light meter, yeah, that little guy is your friend. Start using the light meter all the time. Make it your first visual stop when looking at the LCD screen or through the viewfinder.
Now, start thinking of these adjustments in stops. In the first example we saw two identical pictures as far as exposure was concerned, but resulting in two very different results. Playing with the exposure trifecta can enable us to create a variety of results by manipulating these three settings.
Think of them this way…
- Aperture will affect the light let through the lens, but creatively speaking, it controls your depth of field.
- Shutter speed will control and account for, or allow movement by both your subject(s) and your handshake.
- ISO controls your sensor’s sensitivity to light.
That’s about it, really. Now, you can start to manually control these three factors to get different results in any shooting scenario. Want to show some movement instead of freezing motion? Close down your aperture, decrease your ISO setting and slow down your shutter speed.
Shooting indoors in low light and you’re needing to gain a quick enough shutter speed to compensate for your handshake and subject movement? Open up your aperture and increase your ISO setting.
Shooting in bright light, and needing to capture a scene? Drop your ISO, close down your aperture and fire away.
A little practice goes a long way. Try shooting on Manual for a few days, and keep this mental checklist handy:
- What is my ISO set to? – For bright, outdoor sun, start at ISO 100-200, for dusk, dawn or in the shade ISO 400-800, and at night, stay as low as you can, but don’t be afraid to push to ISO 1600+. As a rule of thumb, the lower the ISO, the better the image quality will be, but a blurry shot will often be worse than a sharp, grainy shot.
- What kind of image do I want to create? Do I want a shallow depth of field to isolate my subject? Use a large aperture setting. Do I need an entire scene in focus? Use a smaller aperture setting. Am I worried about motion, mine or my subject’s, or would I like to introduce some motion in my image? Adjust your shutter speed accordingly.
- Fire off a shot. If it doesn’t look as you’d like, figure out why and change the appropriate settings.
Doing this will begin to build this type of thought process into second nature while shooting. It is a little tricky at first, but stick with it. The beauty of digital photography is that it only costs you the time it takes to delete the images that you don’t want to keep, and you can control your exposure from shot to shot AND see exactly what the results are. You can always jump back to auto modes, and trust me, I shoot on Aperture priority a lot, but understanding how and why to change these settings can give you so much more knowledge in, and control over creating images as opposed to merely capturing moments.
Alright, if you’re feeling like diving a little deeper into the ISO rabbit hole, come on in.
If you spend time reading photography article comments, or online forum discussions, ISO sensitivity will often be thrown into conversation with terms like “total light” or “signal to noise”, “pixel pitch” or “crop factor” which are all very valid metrics when looked at on their own in terms of a sensor’s ability to record light and translate it from analog to a digital file.
From an exposure standpoint, as in “I need to know what exposure settings I need to set to, to get proper exposure for X” it makes no difference as to the s:n ratio, or the way that one sensor’s ability or inability to efficiently record light comes into play. HOW that image looks compared to the same exposure recorded by way of an entirely different format, different sensor and through a different lens can, and will differ when comparing, and looking at a pixel level, but in most all cases when shooting at lower ISO settings, it is very difficult to distinguish between an image taken on a modern phone vs a 50mp medium format camera if viewing these images when printed small, or viewed on a computer screen if the images were properly exposed.
For instance, if needing to achieve proper exposure in any given scenario, and assuming the optics being used will have relatively congruous light transmission abilities, regardless of the sensor size being used to record the light, the same f/stop, shutter speed and ISO settings will record the same exposure. Where people like to wax lyrical, or puff their chests out is by isolating a specific metric like total light vs density of light, or signal to noise amplification (which are all very valid, scientific things), it has little bearing on taking a picture by recording the light available, but can have an effect on the quality of that picture. Important distinction.
If we are talking exposure, I feel that we can ignore the more scientific nuances that will become apparent when doing bench testing or the like. If we are talking about image quality at the pixel level, then yes, we can, and should look at how pixel pitch, A:D conversion, signal to noise, sensor technology and format all come into play, but that is not what we’re looking at here. We’re discussing the exposure trifecta.
Here’s an experiment.
- Take two different formats (sensor sizes) be they a phone and a fixed lens compact camera, a 1″ sensor camera, and a full frame camera, etc that can achieve the same, manually controlled exposure values using our exposure trifecta here.
- Set up a scene where the light in that scene will not vary.
- With one camera, establish your settings for proper exposure using the Manual mode setting, preferably from a tripod so you can replicate the same framing and focus distance, take a shot.
- With the other camera, framing the exact same portion of the scene if possible, from the same distance away, set it to the EXACT same settings (ISO value, Aperture and Shutter Speed), take a shot.
Compare the two images. What differences do you see when viewed on a computer screen? I’d venture, very little. Sure one may be grainier, and colors may look different, the depth of field will change if you’ve used two different physical focal lengths, but we’re looking at the exposure in terms of tonality, luminance and how the scene looks and is exposed.
Now, if you’ve done this with a 7 year old iPhone versus a $38,000 80mp Medium format Leaf Credo back, or if you’ve captured a RAW file on one, but a compressed JPEG on the other, then yes, we’ll probably see some pretty visible differences. but have a look at my comparison and let me know which was shot with my m4/3 Panasonic GX7 (a 4:3 sensor employing 225mm^2 by way of its 17.3x13mm sensor) with a 25mm lens, and which was shot with my full frame Sony a7II camera (using an 856mm^2 35.8×23.9mm sensor, almost 4 times the size) with a 55mm lens. I had both cameras set up to RAW capture, the in camera Incandescent white balance (the lightbulb) converted and processed in Aperture. I’ve cropped each to match the same formatting, and exposure was identically set at ISO 200, f/8 with a shutter speed of 2 seconds from a tripod with the scene lit by one single 60w bulb. Click on the file to see it larger.
What do you think? Can you tell which was shot with the smaller sensor? Can you tell a difference in exposure? I can’t.
Okay, how about we look at crops of both at 100% at their native resolution.
The full frame sensor, when looking at 100% crops shows a couple things. Firstly, it has a higher resolution resulting in a larger magnification when looking at the same amount of pixels. Secondly, this also shows how from a fixed location, a focal length over twice as long will render a shallower DOF when the relative angle of view is near equal. Both of these factors should be ignored for our purpose here though as we are concerned with exposure, not pixel quality, noise performance, resolution or depth of field. That said, these are the differences, the exposure value and settings are the same.
To make it a little easier to see, I’ve converted the images to black and white, so that we can ignore the color, and look purely at how congruous the tonality is between the two. Just as it was before, the smaller sensor image is on the top, the larger sensor image is on the bottom. Again, click to see larger:
Again, tonality is nearly identical, blacks are black, greys are grey, whites are white, and both show, to my eye, the same shift from highlight to shadow. If you ignore the depth of field which results in more of the scene being in focus and appearing sharper in the m4/3 image, and view them at identical sizes as I’ve presented them, the two images are remarkably similar. As far as exposure is concerned, the images lack any real difference.
While we have started to wander into the comparison of IQ at the pixel level, I want to stop here and return back to the idea of exposure as this is what we’re exploring in these articles. While the pixels themselves may perform differently based on a sensor or format’s ability to gather and record light, and the signal to noise amplification can be vastly different at the same ISO value between different formats, the actual exposure values do not change, and result in two images that at screen resolution are nearly impossible to tell any difference between, exposure wise. I couldn’t anyway. This is what we wanted to get into here.
If you need to take a shot in a given amount of light, measuring and metering that light does not change by format. It just doesn’t (otherwise our handheld light meters would have a setting to change for sensor size on it). Don’t confuse exposure with performance. HOW an image taken at the above settings as we did between the two formats looks can, and will differ based on a lot of things, but the way that reflected light is exposed will not based on your ISO, aperture or shutter speed if all are equal (*again, the only real variable here that may affect the exposure trifecta, regardless of format, would be the light transmission of a particular lens which could affect the amount of light let through it at a given aperture setting).
So when we hear someone say that a compact camera with a “small” sensor, with an f/2.8 optic is actually the full frame equivalent of f/64 (I exaggerate for effect here), they are wrong when it comes to exposure. f/2.8 is f/2.8 in this case as far as enabling the same amount of light to allow for an exposure to be made at a set ISO value and shutter speed because f/2.8 is a physical measurement relative to whatever focal length is being used relative to the sensor size it is projecting light onto to be recorded, not the “equivalent” focal length as that angle of view would appear on a different format.
Much the same, ISO 100 is ISO 100, be it a roll of film or digital camera setting (remember even different films at the same ISO value could produce entirely different renderings of grain, but all enabled the same exposure values). Are there variances between manufacturers? Sure, there will be slight, measurable shifts from one to another at the same ISO setting, but they will be insignificant enough to ignore for 99.9999% of us. How a particular sensor and processor record that s:n amplification at a given value may look different at the pixel level as a result of some of the digital magic that your camera makes happen whenever you push your shutter button, and similar to different films at the same ISO value rendering grain differently, the light values recorded in relation to a congruous shutter speed and aperture setting across format (or film) will not, aside from a lens’ transmission difference.
- ISO is a standard sensitivity rating established by the International Organization of Standardization
- Increasing your ISO sensitivity will enable you to shoot at a faster shutter speed in low light
- Increasing your ISO sensitivity will affect and increase the noise (digital grain) in your image
- Using ISO, Shutter Speed and Aperture can allow you to capture images in a variety of lighting with a variety of effect
There you go! We’ve completed our Exposure Trifecta and if you missed either of the first two, you can go back and read them via these links:
And of course, they’ll always live, along with more articles as we get into them, on the Freebie Photography 101 Page HERE.
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Thanks for the read and happy shooting,