EXPOSURE CONTROL
This article covers some exercises that you can do to learn more about how your camera works for particular situations. It is critical for the new or struggling photographer to master these camera settings and their use. This is the nitty gritty of photography, and for the new user may require quite a bit of time to digest and master. Take your time, but get started right away with the exercises. Think of these exercises as drills similar to what someone learning a musical instrument would do prior to playing music skillfully. You can pound on a piano and make noise, just as you can push on a camera trigger and capture an image. But creating music and creating a masterpiece require a knowledge of the tools available and skill in using those tools. You can do this!
I could have presented this lesson over three months, but some of you are chomping at the bit and will attack the lessons. Others are more deliberate. Choose the learning speed that is comfortable for you. If you have questions, email me!
Before we get to that, here is a quick review of the exposure triangle. There are three controls that you can manipulate to create the best exposure(s) for a scene. Once everything is set for a proper exposure (amount of light hitting the sensor or film), changing one of the controls would necessitate a compensating change of one or both of the other controls to maintain that proper exposure.
The three controls are ISO, f/stop and shutter speed.
The Exposure Triangle demonstrates that for a proper exposure, ISO, f/stop, and shutter speed are all connected. You could say that they balance each other in a properly exposed photograph. Eventually, you will be in control of the results of your image by selecting the most important (controlling) side or sides of the triangle to create the effect you want. The other side or sides will then have to fall in line with the controlling side.
ISO is the sensitivity of the sensor or film. In general, the lower the ISO number, the less noise or grain will be present in your image. Depending on the camera, ISOs may range from as low as 32 to 64,000 or more. Every time you double the ISO, you are increasing the sensitivity by one stop. So 400 ISO is twice as sensitive (one stop more sensitive) than 200 ISO and four times more sensitive (two stops) than 100 ISO. For some current sensors it is difficult to start seeing the increased noise in an image until you get up to 1600 ISO. You will be able to see how ISO affects the image in the exercises.
F/stop has to do with the width of the lens opening or diaphragm that allows light through the lens into the camera. F/stops generally range from f/1.2 to f/32 depending on the lens in use. The lower the f/stop, the more light gets to the sensor. The higher the f/stop, the less light gets to the sensor. Every full f/stop marks half or double the amount of light to the sensor depending on whether you are closing or opening the diaphragm. Standard f/stops are 1.4, 1.8 (2.0), 2.8, 4, 5.6, 8, 11, 16, 22, 32 and 45. Lenses are made to cover a range of these f/stops. Physical optics characteristics control how wide the range can be for a particular lens. For all lenses there is a sweet spot or sweet range in the middle f/stop numbers. As you get away from this range, images get less clear. For many lenses it is best to avoid the highest and lowest ends the available f/stops. Most lenses can be adjusted in one-half or one-third increments between full f/stops. For example, your lens may be adjustable f/6.3, f/7.1 as third stops between f/5.6 and f/8. For the sharpest photos we like to stay in the “sweet range”, but there may be occasions when we don’t want parts of the photo sharp, especially those areas that are closer or farther from the camera than our main subject, so we use a wider f/stop. There also may be occasions when we want as much in focus as possible from near to far in the photo, so we use a high f/stop such as f/16 or f/22. You will learn how your lenses work with different f/stops in the exercises.
Shutter speed is the length of time the sensor is exposed to light. This is either controlled by a mechanical curtain in the camera or by electronics that basically turn the sensor on and off. Shutter speeds are pretty easy to understand. The longer the shutter speed, the more light. Cutting the shutter speed in one-half, say from 1/60 second to 1/125 second (rounded to be close) allows one half the light in. Going the other way would double the light. Shutter speeds can be as long as you want….sometimes up to days or as short as your camera allows. This may be around 1/8000 second for a mechanical shutter but could be as little as 1/32,000 second for an electronic shutter. You may want a long shutter speed to let extra light in during dim situations, to allow for a lower ISO to be used or a higher f/stop to be used, to intentionally blur moving areas (when the camera is on a tripod), or to blur an image with intentional camera movement (on or off a tripod). You will learn how to creatively employ these variables in the exercises.
If you have not already completed the “Learn Focus” exercise and do not understand focusing with your camera and lens setup you should do that now.
ISO Exercise
Find a shaded location that is not too bright or an indoor location next to a window. You will want to find a scene that has a wide range of highlights and shadows.
Place your camera on a tripod so all of your pictures will be taken the same. Distance from your main subject will not matter much so long as you can get it in focus.
Set your f/stop to f/5.6 and your shutter speed to Auto (usually indicated by an “S” or “T”; cameras with a shutter speed dial will have an “A”).
Start with your ISO set to 100 (or the lowest your camera allows)
Set your delayed shutter timer to 2 seconds. If you don’t know how to do this, refer to your camera manual.
Expose your first picture.
Now change the ISO to 400, 1600, 6400 and 12800 (some cameras don’t go to 12800), taking a new image at each setting. Note that your camera will automatically make shorter exposure times as you go. This will not affect the resulting correct exposure of your picture so long as everything is still in the picture and you are on a tripod.
Download your pictures to your computer.
View a bright (almost white) section, a mid-tone section and a darkest section of the same are of each picture. When you do this, enlarge the picture so it fills the screen or up to a 300% view. Notice the difference in graininess at each ISO selection. Note how much more grain shows in white areas compared to blacker areas.
Compare the noise in the shadow areas and the white areas especially. Note that I did not precisely follow the instructions. I started at f/5.6 and my camera automatically adjusted the f/stop as well as the shutter speed. The center image was taken at f/1.4 which is on the low end of the f/stop range. I discuss below how images are softer like this at extreme f/stops. A portrait photographer may be able to use this to advantage, but generally avoid those extremes. For my camera, ISO 160 (lowest available) is definitely sharper than ISO 400 so I should try to shoot at ISO 160 when I want the sharpest results for enlargements. If I am only shooting for Instagram, though, it may not matter how high an ISO I choose.
What you should have learned
The lower the ISO, the less the noise. But you may be able to use and ISO higher than 100 without unacceptable noise levels. You should know what level this is. It is not the same for all cameras and sensors or even for all scenes. For some photographs, say you want to achieve a vintage (film) look, you may find more noise desirable.
How will you apply what you have learned?
There will be times when you just don’t have enough light to hand hold your camera and take a proper exposure. This often happens with wildlife photography, sports photography, indoor photography, in twilight hours and at night. Turning up the ISO may be your best or only option. You need to know if it will be an acceptable option. Using a lower ISO in these situations may result in a blurred photo or a lack of depth of field (areas in focus closer and farther than your main subject). Even on a tripod, you may need to use a very high ISO to obtain a useable recording on your sensor. In a future article we will share how to reduce noise even with a high ISO.
F/ Stop and focal length exercise
Opening your lens aperture by lowering the f/stop number increases the light that hits the camera sensor, while raising the f/stop decreases the light. Each full f/stop number changes the light by a factor of two. But something else happens along the way. Light that comes through a larger aperture bounces around more (it is scattered) while light coming through a smaller aperture travels in a straighter line (it is collimated). Scattered light will result in a somewhat softer image. Collimated light will result in a somewhat sharper image. Both of these results are dependent on the lens’s ability to focus accurately.
Optical engineers design most lenses for sharpness around some of the center f/stops like f/5.6 and f/8. The farther away from the center f/stops we get, the less sharp the image. Lenses with very low f/stops (f/2 or lower) are often more expensive because of the extra elements necessary to achieve good focus (less light scattering) at or near this extreme.
f/stop Exercise 1 – Depth of Field
Set up objects with distinct edges at a distance of approximately 1.5 feet, 3, feet, 6 feet, 12 feet and 25 feet from your camera. This could be a series of fence rails, cups on the ground or anything easy to move.
Place your camera on a tripod. Start with a lens in the focal length range of 33 to 55 mm (full frame equivalent). Set the ISO to 100, the f/stop to f/4 and the shutter speed to automatic (A, T or S depending on your camera). Use your two second timer.
Focus on the object at 1.5 feet if that is possible and take a picture. If it is not possible to focus at that distance, focus your lens as near as possible and move the closest object to that distance.
Repeat this focusing carefully on the other objects at 3, 6, 12 and 25 feet.
Now change to f/8 and do the same thing.
Now change to f/16 and do the same thing.
Upload the images to your computer to study.
Compare the three images taken with the nearest object in focus. Notice that at f/4 even the object at 3 feet is out of focus and your farther objects are very out of focus, but at f/8 the more distant objects are more in focus. At f/16 the more distant objects are much more in focus.
Now compare the images taken with the object at 3 feet in focus. Is the 1.5 foot and 6 foot object also in focus? How about the farther objects. Pay particular attention to whether the object half the distance of your focus point is in similar focus to the object twice the distance.
Now just concentrate on the f/8 images. If you focus at 12 feet, is the 6 foot object in good focus?
If you are using a zoom lens or multiple prime lenses, repeat this exercise with a wide angle focal range around 18 mm to 24 mm and again at a telephoto focal range around 70 mm to 100 mm.
In the following two sets, the one on the left was taken at f/5.6 with the focus point where the arrowhead indicates. The one on the right was taken at f/16. Note the areas that remain in reasonable focus for each setting and how the depth of field (sharp areas) are much greater at f/16. Click on the images to see larger views.
What you should have learned
The range of focus at lower f/stops is much narrower than the range of focus at higher f/stops. It is impossible to have good focus at all distances with lower f/stops. When focusing at any of the middle distances the next objects closer and farther are in approximately the same focus as each other although the farther object is twice as far. If you did the wide angle exercise, you learned that a much wider range of distances stays in focus. If you used a telephoto lens, you learned that a much narrow range of objects stays in focus. Although an lens might not be as sharp at the extreme (as when f/16 is the smallest aperture), it may be more important to have good depth of field than to have the very sharpest image.
How will you apply what you have learned?
Use a lower f/stop to selectively focus on a subject and intentionally put the background and foreground out of focus. This is most often done for close-up photography and portraits. It is more effective at close distances. Use a higher f/stop to keep a wider range of distances in focus. When the goal is to get the sharpest focus throughout an image, the best choice is to focus on an object one-third of the way from your closest to farthest distance. While this is approximate, it is a good rule to follow in the field. If you did the exercise with a wide angle lens you will have discovered that it is fairly easy to keep a wide range of distances in focus even when you focus at a fairly short distance. Likewise, if you use a telephoto lens it is difficult to keep a wide range of areas in focus. This makes it harder to focus on wildlife, but if your subject is in focus it will be more isolated from the foreground and background.
Professional Tip: Lenses for cameras used to have an approximate depth of field scale on them. Today’s lenses for digital cameras do not. If you know what you are planning to shoot, what distances are important to keep in focus and and what lens you are shooting with you can calculate a best f/stop in advance. There are apps that do this for you (DoF in PhotoPils app is recommended), some advanced camera and lens combinations do this, or you could set up a trial at home in advance. If you are shooting with a 50 mm lens and your nearest object is eight feet away and you want the hills in the distance in focus, you will find that you cannot have everything in focus with a single exposure even at f/22. Your only option would be to combine images (called stacking, which we will cover later) or using a wider angle lens. With a 35 mm lens you could shoot at f/22 and have everything in focus. But if you were to shoot at f/8, you would need a 22 mm lens or wider. Next month we will discuss how lens selection affects the various objects in your image.
Shutter speed exercises
You will use your shutter speed controls to intentionally stop action with moving subjects by using a very short shutter speed and you will use long exposures to let in more light in dark situation or to intentionally blur through camera or subject movement. A tripod is necessary for those long exposures, but let’s first determine when a tripod might not be as useful.
Hand hold your camera with a standard length lens (35-55mm). Some cameras have the ability to help you “stabilize” the camera so you can get away with longer hand held exposures. If your camera has this (called IS, IBIS or OCS) turn it on now. You may have to read your camera and lens manuals to learn how to do this. If that is too much for you for now, skip it and you can pick that up later. If you have image stabilization it is worthwhile to repeat this exercise without the images stabilization to see just how well it works in your hands.
You will be taking a series of five images of a motionless object 10-15 feet away. The object should have some sharp edges in both a vertical and horizontal direction with good light and good contrast between the object and the background. A box on a table or the back of a chair would work well.
Set your ISO at 200 and your f/stop at auto. Be sure you can manually focus accurately a sharp edge of your subject. Do not move or change your focus throughout the exercise. Take five images each at 1/125 sec, 1/60 sec, 1/30 sec, 1/15 sec and 1/8 sec. Be sure your automatic timer is off. Do your best to hold the camera still and depress the shutter release slowly. Note that your f/stop will change to accommodate the change in shutter speed. Upload the images to your computer. Enlarge them to 100-200% to view on your screen. Starting with the 1/125 second images, how many out of the five are in excellent focus? How about the 1/60 second images? 1/30? 1/15? 1/8?
Repeat this at various focal lengths, especially with telephoto lenses that you might use often.
What you should have learned
The ability to hand hold a camera and end up with a sharp image depends on the shutter speed and your ability to hold the camera still. Sometimes we are more successful than others. If your images are blurred more than 20% of the time you should not count on being able to hand hold at that shutter speed when you are in the field. If you absolutely need a good image but do not have a tripod, use a shutter speed that will make that happen, adjusting the f/stop and ISO as necessary. If you are on the border, take multiple images to make sure one is useable.
How will you apply this information?
It isn’t always necessary to shoot on a tripod when there is adequate light. This is valuable when you are shooting a scenic or street photography without a very close object. Longer lenses are valuable for wedding and wildlife photography, but you may not be able to get away with longer shutter speeds that would work with a shorter lens. In the absence of these exercises, you can use a formula that says to divide the number “1” by the length of the (full frame) lens. So for a 35 mm lens your slowest shutter speed handheld would be 1/30 second. For a 100 mm lens, your shortest shutter speed would be 1/100 second. Crop sensors and micro four-thirds (MFT)sensors magnify the movement in the same way they increase the effective focal length of a lens. So a 35 mm APS-C sensor would have an effective focal length around 54 mm and your safe shutter speed would be 1/60 second. A 35 mm lens with an MFT sensor would be have a safe shutter speed of 1/70 second, so you would go to the next faster available shutter speed.
The following fun shutter speed exercises can be added depending on your interest.
Shutter speed exercises
You will use your shutter speed controls to intentionally stop action with moving subjects by using a very short shutter speed and you will use long exposures to let in more light in dark situation or to intentionally blur through camera or subject movement. A tripod is necessary for those long exposures, but let’s first determine when a tripod might not be as useful.
Hand hold your camera with a standard length lens (35-55mm). Some cameras have the ability to help you “stabilize” the camera so you can get away with longer hand held exposures. If your camera has this (called IS, IBIS or OCS) turn it on now. You may have to read your camera and lens manuals to learn how to do this. If that is too much for you for now, skip it and you can pick that up later. If you have image stabilization it is worthwhile to repeat this exercise without the images stabilization to see just how well it works in your hands.
You will be taking a series of five images of a motionless object 10-15 feet away. The object should have some sharp edges in both a vertical and horizontal direction with good light and good contrast between the object and the background. A box on a table or the back of a chair would work well.
Set your ISO at 200 and your f/stop at auto. Be sure you can manually focus accurately a sharp edge of your subject. Do not move or change your focus throughout the exercise. Take five images each at 1/125 sec, 1/60 sec, 1/30 sec, 1/15 sec and 1/8 sec. Be sure your automatic timer is off. Do your best to hold the camera still and depress the shutter release slowly. Note that your f/stop will change to accommodate the change in shutter speed. Upload the images to your computer. Enlarge them to 100-200% to view on your screen. Starting with the 1/125 second images, how many out of the five are in excellent focus? How about the 1/60 second images? 1/30? 1/15? 1/8?
Repeat this at various focal lengths, especially with telephoto lenses that you might use often.
What you should have learned
The ability to hand hold a camera and end up with a sharp image depends on the shutter speed and your ability to hold the camera still. Sometimes we are more successful than others. If your images are blurred more than 20% of the time you should not count on being able to hand hold at that shutter speed when you are in the field. If you absolutely need a good image but do not have a tripod, use a shutter speed that will make that happen, adjusting the f/stop and ISO as necessary. If you are on the border, take multiple images to make sure one is useable.
How will you apply this information?
It isn’t always necessary to shoot on a tripod when there is adequate light. This is valuable when you are shooting a scenic or street photography without a very close object. Longer lenses are valuable for wedding and wildlife photography, but you may not be able to get away with longer shutter speeds that would work with a shorter lens. In the absence of these exercises, you can use a formula that says to divide the number “1” by the length of the (full frame) lens. So for a 35 mm lens your slowest shutter speed handheld would be 1/30 second. For a 100 mm lens, your shortest shutter speed would be 1/100 second. Crop sensors and micro four-thirds (MFT)sensors magnify the movement in the same way they increase the effective focal length of a lens. So a 35 mm APS-C sensor would have an effective focal length around 54 mm and your safe shutter speed would be 1/60 second. A 35 mm lens with an MFT sensor would be have a safe shutter speed of 1/70 second, so you would go to the next faster available shutter speed.
The following fun shutter speed exercises can be added depending on your interest.
- Stopping Action – take a series of photos with whatever moving subject you wish. This could be something moving slowly (a duck in water) or moderately (people walking) or very fast (automobiles). Determine what speed you need to shoot to stop the action.
- Panning to (partially) stop the action – try this with a short telephoto lens first to create more artistic images. Determine if you to show a bit of motion with your subject. Take vehicles, people walking, birds flying, etc.
- If you are into sports or wildlife photography, you may repeat these exercises using a monopod or tripod to see if these tools give you additional latitude.
- Shutter speed is less important for still objects when using a tripod. But these exercises will help you learn what you can and can’t do on a tripod:
- Is there an advantage for using a two second timer vs just hitting the trigger? Use a focal length of 50 to 100 mm and focus on an object about 10 feet away. In twilight or indoors take exposures at around one second time. Do this with a two second timer and without the timer. Are your images sharper with the two second timer? Repeat with the longest lens you have. If you are going to use a remote shutter release, this is less important to you, but remote shutter releases have a habit of getting lost when you most need them.
- With a focal length of 24 to 35 mm (or your shortest focal length available if higher), set up with the tripod having some tall grass (just short of camera height) in your foreground, maybe 5 to ten feet from the camera. Make sure there is at least a light breeze on an overcast day or at twilight. Otherwise you are likely to need an ND filter to achieve the longer exposures. Set up so there is something interesting in the background…a tree, building or mountain. Shoot at auto ISO at f/16. Focus at 10 feet. Try shutter speeds of ½, ¼, 1/8, 1/15, 1/30, 1/60 and 1/125 second. What shutter speed do you like the most in this photo? Wind can be a real nemesis for landscape and flora photographers. Learning to manage and even take advantage of wind can be a rewarding part of mastering photography. Using very slow shutter speeds in bright situations often requires a neutral density filter to avoid overexposing the images. If you do not have an ND fllter, do this exercise in overcast conditions.
In the following images, pay particular attention to the tall grass on the right. It starts getting "frozen" in the wind around 1/60 second. Note that the last few images have less depth of field due to a wider aperture. A four stop ND filter was used for these images. I could have removed the ND filter to achieve greater depth of field.
What you should have learned
Shorter exposure times may be necessary in windy conditions, however, longer exposure times can be used for effect, either to show motion, or to emphasize a subject that has moving surroundings;
We will discuss more these long exposures in a future article. Night sky photography requires some special long exposure techniques and a tripod. We will cover this in a future article.