Understanding Camera Aperture and Shutter Speed (Tips for Better Photos)
A Beginner's Guide to Taking Better Quality Photos
Good quality photos enhance a webpage. Composition, exposure, focusing and depth of field are just some of the factors which should be considered when adding images to your website. These tips apply when using smartphones, compact cameras and SLRs.
In this guide you will learn the basics of how an image is formed in a camera and how to apply techniques to take better photographs for personal use, to sell on microstock agencies or for use on your website.
SLR Cameras, Compact Cameras and Smartphones
All the details below apply to both cameras and smartphones. Cameras will have knobs and buttons for changing the settings, whereas camera apps on smartphones will allow you to change these settings in the menus.
How Does a Camera Work?
A camera works by focusing light from the subject (the thing or person you are photographing) onto either photographic film or an electronic sensor known as a charge coupled device (CCD), located just inside the back of the camera. Light firstly passes through the lens at the front of the camera, then through an aperture (hole), and finally through a shutter before finally landing on the sensor or film. When a photo is taken, the shutter opens for an instant to allow light into the camera and create a snapshot in time of the scene. The function of the lens is to gather light and create a focused image at the focal point, on the CCD or film.
How Does Exposure Work on a Camera?
Irrespective of whether photographic film or a sensor is used in a camera, a certain amount of light must land on the sensitive element. There can't be too much or too little, i.e. the film or CCD element has a limited dynamic range. This means it can only work over a limited range of illumination levels. Unfortunately, there can be huge variations in the illumination of a subject depending on whether photos are being taken in dim light or bright sunlight.
There are two ways of controlling how much light is allowed into the camera, known as the exposure.
- Vary the amount of time for which the light enters the camera
- Vary the size of the hole through which it passes
- Use different speed films or ISO settings on a digital camera
So how do you know which to vary? Most modern cameras nowadays provide you with auto exposure. However, you still need to understand the consequences and effects of varying shutter speed and aperture size. Depending on the type of camera, there may be no control, little control or a lot of control over exposure settings. Cameras often have several exposure modes (e.g. "sports", "children", "nighttime",) which try to automatically adjust exposure and other settings to take the guesswork out of taking photos and make an image appear ok. Which mode you use depends on the application.
What is an Aperture on a Camera?
This is a variable sized hole behind the lens, through which light passes. Basically, it works just like the pupil in your eye. Changing the "f - stops", "focal ratio" or "f numbers" setting on your camera results in an alteration of the diameter of the aperture. Large "f" numbers correspond to a smaller hole and less light entering the camera. Small "f" numbers correspond to a larger hole which lets more light in. However, the drawback is a reduction in depth of field or range over which objects are in focus. This may or may not be advantageous as we will see below. Typical f stops on a lens are f/2.8, f/4, f/5.6. On a smart phone, the aperture is often fixed in size, so you can't change it in the camera app.
For a more detailed discussion, see f-number on Wikipedia.
What is the Shutter Speed Setting for on a Camera?
The second way of varying the exposure is by altering shutter speed. Shutter speeds can be varied from tens of seconds to fractions of a millisecond. So why not have a really slow shutter speed to let in lots of light in dim lighting conditions? The problem with low shutter speeds is that when attempting to capture images of moving subjects, the resulting image suffers from motion blur. This is because the shutter is open for such a relatively long time, that the image formed at the back of the camera actually varies because of the motion of the subject. Using a fast shutter speed, allows you to freeze motion. (In olden times, photographic plates, the precursor of rolls of film, were so insensitive that the plate had to be exposed for several minutes, so if the subject was a person, they had to keep still for this length of time. Hence the stiff poses).
What Does Film Speed and the ISO setting Mean?
A third way of increasing exposure is to use a faster film speed or the equivalent for digital cameras. A fast film is more sensitive to light, which allows a faster shutter speed or higher f-stop (smaller aperture) to be used than normal. It is advantageous in situations when light levels are low, the aperture cannot be made any bigger, but a fast shutter speed must be used, reducing the amount of light entering the camera (e.g sports photography). Also if you use a long focal length or zoom lens (which is often the case when photographing subjects in sport), the upper f-stop limit will allow less light into the camera than when zoomed out. This may limit the fastest shutter speed to an unacceptable level, so this is a situation when you can increase the film speed setting. This is normally indicated as "ISO" or "ASA" in the setup of your camera. The drawback of a faster film is a "grainier" or sandy looking image.
Exposure Modes on Cameras
SLR and compact cameras usually have 3 basic modes for automatically setting exposure. Smartphones usually don't have these settings because the aperture is fixed in size.
Shutter Priority (S)
You set the shutter speed and the camera then varies the aperture size for correct exposure. If you want to freeze motion, a fast shutter speed is necessary. If you choose too high a shutter speed in low-light conditions, the camera may select a large aperture (small f-stop), resulting in a decrease in depth of field, which could be an issue when close to a subject or zoomed in. Also the chosen shutter speed may be too high (or too low in bright conditions) to give proper exposure (the camera will tell you this on the display)
Aperture Priority (A)
You set the size of the aperture to control the depth of field (see discussion of depth of field in Tip 3 below). The camera then changes shutter speed to give correct exposure of the subject. If you want a large depth of field in your image, you can make the aperture small. However, if you choose too small an aperture (large f-stop), it can result in an unacceptably slow shutter speed. Also an aperture which is too big or too small may result in overexposure or underexposure in very bright or low light conditions respectively. Again the camera will indicate over underexposure so you that you can make corrections
You can change aperture, shutter speed and ISO. The camera doesn't alter the settings, irrespective of light levels
Program Mode (P)
Both shutter and aperture are adjusted. So in lower light conditions, shutter speed is decreased and aperture made bigger (and vice versa under brighter lighting). The result is that neither is changed as much as they would have been in "A" or "S" modes.
Newer SLR cameras often have lots of other modes which take the thinking out of taking a photo so that you can just point and shoot. These include an Auto mode which optimises everything, including setting the aperture, shutter speed, ISO, focusing controls and turning on flash if needed. Other modes optimise the settings for the particular subject. These include a macro mode, portrait mode, child mode, sports mode, landscape mode etc. Smartphone apps often have a few different modes for the type of scene.
Picking a Shutter Speed to Stop Motion
Movement Left to Right in Front of Camera
Slight or stationary movement
Traffic and Pedestrians
Resolution, Pixels and Image Quality
Images are stored in a digital camera with varying resolution which you have control over. The resolution is specified in pixels e.g 640 x 480. You can visualize an image as being like a chessboard, and each pixel is like a square on the chessboard. The greater the resolution, the more detail of the original scene is preserved. Higher resolution images take up more space on flash cards in a camera, require more storage space on a hard drive and take longer to download and process in your image processing package. However since computers have become more powerful, have more RAM and larger capacity disk drives, and USB communication speed has increased over the past few years, this is less of an issue. Adding effects to images or carrying out certain image manipulations can take some time however with high-resolution images. If you want to print enlargements of your photos and not just standard 5 x7 s, or crop them (select a section and discard the rest), then the higher the resolution, the better. If you just want to take snapshots, you can opt for a lower res setting on your camera.
When you take your photos, they are normally stored in JPG format in your camera. This is an image storage format which compresses images so that they take up less space on the flash card. The result is that some quality is lost. Usually, your camera will have an option in the setup to store the image with different qualities (low, medium, high or similar) for a given resolution. In the days when flash memory was low capacity, this was an issue and if you wanted to fit lots of photos on a card, you had to go for lower resolution and lower JPG quality. Now, however, this is less of a problem, but users still take photos on their cameras without realizing that they may not have setup the camera to get the highest resolution and best quality image.
How Do I Take Better Photos?
- Pick a good background
- Focus properly on your subject
- Get your depth of field right
- Get exposure right
- Set the color balance on your camera so colors look natural
- Use natural daylight for photographing subjects
- Crop your image
- Be aware of the effects of using a wide angle lens
- Use a tripod
- Use flash, digital zoom and interior lighting effectively
Tip 1: Pick a Suitable Background
Try to find an uncluttered plain background if you're photographing objects. You could use grass, sheets of paper, plain colored cloth, the sky etc.
Good and Bad Backgrounds
Tip 2: Focus Properly on Your Subject
Focusing means adjusting the lens on the camera so that the image is sharp and clear. Low end and older camera phones have a fixed lens which can't be focused. Lenses are focused at infinity and if you get too close to your subject, the resultant image will be blurred. The lens on most compact digital cameras and smartphones will auto-focus , and on SLR cameras you may be able to turn the focusing ring on the lens of the camera to manually focus the image (in addition to auto-focusing)
Isolating Elements of a Photo
Focusing and depth of field (see below) go hand in hand. You need to decide whether you want everything in the image to be in sharp focus, or whether you want to isolate specific elements in the image.
Tip 3: Get Your Depth of Field Right
When you focus on a point in an image, points closer to the camera or further away from this point will be less in focus to a greater or lesser extent. The depth of field is the region of an image which is in sharp focus. Sometimes you may want a large depth of field to show everything in sharp focus and add perspective to a shot, at other times it may be better to throw part of the image out of focus, e.g. the background. Large f stops (small apertures) give greater depth of field and small f stops (large apertures) reduce depth of field allowing you to isolate your subject. Also as you move your camera close to the subject, depth of field decreases even if the f stop isn't changed. A third cause of reduction in depth of field is an increase in the focal length of the lens as you zoom in on your subject.
So to summarize, depth of field increases when you:
- Select a shorter focal length, i.e zoom out
- Pick a smaller aperture (large f/stop)
- Move further away from subject
You need to play around with the f stops on the camera to produce the results you want. In aperture priority (A) mode, in lowish light conditions and using a large f stop (small aperture) to produce a large depth of field, shutter speed may become too low to freeze movement. This can be the case even when a tripod is being used e.g. when photographing flowers close up, which are moving in the wind. In this scenario, it's better to select the shutter priority (S) setting on the camera and experiment with various shutter speeds. Reduce the shutter speed just sufficiently to freeze movement. The camera will then decrease the aperture size (remember, a bigger f stop), which will maximise depth of field. You can also increase the ISO setting, which will make higher shutter speeds and/or bigger f stops possible. You can of course use one of the pre-set modes (e.g. sport, macro etc) on the camera which optimise all of the settings to give the best results.
Depth of Field
Depth of Field Indications on an SLR Camera Lens
Tip 4: Photos Should Be Properly Exposed
Sometimes it's difficult to get the exposure right. For instance if you are photographing a subject which is lit from behind, this will produce a silhouette effect (which may or may not be desired). Also if there is high contrast between objects in a frame, e.g. black and white, exposure can be difficult. Your camera may have an option which allows bracketing of shots, which means taking photos with slightly higher or lower exposure levels than the normal auto exposure would produce. Also you may be able to set the weighting for exposure. Normally the camera will adjust exposure by looking at the average amount of light in the frame. Exposure can also be center weighted so that what is in the center of the frame, on the "cross hairs" is properly exposed
Tip 5: Color Balance
Usually this is automatic on a camera, but sometimes auto color balance produces colors which are not quite natural. Color balance weights, or filters an image to make it look more natural under various lighting sources. Better results can be obtained by choosing the manual settings on your camera, depending on the ambient lighting conditions, rather than the auto setting. Choices include tungsten (for "normal" bulb and halogen lighting), daylight, fluorescent, cloudy and flash.
Tip 6: Use Natural Lighting - Take Photos on a Bright, But Cloudy Day
If you don't have the luxury of an indoor studio with lighting, an alternative is to take photos outdoors. Natural daylight produces great results but bright sunshine can produce ugly shadows in an image, and excessive contrast. Try to take photos on a day which is very bright but semi-cloudy or when the sun goes behind the clouds. Clouds act as a diffuser and scatter light so that it comes from every direction, producing softer shadows. You can also use a white bed sheet or large sheet of white card to reflect and diffuse light into the shadows cast by the subject. Professional photographers use this technique for "filling" in shadows and lighting backlight subjects (which would otherwise be silhouetted against a bright background).
Ideal Camera Angle
Using a reflector
Tip 7: Crop Your Image
Cropping means cutting out sections of your image to remove uninteresting and irrelevant content. Remember also that if the subject only takes up a small amount of area in the frame, cropping discards pixels and this may result in a low-resolution image if the original image was low resolution. So try to fill the frame with the object or region of interest when taking the original photograph. Also take photographs at the highest possible resolution so that a user can zoom in on the photo if this facility is allowed on a webpage. You can always reduce resolution later in your favorite image processing application.
Tip 8: Watch out for the Effects Caused by Using a Wide Angle Lens
- A camera lens focuses an image onto an optical sensor or film. The focal length of a lens is the distance from the lens to the image, when the image is in focus.
Lenses for cameras can be telephoto, standard, wide angle or zoom. Telephoto lenses have long focal lengths, and wide angle lenses have shorter focal lengths. A telephoto lens makes the subject look closer, so it's useful for wildlife and sport photography etc. A standard lens makes the subject appear to be at the same distance as the human eye would see it, and a wide-angle lens lets you fit more of a scene into the resulting image. This is useful if you want to take shots of room interiors or can't get far enough back from a subject to fit it into the frame. Often, though, cameras are fitted with zoom lenses which have variable focal length and allow you to zoom up close or far away from your subject. If you extend a zoom lens out to the wide-angle end of its range, it can stretch perspective when used close to a subject. The same can happen if you're using a fixed focal length, wide-angle lens. So parallel lines seem to converge and square things look trapezoidal (i.e. narrower at the back than at the front). The lens on a smartphone is designed to be wide angle so that you can do selfies and fit everything into the frame, so it can produce the same effects. Sometimes perspective might be the desired effect, however, if you want to avoid this phenomenon, move further away from your subject, and zoom in closer.
Tip 9: Use a Tripod
Camera shake can result in blurred images and a tripod helps to keep a camera steady.
A tripod is useful under several conditions:
- At low shutter speeds (below 1/100 second), camera shake can result in blurring of images. If light levels are low, even with the largest aperture setting (lowest f -stop), the camera may select a low shutter speed to get in enough light for correct exposure
- When doing close up work or macro photography, small movements of the camera can cause image blur
- When zooming in on a subject
Tip 10: Miscellaneous Stuff - Flashes, Digital Zoom and Interior lighting
- Don't use the digital zoom on your digital camera or phone. Digital zoom doesn't add any more detail to an image, it just "joins the dots" or interpolates between the actual pixels in an image.
- If you use a flash, try to avoid reflections from reflective surfaces by angling the camera so that the light from the flash bounces off the subject. Photographing too close to a light surface can produce harsh shadows.
- You can use low cost, 500 watt, halogen work lights for illumination indoors. They are costly to run and get very hot, but for low-resolution photos for web pages, they are quite useful. The color balance on your camera needs to be set to tungsten when using this type of lighting.
- Every time you save a JPG file, it is compressed and loses some of its quality. Don't continually save and reload a JPG file after every operation in an image processing program. Save the file only when you are happy with the final result.
Food Photography Tips
The essence of food photography is to make food look appetizing and scrumptious!
- Pick fresh ingredients which look plump, firm and colourful. Old ingredients will tend to be duller and wizened looking
- Use natural light if possible to eliminate shadows and bring out the full colour of the food
- Use a mist bottle to spray fresh vegetables to give the impression they've just arrived from the garden!
- Texture is just as important as colour when photographing food. So use a large depth of field to have everything in focus, or a shallow depth of field to isolate, e.g. food being eaten
- Make sure cooking utensils, cutlery and tableware are clean
- Show food being cooked/prepared - A hand stirring a pot or chopping vegetables adds a human element to the image
Good Photo Editing Apps
There are lots of image editing software applications out there for manipulating and retouching images from your camera, some freeware and others you have to pay for. Most free software packages will allow you to carry out basic photo manipulation such as cropping, changing brightness, contrast, color saturation and altering hue.
An image processing software package used by professionals. Expensive, but it can do lots and you can get "plugins" which allow you to add effects to images
This is a comprehensive, free application. The user interface, however, takes some getting used to
Windows Photo Gallery
This comes either with Windows or as part of the Windows Live Essentials Suite
A free image editor and organizer from Google
Paint Shop Pro
An excellent application by Corel Software and much less expensive than Photoshop, is a very powerful editing package. Like Photoshop, it does all the basic stuff, with support for bitmapped images and also vector graphics (You can draw objects such as lines, curves, shapes, text and clip art onto images and rescale, reshape, rotate and change their colours later). In addition, it supports layers. This means you can have an underlying image and then add multiple layers on top of it, with different stuff on each layer to form a composite image. Paint Shop Pro
I use this application constantly for image processing, adding captions to photos, cropping, creating Pinterest images and also for creating graphics/diagrams for articles.
© 2014 Eugene Brennan