Digital Photography/Taking Digital Photos
This section deals with the nuts and bolts of actually taking pictures. This is the part where most of us like to spend time on.
- 1 Camera Basics
- 2 Choosing your Level of Control
- 3 Controlling Exposure
- 4 How to achieve sharp digital photographs
- 5 What's the slowest exposure time you can get away with ?
- 6 The non-human approach to reducing camera shake
- 7 When is long exposure time useful ?
- 8 Why do images become darker with short exposure times ?
- 9 At larger apertures, why do images become brighter ?
- 10 Why should I take control of exposure time ?
- 11 Why change the aperture ?
- 12 Changing what automatic/semi-automatic mode aims for
- 13 Speeding up recovery time ?
- 14 Image sharpening
- 15 Photo effects/Color modes
- 16 White balance
- 17 Depth of Field and achieving blurring effects
- 18 Taking infra-red photos
- 19 Example shots
A camera is made of two basic parts - the lens, and the camera body. The lens and camera body work together to form all the functions found on this page.
Choosing your Level of Control
Taking a digital photo can be as easy as turning on the camera, pointing it, and pressing the shutter button. The camera will make all the necessary decisions for you. This of course, assumes that you have your camera controls set to auto or program mode. A point and press camera will not make correct adjustments when scenes are heavily back-lit or in mixed light situations for example. Advanced cameras allow you to take more control of this process, to allow you to hopefully take better photos. But care must be taken, otherwise you may actually take worse photos. You will need to decide what level of commitment you want to make to taking terrific photos. There is no guilt here, just do what is best for you.
Digital cameras capture a limited range of brightness. File formats like jpeg and tiff, and computer monitors and printers have limits also.
When a digital image is significantly underexposed, certain parts of the image will be simple black, other parts will not express colors accurately, and digital noise will be visible.
Overexposure can cause areas to become simple white, without detail. This is known as "blowing out the highlights."
In automatic mode, most digital cameras try to adjust exposure to make every picture average brightness. This may not be what you want if you are taking a picture of a bride, or a flamingo, or fireworks. You can improve your pictures by controlling exposure.
Exposure Value of an Image
There are four factors which affect the brightness of your image:
- Exposure value (EV). Brightness of the scene itself.
- Aperture. The size of the entrance pupil of the lens. The larger the aperture, the more light; the smaller the aperture, the less light.
- Shutter speed. The length of time over which an exposure is made. The longer the exposure, the more light that falls on the imaging medium; the shorter the time, the less light.
- ISO speed. Increasing the ISO setting on a digital camera increases the sensitivity of the sensor to light.
Exposure - controls the amount of light which reaches the image sensor. Exposure is measured in ev. The Aperture and Shutter work together to allow the correct amount of light into the camera. If, for reasons to be discussed later, you wish to make the shutter speed faster (letting in less light); you must compensate by having the aperture open wider (letting in more light). This relationship is known as reciprocity (as it is a reciprocal relationship). As stated in the introduction, you can feel free to play with your camera and get a feel for how this principle can be used without worrying about wasting valuable film.
- Aperture - defines the size of the opening in the lens. Aperture is measured in f-numbers and often referred to as "f-stops." Discussion of f-stops is counterintuitive in that the larger the f-stop - the smaller the opening of the lens. The correct unit usage of f-stops appear like: f/2, f/4, f/5.8, etc... However, most cameras find it more economical to truncate the display to show: 2, 4, 5.8, etc... Forgetting that the larger the f-stop - the smaller the hole is a common pitfall of early camera students.
- Shutter speed - defines the exposure time i.e. the time for which the shutter is held open during the taking of a photograph to allow light to reach the sensor. Shutter speed is measured in seconds or fractions of a second (e.g. 1s, 1/30s, 1/60s, etc.).
Sensitivity of the sensor - setting ISO speed
In film photography, ISO measures the sensitivity of the film used. The more sensitive the film, the less light required to make an appropriate exposure. Consequently, the more sensitive the film, there is a noticeable increase in grain. In digital photography, the metaphor is maintained. The more sensitive you tell your sensor to be, the less light you need to create an exposure; but, it will also be more sensitive to noise. The difference is slight and only a matter of terminology (grain versus noise) but the idea as a whole is transferable.
There is always a correlation between ISO and noise; however, the amount of noise present at a particular ISO setting is dependent on the specifications of the image sensor - and thus, every camera is different. Generally speaking, professional level cameras have less noise for each of the ISO settings compared to the same settings on consumer level cameras.
Prosumer SLR cameras tends to perform very well up to ISO800, and even at ISO1600, the noise is noticeable but tolerable. As can be expected, ISO1600 offers a tremendous advantage to photographers in low light/ night environment.
What is light metering ?
It should be stated that "metering" is photographer talk for "measuring." Metering, in photography, can either refer to measuring the light or measuring the actual distance from the camera to the subject.
There are normally three types of light-metering: evaluative, center weighted average and spot. Your camera uses these to decide on what exposure it should aim for.
Evaluative means your camera will try and choose an exposure which will work well for the entire image. However the implementation of this feature can vary vastly from camera to camera meaning that different cameras will make different decisions in the same lighting conditions. Evaluative metering usually is preferable when you use automatic or semiautomatic (Av aka Aperture Priority, and Tv aka Shutter priority) exposure setting.
Spot is the exact opposite of the Evaluative setting, rather than taking into account the whole of the image it tries to choose an exposure that is appropriate for whatever appears in the center of the image ignoring the rest of the image. This metering method is useful if you set the camera to manual exposure mode. A typical camera has dynamic range of about 6 ev steps. Areas for which camera show +3 ev in picture will be absolutely white, and areas with -3 ev will be absolutely black. The easiest way to set correct exposure will be to meter highlights (brightest white spots) in your composition and set exposure so that highlights read at +2.7 or +3 ev.
Center weighted falls between these two settings, the camera chooses an exposure which will work well for the entire image, but places more importance on getting the exposure right for the center section.
Exposure modes of digital camera
Usually a digital camera has three types of exposure modes:
- Automatic modes (A, Autopicture, different picture modes (portrait, landscape etc.), P (Program)), in which the camera sets your aperture and shutter speed.
- Semi-automatic or priority modes:
- Shutter priority (Tv) - you set the shutter speed and the camera sets the correct aperture.
- Aperture priority (Av) - you set the aperture and the camera sets the shutter speed.
- Manual mode (M and B) - you set the aperture and shutter speed.
How to achieve sharp digital photographs
The reasons for the lack of sharpness in your digital photos can be attributed to one or more of the following reasons:
- Camera movement.
- Lack of proper focus.
- Using a "soft" camera setting.
Camera movement (or camera shake) usually comes from hand-holding your camera while using a slow shutter speed. To minimize camera movement while using slow shutter speeds of 1/25th of a second or lower you should use a tripod. If you don't have a tripod with you, try placing the camera on a flat surface and using the camera's self timer (obviously, this works best when there is not much movement in the scene). Sometimes, if the lighting conditions are marginal where your shutter speed is right at 1/25th of a second, if you have a very steady hand, you can try holding your breath briefly as you snap the shutter. You can also try manually increasing the shutter speed at the expense of using a wider aperture (lower f-stop). Generally, a higher shutter speed decreases the effect of camera movement, but the lower f-stop decreases the depth of field and requires more careful focusing.
Lack of proper focus is another cause for lack of sharp photographs. Fortunately, most digital cameras today come with autofocus capabilities. In a few fixed lens cameras and in almost any digital SLR, the autofocus can be disabled allowing you to focus the lens manually. Greater care must be exercised to make sure the object that you wish to be the center of attention in the photo is sharply focused.
In more inexpensive cameras, the only focus adjustment may be a normal and macro mode. The normal mode is usually represented by a mountain icon and the macro mode is usually represented by a flower icon. If your camera only supports these two modes, make sure it is in the proper mode before you snap the shutter to achieve the sharpest photos.
Camera with normal and macro focusing modes
Poor lighting conditions may cause your photos to lack definition and contrast. You may notice that even when you use a tripod and with your camera handling the autofocus, your photographs may not appear as sharp as you might wish. This is especially true for available light photographs where you do not wish to use a flash. The fault for this lies not with your camera but with the scene itself. In cases like this, try increasing the available light shining directly on the subject. This can improve the photograph by allowing the edges to be more sharply defined against the background.
In camera sharpening can also affect the sharpness of an image. Some higher end cameras offer a sharpness adjustment that usually ranges from +2 or +3 to -2 or -3 with zero in the center. Increasing the sharpness can give you crisper looking images, and decreasing it will give a more "soft focus" effect. Some photographers like to use a soft-focus effect when taking portraits, especially of women, because it tends to smooth out the appearance of the skin. Increasing the sharpness will not compensate for camera shake or lack of proper focus. Many photographers choose to leave the sharpness setting at zero and perform any sharpening in the post-processing stage.
What's the slowest exposure time you can get away with ?
"Camera shake" is what happens when you don't hold the camera sufficiently still. The longer the exposure time, the longer you have to hold the camera perfectly still, and the more chance there is for shake.
How long an exposure time you can use before being affected by camera shake depends very much on the individual. With a lot of practice it's possible to hold the camera still for as much as half a second, but most people should be able to hold a camera still for 1/20 of a second with a little practice. Beginners should be able to hold for 1/25 of a seconds without problem.
As a general rule of thumb, it is recommended to not use a shutter speed lower than the inverse of the focal length of the lens used. For example, if you use a 50mm lens, try not to use a shutter speed slower than 1/50.
Another way to find out what shutter speed to use is by testing.
- Pick something which will stay motionless and has straight lines which can easily be used to detect blurring. A good option would be a piece of paper which has large lettering printed on it, or use a suitable book cover.
- Be somewhere that has a reasonable amount of light (not necessary - but then all of your photos won't have the same brightness). If light is sufficient, feel free to turn off the flash to allow you to take photos faster.
- Switch your camera to exposure-time/shutterspeed priority mode.
- Set the camera to a reasonably long exposure time (say 1 second).
- Take a photo of your target in the way you normally take photos. Don't go out of your way to try to be more stable unless you are willing to do that every time you take a photo.
- Reduce the exposure time by one or two steps (how long this is in seconds will depend on your camera).
- Repeat the last two steps until you get down to about 1/30th of a second.
Now load the photos onto your computer, the one taken at 1 second will be blurred unless you are some sort of statue, but as the exposure time decreases the amount of blurring decreases. Go through the photos in order until you find where the blurring is no longer noticeable. That photo will represent the maximum exposure time you can take photos without "camera shake". Don't worry if you didn't note down the exposure times while taking the photos because most modern digital camera will store the information alongside the photo using what is known as EXIF. Most photo-manipulation packages can read this EXIF information as can many stand-alone EXIF-readers.
(If you use Windows XP you can get the EXIF information by right clicking on the photo and choosing properties, then the summary tab and clicking on advanced.)
The EXIF-data will include a lot of information, but the field you'll want to find is "exposure time" which, logically, will tell you the exposure time used when that photograph was taken.
Now you know what exposure-time you can get away with. Many photographers have their own techniques for stabilizing the camera so that they can use longer exposure times. These normally involve levering body parts against each other for greater stability. One common technique is to hold the camera directly against the brow or nose. Another is to try to lean against the nearest stable object like a tree, wall, etc., and then hugging your elbows into your chest. How well these work for you will very much depend on you, and of course, practicing.
Now that you know how long an exposure time you can get away with using your normal technique, you can start experimenting with other ways to hold your camera that will allow for longer exposure times without causing camera shake.
When taking shots with exposure times longer than you normally use, it's a good idea to take several shots if you have the spare memory. The more shots you take the better the chances that you manage to hold sufficiently still for one of them to come out well.
As a general rule of thumb, the longest exposure time that tends not to be affected by camera shake is about 1/60th of a second or 1/125th of a second. At those values, the camera shutter is operating fast enough that the image captured is typically not affected by camera shake.
However, such values are typically achieved only at locations with good lighting, say, a typical afternoon outside. It is tricky to achieve this lighting indoors and photography at those shutter speeds without compromising on ISO (see below) or aperture is difficult at times
In addition to this, high end digital cameras are starting to appear with image stabilization or vibration reduction technologies. These can help to increase the longest exposure time to about 1/30th of a second or even 1/15th of a second when used right, and it is a huge advantage in indoors/ low light environment. Unfortunately, the technology is expensive at the moment, but it would eventually trickle into the more consumer-friendly models.
The non-human approach to reducing camera shake
Use a tripod or monopod. Failing the availability of either, find a flat, stable surface you can set your camera on. You may find that a small bean or wheat bag helps when placing your camera onto an uneven surface. If your camera allows you to set it off remotely or to use a timer, these also help reduce camera shake to an absolute minimum.
Another technique that can be used for stabilizing your camera is, if you have a camera strap, turn your self into a bipod. This is done by steadying your legs and then pulling the camera away from yourself.
Some cameras have a function that attempts to compensate for camera shake by moving the sensor or parts of the lens.
When is long exposure time useful ?
Sometimes a long exposure time is the best way to increase the brightness of a shot in the low light situations. However longer exposure time can also increase "noise" in images. Many cameras have an automatic noise reduction system which kicks in at about 1.25-1.5 seconds. This means that the camera has to do more post-processing after the shot is taken so it may take slightly longer before the camera is ready to take another shot.
There are also times when you want to deliberately cause light streaks. Moving objects such as stars (for the ultra-long exposures) and cars (at night, when the headlamps are on) can create quite beautiful photographs when you utilize long exposure deliberately.
There can be cases when one wants to capture a portrait at night with usual exposure and flash no details in background can be captured. Here a longer exposure is taken with flash, flash can freeze and provide detail of person's face while longer exposure time will generate details of small lights in the background.
Why do images become darker with short exposure times ?
Let's say you want to shoot a little leaguer running to first base, and not have it blurred. If your camera is in a semi-automatic mode (for example shutter-speed priority), you can adjust the shutter-speed to be faster (i.e. shorter exposure time). The camera then tries to modify the other settings (flash and aperture size) to make the image have an appropriate brightness.
But there are limits to how far the camera can go. The amount the aperture can be opened is physically limited. Once the aperture has been opened to its widest and the camera is out of other options, the brightness can't be increased further. This means that when you decrease the exposure time beyond that point the image will get darker, or "underexposed".
Luckily your camera will be able to tell you when it reaches this point. How it does this varies from camera to camera but the most common way is to make the aperture size change to red on the display (you may have to have the LCD display turned on to see this). On many cameras this information is only updated when the shutter button is pressed half way. Further details on this should be available from your camera manual.
At larger apertures, why do images become brighter ?
Just as in the case above, where short exposure time images can become darker, or underexposed, when you exceed the camera's ability to "open up" the aperture, the camera is limited by how much the aperture can be closed down. So, in very bright conditions, if the camera cannot close down further, images will be brighter, or "overexposed". Again, most cameras have a way of warning you when this point is reached, and unless in manual mode, will not allow you to shoot.
Why should I take control of exposure time ?
Hopefully by now you understand the basics of exposure time and how it affects your shots. If you have shots that you've taken before that have turned out blurred now is a good time to go and have a look at their EXIF information and pay attention to the environment the photos were taken in. Almost certainly, your blurred photos will have been taken in low light situations and the EXIF information will reveal that the exposure time was fairly long (longer than your "stability limit").
You should now be able to make educated guesses as to what your camera's automatic system was doing that resulted in blurred images. The camera detected low light so it probably tried to compensate by turning the flash on and opening the aperture as far as it could. However, even after doing this, the camera thought the photo would be too dark, so it increased the exposure time. Here it made the fatal mistake! Since the camera doesn't know how stable you can hold the camera or if it is on a tripod, it assumes that you can hold perfectly still for as long as you want.
Since you know that's not true, this is a perfect example of a situation where you should step in and take control. In most situations you don't want a blurred photo, (though you do have to consider what you want). If, for example, you would prefer a darker photo but without blur or camera shake, then all you have to do is switch to shutter-speed priority mode, set the exposure time to a setting which you are comfortable with, and let the camera handle the rest of the settings.
What if you want the image brighter? Well, the simple answer is to increase the lighting. If you're indoors, then turn the lights on if they aren't on already or set up what you want to shoot near window light. If that's not an option, you can start playing with other settings such as the ISO. Increasing the ISO can increase the brightness of the shot by increasing the camera's sensitivity to light, but at the expense of causing more noise to appear in the image (more on ISO later).
All of these choices involve compromise, and your camera can't choose which compromise to make for you as it doesn't know why you want the photo and what's important about it. Only you can make that decision, and that's why you have to take control.
Why change the aperture ?
In general, cameras are fairly good at automatically changing the aperture to deal with the light situation.
However, as mentioned earlier, if you want to increase Depth of Field (the range around your subject that remains in focus) or improve the focus on distance shots, you might want to step in and make the aperture smaller.
Without getting into a lot of theory and mathematics, aperture widths are measured in what are called "F-Stops" written like this: f/1.0, f/2.8, f/4, f/5.6 f/8.0, f/11, f/16 etc. As these numbers get larger, the aperture gets smaller. So from these numbers f/1.0 means the aperture is the widest (wide open in fact), while f/16.0 is the smallest. When you increase the size of the aperture by setting it to a lower numbered f-stop, it is called opening up. When you decrease the size of the aperture by setting it to a higher numbered f-stop, it is called stopping down.
Put your camera into manual aperture priority and move the dial back and forth to adjust it. You will see the numbers in the view finder change as you open and close, and can see the range of options your specific camera has. Each of these numbers represents one "stop" more or less of light reaching the camera. Another, more indirect way of changing the aperture, is to switch to time mode and do the same drill, observing that the time notation changes for the amount of the light reaching the camera. The numbers show what part of a second the aperture is open. For example, t/90 means 1/90th of a second. You will see the numbers change something like this: t/90, t/125, t/180, t/250, t/350, t/500. Again, as the numbers change, so does the amount of light—there's one "stop" less light with each shorter exposure.
If you use aperture-priority mode on your camera, beware of the same problems that you can get in fully automatic mode. Your camera may increase the exposure time significantly to compensate for less light through the aperture, so make sure the exposure time isn't too long when taking the shot.
If it is too long, then you have to use a tripod or other method to stabilize your camera, and switch to manual mode. This will mean that you have to set both the aperture and exposure time by hand. But that's not too hard, now that you see that the numbers simply represent step changes in the amount of light reaching the camera.
Remember, as shown above, each step increment change of either the f/stop or time exposure represents one "stop" of light. As long as the change is proportional between these measurements, the amount of light is the same. I.e. If you open the lens up more, shorten the time the same number of steps to still get the same amount of light... if you close the lens more, increase the time the same number of steps to still get the same amount of light.
So, here's how you can set manually without fancy light meters. Simply find out what the camera's light meter is recommending in the automatic mode. For example, it may think you need t/250 with f/8. But you want to get a greater depth of field, say f/16. That is two steps smaller aperture than f/8, hence, two stops less light. So in manual mode, set f/16 (which is two clicks less light than recommended to get the right amount of light) and then INCREASE the amount of light two stops above what the automatic setting recommended, in this case, moving two clicks from t/250 to t/125. Actually, you can simply think of it as turning two "clicks" up or down for each setting and don't worry about the numbers.
Again, a simple solution for manual mode is to take the automatic mode setting, then switch to manual and "click" the same number of steps up or down to get your new aperture and speed settings.
Most camera lenses do not produce images of the best resolution with the aperture wide-open (e.g. f/1.4 on a 50 f/1.4 lens). Stopping down (increasing the f-stop setting) can improve their resolution, often drastically. This can be referred to MTF charts. Using f/8 or f/11 on most lenses produces an image with fine detail. Beyond this would actually degrade images due to diffraction, so don't overly stop-down unless you need greater depth of field.
The major trade off a photographer will encounter when fiddling with the aperture is this: low aperture allows more light in, but at the cost of Depth of Field; high aperture allows less light in, but have more Depth of Field.
Normally, you would want to shoot with aperture as low as possible, as not having enough light is typically more common than having too much light. Under some circumstances though, a low aperture gives more headaches than the increased light. One very obvious case is when you are taking photographs in macro mode.
In macrophotography, you are pushing the camera to capture details on a small object, typically close to the lens. In these cases, when the object is close to the lens, Depth of Field is critical. Having insufficient Depth of Field means only part of the object is in focussed. This is good if it's your artistic intention, but that's rarely the intention.
In these cases, you have to stop down to higher aperture numbers, and balance the trade offs elsewhere. Normally these come out from shutter speed (longer shutter speed) or ISO (higher ISO settings), which is why macrophotography tends to occur in controlled environment.
Thus, as a general rule of thumb, an aperture of around f/4 is probably adequate for normal photography; anything lower and you begin to get noticeable loss of Depth-of-Field. At f/2.8, the Depth-of-Field is visibly constrained to fairly narrow bands.
For macrophotography, apertures around f/8 or f/10 or even higher are common. such high aperture values would mean a corresponding increase in shutter speeds.
There is another aspect of apertures that may not be obvious to casual users. Higher apertures gives you more Depth-of-Field, which means more things are in focus -- which means you have more room for errors in terms of focussing.
This is most obvious when you have a low-aperture lens, shooting a distance (really distant! Say, 150~200+ metres away) object, in poor light and/ or on a moving platform.
(Aside: One has to wonder why a photographer is in these conditions, but we digress... )
Even with autofocussing technologies in today's camera, getting a sharp picture in those circumstances is difficult. Autofocussing relies largely on contrast and not so much on image context, so it is easy for the autofocus to focus on the wrong portion of the subject.
If your aperture is set high enough, this isn't an issue; depth-of-field will ensure your subject is in focus. However, if you are shooting at low apertures—say, f/2.8 -- the low depth-of-field will mean you need to be very precise in your focussing to ensure the subject is in focus. Make a mistake (easy enough when your lens is hand-held and shooting at 150+ metres), and your subject slips out of the depth-of-field and you end up with a blurred shot.
As such, using a high aperture gives you more margin of error when it comes to focussing on a subject. As usual, you have to adjust for the (generally) lower amounts of light a higher aperture implies, and it becomes a balancing act.
Changing what automatic/semi-automatic mode aims for
When you use automatic, shutter-priority, or aperture-priority modes the camera has a fixed idea about what exposure (brightness) it should aim for. What if you want to change this without having to use manual mode ?
Luckily most cameras come with a feature known as "exposure compensation" which allows you to underexpose or overexpose shots easily. However how much you should change the exposure depends on the situation and on your camera, so the best way you can learn is by experimentation.
Many digital cameras tend to overexpose and it's common for photographers to use an exposure compensation of -1/3 to -2/3 as default.
Many photographers use "bracketing", this is the name given to when you take several photos with a range of exposures to ensure one photo comes out with the correct exposure. Automatic mode normally gets fairly close to a good exposure so taking photos at one level above and below its defaults will probably get you a good shot.
Speeding up recovery time ?
recovery time (also called latency) is the time taken between shots (i.e. after you take a photo how long do you have to wait before you take another)
You can speed up the recovery by turning some or all of the following things off,
- image sharpening
- getting a better memory card
Latency time is one of the downfalls of point and shoot type digital cameras, but as time goes by and technology improves the latency time has been reduced dramatically. More advanced digital SLR cameras are as fast as their film counterparts ever were with some professional SLRs offering up to eight frames per second with a buffer of forty frames.
The general opinion is that image sharpening should be left to the post-processing stage. Some cameras offer in-built sharpening, however these are normally less sophisticated than those available on most photo-manipulation packages. There is no technical advantage in using in-built sharpening over using a computer based sharpening tool. Actually image sharpening must be the last step in image manipulation, so if you will need some post processing the in camera sharpening will only decrease the quality of the final image.
The canon user manual will suggest which settings to use with their higher end digital SLRs.
Photo effects/Color modes
These let you take shots in Black and White, Sepia, vivid mode, etc. The basic rule is don't use them, shoot in colour and apply these effects in post-processing if you want them. Like with sharpening, your computer is able to take advantage of more sophisticated algorithms resulting in a better end-result.
White balance often confuses beginners; after all, white is white, isn't it?
Actually, it isn't. Your camera sees what colour an object is; unfortunately this won't be the same colour as humans see. This is because the human brain makes people see non-white colours as white.
The colour of an object is dependant on the light source, however humans automatically adjust so that anything which roughly combines the primary light colours together appears white.
"White-balance" is the name given to the technique cameras use to try and depict the image as humans see it. Most cameras will have at least three options (daylight, fluorescent, and tungsten) and may have many more which are designed to adjust to the light source.
Some cameras will also have a custom option, the custom option will allows you to setup a "White-balance" for a specific lighting situation. The way it works is that you have to show it something which is white (or more often a grey card) and using that it makes corrections to the photos taken.
Luckily automatic white-balance detection is fairly sophisticated so most of the time leaving white-balance on auto mode will get you the result you want.
Depth of Field and achieving blurring effects
The depth of field (DOF) is the distance in front of and behind the subject which appears to be in focus. Areas which are out of DOF look blurred. Sometimes it's very useful to have shallow DOF to separate the subject from the background (and/or foreground). Photographers try to get the subject in focus and the background slightly blurred.
DOF for given camera depends on three factors:
- Distance to subject. Getting closer to subject will make DOF shallower;
- Lens focal length. The longer focal length will make DOF shallower;
- Aperture. The larger aperture will make DOF shallower;
Despite there are three factors which affect DOF, only aperture can help you control it. If you choose a longer lens to get the full subject in frame you need to increase the distance to your subject and these two factors will compensate effects of each other.
So to have shallow DOF you need:
- fill as much of the frame as possible with your subject (it is usually easier with a long lens)
- set big aperture (f4.0, f2.8 or even f1.4 if you have such lens)
Worth noting that cameras with bigger sensors will have shallower DOF for the same f-number, because of the same focal length of the lens you will need to get nearer to your subject to fill the frame. So with a digital SLR getting shallow DOF is much easier than with a compact Point & shoot camera.
It is also possible, relatively easily, to introduce blurring at the post-processing stage although the effect may not be as good compared to that done in-camera.
Taking infra-red photos
Some digital cameras have sensors which are capable of detecting infrared, if your camera is capable of doing so then you should be able to obtain a infrared filter relatively cheaply (about £10 GBP/ $15 USD) which allows you to take infrared photos.
The simplest way you can tell if your camera is infrared-sensitive is to point an infrared source into your lens and see if it is visible on your LCD screen. Almost any infrared source can be used including remote controls (point the emitter at your lens and hold down a button on your remote).
A more technical explanation follows:
All digital camera sensors are capable of detecting infrared; this is actually a problem with early digital cameras, because they pick up infrared and as such alters the captured image.
To deal with this issue, camera manufacturers build something called a hot mirror into digital cameras. Effectively this is an IR filter, designed to filter out IR so that the final images are not affected by the extra 'light' coming in.
Hot mirrors aren't 100% effective, thus some cameras are more sensitive to IR than others. Of course, if you are daring enough, you can open up your digital camera and replace the hot mirror with a glass of matching optical index, but this is not recommended and not advised. Doing that will almost certainly void your warranty, and sometimes break the camera.
IR filters are filters which filter out non-IR light; the filter itself appears black or reddish-black. When you hold it up to a light source, you may see a dim image of the light source showing through, but pretty much nothing else will show up.
But attach the filter to a IR-sensitive camera, and when you take photographs, you will see some images captured. How does this work?
Essentially, it's the same idea how photographs are taken. IR light are reflected off objects the same way 'normal' light is, and the IR filter will remove the 'normal' light, leaving the camera to interpret only the IR light. This results in an image that can be eerie in the extreme: Trees are white (IR reflects off leaves strongly), dark clothing becomes white and vice versa, things simply aren't what you expect.
IR photography does have some issues to take note of. First, IR light tends to be lower in intensity, so you need to compensate with lower aperture, longer shutter speed, and/or higher ISO. Also, IR focuses slightly differently from normal, which is why some SLR lens have IR markings for them. So you may end up with slightly out-of-focused images.
The last issue is not technical, but moral. IR can and does reflect straight through clothing, especially thin clothing. This can lead to some morally questionable photography, although it's really really much harder to achieve than people are led to believe. The ability does exist though and it has to be left to the individual photographer's morals to determine what to take in IR.
- An action shot
- Obviously we want a short exposure time here, to compensate we would open up the aperture. We might also use the flash, but remember using the flash will mean you have to wait for the flash to warm up/fire.
- A landscape shot
- This time we'd want a narrow aperture as we want to photograph a large area with a deep depth of field. If we want to increase the brightness of our shot then we'll need to increase the exposure time (as the flash probably won't be powerful enough to light up our scene). In a landscape shot the most likely source of motion is the photographer, so it's best to take these shots using a tripod to avoid motion.
- A framed painting
- If there is glass in front of the painting you will almost certainly want to turn the flash off otherwise you'll get effects like this:
- Which obviously you want to avoid. Using a wide-aperture is an obvious move, if you have a tripod or otherwise stable place where you can place the camera a long-exposure time will also help. If you still don't have enough light then you might consider increasing the ISO but going over ISO 400 is likely to cause a noticeable noise effect on the final image.
- Another solution would be to take the photo at an angle to reduce the reflection of the flash, however "straightening" the photo in post-processing may take more effort than it is worth.
- Glass enclosed exhibits
- Most of what we've said about framed paintings also applies here, however you're more likely to be able to get away with taking photos at angles. Consider the following two images which are both taken with flash,
- In the second the reflection from the glass is almost unnoticeable, while in the first it destroys the balance of the image. However all is not lost in the first image either as the majority of the flash reflection happens away from our main target we should be able to remove most of the flash reflections in post-processing:
- Another problem with this sort of image is that the glass can often reflect other items in the room including the photographer. One way to avoid this is to take the photo while holding the camera very close to the glass. A secondary advantage of this approach is that you can make it appear that there is no glass between yourself and the exhibit for example in the following photo,
Another way to dramatically reduce reflections is with the use of a polarizer.
- Use a shallow depth of field and try to avoid using an on-camera flash. If you can't increase the surrounding lighting use an external (preferably bounce flash) flash instead. Using the on-camera flash will create harsh shadowing and is responsible for red-eye.