Basics of photography
Adapted From Beginner's Digital SLR crash course ebook
I have just finished a short ebook indroducing a few concepts about DSLR functions. I was discussing camera features with one of my colleagues and realised that I had forgotten most of the theory about photography. Although in my day to day practice photography doesn't require much thought due to the standardised nature of the photographic framing and lighting it is useful to know about the theory behind those photos to troubleshoot when the image doesn't seem right. Also, to achieve high level photographic effects it is important to know the basics so you can play with certain aspects of the exposure and lighting.
This ebook was about general photography and so describes how to play with camera settings in different situations. Much of it is not relevant to dental photography so I will summarise that which I would find useful to know about dental photography. I also supplemented this knowledge including that about lenses and digital sensors from a fantastic website: https://www.cambridgeincolour.com/
Image size and quality
Under settings, you need to choose the largest size and best quality settings. Digital storage is quite cheap and if you want to do anything with the photos in the future you want it to be as large and high quaility as possible. For image quality there are two choices: JPEG and RAW. The main difference is that RAW images can have certain aspects e.g white balanced changed after the photograph. Special software may be needed to edit RAW images on the computer so if you don't intend to edit the photo afterwards JPEG is more than sufficient. If you are unsure, most DSLRs will allow you to have two copies of the photograph (JPEG+RAW) but it will take up more than twice the memory of a JPEG. For image quality you should choose Large fine (Figure 1) which indicates that the largest photo by pixel size and the finest quality of image. By using the JPEG Large fine setting you guarantee the highest quality of image possible with the camera.
Elements of exposure
There are three basic elements of exposure and they work together to create the final exposure/picture. If they are out of balance then the picture will end up looking over exposed (too light) or underexposed (too dark). These elements are:
-Shutter speed: Decides how long the shutter is left open. The larger the number the more light falls on the sensor. It is measured in fractions of seconds or seconds. 1/2= 1/2 seconds, 3"3=3.3 seconds. in handheld photography you will need at least below 1/60 seconds or the photo will turn out blurry. If you want a faster shutter speed, to keep the same lighting consider using a larger aperture or increasing the ISO speed
-Aperture: The size of the opening in front of the lens. Denoted in f-stops (focal length stops) which is a fraction of the focal length of the lens e.g if the focal length of the lens is 100mm and the lens diameter of the lens pupil is 12.5mm then the aperture is denoted as f/8 as the pupil size is opened to 1/8th of the focal length of the lens. Considered alternatively, an aperture of f/22 of a 100mm lens would indicate a pupil entrance size of 100 divided by 22=4.54mm. As the aperture is indicated as a fracture, f/8 is a larger fraction than f/22 therefore the size of the lens opening is larger in an f/8 setting. Increases in aperture size i.e higher f stops will result in larger depth of field.
-ISO: The digital chip's sensitivity to light. The term is inherited from camera film times where a film with a specific ISO had to be selected for each situation. Higher ISO numbers are more sensitive to light and are useful in low light situations but the texture will be more grainy (digital noise). Low ISO numbers require more light but offer higher quality, smoother pictures. Ideally you would use the lowest ISO setting possible given the lighting conditions.
Aperture and shutter speed control the quantity of light falling on the digital light meter while ISO speed affects the sensor's sensitivity to the light falling on it. Low light conditions favour slow shutter speed, larger aperture (low f-stop) and high ISO speed.
Camera lenses
When choosing a lens for your camera, several specifications will need to be understood. The dental setting is fairly consistent so a specific set of specifications will be ideal to capture the best image.
-Lens focal length: The distance between the camera lens and the digital sensor. Focal length indicates the angle view of a lens (how much of a scene the lens will capture) and how large the subjects in the frame appear. A wide angle lens (35mm) has a close focal point, telephoto lens (>70mm) have longer focal lengths. Telephoto lenses tend to have higher influence of camera shake as small hand movements become magnified. Therefore for higher focal lengths, shutter speed becomes more important to avoid blurred images. A rule of thumb is that the shutter speed should be at or faster than 1/focal length. e.g a 100mm lens on a 35mm camera requires 1/100s or faster shutter speed to avoid blurring. Note: The focal length needs to be considered in the context of the sensor size and crop factor
-Zoom lenses vs prime lenses: A zoom lens can have the focal length varied within a pre-defined range whereas prime lenses can't have the focal length altered. Zoom lenses tend to be heavier and more expensive due to the complexities in design required to move internal mechanisms to zoom. The camera has to be moved closer or further from the subject if the framing is to be changed. The complexity means the images may be less sharp and more prone to distortion. Prime lenses can be made with larger apertures and allow photos in lower light conditions. They can be distinguished as zoom lenses will have a range of focal lengths in their description e.g 24-105mm whereas prime lenses will have a single focal length e.g 90mm.
-Maximum aperture: The smallest f-stop (largest diameter) that a lens aperture can open. The maximum (and sometimes) minimum aperture is described for a particular lens. For a maximum aperture of 2.8, it can be denoted as f/2.8 or 1:2.8. Some zoom lenses will give a range of maximum apertures because it depends on the position of the zoom. Lenses with larger maximum apertures (smaller f-numbers) are generally larger, heavier and more expensive.
Digital camera sensor sizes:
Compared to the traditional full frame, 35mm film size, most modern digital sensors are smaller and therefore crop out much of the external area of the image seen through the lens. The crop factor is the sensor's diagonal size compared to a 35mm full frame sensor. This has some advantages: Almost all lenses are sharpest at their centres so cropping the outside removes the low quality portion of the photo. However, to achieve the same framing of a photo, a cropped sensor requires a wider angled lens which tends to have lower quality. To calculate the equivalent 35mm focal length of a lens, multiply the lens's focal length by the crop factor e.g 60mm lens multiplied by a crop factor of 1.6x for a particular camera body is equivalent to a 96mm equivalent focal length in a 35mm camera.
However it is important to note that the actual focal length doesn't change for the lens just because there is cropping of the digital sensor. The only thing that changes is the angle of view of the lens (as the image will seem more zoomed in and have a more limited angle of view due to the cropping). Smaller sensors require lighter lenses (lower focal lengths) for equivalent angles of view, zoom ranges build quality and aperture range).
As the sensor size increases, the depth of field will decrease for equivalent aperture sizes (when photographing the same subject with the same framing). This is because larger, uncropped sensors will require the camera to be closer to the subject or the use of longer focal length lenses to fill the frame with the subject.
Histograms
A histogram is a visual graph representation of the tone of every single pizel in the image from pure black on the left to pure white on the right. The advantage is you can see a simple representation of the exposure of the image which isn't always so easy to judge from the small display of a DSLR> Dental photographs are properly exposed when the histogram is relatively centred meaning it isn't too dark or too light. You can check this with the first photo from a particular position with a particular framing to see if your flash and exposure settings are ideal before proceeding with the rest of the photo series. Most brands will access a histogram by pressing disp. once or twice when viewing the image.
White balance
Each type of light has a different colour value e.g fluorescent is cold and blue, daylight is warmer. The white balance setting compensates for the background lighting. Incorrect settings can cause the photo to be vaguely discoloured. Auto white balance setting works pretty well in most situations. However dental photography is fairly uniform as we will be using a flash that provides most of the light in the photo. Custom white balance can be set by taking a photo of a white piece of paper filling the photo frame in the lighting that the subject will be in. Select custom white balance in the menu and set the picture of the paper as the white balance. Then set white balance to custom in the photo menu. RAW photos will allow white balance to be changed after the fact.
Camera modes
The camera mode is changed by turning the wheel on top of the camera. Each camera mode is optimised for certain shooting situations by altering the exposure settings. Auto mode chooses the variables that best suit the lighting and distance from the subject but doesn't allow any control as to depth of field, brightness, shutter speed etc. Semi automatic modes e.g Av/A, Tv/S you control two variables and the camera optimises the third variable. Manual mode allows the greatest level of control of the exposure settings of the photograph.
Av/A: Aperture priority mode: Allows control over the blurring of the background as the aperture controls the depth of field of the photograph. A low f-stop blurs the background due to a smaller depth of field whereas a higher f-stop has more of the image in focus. The ISO must be adjusted manually but the shutter speed will be automatically selected.
Tv/S: Time value/Shutter speed mode: Allows freeze action or blur motion. Not used in dental photography but in Tv mode the aperture is automatically selected according to correctly expose the shot but the ISO must be selected by the photographer.
M: Manual mode: Allows control of every aspect of the exposure triangle. With control comes unpredictability and you have to know what you are doing and know your lighting to allow a good exposure. Dental photography is quite consistent in terms of framing and lighting. Overhead lighting doesn't tend to change and the flash will provide almost all the light for the photo. Therefore manual mode can be used to allow control over all aspects of the exposure not allowing anything to be set by the camera but we can use a standard set of exposure variables to make consistent photos. In general, the ISO should be set to a constant ~100 or 200 the lower the ISO the crisper the image. Then the shutter speed set according to the aim of the photo i.e faster than 1/60 for handheld, non blurred photography. In the dental setting, between 1/125 and 1/200 can be used. Then the aperture is set based on the position of the light meter (Figure 2). Increase or decrease the aperture till the light meter lines up in the middle then exposure the photograph. For dental photography, the two main distances are extraoral (full face) and intraoral (close up). Extraoral photos will be taken further from the patient and so more light is needed to expose the image correctly. The aperture should be widened to allow more light in through the lens and generally sits at f8.0 or f10.0. Intraoral photos benefit from a higher f-stop which allows less light in and a larger dephy of field. Depending on how far you are from the patient you should adjust the aperture accordingly. Close up smile photographs generally sit at around f22.0. Mirrored photographs e.g buccal or occlusal shots may benefit from a larger aperture as poor quality mirrors can lose some of the light in the reflection. Extreme closeups e.g one tooth only may need a higher f-stop e.g f32.0. Play around with the settings before you are in a patient situation as every camera system and room lighting is different.
Composition tips
For general photography it can benefit from following the rule of thirds. Split the view of the photo into a 3x3 grid. When framing the photo, try to put the subject of the photo along the lines or at itnersections of these lines e.g horizon, person. Filling the frame with the subject is an important part of close up photography so taking close up photos of small details of a subject rather than the subject from afar can show interesting perspectives. In dental photography our aim is quality records showing what the subject is as simply as possible. Therefore the rules are simple: Frame the subject in the centre of the photo level with the borders of the photo, in focus and with good lighting.
Photo storage
With digital storage so cheap these days it is important to store the photos with redundancies in place. Transfer the photographs as soon as possible onto your computer and practice management software. It isn't ab ad idea to save backups on an external hard-drive and even on cloud storage just in case the worst happens and back these up regularly.
Photography is an absolutely essential part of good quality dentistry but it is important to walk before we can run. Fancy lighting and artistic shots aren't out of reach of any clinician but the basics needs to be mastered first. Learning about lighting and exposure are critical to producing quality photos and knowing the rules can help you bend them after gaining a certain level of mastery.
I have just finished a short ebook indroducing a few concepts about DSLR functions. I was discussing camera features with one of my colleagues and realised that I had forgotten most of the theory about photography. Although in my day to day practice photography doesn't require much thought due to the standardised nature of the photographic framing and lighting it is useful to know about the theory behind those photos to troubleshoot when the image doesn't seem right. Also, to achieve high level photographic effects it is important to know the basics so you can play with certain aspects of the exposure and lighting.
This ebook was about general photography and so describes how to play with camera settings in different situations. Much of it is not relevant to dental photography so I will summarise that which I would find useful to know about dental photography. I also supplemented this knowledge including that about lenses and digital sensors from a fantastic website: https://www.cambridgeincolour.com/
Image size and quality
Under settings, you need to choose the largest size and best quality settings. Digital storage is quite cheap and if you want to do anything with the photos in the future you want it to be as large and high quaility as possible. For image quality there are two choices: JPEG and RAW. The main difference is that RAW images can have certain aspects e.g white balanced changed after the photograph. Special software may be needed to edit RAW images on the computer so if you don't intend to edit the photo afterwards JPEG is more than sufficient. If you are unsure, most DSLRs will allow you to have two copies of the photograph (JPEG+RAW) but it will take up more than twice the memory of a JPEG. For image quality you should choose Large fine (Figure 1) which indicates that the largest photo by pixel size and the finest quality of image. By using the JPEG Large fine setting you guarantee the highest quality of image possible with the camera.
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There are three basic elements of exposure and they work together to create the final exposure/picture. If they are out of balance then the picture will end up looking over exposed (too light) or underexposed (too dark). These elements are:
-Shutter speed: Decides how long the shutter is left open. The larger the number the more light falls on the sensor. It is measured in fractions of seconds or seconds. 1/2= 1/2 seconds, 3"3=3.3 seconds. in handheld photography you will need at least below 1/60 seconds or the photo will turn out blurry. If you want a faster shutter speed, to keep the same lighting consider using a larger aperture or increasing the ISO speed
-Aperture: The size of the opening in front of the lens. Denoted in f-stops (focal length stops) which is a fraction of the focal length of the lens e.g if the focal length of the lens is 100mm and the lens diameter of the lens pupil is 12.5mm then the aperture is denoted as f/8 as the pupil size is opened to 1/8th of the focal length of the lens. Considered alternatively, an aperture of f/22 of a 100mm lens would indicate a pupil entrance size of 100 divided by 22=4.54mm. As the aperture is indicated as a fracture, f/8 is a larger fraction than f/22 therefore the size of the lens opening is larger in an f/8 setting. Increases in aperture size i.e higher f stops will result in larger depth of field.
-ISO: The digital chip's sensitivity to light. The term is inherited from camera film times where a film with a specific ISO had to be selected for each situation. Higher ISO numbers are more sensitive to light and are useful in low light situations but the texture will be more grainy (digital noise). Low ISO numbers require more light but offer higher quality, smoother pictures. Ideally you would use the lowest ISO setting possible given the lighting conditions.
Aperture and shutter speed control the quantity of light falling on the digital light meter while ISO speed affects the sensor's sensitivity to the light falling on it. Low light conditions favour slow shutter speed, larger aperture (low f-stop) and high ISO speed.
Camera lenses
When choosing a lens for your camera, several specifications will need to be understood. The dental setting is fairly consistent so a specific set of specifications will be ideal to capture the best image.
-Lens focal length: The distance between the camera lens and the digital sensor. Focal length indicates the angle view of a lens (how much of a scene the lens will capture) and how large the subjects in the frame appear. A wide angle lens (35mm) has a close focal point, telephoto lens (>70mm) have longer focal lengths. Telephoto lenses tend to have higher influence of camera shake as small hand movements become magnified. Therefore for higher focal lengths, shutter speed becomes more important to avoid blurred images. A rule of thumb is that the shutter speed should be at or faster than 1/focal length. e.g a 100mm lens on a 35mm camera requires 1/100s or faster shutter speed to avoid blurring. Note: The focal length needs to be considered in the context of the sensor size and crop factor
-Zoom lenses vs prime lenses: A zoom lens can have the focal length varied within a pre-defined range whereas prime lenses can't have the focal length altered. Zoom lenses tend to be heavier and more expensive due to the complexities in design required to move internal mechanisms to zoom. The camera has to be moved closer or further from the subject if the framing is to be changed. The complexity means the images may be less sharp and more prone to distortion. Prime lenses can be made with larger apertures and allow photos in lower light conditions. They can be distinguished as zoom lenses will have a range of focal lengths in their description e.g 24-105mm whereas prime lenses will have a single focal length e.g 90mm.
-Maximum aperture: The smallest f-stop (largest diameter) that a lens aperture can open. The maximum (and sometimes) minimum aperture is described for a particular lens. For a maximum aperture of 2.8, it can be denoted as f/2.8 or 1:2.8. Some zoom lenses will give a range of maximum apertures because it depends on the position of the zoom. Lenses with larger maximum apertures (smaller f-numbers) are generally larger, heavier and more expensive.
Digital camera sensor sizes:
Compared to the traditional full frame, 35mm film size, most modern digital sensors are smaller and therefore crop out much of the external area of the image seen through the lens. The crop factor is the sensor's diagonal size compared to a 35mm full frame sensor. This has some advantages: Almost all lenses are sharpest at their centres so cropping the outside removes the low quality portion of the photo. However, to achieve the same framing of a photo, a cropped sensor requires a wider angled lens which tends to have lower quality. To calculate the equivalent 35mm focal length of a lens, multiply the lens's focal length by the crop factor e.g 60mm lens multiplied by a crop factor of 1.6x for a particular camera body is equivalent to a 96mm equivalent focal length in a 35mm camera.
However it is important to note that the actual focal length doesn't change for the lens just because there is cropping of the digital sensor. The only thing that changes is the angle of view of the lens (as the image will seem more zoomed in and have a more limited angle of view due to the cropping). Smaller sensors require lighter lenses (lower focal lengths) for equivalent angles of view, zoom ranges build quality and aperture range).
As the sensor size increases, the depth of field will decrease for equivalent aperture sizes (when photographing the same subject with the same framing). This is because larger, uncropped sensors will require the camera to be closer to the subject or the use of longer focal length lenses to fill the frame with the subject.
Histograms
A histogram is a visual graph representation of the tone of every single pizel in the image from pure black on the left to pure white on the right. The advantage is you can see a simple representation of the exposure of the image which isn't always so easy to judge from the small display of a DSLR> Dental photographs are properly exposed when the histogram is relatively centred meaning it isn't too dark or too light. You can check this with the first photo from a particular position with a particular framing to see if your flash and exposure settings are ideal before proceeding with the rest of the photo series. Most brands will access a histogram by pressing disp. once or twice when viewing the image.
White balance
Each type of light has a different colour value e.g fluorescent is cold and blue, daylight is warmer. The white balance setting compensates for the background lighting. Incorrect settings can cause the photo to be vaguely discoloured. Auto white balance setting works pretty well in most situations. However dental photography is fairly uniform as we will be using a flash that provides most of the light in the photo. Custom white balance can be set by taking a photo of a white piece of paper filling the photo frame in the lighting that the subject will be in. Select custom white balance in the menu and set the picture of the paper as the white balance. Then set white balance to custom in the photo menu. RAW photos will allow white balance to be changed after the fact.
Camera modes
The camera mode is changed by turning the wheel on top of the camera. Each camera mode is optimised for certain shooting situations by altering the exposure settings. Auto mode chooses the variables that best suit the lighting and distance from the subject but doesn't allow any control as to depth of field, brightness, shutter speed etc. Semi automatic modes e.g Av/A, Tv/S you control two variables and the camera optimises the third variable. Manual mode allows the greatest level of control of the exposure settings of the photograph.
Av/A: Aperture priority mode: Allows control over the blurring of the background as the aperture controls the depth of field of the photograph. A low f-stop blurs the background due to a smaller depth of field whereas a higher f-stop has more of the image in focus. The ISO must be adjusted manually but the shutter speed will be automatically selected.
Tv/S: Time value/Shutter speed mode: Allows freeze action or blur motion. Not used in dental photography but in Tv mode the aperture is automatically selected according to correctly expose the shot but the ISO must be selected by the photographer.
M: Manual mode: Allows control of every aspect of the exposure triangle. With control comes unpredictability and you have to know what you are doing and know your lighting to allow a good exposure. Dental photography is quite consistent in terms of framing and lighting. Overhead lighting doesn't tend to change and the flash will provide almost all the light for the photo. Therefore manual mode can be used to allow control over all aspects of the exposure not allowing anything to be set by the camera but we can use a standard set of exposure variables to make consistent photos. In general, the ISO should be set to a constant ~100 or 200 the lower the ISO the crisper the image. Then the shutter speed set according to the aim of the photo i.e faster than 1/60 for handheld, non blurred photography. In the dental setting, between 1/125 and 1/200 can be used. Then the aperture is set based on the position of the light meter (Figure 2). Increase or decrease the aperture till the light meter lines up in the middle then exposure the photograph. For dental photography, the two main distances are extraoral (full face) and intraoral (close up). Extraoral photos will be taken further from the patient and so more light is needed to expose the image correctly. The aperture should be widened to allow more light in through the lens and generally sits at f8.0 or f10.0. Intraoral photos benefit from a higher f-stop which allows less light in and a larger dephy of field. Depending on how far you are from the patient you should adjust the aperture accordingly. Close up smile photographs generally sit at around f22.0. Mirrored photographs e.g buccal or occlusal shots may benefit from a larger aperture as poor quality mirrors can lose some of the light in the reflection. Extreme closeups e.g one tooth only may need a higher f-stop e.g f32.0. Play around with the settings before you are in a patient situation as every camera system and room lighting is different.
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| Figure 2: Light meter. This will be present seen through the eyepiece and will appear when the shutter button is held halfway down. It gives an idea of the brightness and darkness of hte photo before it is taken. The aim is to have the top and bottom arrow at 0 which indicates a correct exposure. |
Composition tips
For general photography it can benefit from following the rule of thirds. Split the view of the photo into a 3x3 grid. When framing the photo, try to put the subject of the photo along the lines or at itnersections of these lines e.g horizon, person. Filling the frame with the subject is an important part of close up photography so taking close up photos of small details of a subject rather than the subject from afar can show interesting perspectives. In dental photography our aim is quality records showing what the subject is as simply as possible. Therefore the rules are simple: Frame the subject in the centre of the photo level with the borders of the photo, in focus and with good lighting.
Photo storage
With digital storage so cheap these days it is important to store the photos with redundancies in place. Transfer the photographs as soon as possible onto your computer and practice management software. It isn't ab ad idea to save backups on an external hard-drive and even on cloud storage just in case the worst happens and back these up regularly.
Photography is an absolutely essential part of good quality dentistry but it is important to walk before we can run. Fancy lighting and artistic shots aren't out of reach of any clinician but the basics needs to be mastered first. Learning about lighting and exposure are critical to producing quality photos and knowing the rules can help you bend them after gaining a certain level of mastery.
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