Teaching Photography - Technical Basics

 

This page contains basic technical information on cameras. It is mostly stills oriented, and does not contain much for videography. It will be a work in progress.

I added exercises to the page. Even if you use this page as a reference, you might profit from reading and especially from doing the exercises.

If you want to learn more about the author, please see About Me.

Content

• Start
• The Camera
• Exposure
• ISO
• Aperture
• Shutter Speed
• RAW and JPEG
• Focal Length
• Focusing

Start

This is probably most useful for photographers who already have some experience in the hobby of photography. But I thought it might be useful to give a few hints upfront for those who want to start with photography. Maybe you are coming from the smartphone and want to explore photography deeper. Or you might have been given a camera, maybe a used one and want to explore it. I don't know your intentions. So, feel free to skip anything that does not apply to you.

Photography is a wonderful hobby which will keep you engaged, e.g., making you walk outside, like a dog does. Just take your camera and go. You will be able to keep precious moments, things you see and would otherwise forget, or even document events for others. There is so much you can do.

If you want to buy a camera for a good start, you can do so spending less than 1000€. An example would be a Nikon Z50 with the 16-50 VR lens. But there are others, especially on the used market. If it is not a too cheap or too old a camera, you can hardly go wrong. I'd recommend a mirrorless APS-C camera, however.

Once you have the camera, go exploring it. Set it to full AUTO and take pictures. Just try everything out. You can also read the manual. Most have a manual online. E.g., here is the one for the Nikon Z50. If you are new to photography, you won't understand everything. Then you can come back to this page to learn. The first target at that stage would be to get out of AUTO. But it is a good start to let the camera do the technical decisions for you.

You should also start to learn good composition of your image. For a start, fill the frame with your subject and keep anything out which could distract the viewer. Be critical about the results, also keep an eye on the background. If you google "photographic composition" you will find enough reliable material to read and learn. 

Most of all, have fun!

Exercises

• Rent or get a camera with a normal lens (ask if you do not know what this is), reset to factory, and set it to AUTO. Go out and shoot pictures. Do that at night or day and in all sorts of light. Learn how to transfer the pictures to a device with a larger screen.
• Learn how to print some of the pictures. There are lots of shops which will print the pictures for you. You just have to bring the camera or the smartphone, or upload to a printing service in the web.
• Compare the pictures with pictures of your smartphone in the same situations. Compare also the printed results, especially the ones in difficult light.
• Judge your pictures artistically. Were you close enough? Does your image contain distracting elements? Is the composition pleasing? Is your subject sharp enough? Get critical!
• Read on only after going through these initial exercises.

The Camera

A modern digital mirrorless camera with interchangeable lenses (MILC) works differently than the film camera above, although the central elements are still the same. Here are the main parts of such a camera:

• A sensor sitting inside the housing on its back side.
• A lens to collect the light beams from a light point in your scene and project it to a single point on the sensor.
• A display which often can be flipped partly or completely to show the image that the sensor received.
• A viewfinder through which the user can see the image on a small LCD screen via an ocular, usually mounted on top of the display at the center on the back of the camera.

There are many variations of this design. The most important one is the single-lens reflex (SLR) system, which dominated the market for decades. It has an optical viewfinder, and you look via a pentaprism at the image reflected by a mirror on a ground glass. The SLR is now more and more vanishing because the mirrorless design is more compact and allows additional information to be displayed in the viewfinder. We call these MILC (mirrorless interchangeable lens camera) in the sequel.

There are also compact cameras without any viewfinder at all. The photographer needs to use the display to compose the image. Since displays are touch sensitive now and can be flipped, these cameras can be nice travel cameras. The main disadvantage is that the display can be obscured by bright sunlight. Moreover, its light might be unwanted in some situations.

Another, more rare type contains an optical viewfinder which sees the scene through a different lens like the camera in the picture at the start of this posting. Leica has made that design popular with its rangefinder technology.

The most frequent type of camera today is the smartphone. In principle, they have the same components as the MILC with the exception of a viewfinder. Of course, the lens and the sensor are very much smaller.

We need to identify two other parts of the camera that are important for the photographer.

• The aperture can close the lens so that less light travels through it. It consists of small blades closing from the edge of the lens and leaving a small circular opening in the center.
• The shutter of a MILC sits in front of the sensor. It is a curtain that closes when the sensor is cleared to receive an image. Then the curtain opens for a precise time and let light shine on the sensor. After the images has been read, the shutter opens so that the viewfinder continues working. We call the time of the exposure the shutter speed.  

Older cameras and smartphones might have another type of shutter sitting in the lens itself. Very modern cameras don't have one at all. They do the exposure electronically. The shutter of an SLR was closed unless an image was taken, but the mirrorless cameras have it open to allow the sensor to see the scene.

Exercises

• Learn to identify the mentioned parts in your camera.
• Have a visit to the camera store to see and identify other types of camera. 
• Ask technical questions about cameras. Can the lens be changed? Does it have a viewfinder? How does the viewfinder work and where is its image coming from? What size is the sensor and how many MP ("Mega-Pixels") does it capture? What storage is used? Can the display flip out?
• Listen to your shutter. Is the screen dark during the exposure? Does your camera have a silent shutter, and how does it work?

Exposure

The exposure is the amount of light that reaches the sensor, measured in light per area. It can be changed via the aperture and the shutter speed, i.e., the opening of the lens and the amount of time the shutter is opened for the sensor to be exposed.

As an example, an average exposure for daylight can be achieved with an aperture of f/8 and a shutter speed of 1/60. As you will learn below, an aperture of f/4 yields 4-times more light, and the shutter speed can thus be decreased to 1/240 (usually denoted 1/250 on the camera).

The sensor, just like the old film, has a specific range of exposure where it works best.

• The minimal exposure a sensor can record is determined by its noise level. Every electronic part produces noise. The light itself can only be measured with noise. The signal, i.e. the exposure, must be brighter than the noise.
• The maximal exposure a sensor can record is determined by the capacity of the sensor elements.

Thus, we get a range of good exposures called the dynamic range of the camera. The job of a good exposure is to fall inside that range. To achieve that, the aperture and the shutter speed can be changed. 

• Overexposure means that the exposure was too high. Some areas or spots in the image may be washed out in blank white ("blown out"). Most colors will look less saturated or distorted when they are overexposed.
• Underexposure means the exposure was too low. Details in the shadows are lost, because they are below the noise level of the camera. The image looks sad and muted, and very grainy due to the noise.
• Correct Exposure usually uses the full dynamic range of the image. 

But it can be artistically desired to over- or under-expose for a special effect. This might be necessary if the dynamic range of the camera is insufficient. An image with lots of blown out white areas is called a high-key image. Likewise, not all shadow details are important. If all shadows remain in pitch black, the image is a low-key image. These terms are often applied also for well-exposed images that are just mostly white or black.

One should not be afraid to make artistic choices. E.g., it is more important to get the main subject in good light than the background. This can be achieved only by excessing the dynamic range, unless we are willing to make two images with different exposure and combine them later in post-processing. This is called high-dynamic-range (HDR) photography. Some cameras can do that automatically. Especially smartphones like to do that. Images can look unnatural, however.

On modern cameras, good exposure can be achieved automatically using light metering. Most smartphone users will never care about aperture or shutter speed. But to learn photography, it is important to get acquainted with these concepts as soon as possible. The reason is that aperture and shutter speed determine the photographic output in more ways than just by the exposure.

For the sake of newcomers, let us talk about automatic exposure modes first. The explanation applies to cameras with a PSAM-AUTO dial. On retro cameras with specific dials for each setting, modes are handled differently.

• The fully automatic (AUTO) exposure handle everything for the photographer. On cameras with a mode dial, it usually marked as AUTO. Besides the exposure, it restricts access to various other settings. Nevertheless, it can be useful for starters or for very quick access to reasonable settings. On smartphone cameras, it is the default mode, and most leave it there.
• Aperture Priority (A) lets the photographer fix the aperture and selects a correct shutter speed. It is used because we may want to handle the aperture ourselves by reasons explained below, mainly to isolate our objects.
• Shutter Speed Priority (S or T) lets the photographer fix the shutter speed and selects a correct aperture. It is used because we may want to handle the shutter speed ourselves, mainly to freeze or show object motion.
• Program Mode (P) is a mix which selects a reasonable combination of aperture and shutter speed. Like in A or S mode, there is usually a wheel to change the combination. This mode works like AUTO, but without the additional restrictions and the ability to change the selection.
• Manual Mode (M) lets the photographer handle both the aperture and shutter speed. There is usually some feedback to get the right exposure, either by a simple indicator or by a histogram. If the light is not changing much, this mode can be more reliable than the automatic ones.

Since all modes rely on a metering, it is important to know where the camera meters the exposure.

• Average metering meters the complete scene and tries to find a good balance.
• Center weighted metering uses only an area near the center.
• Spot metering uses only the very center. This is useful for low- or high-key images. Most cameras use the focus point for the metering.
• Preserve Highlights is a special metering which some cameras feature. It does not overexpose anything in the scene. It is good for dark scenes with bright spots in it, like on a stage, where the bright areas need to be exposed correctly.

As an example, see the image below, where the dynamic range of the camera does not satisfy. It is important to expose for the tulip in the foreground. I think there is no problem with the background getting into complete darkness. Beginners tend to fear to lose information in the dark areas. But photography is not about information, but about art and beauty.

Exposure Compensation is available on all cameras including smartphones. Often it is marked as +/- on some button or wheel. 

The modern way is to set exposure compensation visually. If the image looks too bright or dark, fix that and take a second image. Most cameras feature a preview which lets you judge the exposure on the display or the viewfinder while you are composing your image. If you do not trust your visual experience, a scientific way is to use the histogram which modern cameras can display.

Often, the exposure compensation is memorized for the next shot even if you switch off the camera. Do not forget to check this! On Nikon Z cameras one wheel can set the aperture and the other can set a non-saved exposure compensation. Many cameras can define user modes with fixed settings. Switching to such a mode should also reset the exposure compensation.

Exercises

• Look through your images to identify pitch dark areas and blown out highlights. Does this look okay to you? Was it intended?
• See if your camera has an HDR mode. Use it and see if you like it or not. 
• Try setting your camera from AUTO to A mode (aperture priority). Learn to set different f-stops, and try them for a portrait. How does the shutter speed change when you change the f-stop? Do the photos look different?
• Set the camera to S mode (shutter priority, sometimes denoted by T). Try setting different shutter speeds on a moving subject. How does the aperture change? How does it change the image?
• Learn how to set the metering to spot metering, and find scenes that clearly show the difference.
• See if your camera has a way to lock the exposure with a button. Often it is locked when the shutter is half pressed, i.e. together with the focusing. 

ISO

We need to talk about a much-discussed feature of modern cameras, the ISO setting. The abbreviation comes from the organisation for international standards for film sensitivity. It is used for sensors as well.

On a modern digital camera, ISO is usually brightening the image simply, including the sensor noise. This might be necessary if there is not enough light to expose the sensor to its full range. E.g., you might not want to use a longer shutter speed because that would blur the image by subject motion or camera shake. Moreover, it is necessary to increase ISO if you only have a limited aperture to work with, or you want to close the aperture to get more depth of field (see below).

If you underexpose an image, you are essentially not using the dynamic range of the sensor completely, thus losing useful light range in your image. Some cameras, however, are able to switch to a different sensor technology for higher ISO which helps a bit.

The end effect is that you see an image which is correctly exposed, but has more noise. Now, modern cameras have a very large dynamic range. Moreover, there is clever noise reduction to cover the noise effectively with only minor loss in details. Thus, you should not be afraid to increase ISO within limits. Test this for yourself on your camera.

It is important to repeat that there might be good reasons to underexpose an image and help out with higher ISO. You may want a high aperture to get big depth of field, or you may want a fast shutter speed to freeze motion. In both cases, it is better to increase ISO than to get an unusable image. Also, hand-held images at night almost always require an increase in ISO.

Most cameras have an AUTO ISO setting which selects the ISO such that the image is correctly exposed. E.g., in aperture priority mode A the ISO will be increased if the shutter speed gets too low. In this case, camera shake might spoil the image. The photographer can set a limit for this increase, or specify how the focal length is weighted into the increase.

Exercises

• Which minimal ISO does your camera allow? Which maximal ISO is possible, and how do images look like with that ISO?
• Set the camera to manual mode M, and to ISO AUTO. Set a reasonable combination of shutter speed and apertures (such as 1/120 and f/8 at daylight) and watch how the ISO changes depending on the scene.
• Print high ISO images or watch them on large screens. See if you can see the increased noise.
• Learn how to set a limit to your AUTO ISO. 

Aperture

We now want to talk about the artistic aspects of the aperture. We already know that it determines the exposure.

Aperture is measured in f-stops. Most denote the apertures by f/2, f/2.8, f/4, f/5.6, f/8 etc. The fraction indicates that we can compute the diameter of the aperture by dividing the focal length by the aperture number. However, we just simply need to remember that f/2 is a very wide aperture, f/8 is a normal one, and f/32 is a very closed aperture. The f-stop determines the amount of light per area on the sensor. Going from f/2 to f/2.8 means doubling the light per area.

A lens can only focus on points in a specific distance. I.e., only points at that distance will appear exactly sharp on the sensor. Closer or wider points will appear blurred. We use that to isolate subjects from the background. 

There is an interval of distances, where the objects appear sharp enough. This is called the depth of field (DOF). It becomes larger with closer apertures. So, f/2 has a very shallow DOF and f/32 a very big one. It does also depend on the focus distance, the focal length and the sensor size.

Related to the DOF is the background blurriness in your image which is part of the so-called Bokeh. The way the background interferes with your subject is important to isolate subjects. 

• A wider aperture decreases the DOF and increases the background blurriness, and thus isolates the subject more. Note, that this means a smaller denominator in the f-stop, i.e., f/2 instead of f/8.
• A closer distance of the main subject makes a smaller DOF and more blurriness in the background. Macro shots can have very small areas of sharpness in the range of millimeters.
• A longer focal length can be used to blur the background. Adjusting the distance so that the subject has the same size in the frame yields almost the same DOF. But the background will look much nicer with the longer lens.
• A larger sensor allows a shallower DOF. Smartphone cameras with their tiny sensors tend to show everything sharp, and often isolate the subject by artificial blurriness only. 

There is a so-called crop factor which can be used to get equivalent f-stops for different sensor sizes. It helps to translate the DOF of f-stops for different cameras. It can also be used to translate the magnification effect of different focal lengths. APS-C cameras have a crop factor of around 1.5, so that f/4 on the APS-C is equivalent to f/6 on a film camera (also called full frame camera, FF).

Good photography uses the DOF in artistic ways. Sometimes, we want everything to be sharp, often we don't.

Exercises

• Look at your images and try to identify the DOF when printed or viewed at a large screen.
• Try vastly different apertures for a portraits and view the results. Which did you like best?
• If you have a modern smartphone, it may be able to blur the background in "portrait mode". Compare that to the results of a camera with a fast lens (say at f/2.8).

Shutter Speed

The choice of the shutter speed has also an artistic meaning besides the effect on the aperture. Shutter speed range from 1/4000 of a second to 30 seconds. The most natural choices are between 1/30 and 1/250. 

There is a practical reason to select a high shutter speed on hand-held photography. Camera shake can easily ruin the sharpness in an image. Today, many cameras have some sort of image stabilization (IS). It can be in the camera body (in body IBIS) by moving the sensor, or in the lens (optical OIS) by moving lens elements. The latter is more effective in the telephoto range. Without stabilization, a good rule is 1 over focal length. With stabilization, up to 6 stops (64 times) longer shutter times might be possible.

Now, here are some artistic considerations for the shutter speed.

• To freeze motion, you need very fast shutter speeds. It depends a bit on the length of the lens and the subject. As a guideline, use at least 1/200 for anything that moves, e.g., for kids. Sport action may even require 1/2000 and less. To achieve such short speeds with reasonable ISO settings, you need a fast lens, i.e., a lens with a wide maximal aperture. The problem is that you will then get small DOF. There is always a compromise to be made.
• To show motion you need a slow shutter speed. This is good for smoothing out water. You need more than 1/10 for this, and thus a tripod. Often the scene is too bright and you cannot shut your aperture enough at basic ISO. In this case, you need a gray density filter to darken the scene. Put to the extreme, you can smoothen the movement of clouds and get an effect that is called fine art by some photographers.

The author of these pages is a travel photographer and rarely does smooth water. Below is an attempt. I had to use a polarizer, because I had no gray density filter with me to manage the light with a reasonable f-stop, and only a tiny tripod.

Exercises

• Experiment with different shutter speeds on a running kid or dog. Be critical about the sharpness.
• Set the camera on a tripod or on a solid surface. Which long exposures can you take and still get a properly exposed image? Note, that f-stops beyond f/16 are usually avoided due to the diffraction which softens images.
• Take an image of a moving car or bicycle with a long exposure while panning the camera along with the subject. This should blur the background.
• Find a neutral density filter for you camera, and try really long exposures of waves or clouds. Even moving traffic might look nice, especially with lights.

RAW and JPEG

For a page like this, aimed at the technical aspects of photography, it is essential to talk about what happens to your image after they leave the sensor. You have two choices.

• JPEG output. JPEG is a standard format for images in the net and on computers. The format reduces the size necessary to store the image by compression, losing image data along the way. The conversion from the sensor data to JPEG is done by a processor inside the camera. You can change many aspects of this compression, such as sharpness, brightness, brilliance etc. You can even change the image size and format in camera. This kind of shooting is called out-of-camera photography (OOC).
• RAW output. This format contains all sensor data (or at least much more than JPEG) plus information on the lens used, the f-stop etc. The format is specific to the camera. However, there is now an effort for a standard RAW format, called DNG, which some cameras support. RAW is later converted on a computer by software like Lightroom, or free camera specific RAW converters.

Smartphones are using OOC almost exclusively. Only few smartphone photographers go through the effort of processing their images. It is usually not worth it. The high noise levels require aggressive noise reductions, and modern smartphones can do that very well. Also, the artificial blurring of backgrounds depends on additional sensors of the smartphone. It is best done in the smartphone. The results can be strikingly good, especially when viewed on the phone or printed at smaller sizes.

Exercises

• If you do not have Lightroom, consider learning this mighty editor and subscribing to a photography plan. It will also give you access to Photoshop and Lightroom Classic, which is the version I use on a desktop computer, an iPad and on a laptop. 
• I understand that you might want a cheaper alternatives. One option is to use the processing software that comes with your camera. It will be good enough for most purposes. You may have to download it from the home page of your camera maker. 
• There is als Darktable which clones Lightroom. It is a lot slower and misses some features or camera profiles, however.

Focal Length

The focal length of the lens is defined by the distance of a sharp point behind the lens which comes from incoming parallel rays, i.e. from points at infinity. It is denoted L in the image below.

The main purpose of knowing the focal length is that it determines the angle of view (AOV) of the lens. You get less with a telephoto lens and more with a wide-angle lens. I.e., a telephoto lens provides magnification.

• A focal length below 35mm is called wide-angle.
• Above 70mm the telephoto range starts.
• In between, we have the 50mm normal lens.

These numbers apply to film sized sensors of size 36mm times 24mm, so called full-frame sensors (FF). For smaller sensors, a so-called crop factor needs to be applied. E.g., on APS-C 35mm becomes equivalent to 50mm, and on Micro Four Thirds (MFT) 25mm become 50mm etc.

Of course, wide-angle lenses can be used "to get everything in", and telephoto lenses "to get the subject closer". But besides those practical reasons there are more important artistic reasons. Often, you have a choice to select the distance to your photographed subject.

• A wide-angle lens emphasizes objects in the foreground. It makes them appear larger relatively to the background, because you have to go closer. The best use is to show objects in their surroundings, but still with emphasis on the subject. The feeling of depth will be enhanced. It will also create more DOF. A room can appear to be larger than it actually is with a wide-angle lens.
• A telephoto lens compresses objects at different distances. So, the background will appear closer to objects, and objects at different distances will appear closer together. The reason is that you go further away from your subject. Since it will create much less DOF and show only a small part of the background, it is good for isolating, e.g., for portraits. A telephoto lens will remove the feeling depth in the image. A building can appear to stand closely to a far away mountain with such a lens.

The zoom lenses combine both options, but usually are no "fast" lenses, starting at f/4 or above. To isolate something from the background you may need other means, such as fog.

Exercises

• Do a portrait session with a zoom lens or different prime lenses at different appertures. Always keep the subject at the same size in the frame. Watch the effect on the background and DOF.
• Take an image of long street with houses with a wide angle and a telephoto lens. Can you generate the feeling of compression, making the houses look closer together?
• Get out on a sunny day with a 35mm lens or similar and f/8. Find a subject and try different composition to isolate the subject from the background.
• Do the same on a foggy morning.

Focusing

As already mentioned, only points at a specific distance can be focused sharply. To be precise, the sharp points are ideally on a plane perpendicular to the lens axis. Ideally only, because the plane is sometimes slightly curved ("field curvature"). Closer or further points are not sharp. The interval of distances where points are sufficiently sharp is called depth of field (DOF). We already explained how to use this to isolate subjects.

The distance of optimal sharpness is changed by positioning the lens or single lens elements forward or backward. There are several methods for the user to achieve the correct focussing. The details may depend on the camera, but we essentially have the following options.

• Manual focussing. This is usually done by turning a focussing ring on the lens. In modern cameras, the user can select a focus point. For feedback, this point changes the color or blinks if the spot is in focus. The number of available focus points depends on the camera. Modern mirrorless cameras can set this point almost everywhere on the screen. 
• Auto focus. In this case, the camera can select the focus point automatically, or focus automatically on a focus point set by the user. In any case, the camera will by default focus when the shutter is half pressed. Optionally, this can be transferred to a special button (back button focus - BBF). There are several methods to tell the camera where to put the focus point.
• Single Point Focus. This sets one specific spot. Usually, this method is the most precise, but slowest method.
• Area Autofocus. The camera will select a focus point in a specified area. Older cameras will simply select the closest point. Newer cameras may have more clever methods. The areas are usually available in several sizes, and can be moved.
• Eye or Object Autofocus. Most modern cameras and many smartphones can focus to faces and even single eyes in the scene or in a predefined area. This technique is available since some years and gets refined all the time. Now, cars, birds and insects and their eyes can be detected.

Many lenses and cameras can use manual override. After the camera has done its autofocusing, the user can turn the focus ring on the lens to change it. Often, this will enlarge the focused area or the details in focus will highlight in some bright color (focus peaking).

There is not only the problem of selecting the focus point. It is also important when to focus.

• Single Autofocus. This mode focusses once when the shutter is half pressed, or the dedicated AF button is pressed (BBF). It is good for static subjects. The user gets precise feedback in this mode.
• Continuous Autofocus. In this mode, the focus is adjusted starting from the activation of the auto focus until the shutter is released. This is good for moving subjects. The user feedback is not as precise as with single focussing, however. Modern cameras are quite good at determining the movement in advance. They can even change the focus point if necessary.
• Dynamic Area. Adjacent focus points can be selected if the subject leaves the main focus point.
• Tracking. The camera will track a subject through the scene. This puts a high demand on the computational capacities of the camera. It the most advanced technique available. Tracking might also be available in single autofocus and will select a focus point before the autofocussing even starts.

How these autofocus areas and modes are best used, should be a topic of another posting. To learn the best use of the camera, requires practice. In any case, focussing should be done without thinking much. Modern cameras with their automatic focusing and tracking modes are a huge assistance to the photographer.

Exercises

• Enable eye detection on your camera and see if it works in portraits. Can you change the eye in your camera? Can you switch the face in group shots?
• Learn the quickest way to change the focusing mode on your camera. Try to switch between auto area and single spot quickly.
• Learn if you camera has tracking and how to use it. You need to quickly disable and enable tracking or change the tracked subject.
• Learn the difference between continuous and single autofocus. See how your camera indicates successful focus. 
• Learn manual override by turning the focus ring after the camera has autofocused. If possible, enable focus peaking. 
• If you camera can do it, learn how to zoom in for precise focusing.
• Try back button focus by disabling the focus on the shutter and enabling focusing on a button in easy reach of your thumb.