The amount of light exposed to the image sensor is determined by the square area of the aperture as seen in the graphic below.

Note: A technical photogrammetry term that you may come across is the “Principal Distance”.  Strictly, the Principal Distance is the distance mentioned above (i.e. distance from imaging plane to the lens optical sensor), and the focal length is the principal distance when the lens is focused at infinity. See below for more information on focus vs focal length. When PhotoModeler lists focal length for a camera, it is actually the Principal Distance that is shown.

Lensfocus

There is also a maximum f-stop value for each lens, but it’s not listed since it doesn’t change the “speed” or how fast the lens can expose for a given scene.

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depthoffield中文

To compensate for these decreases in DOF the photographer can increase f-stop values or use methods such as focus stacking.

In many cases though, the advantages of using focus (i.e. crisp targets and distinct features) with subtle effects on principal distance/focal length, outweigh the advantages of keeping focus and principal distance constant (i.e. potentially causing blur in some photos taken at a different distance).

The focal length number tells us how much of the scene is captured in the picture. The lower the number the wider the view, and the more we can see.  The higher the number, the narrower the view, and the less we can see.   This is illustrated below – where the camera is stationary and the focal length (in white numerals) changes:

Sometimes it’s required to shoot at f/16 or f/22 to increase the shutter speed for long exposures or to increase the depth of field for very distant scenes.

Each camera lens has a minimum f-stop value, or widest aperture diameter, in which it can operate for any given focal length.

By selecting the correct focal point location and f-stop settings, the photographer controls the depth of field for each image.

Depth of field is defined as the distance between the closest and furthest objects within a composition, both of which are in focus.

Depthof field

The focal length range for this specific lens is labeled in gold letters as 28-300mm, seen just above the “AF-S NIKKOR” label.

For ISO, exposure stops provide the increase or decrease in signal (light information) amplification, thus how much light is required to produce the optimal exposure.

Shallow depthof field

A strict technical definition of focal length is difficult without providing a lot of background in lens theory, so we will use a simplification. You can think of focal length as the distance between the imaging plane (e.g. the image chip in a digital camera) and a point where all light rays intersect inside the lens (the ‘optical center’). So a focal length of 20mm means that the distance from the optical center to the imaging plane is 20mm long (about ¾ of an inch). What does the focal length number mean?

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Cameras can have fixed lenses (sometimes called ‘prime’ lenses) which have just one focal length, or zoom lenses which allow the focal length to be varied (for example between 18mm-55mm, or 55mm-200mm). For high accuracy photogrammetric work in PhotoModeler, a fixed (or prime) wide lens (such as a 20mm lens on an APS-C frame camera) is recommended as the primary option, but different applications may require different focal lengths, and cameras with adjustable zoom lenses can still be used to achieve very good results with some extra procedural care over the focal length.

The range of f/3.5 to f/4.5 provides the minimum f-stop values (widest aperture diameters), that this specific lens can maintain while shooting at the minimum and maximum focal lengths, respectively.

For example, Shooting at an f-stop of f/1.4 provides a 314 square millimeter opening for light to enter the lens as seen in the Aperture Area Column.

Depthof fieldcalculator

Let’s get started… Table of Contents Depth of Field Photography VideoDepth of Field Photography BasicsCamera Lens Basics for Depth of FieldExposure Stops & Depth of FieldExample Photos & Camera SettingsSelecting the Correct F-Stop & Depth of FieldHow to 10X Your Learning Speed Depth of Field Photography Video Watch this video to learn the best f-stop settings to maximize depth of field and image sharpness. Next, read the guide to dial in your camera technique. Depth of Field Photography Basics In photography, aperture diameter, determined by f-stop, controls two important factors: Depth of Field (DOF) determines the closest and farthest objects in an image, both of which are in focus. The entire image between these objects also maintains sharp focus. Amount of Light exposed to the image sensor, which controls the image brightness, rated in stops. Mastering depth of field requires a basic understanding of f-stop, focal length, focus range, and camera lenses. We will quickly cover these first. What is Aperture in Photography? The terms f-stop and aperture are often used interchangeably, this is incorrect. Aperture is the opening in the front of the lens where light enters the camera. F-stop is the ratio of lens focal length to aperture diameter. F-stop is a dimensionless number, denoted by a hooked “ f ”, with an underlying number denoting the f-stop value. f/2.8 and f/8 are two examples of common f-stop settings, where 2.8 & 8 are the f-stop values, respectively. F-Stop  = Lens Focal Length (mm) / Aperture Diameter (mm) The aperture diameter is the straight distance across the widest part of the aperture. The focal length of the lens determines your field of view (composition) and the magnification of the scene. The graphic shows increasing f-stop values with decreasing aperture diameters. Attribution – Wikipedia If the lens focal length is 20mm and the aperture diameter is 10mm, then f-stop = 20mm/10mm = 2. This is denoted as f/2. The photographer controls the f-stop, which determines the depth of field and how much light enters the lens. The larger the f-stop value, the less light enters the lens, over a set exposure time. The smaller the f-stop value, the more light enters the lens, over a set exposure time. What is Depth of Field in Photography? Depth of Focus vs Depth of Field (DOF) – To clear up any confusion, these terms mean the same thing. They can be used interchangeably with focus range and DOF. Depth of field is defined as the distance between the closest and furthest objects within a composition, both of which are in focus. All objects between the closest and furthest objects are also in focus. By adjusting the f-stop, the photographer controls the depth of field. Smaller f-stop value = larger aperture diameter = smaller DOF Larger f-stop value = smaller aperture diameter = larger DOF The following examples show small or shallow depth of field vs large or deep depth of field. The first photo was taken at f/5.6 and the second was captured at f/16. Photographed at f/5.6 The red lines show the closest and furthest objects that are in focus. Notice how everything between these lines is also in focus. The red box denotes the focal point within the image. This is the location that I focused on to take the shots. The focal point always lies within the focal range or depth of field. Photographed at f/16 In the images above, the focal point, denoted by the red box, stays at approximately the same location. The depth of field or focus range extends beyond the focal point, as the f-stop increases from f/5.6 to f/16. Here is another example of two landscape photos showing varying depths of field. The first example below shows a deep also known as large depth of field. Everything in the entire image, foreground to background is in focus. Large Depth of Field @ f/8 The second image shows a shallow depth of field example. Only the subject is in focus, while the foreground and background are not in focus. The focus range is very shallow providing a small depth of field. Shallow Depth of Field @ f/4 What is Focal Length in Photography? The lens focal length, selected by the photographer, determines the field of view (FOV) The field of view defines your composition. It’s everything seen for a selected focal length. The larger your focal length, the smaller the field of view becomes & vice versa. Focal length also determines the depth of field, as we will cover below. Example Images – Focal Length & Field of View When the focal length increases, the field of view decreases, and the subjects in the image become magnified. 14mm Focal Length 24mm Focal Length 80mm Focal Length Camera Lens Basics for Depth of Field Prior to selecting the correct f-stop & focal length settings, producing the desired depth of field, the basics of a camera lens must be understood. Different Types of Camera Lenses Human vision is approximately 50mm focal length. Focal lengths larger than approximately 50mm will magnify the composition. Focal lengths less than 50mm are denoted as “wide-angle”. Wide Angle Lenses produce a field of view larger than our standard vision & usually range from 8mm to 35mm in focal length. Standard Lenses produce a field of view similar to our standard vision & usually range from 40mm to 60mm in focal length. Telephoto Lenses produce a field of view smaller than our standard vision & usually exceed 70mm in focal length. Camera Lens Focal Lengths The 28-300mm lens shown in the graphic below has a focal length range of 28mm to 300mm. This is denoted as a wide-angle telephoto lens since it covers above & below 50mm focal length. The focal length range for this specific lens is labeled in gold letters as 28-300mm, seen just above the “AF-S NIKKOR” label. The photographer can select any focal length, within the focal length range. This is what determines the composition. The white dot on the lens above shows the currently selected focal length of 28mm. The 14-24mm lens, shown below, is known as a wide-angle lens. It covers fields of view greater than what the human eye can see. The smaller the focal length the “wider” the field of view. Crop Factors & Focal Lengths Cameras with crop factors above or below 1 change the field of view and focal length. Using your camera’s crop factor an effective focal length can be calculated. A full-frame sensor has a crop factor of 1. A 28-300mm lens used on a 1.6 crop factor camera would have an effective focal length range of 45mm – 480mm, calculated as follows: ( 28mm X 1.6 ) – (300mm X 1.6 ). The following image was taken on a full-frame camera with a crop factor of 1. The same image taken at 14mm on a 1.6 crop factor camera would look like it was taken on a 22mm lens (14 X 1.6) The red box shows what this composition would look like on a 1.6 crop factor camera. Camera Lens F-Stop Values Each camera lens has a minimum f-stop value, or widest aperture diameter, in which it can operate for any given focal length. Most lenses are designed so the minimum f-stop value increases as the focal length increases. The lens label shows the focal length range to be 18-35mm in the example below. The photographer can shoot at any focal length, in the range of 18-35mm, producing their desired field of view. Following the focal length range is the minimum f-stop range of f/3.5 to f/4.5, noted on this lens and most others as 1:3.5-4.5. The range of f/3.5 to f/4.5 provides the minimum f-stop values (widest aperture diameters), that this specific lens can maintain while shooting at the minimum and maximum focal lengths, respectively. For example, the minimum f-stop value this lens can maintain is f/3.5 while shooting at 18mm. As the focal length increases, from 18mm to 35mm, the minimum f-stop also increases, until it reaches f/4.5 at 35mm. All focal lengths between 18mm and 35mm will have minimum f-stop values ranging from f/3.5 to f/4.5. You can always increase the f-stop to larger values. The noted values are only the minimums. Lens Speed, Explained The lens speed refers to the minimum f-stop value a lens can shoot at for any focal length. As the focal length increases, from 18mm to 35mm, on the lens above, the aperture diameter becomes smaller, reducing the f-stop from f/3.5 to f/4.5. To capture the same amount of light from the scene, as the focal length increases, the shutter speed would also have to become longer. The “faster” the lens, the lower the f-stop value it can maintain over its entire focal length range. Lens Speed Example Looking at the 14-24mm f/2.8 wide-angle lens above, there is a single minimum f-stop value given of 1:2.8. This means that this lens can maintain f/2.8 minimum f-stop value no matter the focal length. Lenses like this are much more expensive because they require more glass and better engineering to produce. There is also a maximum f-stop value for each lens, but it’s not listed since it doesn’t change the “speed” or how fast the lens can expose for a given scene. Exposure Stops & Depth of Field An exposure stop, or stop for short, is a scale to measure the change in light, exposed to the image sensor, due to different exposure settings such as f-stop and shutter speed. For ISO, exposure stops provide the increase or decrease in signal (light information) amplification, thus how much light is required to produce the optimal exposure. Stops provide an easy way to balance the exposure triangle while changing settings. Click Here & Download the chart as a PDF to reference while reading. The Stops Column shows the difference in stops between different f-stop values. The F-Stop Value Column shows different standard f-stops in 1 stop intervals. Each change in stops doesn’t correlate to a specific f-stop value. Stops show you how much light is captured from one f-stop setting to the next. This makes it easy to maintain the correct exposure when changing settings.f Increasing the f-stop, thus producing a smaller aperture diameter, forces the image sensor to collect less light information, producing a darker image, with increased depth of field. By increasing the f-stop value, the aperture diameter gets smaller. Doing so produces an increased depth of field, and a darker image if no other settings are changed. This is known as stopping down.  Decreasing the f-stop, thus producing a larger aperture diameter, allows the image sensor to collect more light information, producing a brighter image, with a decreased depth of field. By decreasing the f-stop settings the aperture diameter gets bigger. Doing so produces a decreased depth of field, and the image gets brighter if no other settings are changed. This is known as stopping up.  Depth of Field & Exposure Stop Examples In the following examples, ISO and shutter speed are constant. Only f-stop changes in 1 stop increments. The first example was taken at f/11, followed by f/8, f/5.6, and f/4. The focal point stays the same for each of the images. As the f-stop becomes smaller, by 1 stop at a time, the image gets brighter, but the depth of field decreases. Notice how the sharpness in the bottom of each image drops off as the f-stop decreases. This shows the depth of field becoming smaller and smaller. Settings: f/11, ISO100, 1/5th second  Settings: f/8, ISO100, 1/5th second Settings: f/5.6, ISO100, 1/5th second Settings: f/4, ISO100, 1/5th second If you wanted to maintain constant exposure (image brightness), while changing the f-stop values, then changes in ISO or shutter speed would have to be made in the opposite direction. Exposure Stops & Aperture Diameter Example The amount of light exposed to the image sensor is determined by the square area of the aperture as seen in the graphic below. Aperture Area = Pi*(Aperture Radius^2) For example, Shooting at an f-stop of f/1.4 provides a 314 square millimeter opening for light to enter the lens as seen in the Aperture Area Column. Shooting at f/2.8 and 28mm provides a 79 square millimeter aperture area. If you changed from f/2.8 to f/5.6, this reduces the area by half, thus reducing the amount of light in the exposure by half. Using exposure stops keeps you from having to do these calculations each time! Shooting Example – Aperture & Exposure Stops Imagine taking an image at f/16 and thinking that it was way too dark. Taken at f/16 Next, you thought, “If this picture was 2 times as bright it would be perfect.”. Changing the settings by one stop, from f/16 to f/11 would provide double the amount of light. Instead of having to guess you just reference the exposure stops chart and made the change. Taken at f/11 Example Photos & Camera Settings Depth of Field is controlled by three factors, each shown with example photos below. Focal Point & Depth of Field The focus point or focal point controls the location of the focal range within the image. I prefer to control this focus point manually, using back button focus. Each image below was captured at f/5.6. The focus point moves, but all other settings stay the same. The focal range is denoted by horizontal red lines. The red box denotes the focus point. In the following image, all settings remain the same. The focus point moves to the middle of the image, shifting the focal range. The focal point is shifted to the back of the image, below, moving the focal range with it. By selecting the correct focal point location and f-stop settings, the photographer controls the depth of field for each image. F-Stop & Depth of Field The following examples show different image attributes correlate to varying f-stop values and depth of field. An image attribute is a specific visual effect obtained from varying camera settings such as f-stop, ISO & shutter speed. In this case, we will look at visual image attributes determined by f-stop, providing varying depths of field. As the f-stop value increases, the aperture diameter decreases, allowing less light into the camera while increasing the depth of field. As the f-stop value decreases, the aperture diameter increases, allowing more light into the camera while decreasing the depth of field. Small F-Stop Values & Image Attributes The following image has a very shallow depth of field, taken at f/1.4. When isolating a subject this is a great setting to use. Using this f-stop during the day requires a very fast shutter speed making it great for action shots. Taken at f/1.4 Shooting at slightly larger f-stop values such as f/2.8 provides the same effect with a slightly larger depth of field, as shown in the following example. Increasing to f/2.8 the same effect can be seen, but the depth of field starts to increase. Shooting at f/2.8 is my favorite setting for star photography. Taken at  f/2.8 Shooting at f/4 or f/5.6 can be great for action shots where there is a subject and some interesting detail in the background. The following image is in sharp focus for the person, but slightly out of focus for the background. This still allows you to see the background, but it’s not the center of attention. Taken at f/5.6 Mid-Range F-Stop Values & Image Attributes F-stop values of f/8 to f/11 are ideal for landscape photography. They provide a sharp focus from foreground to background. I shoot at these settings for 99% of my landscape photos. Taken at  f/11 Large F-Stop Values &  Image Attributes Sometimes it’s required to shoot at f/16 or f/22 to increase the shutter speed for long exposures or to increase the depth of field for very distant scenes. By shooting at f/16 the amount of light entering the lens is reduced, requiring a longer shutter speed. This is great for long exposures at sunrise and sunset. Taken at  f/16 Shooting at f/22 degrades image quality due to lens diffraction but provides a sun star due to the optics of the lens. I only recommend shooting at f/22 when you want the sun star effect. Taken at f/22 Taken at f/22 Focal Length & Depth of Field When the focal length gets larger, the scene becomes more magnified. This causes the depth of field to decrease. The opposite also is true when the focal length decreases. When shooting at 10mm all the way to 100mm it’s almost impossible to see these changes. When you start shooting in the 100mm or greater range, then these effects start to become very apparent. To compensate for these decreases in DOF the photographer can increase f-stop values or use methods such as focus stacking. Example Photos: Depth of Field Vs. Focal Length The first example below shows an image taken at f/9 & 145mm effective focal length. Even at f/9 the background is out of focus. Due to the increased focal length, the depth of field decreased. If this image was taken at 50mm instead of 145mm, f/9 would have provided sharp focus over the entire depth of field. The next example shows an image taken at f/11 and 250mm effective focal length. At first glance, it may appear to be focused throughout the entire depth of field. Looking at the bottom-righthand corner, the image sharpness starts to degrade significantly. This is due to the decreased depth of field from increased focal length. To compensate for this issue the f-stop value could be increased to f/16, slightly extending the depth of field. Selecting the Correct F-Stop & Depth of Field All of the information above provides the foundation for selecting the best camera settings using the Photography Exposure Triangle. To correctly select the best f-stop and depth of field a firm understanding in shutter speed & ISO are required. First learn the main 3 settings, f-stop, shutter speed, and ISO. Then continue on to the Photography Exposure Triangle Guide, for complete details on combining all of the settings. How to 10X Your Learning Speed The best way to improve quickly is by learning firsthand from someone that’s optimized their skills, over a decade or more through trial and error. You can’t read blogs and watch internet videos to do this. I offer workshops & tours for all skill, fitness, and age levels. Over a 3-day weekend, I can teach you everything I know, plus provide 1 on 1 feedback that will quickly improve your skills. I’ve seen students learn more in a 3-day trip than they have in 20 years of trying to learn on their own. Check out my workshops & tours, right here.

Above we mention that focal length is related to focus distance.  Focal length is the principal distance of a camera when it is focused at infinity. In photogrammetry we are interested in the camera’s internal geometry at the time photos were taken – so it is the principal distance that we want to know precisely in photogrammetry.

An image attribute is a specific visual effect obtained from varying camera settings such as f-stop, ISO & shutter speed.

PhotoModeler is one of the leading tools for photogrammetry (the science of generating measurements and accurate 3d data from photography).

An exposure stop, or stop for short, is a scale to measure the change in light, exposed to the image sensor, due to different exposure settings such as f-stop and shutter speed.

Increasing the f-stop, thus producing a smaller aperture diameter, forces the image sensor to collect less light information, producing a darker image, with increased depth of field.

A 28-300mm lens used on a 1.6 crop factor camera would have an effective focal length range of 45mm – 480mm, calculated as follows: ( 28mm X 1.6 ) – (300mm X 1.6 ).

Decreasing the f-stop, thus producing a larger aperture diameter, allows the image sensor to collect more light information, producing a brighter image, with a decreased depth of field.

DOF simulator

Depthof focus

A camera typically has focal length in a range of 10mm to 500mm.  Different types of camera can have different ranges and speciality lenses can extend outside this range as well.  A 10mm focal length would be a very wide lens (capturing a lot of the scene), and 500mm would be a very narrow lens (capturing only a small part of the scene – giving a large magnification like binoculars or a telescope).

If you changed from f/2.8 to f/5.6, this reduces the area by half, thus reducing the amount of light in the exposure by half.

All lenses have a stated or specified focal length value (or range of values for a zoom lens). This printed number is actually its nominal length or the principal distance when the lens is focused at infinity. As you focus on objects that are closer to the camera, the principal distance changes.  So for example, a 50mm lens focused on an object a few feet away might have a principal distance of 55mm lens at that time. The most extreme example of this is with a macro setting (a lens setting that allows you to focus on very close, very small objects, under 5″ in size for example). A lens that has a 50mm nominal focal length (so a 50mm principal distance when focused at infinity) might in fact have a 100mm principal distance when focused at a few inches! This is why it is good with photogrammetry (where precise geometry is needed) to calibrate a camera at the distance you will be working with.

Shooting at f/4 or f/5.6 can be great for action shots where there is a subject and some interesting detail in the background.

There is some ability to calibrate a camera (which solves the principal distance) at one focus and execute your photogrammetric project at another focus.  The actual discrepancy that is acceptable depends on your accuracy requirements and how much the focus changes.  Generally a calibration done at 2m/6ft focus distance is acceptable for projects up to infinite focus (again depending on accuracy requirements), but may not be acceptable for a project where the focus distance was 50cm/20in.

Prior to selecting the correct f-stop & focal length settings, producing the desired depth of field, the basics of a camera lens must be understood.

Exposure Stops & Aperture Diameter Example The amount of light exposed to the image sensor is determined by the square area of the aperture as seen in the graphic below. Aperture Area = Pi*(Aperture Radius^2) For example, Shooting at an f-stop of f/1.4 provides a 314 square millimeter opening for light to enter the lens as seen in the Aperture Area Column. Shooting at f/2.8 and 28mm provides a 79 square millimeter aperture area. If you changed from f/2.8 to f/5.6, this reduces the area by half, thus reducing the amount of light in the exposure by half. Using exposure stops keeps you from having to do these calculations each time! Shooting Example – Aperture & Exposure Stops Imagine taking an image at f/16 and thinking that it was way too dark. Taken at f/16 Next, you thought, “If this picture was 2 times as bright it would be perfect.”. Changing the settings by one stop, from f/16 to f/11 would provide double the amount of light. Instead of having to guess you just reference the exposure stops chart and made the change. Taken at f/11 Example Photos & Camera Settings Depth of Field is controlled by three factors, each shown with example photos below. Focal Point & Depth of Field The focus point or focal point controls the location of the focal range within the image. I prefer to control this focus point manually, using back button focus. Each image below was captured at f/5.6. The focus point moves, but all other settings stay the same. The focal range is denoted by horizontal red lines. The red box denotes the focus point. In the following image, all settings remain the same. The focus point moves to the middle of the image, shifting the focal range. The focal point is shifted to the back of the image, below, moving the focal range with it. By selecting the correct focal point location and f-stop settings, the photographer controls the depth of field for each image. F-Stop & Depth of Field The following examples show different image attributes correlate to varying f-stop values and depth of field. An image attribute is a specific visual effect obtained from varying camera settings such as f-stop, ISO & shutter speed. In this case, we will look at visual image attributes determined by f-stop, providing varying depths of field. As the f-stop value increases, the aperture diameter decreases, allowing less light into the camera while increasing the depth of field. As the f-stop value decreases, the aperture diameter increases, allowing more light into the camera while decreasing the depth of field. Small F-Stop Values & Image Attributes The following image has a very shallow depth of field, taken at f/1.4. When isolating a subject this is a great setting to use. Using this f-stop during the day requires a very fast shutter speed making it great for action shots. Taken at f/1.4 Shooting at slightly larger f-stop values such as f/2.8 provides the same effect with a slightly larger depth of field, as shown in the following example. Increasing to f/2.8 the same effect can be seen, but the depth of field starts to increase. Shooting at f/2.8 is my favorite setting for star photography. Taken at  f/2.8 Shooting at f/4 or f/5.6 can be great for action shots where there is a subject and some interesting detail in the background. The following image is in sharp focus for the person, but slightly out of focus for the background. This still allows you to see the background, but it’s not the center of attention. Taken at f/5.6 Mid-Range F-Stop Values & Image Attributes F-stop values of f/8 to f/11 are ideal for landscape photography. They provide a sharp focus from foreground to background. I shoot at these settings for 99% of my landscape photos. Taken at  f/11 Large F-Stop Values &  Image Attributes Sometimes it’s required to shoot at f/16 or f/22 to increase the shutter speed for long exposures or to increase the depth of field for very distant scenes. By shooting at f/16 the amount of light entering the lens is reduced, requiring a longer shutter speed. This is great for long exposures at sunrise and sunset. Taken at  f/16 Shooting at f/22 degrades image quality due to lens diffraction but provides a sun star due to the optics of the lens. I only recommend shooting at f/22 when you want the sun star effect. Taken at f/22 Taken at f/22 Focal Length & Depth of Field When the focal length gets larger, the scene becomes more magnified. This causes the depth of field to decrease. The opposite also is true when the focal length decreases. When shooting at 10mm all the way to 100mm it’s almost impossible to see these changes. When you start shooting in the 100mm or greater range, then these effects start to become very apparent. To compensate for these decreases in DOF the photographer can increase f-stop values or use methods such as focus stacking. Example Photos: Depth of Field Vs. Focal Length The first example below shows an image taken at f/9 & 145mm effective focal length. Even at f/9 the background is out of focus. Due to the increased focal length, the depth of field decreased. If this image was taken at 50mm instead of 145mm, f/9 would have provided sharp focus over the entire depth of field. The next example shows an image taken at f/11 and 250mm effective focal length. At first glance, it may appear to be focused throughout the entire depth of field. Looking at the bottom-righthand corner, the image sharpness starts to degrade significantly. This is due to the decreased depth of field from increased focal length. To compensate for this issue the f-stop value could be increased to f/16, slightly extending the depth of field. Selecting the Correct F-Stop & Depth of Field All of the information above provides the foundation for selecting the best camera settings using the Photography Exposure Triangle. To correctly select the best f-stop and depth of field a firm understanding in shutter speed & ISO are required. First learn the main 3 settings, f-stop, shutter speed, and ISO. Then continue on to the Photography Exposure Triangle Guide, for complete details on combining all of the settings. How to 10X Your Learning Speed The best way to improve quickly is by learning firsthand from someone that’s optimized their skills, over a decade or more through trial and error. You can’t read blogs and watch internet videos to do this. I offer workshops & tours for all skill, fitness, and age levels. Over a 3-day weekend, I can teach you everything I know, plus provide 1 on 1 feedback that will quickly improve your skills. I’ve seen students learn more in a 3-day trip than they have in 20 years of trying to learn on their own. Check out my workshops & tours, right here.

Camera manufacturers sometimes list these equivalents because some photographers are more familiar with 35mm cameras and they want to make it easier to understand. It also gives us a standard of reference for all the different format sizes. They may also list the multiplier factor. For example, the APS-C multiplier is around 1.6x.  So a 32mm lens on an APS-C camera (like the Nikon D3200) would act like a 50mm lens on a 35mm film camera. Does focusing affect the focal length?

Shallowfocus

Following the focal length range is the minimum f-stop range of f/3.5 to f/4.5, noted on this lens and most others as 1:3.5-4.5.

All of the information above provides the foundation for selecting the best camera settings using the Photography Exposure Triangle.

Shooting at slightly larger f-stop values such as f/2.8 provides the same effect with a slightly larger depth of field, as shown in the following example.

To capture the same amount of light from the scene, as the focal length increases, the shutter speed would also have to become longer.

Focal length is a number that is vital to photography and photogrammetry but often misunderstood. What is focal length?

When you buy a digital camera you will often see the specification “equivalent 35mm focal length”. What does this mean? Most digital cameras have imaging chips that cover much less area than a standard 35mm film frame. Since 35mm film cameras were the standard for so long in photography, much of the techniques and methods were developed around them. A 35mm film camera has a negative that is about 36mm wide by 24mm high (the “35” comes from the physical width of the film stock that is exactly 35mm wide).  A ‘normal lens’ (has a field of view that appears ‘natural’ to humans) on a 35mm film camera has a focal length of 50mm.

Let’s say you take a picture of an automobile with two cameras, a 35mm film camera and a smartphone camera. You stand in the same spot and take two photos, one with each camera. In both cases you want to take a photo of the automobile that fills the frame. If the 35mm film camera lens has a 50mm focal length, the digital camera’s focal length might be 4mm. So even though they are very different numbers they produce the same result because of the size of the imaging surface. So the “equivalent 35mm focal length” for this smartphone camera at 4mm is 50mm.

Modern digital cameras can have imaging chips that are as small as 6mm by 4mm; some Smartphone cameras are even smaller, and then up to full 24mm by 35mm size.  A very common size is the APS-C format at 16mm by 24mm. This smaller size affects what is considered to be a ‘normal’ focal length.

If you wanted to maintain constant exposure (image brightness), while changing the f-stop values, then changes in ISO or shutter speed would have to be made in the opposite direction.

As the focal length increases, from 18mm to 35mm, on the lens above, the aperture diameter becomes smaller, reducing the f-stop from f/3.5 to f/4.5.