It is finally time to explore everything you never wanted to know about Depth of Field (DOF) in this final post of the “Photography Guide to Sharper Photo’s” series. In fact, proper use of depth of field is one of the best ways to set your photography apart from casual and beginner photographers.
Let’s begin this discussion with a look at some key definitions so we can eliminate some of the confusion surrounding DOF calculations. Make no mistake, this is a bit complicated. Thankfully, once the definitions are understood, it becomes easy to use DOF apps such as PhotoPills or The Photographer’s Ephemeris to produce perfectly sharp images.
What is Depth of Field?
Depth of Field is the area in an image that is in acceptable focus. This area can be a very small area around a specific subject or a large area that extends from the foreground to the background of an image.
Shallow Depth of Field– When an image is said to have a shallow depth of field it typically means the main subject is in focus such as the roseate spoonbill below and everything else is blurred. This is a great technique for separating subjects from their backgrounds regardless if it is a bird, animal, building or a person.
Wide /Large Depth of Field – A large DOF means that an acceptable portion of the foreground to background area in an image is in focus. Clicking on my lake image, you will see that the rocks in the foreground to the distance mountain are in focus. Maximum DOF is great when you want to include multiple layers in a scene as one would do when photographing a grand landscape.
What is Hyperfocal Distance?
This is the closest point you can focus in a scene to produce the maximum DOF possible.
- Hyperfocal Distance points vary based on sensor size, aperture settings and lens. Let me again stress how important it is to remember that this distance varies based with all three of these factors.
- Any Hyperfocal Point is only a guide for where to focus in a scene as you will see in the examples that follow. In fact, I firmly believe that there is no substitute for a photographer’s assessment of a scene in order to achieve a vision for an image.
What is Minimum Focal Distance?
- This is the shortest distance from the camera that a lens is capable of focusing on an object.
- To identify your specific gear’s Minimum Focal Distance, be sure to check your lens manuals.
- Be aware that the Minimum Focal Distance is usually not the same distance at the Near Limit Distance based on a Hyperfocal Distance. Yes I know this seems clear as mud but stay with me to see the examples and it will begin to make sense.
- Photographer is using a full sensor camera and a 100mm lens
- The subject is 20 feet from the camera
- Birds begin to appear in the scene at 3 feet and
- The last object in the scene, a shopping cart, is 27 feet from the camera
The first object to be in focus under the above example are the birds that are at 4 feet from the camera. However, since the Minimum Focal Distance of the 100mm lens is 4 feet, the bird at 3 feet from the camera will be out of focus.
How many of you have focused on a subject in a scene thinking you did everything right only to have foreground objects out of focus such as flowers or tree limbs? If your answer is yes, the reason could be that foreground objects were closer than the Minimum Focal Distance of a given lens.
I hope this example helps you understand why it is so important to know the Minimum Focal Distance of your lens. Equipped with the knowledge, one can either move back (in this case a foot) or recompose the scene to eliminate out of focus foregrounds.
No changes to the Hyperfocal Distance with shorten the Minimum Focal distance of a lens. In other words, no matter where you focus in a scene, any objects closer to the camera than the Minimum Focal Distance will always be out of focus.
Next-How DOF and Hyperfocal Distance Work Together?
Now with an awareness of Minimum Focal Distance, let’s explore how to calculate a Hyperfocal Distance point that produces maximum DOF. For this we will use the Photopills app. (I have no affiliation but love this app) Warning- Photopills can be an intimidating app initially so start slowing by getting familiar with only the DOF calculator. To check out all the apps I use when planning photo shoots see: Great Apps for Landscape and Travel Photography Planning.
PhotoPill DOF Calculator Examples:
In the following examples, my DOF calculations were made with the following inputs:
- a full sensor camera,
- an aperture of F/11
- a subject distance of 20 feet.
- Identification of a focal point that would provide the maximum DOF for each lens.
All factors were then applied to a 17mm lens, a 50mm lens, and a 100mm lens. Comparing the three results below, it is easy to see how changing lens dramatically impacts both the Hyperfocal Distance as well as the DOF in an image.
Before we look at the charts, let’s go over some additional key definitions:
- Near Limit: This is the distance from the camera to the nearest object in a scene that will appear sharp when the camera is focused on a Hyperfocal Distance that produces the maximum DOF. Do not confuse this with the Minimum Focal Distance.
- The difference between these two numbers is that the Minimum Focal Distance is dependent on a specific lens.
- The Near Limit is determined based on the specific point where the camera is focused in a scene. For example:
17mm lens Near Limit in below example is 2.46 feet
17mm lens Minimum Focal Distance is about 11 inches.
- Far Limit: This is the distance from the camera to the farthest object in a scene that will appear sharp.
- Total: Is the total number of feet that will appear sharp from Near Limit to Far Limit. All factors are based on camera, lens and aperture selections.
In the example below photographing with a 17mm lens, the calculator determines that
- A Hyperfocal Distance of 2.85 feet from the camera will produce the greatest Depth of Field in an image.
- The closest point from the camera that will be in focus, Near Limit, is 2.46 feet.
- Any objects closer to the camera than 2.46 feet will begin to lose sharpness.
- The Far Limit of focus for this set up is infinity.
Next I entered a 50mm lens in the table.
- The Hyperfocal Distance changed from 2.85 feet to 24.3 feet.
- The Near Limit of where everything from the camera will be in focus is now 11 feet and
- The Far Limit is no longer infinity but 111.6 feet from the camera.
So what does all this mean when out in the field?
Well let’s again look at the example of birds, a woman and a shopping cart using a 50mm lens. The Hyperfocal Distance is 24 feet as noted by the red line and the Near Limit is now 11 feet. Those birds in the foreground at 4 feet will now be out of focus while the shopping cart remains in focus.
- Objects closer than 11 feet may not have an acceptable level of sharpness.
- Objects farther away than 111.6 feet will begin to appear out of focus.
- Since my subject is 20 feet from the camera, my subject; the person, will be in focus.
Lastly, I changed lens again to a 100mm lens which produced a new Hyper-focal Distance of 97 feet.
Now we have a problem keeping the subject in focus. How can we focus at 97 feet with a total DOF of only 8.49 feet and have a subject 20 feet away be in focus? Well we can’t so now it’s time for choices. Remember, the Hyperfocal Distance indicates where to focus for maximum depth of field, not the near focus point. We can always sacrifice some DOF for subject focus.
In the table below, the Near Limit is 16.6 feet so our subject can still be in focus as long as we are willing to sacrifice some DOF. Also I should point out that this is a good time to look at the Minimum Focus Distance of a given lens as it compared to the Near Limit. Let’s assume the Minimum Focus Distance of a 100mm lens is a little over 4 feet, as you can see the Near Limit below is 16.6 feet.
- I can sacrifice maximum DOF and change my focal point so that my subject is in focus.
- I can move back from my subject.
- I can change lens.
- I can change apertures
- I can make a combination for changes to subject distance, lens and aperture settings to achieve maximum DOF.
I ruined many photos with out of focus subjects before I understood how to properly apply DOF in conjunction with the Hyperfocal Point to my compositions. I hope the above examples helps you avoid the same pitfalls.
I should point out the of course with Live View, it is much easier to know if your subject is in focus. However, without going through the above calculations, I do not believe it is possible to fully appreciate the focus decision implications on an image.
What is Infinity?
Infinity is not infinity but the maximum focal distance of a given lens at a specific aperture as illustrated in the above table calculations. Using the 100mm lens example again, the Depth of Field of only 8.49 feet is a far cry from infinity. Always be aware of the Near and Far Limits of every lens when photographing a scene.
- Depth of Field is the total distance within a scene that is in acceptable focus.
- Hyperfocal Distance is the focus location from the camera sensor that will produce the maximum depth of field in an image.
- Near Limit is the closest distance from the camera that an object will appear sharp based on a given lens when focused at the Hyperfocal Point.
- Far Limit is the farthest distance from the camera that an object will appear sharp based on a specific Hyperfocal Point.
- Minimum Focal Distance is the closest distance from the camera that a lens is capable of focusing on a subject. This distance is irregardless of the Hyperfocal Distance.
What is Circle of Confusion?
Since I promised no formulas, I will try to explain this term as simply as possibly. Circle of Confusion refers to the amount of tolerance our eyes/brain have between objects that are sharp to where we begin to notice objects are out of focus.
For example, if I photographed four cats with a focal point on one of the cats, only the cat with the focal point is perfectly sharp. Two adjacent cats may appear sharp because their lack of sharpness is not perceptible to the human eye. The last cat may be noticeably out of focus. The area between the three cats that appear in focus and the last cat that is out of focus is called the Circle of Confusion. Obviously this is a very dumbed down explanation but I hope it at least sheds a bit of light on Circle of Confusion.
How Lens impact DOF (just a brief overview)
Wide Angle Lens-
- Can focus on objects very close to camera,
- Have the greatest DOF
Normal lens- 35-70mm.
- Focus on objects relatively close to camera
- Good DOF
Telephoto lens- 70-300
- Objects need to be a distance from the camera to be in focus
- Shallow DOF so backgrounds will not be in focus even at small apertures.
Super telephoto lens 400mm or greater
- These lens can not focus on objects close to the camera and need to be quite a distance from the foreground subjects for objects to be in focus
- Extremely shallow DOF
DOF is a very complex issue that involves more factors than I addressed in this post. The goal of this post was to provide an introduction to the process of calculating DOF in the field. For those of you who would like to delve deeper into this topic, I recommend the following two sites: http://www.dofmaster.com/index.html and https://www.photopills.com/calculators. DOF Master and PhotoPill both provide tables and charts to calculate DOF in an image as well as useful articles.
Thanks as always for joining me on this Technical Tuesday post and I hope to see you back this Friday for a Road Trip Adventure.