Among the aspects in photography that most often grab our attention when we start learning are the depth of field games: how can the background be blurry? Which factors are important? Why are there times when I do not even try when I try? What can I do to get it? If you’ve ever asked any of these questions, stay with me and I’ll explain in detail.
Would You Tell Me What is the Depth of Field?
Surely if I ask you if you could tell me if the photo that I show you below has a lot of shallow depth of field, you probably guess right.
Let’s add a little more complexity to the issue. If I tell you now that you compare the previous photo with the one I add next, and I ask which of the two photos has more and which is less shallow, what would you say?
What if I told you that the depth of field is the same on both photos? Would you believe me? The photograph is made with the same values, only one changes, and it is the distance of the secondary elements with respect to the main element (and therefore also with respect to the camera). So when we speak of the concrete example, the main marble, which is completely opaque, is our focus. The depth of field is the same in both shots, although only one appears in one of the three focused balls and in the other. This is because we have displaced two of the marbles, and therefore we have removed them from the area we will see, ie the depth of field.
This makes us think that the depth of field is not as objective as it seems. Not seeing more focused elements inside the shot will mean that we have a greater depth of field. It is not a concept that we can encorse, because it will depend on different factors, and it is very easy, but very easy, to affect the final result of the shot.
What is depth of field?
When we play with the depth of field, we have the power to direct the gaze of the one who sees our photograph to a particular place in the picture or to its general arrangement.
OK yes you know what it can be used for … but what exactly is the depth of field? Depth of field is the part of the image we can consider sharp or focused. That is, if we see a photo showing sharper and blurrier areas, the depth of field would correspond to the image area we see as clear. The area in front of and behind the subject or object that we have focused on and that sees our eye with an acceptable sharpness.
If we are strict and 100% focused, there is only one plane that, as it were, translates a point of reality into a point of our sensor. The rest will be out of focus. However, it is true that this blur is very small among the elements that are near our chosen focal plane, and that our eye can perceive it as focused. As we move away from the focal plane, this blurring becomes more apparent.
As a rule, it should be noted that in this focus range, the depth of field, the focus distance is 1/3 before the focus point and 2/3 behind the focus point. However, what you need to know is that the depth of the field does NOT have to match the greater or lesser number of sharp elements that appear in the frame. We should not get confused, because that’s NOT the depth of field.
Factors that influence the Depth of Field
Now that we understand a little more the concept of depth of field, we will see what are the factors that will influence the greater or less depth of field that a photograph may have.
1. Opening diaphragm (nºf)
The first variable that influences depth of field is the diaphragm aperture.
The more open we have the diagram, that is, the smaller the number f, the smaller the depth of field of our image, so that there will be more elements that appear out of focus in it.
And the other way around, the less open the diaphragm is (or the closer it is), that is, the greater the number f, the greater the depth of field will be, and the more elements will appear with an acceptable sharpness.
Let’s see it in the picture.
As seen in the picture, with a greater number f the distance that will appear with an acceptable sharpness will be greater than if we use a smaller f number.
Thus, a photograph taken from a point of view and with an objective with an aperture at f16 will have greater depth of field (more sharp area) than another taken with the same objective and from that same point with an aperture of f2.
As we see in the example, the first of the images is made at a lower number f, so the sharp area is very specific. As we close the diaphragm we observe how we begin to distinguish the elements that are located behind the focus point. With the last example, we can even guess the number s that appear in the objective.
The number f is the element used in photography to identify the aperture.
2. Distance to the focus plane
The second of the variables is the distance between the camera and the focus plane.
Since the subject or object we are taking is closer to the camera, the depth of field will be less. If our subject or object is farther away from the camera, the depth of field will be greater.
This means that the closer we get to the element we’re focusing on, the farther we get from the fact that we’re doing the photography with the same lens and pre-defined aperture, the lower the depth of field Element that we focus, the depth of field will be greater. In the following graphic we can check it.
And to see how it affects, in the following photographs you will see how with the same frame and the same focal distance, the depth of field has been changing as we have moved the object to be photographed. As the figure was closer to the bottom and further away from the camera, the depth of field was greater. However, as the figure is moved and moved away from that background to bring it closer to the camera, the depth of field is reduced.
Lastly, the focal length of our lens will also influence the greater or lesser depth of field of our photographs.
Since we use lenses with a longer focal length, z. For example, telephoto lenses (85mm, 200mm, 300mm, etc.) have a lower depth of field when magnified with a lens. If we use short focal lengths (10mm, 16mm, 20mm, etc.) that are very slightly out of the picture, our photo will have a greater depth of field. See it in the graphic.
This could be simplified by saying that at least millimeters of focal, more sharp area will get in your picture, as reflected in the following shots.
Calculate the Depth of Field!
As mentioned before, the depth of field depends on these three factors: iris aperture, distance to the object and focus of the lens. From these parameters, the value of the depth of field that we receive when taking pictures can be calculated.
If you want to calculate the depth of field for certain features, we recommend using some calculators to help you determine the depth of field of your digital camera based on the various variables we have discussed.
All you have to do is enter the parameters on which the depth of field depends, and the tool will tell you which depth of field you will get.
Premises Before Going into the Wonderful World of Depth of Field
Okay, you got me. Not only the three factors that you have explained affect the concept of depth of field. As many of you have guessed, the size of your camera’s sensor and the size of the confusion cycle will greatly affect the concept we’re dealing with, but we’ve preferred over the three most notable and on the basis of, too speak the fact that we are working with the same confusing circle and sensor size. To help you understand why there are more factors that affect depth of field, let’s give you a brief explanation.
We have already discussed the circle of confusion in this other article, but let us remember. This complex notion is meant to tell us that the range of sharpness that our images will have, the range that we consider acceptably clear and call the depth of field, will depend on several variables.
I do not want to deal with it, but try to make it clearer … It’s not the same to see a picture on our 24-inch computer screen, such as the 5-inch format of our mobile phone. If we see the same picture, there seems to be more elements on the phone that focus on how small we see the shot. But when we see it on a much larger monitor, we find that not so many things were focused as we thought.
Surely you have taken a picture with your camera and you thought it was perfectly focused, but when you got home and saw it on your computer, you found that you could refine the focus.
This is because when we see it on a much smaller screen, the “errors” go unnoticed, and our depth of field or “acceptable range” criterion is much wider than a large monitor.
And this is just one of the examples that can cause the circle of confusion to vary, affecting the depth of field. Also influences the distance we see for example in these photos or the visual acuity of the viewer, as well as the size of the printout and, of course, the size of the camera sensor with which we take the picture.
The size of the sensor affects the greater or lesser depth of field in the shot, because the larger the sensor, the lower the depth of field, and the smaller the sensor, the greater the depth of field.
And this is understood when we think of the camera on our mobile phone or an action camera like the Gopro, which has a very small sensor and therefore almost everything seems focused. However, if you take a full-frame or full-frame SLR, the depth of field is much lower with the same values.
So if you see a shot that shows a perfect portrait with a nice blur and you want to try it on your phone, you should know that you can hardly reach it because of the size of the sensor.
Do not Tangle!
Exhausted? This has not been one of the funniest articles that you have read for sure, but my intention has been to get you to understand the variables that influence the important concept of depth of field.
I hope I have dispelled some doubts, and now I invite you to try yourselves to take shots in which you vary the factors that we have reviewed to fully understand their implication.
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