How The Diaphragm In Photography Works

How the diaphragm in photography works is one of the first theoretical lessons we should learn. Because once you know how the diaphragm opening works, you will be able to understand. And create most of the images that go through your head. Surely many times you have wondered why some images get a blurred background, or totally sharp. Or how to get the power to take photographs with low light and without flash …

How The Diaphragm In Photography Works

If you are still in the automatic mode of your camera, are unknown that you will never solve. That’s why I invite you to dare to practice with the semi-automatic modes and the manual after you’ve taken a look at this article.

What Is Diaphragm Opening?

The diaphragm aperture is the one that regulates the amount of light that passes through our lens to the camera sensor. The diaphragm is part of any objective, and consists of a series of plates or fins that move inward or outward forming a circle more or less large make it to the center or outward through which more or less light passes, depending on the diameter of it.

Open diaphragms allow more light to enter, while closed diaphragms allow less light to enter

How Are The F/ Values Interpreted?

The different diaphragm apertures are measured or named by the numbers or values in f/. Depending on the luminosity of the objective, we will have smaller or larger f/ minimum values.

Here comes what I think is the most important and what we usually mess up when we start and try to understand the diaphragm opening. The lower the f/ value, the more light will enter through the target, and the higher the f/ value, the less light will enter through the target.

Look at the following image and imagine that the light must pass through those “holes”, which of them do you think the most light will enter? f/2, right? And on the contrary, by which of them will the least amount of light enter? In this case it would be f/22, but these openings are always defined by the objective.

Opening Diaphragm

The Diaphragm Steps

The diaphragm step is nothing more than a jump from one f/ value to the next. For example, in the previous image we would say that between f/2 and f/2,8 there is a diaphragm step. Or between f/2 and f/4, there are two diaphragm steps.

And you’ll say… All right, so what does that mean? Well, every step up in the scale means that you are dividing by two the amount of light entering through the target. (For example f/4 has half as much light as f/2.8). And on the contrary, every step down you take on the scale means that you will be doubling the amount of light entering with respect to the previous step. (For example f/8 has twice as much light as f/11).

The “standard” scale would be as follows:

f/1, f/1.4, f/2, f/2.8, f/4, f/5:6, f/8, f/11, f/16, f/22, etc.

Intermediate Steps

Now, the previous steps are those considered whole, the classics, the theoreticians. But as always, things are evolving and it is very possible that, today, your camera has quite a few more f / diaphragm numbers than those we have discussed, right? You were probably wondering what to do or where values like f/3:5 or f/5 come from. Well, all the values between the different steps are what we consider to be intermediate steps.

The intermediate steps are not universal and have been added to allow the diaphragm opening to be adjusted more precisely.

The Luminosity Of The Lens And The Aperture Of The Diaphragm

When we talk about more or less luminous objectives, we are actually talking about the maximum diaphragm opening capacity that these have associated with them.

As we have seen in the previous point, the lower the f-value, the more light enters through the lens and therefore, we consider it more luminous.

For example, an 18-55mm 1:3,5-5,6 zoom lens tells us several things:

That the focal length of the lens varies between 18mm and 55mm.
The maximum aperture of the diaphragm is f/3.5 at its minimum focal length (18mm)

That the maximum diaphragm aperture is f/5.6 at its maximum focal length (50mm)
That is to say, with this objective, we will be able to open the diaphragm until a maximum of f/3,5 when we work in 18mm, and a maximum of f/5,6 in 50mm.

In fixed optics, the lens indicates only the maximum aperture and the fixed focal length: 50mm 1:1.4. In other words, the maximum aperture for this objective is f/1.4.

Between the two examples, (zoom and fixed optics) the fixed 50mm is the brightest lens.

Depth Of Field And Diaphragm Opening

I remember when I started in this passion for photography, that one of the things that fascinated me most about an image were the blurred backgrounds, the possibility of enhancing an area of the image only through the focus. Evidently I didn’t have much idea of how to get what for me was an almost magical effect… Until I got a reflex and discovered the diaphragm opening and its relation with the depth of field.

Diaphragm Steps

The diaphragm aperture is closely related to what we know as depth of field, which is nothing more than the amount of area focused on the image. The more aperture (f/small value), the smaller the depth of field or area focused on the image, and the smaller the aperture (f/high value), the greater the depth of field or area focused on the image.

In short, the large openings will not only allow you a greater entry of light, but you will also be able to focus attention through the blur it provides. Conversely, if you want a lot of depth of field or reduced light input, you’ll need to close the diaphragm.

A more open diaphragms (F low) shallower depth of field

Closer diaphragms (high F) allow for greater depth of field, ideal for landscapes

Sharpness And Aperture Diaphragm

The aperture is also related to the sharpness of the image. All lenses have an aperture to which they achieve maximum sharpness, also known as Sweet Spot. Contrary to what it may seem, the sweet spot is not located at either end of the diaphragm aperture, but is located at the intermediate apertures, but depends on each lens and the focal point used. Just remember that if you want an “extra” sharpness you should try not to place yourself at the ends of the aperture or focal, because it is where “worse” or more aberrations produce the objectives as a general rule.

Exposure Triangle

Finally, don’t forget that an image is made up of several related parameters. The most important are what we know as the exposure triangle: Speed, ISO Sensitivity and aperture. Through the knowledge and relationship of these three parameters, you will be able to get almost any photograph that you propose.┬áIt is worth the effort, you will see.

Exposure Triangle: ISO, Shutter Speed and Aperture

I know it might seem complicated to you, but it’s not at all. It does require you to stand in front of your target and memorize as you open and close the diaphragm. “If I open the diaphragm, more light comes in, less depth of field, value f/lower”, “If I close the diaphragm, I see that the hole in the diaphragm is smaller, so less light comes in, more depth of field, value f/ higher”, “If I close the diaphragm, I see that the hole in the diaphragm is smaller, so less light comes in, more depth of field, value f/ higher”. Or as it suits you.



No matter how long it takes you to internalize this concept. Once you do, you’ll be able to play with the opening in many ways. Surely in nothing you have it completely internalized, imagine the scene you’re looking for, and know exactly what parameters must be given to the camera to get the image you want. Don’t you believe me? Practice a little and you will see how this will happen sooner than you imagine.

Diaphragm Opening And Depth Of Field

We will try to explain in a brief and simplified way how the opening of the diaphragm in the depth of field influences, when taking a photograph. Very simply, depth of field is defined as that area that appears sharp (focused) in the resulting photograph. The depth of field basically depends on four factors: aperture, distance to the object, focal length of the lens, and the circle of confusion.

Here is a quick example of how to play with depth, modifying only one of its variables: the aperture of the diaphragm. We will therefore maintain the same distance to the object in the two example shots and use the same focal distance (we mount a fixed 85mm optic) and consider the circle of confusion invariable as we are the same observers and use the same body and objective for the shot.

When we open the diaphragm too much (low F-values) we reduce the depth of field. The next shot was taken at f/1.8:

Example a f/1.8Closing the diaphragm more and more (increasing the F values), we can progressively increase the depth of field. Keep in mind that when performing this action, we are limiting the entry of light to the sensor and we will have to lower the shutter speed or increase ISO sensitivity to not end up underexposing the picture. Therefore, the result we get when shooting at f/7.1, is as follows:

In large openings, it will be up to us to select the point to focus on to give more artistic value to the shot.
As can be seen in the two photographs, the higher the f-value the photograph shows a greater depth of field.

Calculating The Depth Of Field

If you want to calculate approximately the depth of field for certain characteristics, in DOFMaster you have a complete calculator that will allow you to know the value of the depth of field for your digital camera from the different variables that we have commented.

We would love to receive samples of what we are discussing here and would be happy to respond or publish the answers to your questions. To do so, all you have to do is send us an email or post a comment on the blog.

I hope you found this article useful. If so, please share it with someone else you think may be interested in knowing the diaphragm opening. Thank you very much and see you next time.