Today I do not promise you the most fascinating article in the world, because I will tell you something that already prepares us for the worst in his name: the circle of confusion. Unbeatable name for something so hard to understand.
If, moreover, this concept is associated with other words or concepts such as hyperfocal distance, focal plane, focus, aperture of the diaphragm, we add distances, millimeters and countless others, the question becomes more complicated.
- I said.
- I don’t promise you the most fascinating article in the world.
- What I promise you is that when you finish it you will know and fully understand what the circle of confusion is and how to calculate it.
As a good photographer (or photographer) I’m sure you’re curious, I know you’ll stay here and give me a chance to explain it to you, so from the beginning, thank you for your patience ;-).
To understand the circle of confusion, you must first understand how the development of our cameras works.
Look at the following image
As you can see, we have a subject (Mario) that we want to photograph, it’s some distance from our target (the one we decided) and that’s called focus distance.
Mario’s image, in the form of light, passes through the lens and is projected onto our sensor or focal plane (where the rays of light converge is known as the nodal point). If the projection of the image (mario or subject were photographing us) matches perfectly with the sensor, Bingo!Focus Habemus! And that translates into a perfect point in the sensor.
If, on the other hand, the image is projected in front of or behind the sensor (light rays converge outside the focal plane sensor), this image reaches the sensor not as a perfect point but as a circle whose size increases or decreases. depending on the proximity or projection distance of the image from the sensor.
In other words, the farther the sensor image converges, the greater the circle reflected in the sensor (think of an increasingly blurry point) and, on the contrary, the closer this convergence is (nodal point) to our sensor, the more it looks like a point or, what is the same, the smaller the circle it projects on the sensor.
If you have read carefully (and especially if I can explain it correctly), you may have already guessed what the confusion circle is ;-).
Before, I mentioned that the perfectly focused area translates to a perfect point on the sensor, but you may wonder what happens to anything that doesn’t exactly match the focal plane, because our camera can’t focus more than one photo. At the same time, so what?
You may have thought that there are many images in which not only does what we focus on appear clearly, but also an area immediately before or after may be larger or smaller depending on the image.
Well, the answer is yes or no?That is to say that in the sensor everything that does not converge perfectly above the focal plane will not be a point, it will be a circle or what is the same, theoretically it will be blurry.
However, our perfectly imperfect eye, these fuzzy circles are not able to distinguish them from a point as long as they are below a certain value that has been set to 0. 25 mm.
That is, in theory and on paper, the image may not be focused on our sensor, but it is for our vision, because everything we look at at a certain distance (fixed at about 25 cm) less than 0. 25 mm, we will perceive it as a sharp tip.
In the end, we can say that the circle of confusion is
The maximum size of a diffuse point on the sensor when projected onto a surface and viewed by a viewer at a specific distance is always perceived as a point and not as a circle.
That is, anything that, although not perfectly focused on our sensor, but that we perceive (in prints, screens, etc. ) as a sharp tip will be, for us, a perfectly sharp image.
If, on the other hand, the circle of confusion is not perceived by our vision as a point but as a circle, we say that this area of the image is blurred, or that it has no acceptable sharpness.
If you have already discovered what the circle of confusion is, let’s see how it relates to the aperture of the diaphragm and, therefore, to the depth of field.
To do this, we move on to the images
As you can see, in the first image we have an open diaphragm aperture that gives us a relatively low depth of field, because we consider the place that matches the circle of confusion to be the maximum acceptable sharpness point.
On the other hand, if you try a tighter diaphragm aperture, as is the case with the second image, you see that the depth of field increases, as the confusion circle is located farther from the focal plane (sensor) and therefore the entire area between the sensor and the confusion circle will have acceptable sharpness.
In its day, I have already explained what hyperfocal distance is and what it is for, but if it is still a term that scares you, do I recommend this article that will make you lose your fear?
In short, hyperfocal distance is the distance you need to focus on to have as much depth of field as possible in a scene, i. e. using the hyperfocal will be equivalent to having the maximum net area at the point (for the eye, because remember that you can only focus a plane on the sensor that will appear as sharp) or what is the same , the confusion circle shall be located as far away from the sensor as possible.
It is calculated by dividing the sensor diagonal size by 1500 (according to Kodak) or 1750 according to Zeiss (stricter?), O?Simply add here in Photopills the parameters needed to calculate it: the camera model, the size at which you will print or magnificate, or the distance at which you will observe the image.
It’s very likely that you asked this question or that you’ve already had the intuition of something, anyway, here are some of its uses:
What do you think? I hope the confusion has cleared up after reading this article, and if not, did you at least do a master’s degree in optics, like me?I hope you found it helpful and reward our common effort (mine to write it and yours to read it) by sharing it on the networks so that someone else can enjoy it. Thank you so much for reading so far and so far?.