Photography: how to fix optical distortion. Optical lens distortion

distortion(from distortionsio lat. - curvature) is an optical distortion of space. Distortion is most characteristic when using wide-angle lenses. There are three types of distortion: barrel-shaped (convex), pincushion (concave) and perspective.

Pincushion distortion is typical for a wide angle. It is absent on telephoto lenses, but pincushion distortion can appear (usually from a focal length of 200 mm and above). Portrait and regular lenses (for example, 85 mm and 50 mm) are the least susceptible to distortion, where it is almost not noticeable. So correcting distortion is most often necessary when shooting with wide-angle lenses.

When is distortion most noticeable?

When there are straight lines in the frame over its entire area. For example, when shooting architecture with a wide-angle or ultra-wide-angle lens, you will definitely need to work on pincushion distortion correction. And if the shooting point was low, then hello, perspective distortion!*

However, there are positive aspects to this as well. As I said earlier, shots taken with ultra-wide-angle lenses (so-called "fisheye") have pronounced optical distortion. But in this case, this is not a minus, but a plus of the lens, its strong point, and this is why it is so valued in the photo community. I assure you, no staff member, portrait lens, and even more so a telephoto camera will not be able to give such a bright wow effect when the space is covered by all 180 degrees! And this, by the way, is not the limit for fish! There are instances that allow you to take a photo of 270 degrees in one shutter operation! Although, of course, each lens has its own purpose and its own strengths, fisheyes still have a certain charm :)

distortion correction

Fortunately, if necessary, each of the above distortions can be corrected. In landscape photography, by the way, distortion is less noticeable than, for example, a photo of architecture, replete with vertical lines.

As an example, we take a photo with barrel distortion, which has both types of lines (horizontal and vertical), this will best demonstrate the effectiveness of the Lens Correction toolkit. If you have read the profile on the right, you already know that the photo was taken by a "sweet couple" - a full-frame camera and a fisheye lens.

First, let's fix the distortion - apply the profile and more accurately adjust the result with the slider. As you can see, we waved the barrel distortion knob. It remains to align the horizontal and vertical lines.

You can also correct perspective distortion here. To do this, we will use the sliders responsible for the appropriate correction. And line up correct geometry frame will help a special grid (appears by pressing the V key). In the illustration, you can see that the vertical distortion has already been corrected.

So, all the lines are lined up almost perfectly (the used sliders are marked in the illustration). Due to the fact that we corrected barrel distortion, we had a slight loss of information in the lower center of the frame. So final touch- cropping (the sixth tool in the upper left corner of the illustration). To automatically crop, leaving all the usable space and exclude the "eaten" - check the box next to the Constrain to Image function (see illustration).

Disadvantages of distortion correction

As a result of distortion correction, it may be necessary to crop (crop) the curved edges of the corrected frame, which may affect the composition. The correction also redistributes the resolution of the image: with pincushion distortion, after correction, the sharpness at the edges of the frame relative to the center may increase. When correcting barrel distortion, on the contrary, the sharpness at the edges of the frame may drop.

*Perspective distortion is not technically a distortion, as it is a natural manifestation of the lens rendering 3D space. Our brain, in turn, “knows” how objects look right in reality, and therefore perceives converging lines in the photo (in those cases when they should be parallel) as not corresponding to reality. For the correct display of perspective, special tilt/shift lenses are used, in which the tilt/shift properties of the lenses make it possible to eliminate the appearance of perspective distortion.

So we examined the main disadvantages of photographic optics and learned how to avoid them. And also mastered the methods of neutralizing them when they appear in the pictures.

I hope your photos are even better now. At least in technical terms, they are simply obliged to become such!

Yuriy Krivenko, especially for funPhoto.ua

Very many photographers and amateurs at the very beginning of their creative way face such an unpleasant thing in a photo as distortion. This article will help you understand what distortion is, why it occurs and how you can prevent it from occurring. So, under the concept distortion» usually refers to the geometric curvature of objects, distortion of lines that appear in the process of imaging.

Types of distortion

The most common types of this defect are considered " pillow-shaped ", as well as " barrel-shaped» distortion. Barrel distortion is characterized by the outward curvature of the lines, and the image becomes convex, mainly for the lines at the edges of the frame. And for pillow-shaped- the bend of the lines, which is directed closer to the center of the frame, while the lines are, as it were, concave. Besides, pillow-shaped distortion is sometimes also called negative, and it is characteristic of a wide angle. And barrel-shaped, or positive distortion, can most often appear at long focuses.

Why distortion occurs

Distortion can occur for several reasons. One of them is the convergence of parallel lines when the camera is tilted or tilted by the photographer - most often this distortion occurs when photographing tall buildings from a low angle. In addition, distortion can also occur when using cheap lenses of dubious quality. Generally, this feature characteristic of zoom lenses, that is, lenses with variable focal length. And lenses that have a constant focal length provide impeccably clear composition without any geometric distortion.

How to avoid distortion

In order to avoid the appearance of distortion in photographs, it is best to purchase an expensive and high-quality lens. In some cases this problem may decide to use a wider-angle lens. And you can also try a long-known and proven trick - move away from the subject at a more distant distance and use the zoom function. You can eliminate distortion from a finished photograph and make it more proportional and harmonious using a special simple option in Adobephotoshop or any other graphic editor.

Distortion as an artistic tool

Not in all cases, distortion can be considered a disadvantage and distortion. Sometimes it is a kind of artistic method. There are even certain types of lenses that are designed not only not to eliminate distortion, but also to deliberately emphasize it. One of these types of lenses is Fish-eye, which means "fisheye". This is one of the most unusual optical systems for SLR cameras. This super wide-angle convex front lens has an imaging angle of 180 degrees and sometimes more. The result is a circular picture, while the frame itself remains rectangular. Lenses of this type present in the arsenal of almost all leading manufacturers of photographic equipment - Nikon, Canon and others.

Another type of lens with intentional (positive) distortion is Tilt / Shift lenses. Most often they are used during architectural or technical photography. The main feature of the Tilt / Shift lens is the control of perspective, as well as the ability to correct it. This is a tilt-shift optical design. The very first lens of this type in the world is f/3.5 PC-Nikkor which was designed and assembled famous company Nikon in 1961. Most often, these lenses are used on 35mm and medium format single lenses. SLR cameras. Currently, Tilt / Shift lenses with a focal length of 24, 28, 35, 45, 85, and also 90 millimeters are becoming more and more in demand.

Distortion and perspective

Never confuse such concepts as perspective and geometric distortion. They are united by one important factor is the angle of view of the lens. However, if distortion, that is, geometric distortion, is a significant defect in composition, then perspective is a special property of the world and our own perception. Human eyes are capable of seeing almost 180 degrees. From this point of view, we always need a wide angle that gives perspective. About the phototv site.

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What is distortion in photography

Very many photographers and amateurs at the very beginning of their career are faced with such an unpleasant thing in photography as distortion. This article will help you understand what distortion is, why it occurs and how you can prevent it from occurring.

I think many readers have noticed more than once that the image in the photograph is different from what we see with our own eyes. This is partly due to the peculiarities of the transmission of perspective at different focal lengths. You can read more about this in the article about. In addition, defects may appear in the image in the form of color halos in contrasting areas, darkening of the frame at the edges, and changes in the geometry of objects. These shortcomings can be safely attributed to optical distortions of lenses, so we'll talk about them in today's article.

distortion

Distortion is the geometric distortion of straight lines when they appear curved. Do not confuse distortion and perspective distortion, in the latter case, straight parallel lines become converging, but not curved. There are two types of distortion according to the type of impact on the picture: pincushion - when the lines are concave and barrel-shaped - when they are convex.

Pincushion distortion, normal image and barrel distortion

Of course, in practice, the image rarely takes such ugly forms as in the diagram. More a real example The photo at the beginning of the article with a slight barrel-shaped distortion can serve as an effect.

First of all, distortion is visible on zoom lenses, and the greater the zoom factor, the more noticeable it is. Usually in the wide-angle position, you can observe the "barrel", and in the body - "cushion". Between extreme provisions lens imperfections in optics become less noticeable. In addition, the level of distortion may also change from the distance to the object, in some cases close object may be subject to them, and the distant one will turn out normal in the photo.

Chromatic aberration

The second type of optical distortion that we will consider is chromatic aberration, you can often see the abbreviated "XA". Chromatic aberrations are caused by decomposition white light into color components, which is why the object in the picture has a little different sizes in different colors and as a result, colored contours appear along its edge. Often invisible in the center of the frame, they become visible on objects closer to the edges of the image. XA do not depend on the value of the focal length, nor on the aperture, but more often and more strongly manifest themselves again in zoom lenses. This is due to the need to introduce into the optical scheme additional elements to eliminate the effect, which is much more difficult for zoom lenses than for primes.

In the picture on the left, CAs are especially noticeable on the hair (purple outline) and on the window grille (turquoise).

It cannot be said that chromatic aberrations greatly spoil the picture, but on contrasting objects, especially in backlighting, they become very noticeable and quite striking.

Vignetting

The last point is vignetting, in other words, darkening the areas at the edges of the frame. It can usually be seen on wide angle lenses at maximum open aperture. This effect is quite rare.

Do not confuse vignetting caused by optics flaws and appearing due to additional accessories. In the picture above, the edges turned out black due to several fairly thick filters wound onto the lens. A similar effect can be obtained when screwing on a long hood.

Initially, all optical distortions are directly dependent on the class and type of optics you use. Expensive series lenses have complex lens layouts and many additional elements that minimize these unwanted effects. Cheaper lenses, especially zooms, are much more prone to these problems due to the simplification of their design.

I hasten to disappoint readers, there are simply no lenses completely devoid of the above problems. To one degree or another, even expensive models of optics with a fixed focal length still distort the picture, although this is noticeable mainly at the edges of the frame. Good news in that for the most part these effects do not spoil the picture very much and can be quite easily eliminated programmatically (we will talk about this in the next article). In addition, on cameras with a non-full-format matrix, and these are all amateur DSLRs, the edges of the image are cut off in any case, and when using good optics, visible distortions are minimal.

I love taking wide angle photos. If someone told me to choose one lens that I can take with me on a trip, it would definitely be a wide angle! As a result, I have a lot of photos taken with a wide angle.

The main problem with all wide-angle lenses is optical curvature, which is called distortion(from distortionsio lat. - curvature).

If you look at the photo above, you will notice that all the lines are not even, this is a prime example optical distortion. Now hover over the photo with the mouse and see how it should be. So, distortion is an optical distortion that is characteristic of your lens.

There are two types of distortion - barrel-shaped (convex distortion) and pincushion (concave distortion):

Distortion is characteristic of a wide angle. You won't notice distortion on telephotos or portraits. Therefore, most often the distortion has to be corrected when you photograph with a wide-angle lens. Distortion is especially noticeable if the photo has a lot of straight lines across the entire frame, for example, when you photograph architecture with some kind of ultra-wide-angle lens (for example), you will definitely have to correct distortion.

Still, distortion is not always a bad thing. If you have ever photographed with fisheye (fisheye) then you have seen a pronounced example of optical distortion, only in fisheye distortion is a feature that everyone loves. It looks like this ():

Hover over the last frame and you will see a photo that has been corrected for distortion.

How to remove distortion.

If you have Photoshop, removing distortion is easy. You need to go to the Filter menu, go to the Distort tab and select the Lens Correction submenu. Now, move the slider left or right until you get the desired result:

Naturally, it will take you a lot of time to correct distortion, so not everyone will want to correct it. And in this case there is a panacea. It's called DXO Optic Pro. With this tricky program, you can correct distortion (and more) automatically. All you need is to install the program and download the plug-in for your camera and lens, the program will do the rest automatically. I corrected the last photo taken by fisheye in it.

I continue the series of articles on computer processing of photographs. The topic of our conversation today will be correcting distortion and perspective in a photograph. Let me remind you that distortion- this is a curvature of straight lines that appears at the edges of the frame, due to which the picture looks convex or, conversely, concave. Effect perspectives- This is an optical effect consisting in the convergence of parallel lines in a photograph. Distortion and perspective are a real scourge when shooting interiors and architecture. It is because of them that the walls of buildings look curved, and the buildings themselves instead of a rectangular shape have the shape of a trapezoid.

However, sometimes distortion and perspective play a positive role and are used as artistic technique, which allows you to better convey the idea of \u200b\u200bphotography to the viewer (although this is all for an amateur).

Nevertheless, the question often arises - how to "subdue" perspective and distortion and make them "work for themselves". For this, many means have been invented, both "hardware" and software. First, let's talk about perspective.

How to fix perspective?

Using a tilt-shift lens

Tilt-shift (rotate-shift) is a lens of a special design that allows you to compensate for perspective distortion. An example of such a lens is the Canon TS-E 24mm f/3.5 L II. The lens consists of 2 parts connected by a movable hinge having two degrees of freedom - the "muzzle" of the lens can be moved up and down parallel to the frame plane (to compensate for perspective) or rotated in a vertical plane (to control the location of the depth of field zone.

You can read more about this lens at photozone.de (though on English language), and looking at the pictures on this page - examples of using the tilt-shift lens - is very interesting! The tilt-shift lens is an indispensable accessory for professional photographers shooting architecture and interiors. However, the cost of such optics rarely falls below the 4-digit dollar mark. A rare amateur photographer can afford this.

Framing that eliminates perspective distortion

If you notice, then the perspective effect appears only when the location of the optical system (camera + lens) is not horizontal. It is necessary to "raise" your head, we immediately get falling walls! On the other hand, if you compose the frame so that the horizon is in the middle (that is, the device is strictly horizontal), then there will be no perspective obstruction. However, this requires a lot of cropping of the image. Something like this (the example was made "after the fact", so I apologize for the possible inaccuracy in the transfer of the picture):
The disadvantages are obvious - a significant loss in resolution, the need to have a powerful wide-angle. I will not risk advising the use of such a method in practice, however, at the most extreme case It can be useful.

Correcting perspective in Adobe Photoshop Lightroom

If you have this program and are in the habit of shooting everything in RAW, you can breathe a sigh of relief, you are spared a lot of pain. Open the photo in Lightroom (read how to do this).
We need to perform 4 actions: 1. Select the Develop section 2. Scroll down the list of options to Lens Correction 3. Select the Manual mode 4. Play with the Vertical engine When you hover over the Vertical engine, a grid appears on the image that helps to "display" the verticals.
Everything is almost good, except for the fact that a semicircular "notch" has formed at the bottom of the photo, which we get rid of by cropping.
That's all!

So, with the prospect sorted out. It remains to defeat distortion. And if you do not win, then use it to your advantage.

Experiments with distortion

The only negative is that the detailing at the corners of the frame becomes simply non-existent. However, given the difference in cost between the Zenitar 16/2.8 and its "equivalent" wide-angle Canon EF 16-35/2.8L or Canon EF 14/2.8L, the Soviet fisherman can be forgiven absolutely everything! At the very least, such an experiment can give you a rough idea - "what will it look like if you shoot it with an ultra-wide angle?" This may influence your decision about the (in) expediency of buying a wide-angle Elka.