Photographing a distant object with a camera lens. Learn more about telephoto lenses. Telephoto lenses for Canon. Lens focal length increase
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628. What exposure is needed when photographing a drawing with a linear magnification V\, if when photographing with a magnification V2, the exposure is t2?
629. A frosted glass is installed in the focal plane of the positive lens. It turned out that the blurring of image details of objects located at a distance a = 5 m from the lens was d = 0.2 mm. Determine the aperture ratio of the lens if its focal length is F = IO cm.
Note. The aperture ratio of a lens is the square of the ratio of the lens diameter to its focal length.
630. A camera whose lens has a focal length F = 20 cm is aimed at an object located at a distance fli = 4 m. To what diameter should the lens be apertured so that the blurring of the image of objects located at a distance a2 = 5 m from the camera does not exceed 0.2mm?
631. When photographing a remote point source in a photograph, due to the low quality of the lens and the photographic material used, a light circle with a diameter of d = 0.1 mm is obtained. From what maximum distance can two point sources, located at a distance of I = 1 cm from each other, be photographed under the same conditions in order to
127photos of their images have not yet overlapped? Focal length of the lens F = 5 cm.
632. In a microscope, the main focal length of the lens Fi = 5.4 mm, and the eyepiece F2 = 2 cm. The object is located at a distance ax = 5.6 mm from the lens. Determine the linear magnification of the microscope for a normal eye and the length of the microscope (the distance between the objective and the eyepiece), assuming that the eye is accommodated to the best vision distance d = 25 cm.
633. The telescope lens has a focal length Fі = 30 cm, and the eyepiece has a focal length F2 = 4 cm. The telescope is set to infinity *). Where should the diaphragm be placed so that the field of view is sharply limited? What is the field of view angle if the aperture diameter is 12 mm? What is the angular expansion of the pipe?
Note. Angular magnification is the ratio of the tangents of the angles formed by the outgoing and incoming beams with the optical axis.
634. A diverging lens with a focal length Fi = -15 cm is placed between the light source and the telescope at a distance U = 85 cm from the source. Where in the gap between the source and the diverging lens should a converging lens with a focal length F2 = 16 cm be placed so that the light source can be seen sharply into the tube set to infinity? At which of the possible positions of the lens will the image in the tube have the largest angular dimensions?
635. The telescope lens has a focal length Fi = 25 cm and a diameter of 5 cm, and the eyepiece has a focal length F2 = 5 cm. The telescope is set to infinity. If a frosted glass is placed behind the eyepiece, then at a certain position, the illuminated circle on the frosted glass has the smallest dimensions and sharply limited edges. What is the distance from the frosted glass to the eyepiece and what is the diameter of the circle?
*) The text of this and a number of subsequent problems does not contain instructions regarding the accommodation of the observer's eye. In such cases, it is recommended to solve problems under the assumption that the eye is accommodated to infinity (see note to the solution of this problem). .
128636. Spotting scope with lens focal length F = 50 cm set to infinity. How far must the eyepiece of the tube be moved in order to clearly see objects at a distance a = 50 m?
637. By moving the eyepiece, a telescope can focus on objects located at a distance from Cil = 2 m to a2 = 10 m. What lens must be attached to the objective so that the telescope can be tuned to infinity? Where will the closest focus point be?
638. An object is placed in front of the objective of the Kepler telescope (with a converging lens as an eyepiece) at a distance a< Fi. Отношение фокусных расстояний объектива и окуляра FiIF2=IO. Труба установлена на бесконечность. Найти линейное увеличение V = у/х (л;-размер предмета, у- размер изображения). Определить характер изображения.
639. An object is placed in front of the objective of Galileo's telescope (with a diverging lens as an eyepiece) at a distance a > Fi. The ratio of the focal lengths of the lens and the eyepiece FJF2 = -10. The pipe is pointed to infinity. Find the linear increase V = y/x, where X is the size of the object, y is the size of the image. Determine the nature of the image.
640. The telescope has a focal length of the objective Fi = 50 cm and a focal length of the eyepiece F2 = 10 cm. What is the angle at which two distant objects are visible through the telescope if this angle is 30" when viewed with the naked eye? The telescope is set to infinity.
641. The objective and eyepiece of Galileo's telescope have focal lengths equal to F i = 57 cm and F2 = -4 cm, respectively. The tube is pointed at the Sun. A white screen is located at a distance b = 12 cm from the eyepiece. At what distance L between the lens and the eyepiece will a clear image of the Sun be obtained on the screen. What will be the diameter D of this image if the angular size of the Sun is a = 30"?
Thin Lens Formula
2. When photographing a very distant object with a camera whose lens is a converging lens with a focal length f, the plane of the film must be at a distance from the lens A - Between the lens and the focus (f) B - Between f and 2f C - Equal to f D - Equal to 2f
3. Using a lens, an inverted image of a candle flame is obtained on the screen. How will the size of the image change if part of the lens is obscured by a sheet of paper? A - part of the image will disappear B - the size of the image will not change C - the size will increase D - the size will decrease
4. An object located near the focus of a thin converging lens is moved to a double focus (see Fig.). At the same time, its image ... A - approaches the double focus of the lens B - moves away from the double focus of the lens C - moves away from the focus of the lens D - approaches close to the focus of the lens
Right!!! Hooray! Five points!!!
When compiling the presentation, the following materials were used: 1.CD “Media Library in Physics”, Virtual School of Cyril and Methodius 2.CD “Preparation for the Unified State Examination. Physics”, PHYSICON For the past 4 years, for a survey in physics lessons, I have been using the game “Who wants to become an excellent student in physics?” (idea borrowed from a TV game). The game takes 3-4 minutes and makes the lesson very lively. Rules of the game: the student at the blackboard (more precisely, at the projector screen) receives 6 questions and has the right to take two hints: ask the computer to remove two incorrect answers and get class help (so all students are on their toes!). Each wrong answer reduces the score by a point.
Photographic optics was known long before the invention of photography and was used by artists as an aid to accurately depicting landscapes. For the first time, the optical design of two converging lenses was described by Kepler in 1611, but was forgotten and reinvented by Barlow in 1834, and in 1891 such a lens was used by Dallmeyer for photographic purposes. It should be noted that Kepler did not embody his design "in glass", but his theoretical research had a significant impact on later developments.
Historically, the main uses of telephoto lenses have been close-up photography of distant subjects and portrait photography. In the latter case, long-focus optics provide minimal distortion of the proportions of the face and good separation of it from the background, which, being outside the sharpness zone, is blurred. These two trends are relevant in photography today. In addition, telephoto lenses allow for many other interesting types of photography.
The largest civilian telephoto lens to date, designed and assembled by Carl Zeiss. It has a focal length of 1700 mm, a maximum relative aperture (aperture) of F / 4 and a weight of 256 kg (photo 1). This lens was produced in a single copy by order of a fan of wildlife photography from long distances, who places very high demands on image quality.
Optical schemes of telephoto lenses
The simplest lens design, which is a single telephoto lens, has a number of disadvantages. The most significant of them are low image quality and very large dimensions of the structure. The length of such a lens when focusing to infinity is equal to its focal length. Therefore, a different optical scheme is currently used, called a telephoto lens. In the simplest case, a telephoto lens consists of one converging and one diverging lens, however, in order to reduce aberrations, they are usually replaced by groups of lenses made of glass with different optical properties (Fig. A). Modern telephoto lenses usually use additional groups lenses that further improve image quality and implement additional features such as image stabilization, while the general idea of the design remains the same.
Between groups of lenses is usually a diaphragm. This device limits transverse section beam and is used to change the amount of light passing through the lens and the depth of field. The shape of the blur in the blur zone is an image of the aperture hole.
With the increase focal length the length of telephoto lenses increases rapidly. To ensure sufficient luminosity, the lens has to be made of a large diameter. As a result, the weight increases and the price of the lens increases. The problem of creating compact super telephoto lenses successfully solved using a mirror-lens optical scheme resembling a classical telescope (Fig. B). In such a scheme, there is no aperture (its optical role is usually played by the frame of the front element), the lens has a fixed aperture and relative aperture, and the image blur outside the sharpness zone has a characteristic annular shape.
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Mechanical properties of telephoto lenses
As already mentioned, telephoto lenses are usually quite long. To obtain acceptable aperture ratios, which affect the amount of light passing through the optical system, it is necessary to use lenses of large diameter. All this leads to the fact that a high-quality telephoto lens cannot be made light and compact. With small sizes of light-sensitive material (for example, in compact digital cameras), this limitation is not significant; however, an increase in the required image size leads to a proportional increase in the linear dimensions of the optics. A moderate telephoto lens with a true focal length of 200mm and aperture of F / 2.8 is no longer easy to hold in your hands for a long time: in such a situation, it is better to use a tripod or monopod.
In addition, the small angle of view of a telephoto lens causes even a very small rotation of the optical system to result in a significant shift in the image. If this shift occurs during exposure, the photograph will be blurry. The empirical formula, true for most cases, says that when shooting handheld, the “safe” (in the sense of blurring the image) shutter speed (in seconds) should be numerically no greater than the reciprocal of the equivalent focal length (in millimeters). Particularly "long" lenses do not allow this condition to be met even with bright scene lighting. To remedy the situation, two fundamentally different approaches are used. One of them is to fix the optical system in space as reliably as possible and prevent its displacement during shooting. For this, tripods or monopods are used. Less commonly used are more expensive and cumbersome gyroscopic platforms that move freely in space, but accurately retain the original orientation. The second method, called optical stabilization, consists in introducing a special movable element into the optical system that compensates for image shift as a result of camera shake. This element can be either one of the lenses of the lens, or a platform on which the photosensitive matrix of a digital camera is mounted.
Very large lenses weigh much more than the camera they are mounted on. Therefore, they have a special mount, usually in the form of a clamp with a platform, for mounting the system on a tripod. Sometimes the design of the device also provides a handle for carrying it. The already mentioned giant Carl Zeiss Apo Sonnar T * 4/1700, due to its weight and size features, is designed for installation on a special platform mounted in a car body. In such extreme cases, it is more logical to talk about mounting the camera on the lens, and not vice versa.
Focusing fast long-focus lenses is associated with the movement of massive lenses. This greatly reduces the speed and accuracy of autofocus and increases power consumption. One of the most important areas of modern research is the improvement of these parameters. Partly for the same reason, the minimum focusing distance increases rapidly with increasing focal length. By introducing this limitation, it is possible to reduce the course of the components in the process of focusing, and therefore, to reduce the focusing time. Some lenses have a switch that allows you to select a range of focusing distances: full - for close-up subjects, or reduced - to speed up the process.
To reduce the length and weight of lenses, they use expensive optical glass with extremely high rate refraction. Some modern developments use diffractive optics for the same purpose.
Lens focal length increase
It happens that the focal length of the lens is too small for a specific photographic task. In some cases, changing the lens to a longer focal length is not possible (for example, when using compact camera with non-replaceable optics) or undesirable (usually super telephoto lenses are very expensive). Optical devices called teleconverters will come to the rescue. They can be divided into two large classes: placed between the lens and the camera in the manner of extension rings and mounted in front of the front lens of the lens.
For increasing the focal length of the optical system by such methods, one has to pay with a decrease in aperture ratio. 1.4x teleconverter reduces aperture by one stop, 2x by two. That is, for example, when using a lens with an aperture of F / 2.8 and a 2x teleconverter, a system with an aperture of F / 5.6 is obtained. Not too much, but quite acceptable. Image quality usually suffers little when using teleconverters from the same manufacturer as the lens, but cheaper third-party products should be purchased with some caution.
Image features
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Photographing any object is geometrically its image on a plane in the central projection. This statement is true when using any lenses with corrected distortion. All existing long-focus optics have this property, so we will not consider other cases.
The size of an object whose image occupies the entire area of the frame depends on the size of the frame, the focal length of the lens, and the distance from the camera to the object. By reducing the area of the frame, you can achieve upscaling when printing an image while maintaining the same paper size. Therefore, the focal length of a lens cannot by itself be a measure of its wide angle. For example, a lens with a focal length of 50 mm would be normal for 135 type film, having a frame size of 24x36 mm, wide-angle for medium format 60x45 mm, and super-telephoto for digital camera with a sensor size of 8x6 mm. To simplify calculations, the concept of equivalent focal length was introduced, which is defined as the true focal length of a lens that has the same angle of view at a frame diagonal of 43 mm, which corresponds to the most widely used type 135 film.
Lenses with an equivalent focal length of about 40-50 mm are called normal, since they give an image similar to what is visible to the naked eye (in both cases, the spatial relationships of objects will be visually the same). A shorter focal length lens is called a wide angle lens. In this article, we are looking at lenses with an equivalent focal length that is substantially longer than normal.
As teleoptics, you can use universal lenses with a variable focal length, which are often installed in compact cameras with fixed lenses. The image geometry is independent of the lens design and is determined only by its equivalent focal length.
No matter how strange it may sound, the spatial relationships between parts of the image of an object do not depend on the focal length of the lens with which the picture was taken. They are determined only by the distance from the camera to the subject. This statement is easy to prove using elementary information from geometry; we propose to solve this problem for inquisitive readers on their own.
Note that the "geometrical" equivalence of digital and optical zoom follows from the invariance of spatial relationships. But in practice, the use of digital zoom leads to a decrease in the maximum resolution of the image. This happens because the digital zoom “cuts out” a smaller fragment from the frame, which means that it uses only a part of the photosensitive elements of the matrix. The exact same effect can be achieved by cropping a picture taken without digital zoom in the camera.
Let's talk about telephoto lenses
Warning - this article is based on personal experience. The focus is on Canon techniques that I have worked with during my photography experience.
What is a telephoto lens for anyway?
Probably at least half of the owners of DSLRs with a standard zoom lens want to buy a telephoto lens. To the question "why do you need a telephoto lens?"
most often you have to hear the answer, which is hard to argue with - "to bring everything closer!" :) As a rule, a telephoto lens is really used to shoot objects that cannot be approached - from banal water lilies and houses "on the other side", ending with professional photography, sports photography, shooting aircraft and so on. Also, telephoto lenses, due to their ability to strongly blur the background, are often used for portraiture. Some telephoto cameras allow you to shoot good macro. In other words, the range of tasks that a telephoto lens allows you to solve is quite wide.
This article covers the main points during the selection, purchase and use of a telephoto lens.
Which telephoto lens to choose
Each manufacturer of photographic equipment, as a rule, has a huge number of telephoto lenses. If we consider Canon, then at least a dozen models come to mind (fixes are not taken into account yet)!
- Canon EF-S 55-250mm f/4-5.6IS
- Canon EF 70-200mm f/2.8 USM L
- Canon EF 70-200mm f/2.8 USM L IS
- Canon EF 70-200mm f/4 USM L IS
- Canon EF 70-200mm f/4 USM L
- Canon EF 70-300mm f/4-5.6 USM IS
- Canon EF 70-300mm f/4-5.6 USM L IS
- Canon EF 100-300mm f/5.6L
- Canon EF 100-400mm f/4.5-5.6 USM L IS
Other manufacturers are in a similar situation. All this diversity is complemented by a large number of telephoto models from Sigma, Tamron. The cost of telephoto lenses can range from a few hundred to several thousand dollars! How to understand all this diversity and choose a telephoto lens with the best ratio of price, functionality and image quality?
First of all, let's do a little freestyle classification of telephoto lenses.
By focal length
Like all optics, telephoto lenses are divided into zooms and fixes. The zoom lens has the ability to change the focal length within certain limits, thus changing the scale of shooting an object from medium to very large (wide-angles give a small scale, they were discussed earlier).
Telephoto lenses with a fixed focal length do not have such an opportunity to crop with them will have to run. Moreover, taking into account their very small viewing angle, you will have to run very long distances, and sometimes even climb mountain slopes, stairs, ladders, trees - depending on what we are going to shoot. The use of long-focus fixes is mainly the lot of hunters, astrophotographers, sports photojournalists. As a rule, special areas are used for shooting, booths, the location of which is "adjusted" so that the scene is clearly visible and the distance to the subjects of shooting is optimal for using a given focal length.
Sports photojournalists with telephoto cameras
IN everyday use zoom lenses are much more practical. In most cases, they have worse aperture and image clarity, although there are also very sharp and beautiful zooms - in this case we are talking about professional "moderate" 70-200mm telephoto lenses.
To more clearly give a concept of how the "degree of approximation" is related to the focal length, a lens simulator will help:
See how the field of view of the lens changes with focal length and when used on a full frame sensor (FX) and crop 1.5 (DX).
By luminosity
Aperture characterizes the maximum light transmission of the lens. The faster the lens, the more light gets to the matrix (with a fully open aperture) and the shorter the shutter speed is required. Another well-known pattern is that the larger the aperture ratio, the wider the depth of field can be changed. This is true for portrait photography, where lenses that give strong and beautiful background blur are highly valued.
High-aperture telephoto optics allows you to realize a large number of creative ideas. As a rule, these are very expensive professional-grade lenses. One of the elements of prestige for each manufacturer is "moderate" telephoto lenses with a focal length range of 70-200mm and a constant aperture of f / 2.8. These are professional zoom lenses, "sharpened" for portrait photography. They, as a rule, give excellent image quality - in the field of sharpness, the detail is huge, while the background is blurred very strongly and beautifully. Contrast, color reproduction, light resistance are also at a very high level. 70-200mm f/2.8 lenses are hugely popular among wedding photographers, allowing you to simultaneously solve the tasks of reportage and portrait shooting. Lenses 70-200 mm also have "light" versions - with a constant aperture of 4. They are significantly cheaper and more compact than their "big brothers", however, they have fewer opportunities, although, in fact, this optics is very good.
The aperture of most amateur telephoto lenses is very low - at the short end of f / 4, at the long end - f / 5.6 and even less. This imposes some restrictions on the use of such lenses in artistic portraiture (which is most often carried out in the range up to 135-150 mm) and shooting fast moving objects - due to the small amount of light falling on the matrix for shooting with a short shutter speed, you have to greatly increase the sensitivity ISO.
If you look closely, among professional telephoto lenses sometimes there are not very fast ones! Here is an example:
- Canon EF 70-300mm f/4-5.6 USM IS (costs about 20,000 rubles)
- Canon EF 70-300mm f/4-5.6 USM L IS (costs about 45,000 rubles)
It seems that the differences are only in one letter, but "Elka" costs more than 2 times more. What's the catch?
In fact, these lenses are quite similar in appearance to each other (the usual 70-300 is black, the Elka is white and slightly larger in diameter). The difference is in the stuffing. Lenses have a different optical design and they use lenses of different classes. As a result, the inexpensive "simple" 70-300 has acceptable picture quality only for 2/3 of its range (somewhere up to 200 mm), then there is a noticeable decrease in sharpness, chromatic aberrations appear. "Elka" gives a brighter, richer and sharper picture over the entire range of focal lengths.
By the presence / absence of stabilization
You probably know that Image Stabilizer helps to compensate for camera movement caused by hand shake (shake), thus allowing you to shoot at slower shutter speeds and still get sharp pictures. Now stabilizers are installed in almost all lenses, but stabilization is most relevant in long-focus optics, that is, in telephoto lenses.
There is such a rule - in order to get guaranteed clear pictures, you need to shoot with a shutter speed no longer than 1 divided by the focal length (in film equivalent). That is, if we have a focal length of 50 mm, then the "safe" shutter speed will be 1/50 second (or shorter). If the telephoto lens has a focal length of 300 mm, then the "safe" shutter speed will be 1/300 second on a full frame and about 1/460 second on a "cropped" camera (in terms of a 1.6 crop, 300 mm turns into 460 mm).
From this it follows that a handheld 300mm telephoto lens can only be shot on a bright sunny day! If the shutter speed turns out to be longer than safe, there are ways out - open a wider aperture (often sacrificing detail at the same time), increase the ISO (this increases the noise level), or use a tripod (this reduces the mobility of the photographer).
And here stabilization comes to the rescue - the included stabilizer is able to increase the safe shutter speed by 2-3 times. That is, instead of 1/300 second, the "safe" shutter speed for 300mm will be 1/100 second (1/160 sec on crop). Agree, the stabilizer gives a serious advantage and in most cases allows you to refuse to use a tripod and shoot at low ISO sensitivity not only in sunny, but also in cloudy weather, sometimes even in the evening.
Thus, it can be concluded that the image stabilization function is extremely useful for a telephoto lens. However, in fairness, it should be noted that the stabilizer is only useful when shooting stationary objects (for example, a landscape). If you are going to shoot moving subjects, such as athletes, stabilization will not help you - in order to "freeze" the movement, you need to reduce the shutter speed by opening the aperture and / or increasing the ISO sensitivity.
What you need to know when buying an inexpensive telephoto lens?
The main disadvantages of most budget telephoto lenses are low aperture, a noticeable decrease in image quality with increasing focal length, chromatic aberration, and vignetting at an open aperture. Some especially cheap models do not have image stabilization - such lenses are included in the special offers of stores and are "sold" along with budget DSLRs as a bonus (of course, not free). Thus, stores get rid of stale illiquid goods. Before "pecking" on such an offer, think about what you will photograph with this lens?
Portrait
Yes, compared to a whale lens, this lens will blur the background better. Below is a portrait taken with a Canon EF 75-300mm f4-5.6 IS USM telephoto lens (focal length 75mm, f/4, Canon EOS 300D)
As you can see, there is blur, but not very strong. To enhance it, you need to increase the focal length to about 200 mm. The following example is a portrait shot with a Canon EF 100-400mm f4-5.6L IS USM telephoto lens (focal length 210mm, f/5.6, Canon EOS 5D)
Already better, but I had to shoot from a very long distance (about 10 meters), which is not always convenient.
But if you try to shoot portraits with a fast fixed lens, even if it is inexpensive and not so long-focused, for example 50mm f / 1.8, you will probably completely lose the desire to continue shooting portraits with a budget telephoto lens and immediately there will be a desire to save up for a good “portrait lens”, for example, 50mm f / 1.4 (better for crop) or 85mm f/1.4 (better for full frame). They cost about the same as a budget telephoto lens, sometimes even cheaper.
The last photo was taken on a Canon EOS 5D with a Samyang 85mm f/1.4 lens wide open. You can see how much blur can be achieved when using a fast "portrait" fix. Moreover, the shooting distance in this case did not exceed 3 meters.
Scenery
Although landscape photography is not the main function of a telephoto lens, it can sometimes be used successfully to capture some interesting parts of the landscape. You can judge from these two photos what quality a cheap telephoto lens will provide when shooting a landscape:
Focal length 220 mm
Focal length 300mm
The pictures were taken with a 6-megapixel Canon EOS 300D and a Canon EF 75-300mm f/4-5.6 IS USM lens back in 2005. We see that at 220 mm the quality can be called bearable with a big stretch, but at 300 mm there is simply no sharpness! However, I recently saw a "double kit" in the store - an 18-megapixel Canon EOS 600D with an 18-55 mm kit lens and a Canon 75-300mm lens (you have already seen photos from it), and the version no stabilizer! Is it worth throwing out small, but still money for such optics?
Someone will rightly argue that the new telephoto lenses have improved image clarity. Yes, but do not forget that at the same time, the resolution of the matrices has increased many times over, therefore, even if the situation as a whole has improved, it will not be radical - 100% of the cropped photos will be about the same. Budget telephoto lenses at the long end are not able to give a really high-quality picture.
Photo hunting
Due to the low resolution at the long end, photographs of animals and birds will only be suitable for printing in small format or publishing on the Internet. Due to the low aperture, you will have to significantly increase the ISO in order to photograph animals and birds in motion - this will cause increased noise in the pictures. It will quickly become clear that 250-300 mm is too small for shooting animals in their natural habitat, the maximum of which you can shoot more or less close-up is animals used to people (cats, dogs, pigeons, etc. ). Wild animals with such a lens can only be photographed in a zoo (through bars and glass walls of pens).
Travel photography
For these purposes, "travel zoom" is much more convenient - a lens that has a range of focal lengths from wide-angle to moderate telephoto. The most popular travel zooms for crop are Canon 18-135mm, Nikon 18-105mm. Having two lenses - a standard zoom and a telephoto lens, you will inevitably face two difficulties - the dimensions and weight of the kit (two lenses are larger and heavier than one), as well as the need to swap these lenses (risking something to drop or pick up dust on the matrix). From my own experience, I can say that during excursions it is quite rare to take pictures leisurely - even if the guide gives you free time, there are a lot of people who want to take pictures and you will have to act quickly. In this regard, it is preferable to have one universal lens than two for different purposes. The image quality of travel zooms is quite good, they often outperform both a whale lens and a budget telephoto.
If you strain, you can still find a bunch of reasons to dissuade you from buying a cheap TV. But if the desire to buy has not yet disappeared, then I will give some recommendations - how not to make a mistake with a purchase and how to enjoy shooting?
1. The main recommendation is that if the lens is not fast, it is highly desirable to have a stabilizer. Image stabilization will significantly reduce the percentage of defective shots due to shake, and will also make it possible to cover the aperture to 8-11 - it is at these values that the best sharpness is achieved.
2. Don't mess with "super zooms" - 18-200mm, 28-300mm, 18-270mm, etc. They have a useless aperture at the long end, the image clarity of such lenses can be an order of magnitude lower than, even, that of a whale 18-55 mm.
3. Be sure to check the lens for front / back focus.
Which lens to buy - "cropped" or "full frame"?
If you have a "cropped" device and you do not plan to switch to full frame, I personally don’t see much point in purchasing a “full-frame” 70-300 mm lens - it costs one and a half times more expensive, at least, and the quality is comparable to “cropped” lenses of the 55-250 mm family.
I remind you that budget televisions have only 2/3 of the "working" range, then there is a noticeable decrease in clarity. At the same time, the difference in "effective" focal lengths between 55-250 and 70-300 generally disappears.
The 55-250 lens is not devoid of mechanical design flaws - it does not have dust protection, with a telescopic design this will inevitably cause dust to get inside and settle on the lenses. But for such a price - this is a very good purchase, especially if it is included in the so-called "double kit" - then its price is generally ridiculous.
There is also a very interesting option - Canon EF 70-200mm f/4L USM. Its cost is about 40 thousand rubles (second-hand can be found cheaper). Despite the fact that this cheapest version of the lens does not have a stabilizer, its picture quality is noticeably better than that of the above mentioned telephoto lenses. For some, this will be a strong argument - when using a tripod, this lens will allow results that are simply unattainable for budget optics.
The lens has an exceptionally robust design with internal focusing and internal zoom to prevent moisture and dust from entering the lens. Disadvantages - rather large dimensions and considerable weight. There is a version of the lens with a stabilizer, but it costs 1.5 times the basic version.
Canon EF 70-200mm f/4 L USM IS
Third-party budget telephoto lenses - is it worth getting involved?
The most popular third party manufacturers are Sigma and Tamron. As a rule, their lenses are cheaper than the original ones, but often they are no worse in their characteristics and provide comparable or even the best quality Images. But there are also pitfalls. The main one is a greater likelihood of running into a low-quality copy. If you are inclined to buy a Sigma, Tamron telephoto, I recommend not taking the first lens that comes across, but testing several copies and choosing the best one.
How to choose the best?
There are two ways - to take photos with all the test lenses, and then looking at a large screen (for example, on a laptop taken with you to the store) choose the one with the best picture quality. The option is reliable, but not always acceptable - it is not always possible to use a laptop.
The second way - put the camera on a tripod, fix its settings and put all the lenses from the test set in order on it, shoot the same thing and look at file size! The larger it is, the better the detail of the photo. This method allows you to quickly select the sharpest instance. But, I repeat, for all lenses you need to create absolutely equal conditions. The most suitable for photography are colorful objects that completely fall into the depth of field zone, for example, a page with text, a shop window, a poster on the wall.
How to test a lens when buying, read my essays.
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