What is the advantage of larger lenses
The lens is a kind of "extension" of the aperture of the pinhole camera.
You can usually use it to set both the shooting distance and (at least that was the case in the past) the aperture. Lenses can be differentiated according to their largest adjustable aperture (the light intensity) and according to their focal length.
Based on the possible angle of view, which depends on the focal length of the lens in conjunction with the sensor or negative size of the camera, they are divided into Wide angle, normal and telephoto lenses a.
In more detail
What do the different markings on the lens mean?The central information on a lens is the focal length and the aperture.
Especially the two pairs of numbers 28-135 and 3.5-5.6 are important because they characterize the special properties of the lens.
28-135 indicates that it is a zoom lens is that between 28mm to 135mm (corresponds to a range from the medium wide angle to the telephoto focal length on the full format sensor) can be continuously changed in the focal length (more about the focal length and its meaning below).
In the case of a lens with only one focal length (a fixed focal length), there would be no area here, only a single numerical value)
The second pair of numbers indicates the largest possible aperture, the so-called light intensity. (More about this below on the page)
If there is only one numerical value, the lens has the same light intensity with every focal length setting.
In this case, however, the largest possible aperture changes when zooming, with the shortest focal length an aperture of 3.5 is available, with the longest, however, only an aperture of 5.6 is available. The longer the focal length is set on this lens, the lower the light intensity.
With this Canon lens, the marking means "EF"that there is a lens for one Full format sensor acts. However, it can also be used with a camera with the smaller "cropsensor".
Lenses marked "EF-S"may (and can) only be attached to the smaller sensors.
The "IS"The label says that this lens has an" Image Stabilizer ", with which (somewhat) longer exposure times can be used without blurring. Other manufacturers use the corresponding abbreviations for example"VR"or"OIS"or"OS"
Be careful, other manufacturers use different abbreviations. Even if the respective lenses are intended for Canon.
Why do you have to focus?
At the point where there is a hole in the pinhole camera, a "real" camera has a lens. This lens can collect the light and thus ensure a stronger exposure of the sensor or the film, which enables significantly shorter exposure times.
However, we have to pay for this advantage with a disadvantage. While everything is (more or less) in focus with a pinhole camera, when we take photos with a lens, we have to focus on the desired distance.
Several lenses (sometimes in groups) are usually used in the lenses, which are intended to improve the sharpness and display performance of the lens.
Different types of lenses are used, one of the most important is the converging lens. It collects the light emanating from one point on the subject and unites it in the focal point.
Very similar to how you can focus the light of the sun to set a piece of paper on fire. This is where the term "focal point" comes from.
In photography, the lens does not collect the light on a simple paper but on the recording material, i.e. the sensor or film.
If the subject point is closer to the camera, i.e. not infinitely far away, one no longer speaks of the focal point, but of the image point.
How large the distance between the lens and the image point (i.e. the area in the camera) has to be for a sharp image depends on the distance of the starting point (subject point) from the lens. If this distance is suitable for a distance, details of the subject that are closer or farther away have their sharpest image point at a different distance between the lens and the sensor.
In order to focus on the details of the subject, it is important that the image point lies on the sensor. The pixel in the figure below is on the sensor / film. In this way, all points of the subject are also reproduced as points on the picture.
If the subject is too close, its image point is behind the sensor plane, and no point is created on the film / sensor, but a circle, the so-called blurring circle. And even if the subject is too far away, i.e. the image point is in front of the sensor, blurring circles arise.
In order to create a sharp image, in which a point in the subject is also depicted as a point, you have to focus on the correct distance from this point.
To do this, the distance between the recording plane and the lens is either shortened (distant object) or lengthened (close subject). I will explain later in this chapter how to check and adjust the distance setting for the different types of cameras and what you have to pay attention to.
There are limits to focusing, you cannot set any distance. Most lenses have one Restriction in the close range, that is, there is a distance at which subjects can no longer be focused because they are too close (the recording plane should therefore be further away from the lens than possible).
If a subject is too close, you can try to use spacer rings to increase the distance between the lens (or objective) and the sensor.
But most of the lenses then only have an inadequate performance in this close-up range, for best performance you should rather use special macro lenses that are specifically optimized for this task area.
For most lenses, the distance is set by turning an adjustment ring. This changes the distance between the lens and the sensor / film and thus also the sharpness.
If the lens moves closer to the recording plane, distant subjects become sharp, if it moves away from the recording plane, nearby objects become sharp. This also happens with autofocus lenses, in which the rotation - and thus the change in the distance between the lens and the recording plane - is carried out with a motor and controlled by the camera.
Changing lenses with different focal lengths for changing angles of view
For many cameras, especially for single lens reflex and system cameras, there are various interchangeable lenses. Depending on the situation and the desired image, you can use another one with a different light intensity and focal length or zoom range.
Of course, the lens has to match the camera.
Among other things, this involves the mechanics of the connection between the camera and lens, in which most manufacturers use different mountings (nowadays designed as bayonet connections). The lenses from camera manufacturer N therefore usually do not fit the cameras from manufacturer C.
Some combinations can be done with tricks and special adapters use it anyway, but functions like the Auto focus lost walk.
Through the different sensor sizes With digital cameras, there may be other difficulties.
Lenses are round and produce circular images in the camera. These so-called Image circles must for the respective film or sensor be big enough, otherwise the corners of a picture will be shadowed, it usually comes to one unwanted vignetting (Shading of the edges / corners of the picture).
Lenses with large image circles are more difficult to construct, which is why there are many lenses that are only intended for small sensors and are therefore offered at lower prices.
The smaller image circle of these lenses would probably not completely illuminate a larger sensor. Such lenses therefore have a slightly modified connection so that they cannot be attached to cameras with larger sensors even if they come from the same manufacturer.
On the other hand, this is not a problem, the lens with a large image circle can easily illuminate the smaller sensor, so these lenses can also be attached to cameras with smaller sensors ("crop cameras"). At least if they have the same connection.
"Large" lenses (with labels like FX or EF) also fit "small" cameras, small lenses (DX or EF-S) do not fit "large cameras.
Interchangeable lenses are a great advantage when you need them, but many photographers get by with a single lens for a large part of their pictures. It is not always good to have too much choice; if you have a lot of lenses, you do not necessarily take the better pictures.
But why should you change the lens at all, what is the difference between the individual lenses? In addition to the quality, there are primarily two points that make the difference: the focal length and the light intensity.
Depending on the diameter of the lens opening and the length of the lens (focal length), different amounts of light reach the sensor. A large opening lets more light onto the sensor (with the same focal length), the lens is "bright".
A higher light intensity makes it possible, with the same sensitivity (ISO) take photos with less lightbecause there is still enough light to reach the sensor or film through the larger opening.
In order to achieve a high light intensity, you need one with the same focal length larger opening, so bigger lenses. Larger lenses are more difficult to manufacture and process. That is why lenses with a high speed are used mostly more expensive.
The light intensity is given in numerical values. It corresponds to the largest possible aperture of the lens and is given with the same numerical values as for the apertures. The larger the possible aperture and thus the light intensity, the smaller the number. A So small number means high light intensity. (I will explain why this is so in the "Exposure" chapter in the section on aperture.)
A lens with a speed of 1.8 is faster than one with a speed of 4.
In order to signal the customer even the last bit of additional opening, the manufacturers like to use "crooked" f-stops such as 2.6 or 2.9 when specifying the light intensity. So do not be surprised if numbers appear in this information that do not appear in the normal aperture row (more details on this subject follow in the "Exposure" chapter).
We saw above that the lens, depending on the recording distance, has to be at different distances from the recording medium in order for the image to be sharp. The further away a subject is, the shorter this distance has to be.
The concept of focal length is directly related to this and goes back to the early days of optics.
At that time, one differentiated between lenses, among other things, by the distance that was necessary for the lens to cast a point-like image of the sun on a (flammable) object. The distance between the lens and this focal point was then the focal length.
Today the sun is no longer used to determine the focal length, but the terms have remained the same.
In photography, the focal length is specified in millimeters, it can differ greatly for the individual lenses, or better: lenses.
Depending on the shape of the lenses in the lens, the focal point (and the image point of a subject detail, if the distance remains the same) can be closer or further away from the lens.
The distance necessary for correct focusing of the lens from the recording plane is then shorter or longer.
These different distances (focal lengths) have one Influence on the reproduction size of a subject.
A lens with a normal focal length results in a "natural" reproduction of the proportions (more on this later).
With a lens with short focal length one pixel is further forward than with a lens with a normal focal length, despite the same distance from the subject. The recording plane must therefore be closer to the lens in order to focus.
The motive becomes thereby shown smaller (like with a short pinhole camera), so it fits more into the picture.
The respective focal length of the lenses has a decisive influence on the image composition / effect.
I will go into this in more detail on the following pages. One differentiates the lenses according to their focal length in Wide angle, normal and telephoto lenses.
Which group a lens belongs to does not only depend on its focal length. It is only through the connection with the size of the sensor or film for which it is used that the appropriate name emerges.
Why does the sensor size influence whether a lens is wide angle or telephoto?
Well, it's primarily about the ratio of the size of the image to the overall size of the sensor or film. First, let's look at a normal situation.
With this sensor size, the image of the person fills the entire image. If we now keep the focal length and change the size of the recording medium, the image changes too.
If you take a smaller recording medium, the subject becomes in relation to reproduced larger than the recording medium.
As a result, the photographed section now corresponds to that which would have been photographed with the larger sensor with a longer focal length.
In the second example, the upper body of the person being photographed now fills half of the picture.
The same result can be achieved by using a longer focal length (the focal point of which is further back for the same shooting distance) and a larger recording medium. The upper body of the person being photographed fills half of the (larger) picture again.
The proportions within the image boundaries are the same as in the previous illustration.
So we have that same image effect, once when using a longer focal length and the other timeby not lengthening the focal length, but rather reduce the sensor size.
For most photographers, this relationship between the creative effect of the focal length in combination with the negative size is not so important, because in practice it is very seldom possible to change the size of the recording medium.
And what is a normal lens now?
A normal lens reproduces the proportions roughly as we perceive them when looking at them with the naked eye.
This is the case when the lens focal length roughly corresponds to the diagonal of the sensor or negative used.
A 35mm negative is 24 x 36 mm in size, so the diagonal is approximately 50 mm (43 mm). A normal lens for 35mm film has a focal length of 50 mm.
All "shorter" lenses (35 mm, 28 mm, 24 mm, 20 mm, ...) are wide-angle, all longer ones (85 mm, 105 mm, 135 mm, 180 mm, 210 mm, 300 mm, ...) are telephoto lenses.
The smaller sensor of many digital cameras only uses a section of the image (better: image circle) that a lens generates for classic 35mm or so-called (digital) full-frame cameras.
With regard to the viewing angle, the section used is exactly the same as if you had used a 35mm negative or a full-format sensor in the same situation with a longer focal length (see images above).
In order to be able to compare the lenses despite different recording formats, the focal lengths are converted. First you determine the factor by which a 35mm negative (24 x 36 mm) is larger than the actually used recording format.
With many digital SLR cameras this factor is 1.5, with Canon 1.6 (or 1.3), with Sigma 1.8, with MicroFourThirds 2.0. With the bridge cameras and especially with the small compacts and the cameras in smartphones, significantly higher values of up to 7 and more can appear.
If you now have the used focal length with this factor, the Crop factor multiplied, you get the corresponding focal lengththat for same size impression of the subject on the full format sensor or 35mm film. This is how you calculate the Small image equivalent focal length.
At a larger recording medium, the normal lens is larger/longer.
For the medium format 6 x 6, for example, the normal focal length is 80 mm (55 x 55 mm negatives). A 50 is a wide-angle lens here. The "normal" 80s for medium format is a slight telephoto for small pictures.
And in front of the comparatively tiny sensor of a small digital viewfinder camera, the normal focal length is only about 11 mm or less (depending on the sensor size).
But the whole thing is not just dependent on numbers. What a normal lens will be determined by personal preference. For many photographers in the 35mm field, the 35 (and not the 50) is the normal lens.
The following pages deal with the different creative effects of the focal lengths.
In my beginner photography courses on the basics of photography, the right lens and focusing naturally play a major role.
Photo courses with Tom! Striewisch3
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