Streetphotography

At 300mm and upwards, we have the super-telephoto range. This is most commonly used by sports and wildlife photographers, where it would be impossible to get close to the subject. At this range, and with such a narrow angle of view, it’s usually advisable to use a monopod or tripod to reduce camera movement (although Nikon’s in-camera vibration reduction (VR) and VR lenses can help with that), and also because lenses this size can be heavy to hold for long periods. Telephoto lenses can also be used with a teleconverter, which can double the focal length of the lens, giving you even more ‘reach’.

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But there’s more. Depth of field determines what part of the image is in focus going from front to back. Lenses with longer focal length tend to have a shallower depth of field, meaning you can focus on and separate (or isolate) a particular object far away, whereas shorter lenses have a deeper depth of field, which means you can get more objects in focus throughout the image.

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Portraitphotography

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Check out these images of the same scene shot from the same position but with focal lengths from wide angle 24mm to telephoto 180mm and you can see how the angle of view gets narrower as the magnification gets larger.

The most important thing about focal length, however, is not what it is, but what it does. Focal length defines two main things about any lens: its magnification and its angle of view.

If you had a simple lens made of a tube with one piece of optical glass at the front that focused the incoming light rays on a point at the back of the tube, the length of the tube would be the focal length of the lens. Modern lenses, however, use lots of different pieces of glass inside the casing to move light around before it hits the sensor and therefore focal length has nothing to do with the physical length of your lens. You can find two 85mm lenses that are completely different in size while, for example, the new NIKKOR Z 600mm f/6.3 VR S is less than 300mm in length.

The figure on the left illustrates this using the example of a diffraction-limited (i.e. perfect) lens for 20 line pairs per mm and f-number k = 22 at a wavelength of 546 nm. The relative illuminance is plotted as a function of image angle.

For extreme wide-angle designs with large image angles, it should be noted that the modulation in the image field decreases with the cosine for sagittal structures and with the cube of the cosine of the image angle for tangential structures.

Any lens with a focal length of between 8mm and 24mm is usually described as an ultra-wide. You’ll be taking in a huge angle of view of what’s in front of the camera. These are lenses for getting in really close with your subject to create drama and are also used extensively for astrophotography. However, at really low focal lengths there will be significant distortion at the sides of the image where straight lines start to look curved. Ultra-wides are one the hardest lenses to master but, with effort, they can deliver incredible results.

Angle of view is how much of the scene your lens will capture from side to side (holding the camera horizontally). A wide angle of view takes in a lot, a narrow angle of view less. Magnification is how ‘close’ you get to the subject of an image with the lens, like a telescope.

From 35mm and 70mm, we have the ‘standard’ focal length, which is pretty close to what the human eye sees. Photographers talk about the ‘nifty fifty’ – a large aperture 50mm prime lens such as the NIKKOR Z 50mm f/1.8 S – because a 50mm lens is an ideal day-long companion, suitable for so many different types of shooting, especially in low light situations or indoors. This type of lens also creates a shallow depth of field and great bokeh blur.

focallength中文

Camera lenses are usually described by two main factors: one is the aperture or f-number (the maximum size of the hole where light gets through to the sensor, where the lower the number, the bigger the hole). The other is focal length, which is in millimetres. You will usually see lenses described by focal length first and then aperture, for example 85mm f/1.8.

As one of the world's leading manufacturers of precision optics, Schneider-Kreuznach attaches great importance to ensuring that only first-class products leave the company. For this reason, every finished lens undergoes a three-stage test procedure. In the 3D precision measurement, computer-controlled measuring devices check the accuracy of the mechanical components. Optical engineers then use MTF measurements to determine whether the assembled optical system deviates from the calculated values. At the end of the testing chain, each lens is visually inspected by Schneider experts. This includes evaluation of the optical performance in the projection test as well as cosmetic aspects (dust, scratches).

Focal length

If you had a simple lens made of a tube with one piece of optical glass at the front that focused the incoming light rays on a point at the back of the tube, the length of the tube would be the focal length of the lens. Modern lenses, however, use lots of different pieces of glass inside the casing to move light around before it hits the sensor and therefore focal length has nothing to do with the physical length of your lens. You can find two 85mm lenses that are completely different in size while, for example, the new NIKKOR Z 600mm f/6.3 VR S is less than 300mm in length.

As angle of view goes down, magnification goes up. For example, a 24mm lens has a wide angle of view (around 84 degrees) and low magnification – perfect for sprawling landscapes. A 600mm lens has a very narrow angle of view and large magnification – great for taking close up shots of faraway wildlife (especially useful when you don’t want to get too close to a lion!).

As you can see, the modulationdeteriorates for finer structures and drops to zero at a certain number of line pairs per millimeter. The impression of sharpness is therefore not determined by this highest spatial frequency, but by the highest possible contrast reproduction over the entire spatial frequency range, up to a maximum spatial frequency depending on the application.

The focal length of a lens also affects the perspective of an image. With a long lens, perspective tends to be compressed, with objects in the background appearing closer to the subject in the foreground, whereas with a wide-angle lens the relative distance between two appears greater.

The ideal lens is one that faithfully reproduces all the coarse and fine structures in an object. This means that differences in the brightness of the object must be reflected in the image in the same way for a wide variety of structures.      For physical reasons alone, this requirement cannot be strictly met. Contrast losses occur to a greater or lesser extent in the entire range from coarse to fine structures. This entire structure range is now measured numerically by the number of line pairs per millimeter (spatial frequency R [1/mm]).

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focallength是什么

The MTF curves valid for the two orientations are shown in the diagrams as dashed (tangential) and solid (sagittal) in the diagrams.

Try: NIKKOR Z DX 24mm f/1.7, NIKKOR Z 26mm f/2.8, NIKKOR Z 28mm f/2.8, NIKKOR Z DX 16-50mm f/3.5-6.3 VR, NIKKOR Z 35mm f/1.8 S

Try: NIKKOR Z 70-180mm f/2.8, NIKKOR Z 85mm f/1.8 S, NIKKOR Z 135mm f/1.8 S Plena, NIKKOR Z 70-200mm f/2.8 S, NIKKOR Z DX 50-250mm f/4.5-6.3 VR

Camera lenses are usually described by two main factors: one is the aperture or f-number (the maximum size of the hole where light gets through to the sensor, where the lower the number, the bigger the hole). The other is focal length, which is in millimetres. You will usually see lenses described by focal length first and then aperture, for example 85mm f/1.8.

Try: NIKKOR Z 20mm f/1.8 S, NIKKOR Z 14-30mm f/4 S, NIKKOR Z 17-28mm f/2.8, NIKKOR Z DX 12-28mm f/3.5-5.6 PZ VR, NIKKOR Z 24mm f/1.8 S

Lens choice can often be difficult, especially with so many options in the Nikon Z mount range (and access to another 300 or so Nikon F mount lenses with the FTZ II converter). So, here’s a quick guide to the different focal lengths and what they often get used for to help you.

Try: NIKKOR Z 180-600mm f/5.6-6.3 VR, NIKKOR Z 100-400mm f/4.5-5.6 VR S, NIKKOR Z 400mm f/4.5 VR S, NIKKOR Z 600mm f/6.3 VR S

Focus distance

Usually between 70mm and 200mm, a telephoto lens is a popular choice for portraiture and weddings (especially an 85mm focal length) and at the longer end is great for wildlife where you can’t get too close to the subject. At the longer end, a telephoto lens gives you the freedom to shoot as an observer where the subject is unaware of the camera, and so is also great for fly-on-the-wall, reportage-style shooting. This is also the focal length range for many macro lenses.

From 24mm to 35mm, lenses are wide angle. These are beloved by landscape, interiors and architecture photographers, as well as being useful for street scenes and dramatic pictures of the night sky. Get close to your subject and you will accentuate the perspective in the scene. A wide angle is a great travel companion, allowing you to shoot landscapes, cityscapes, people and much more.

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In addition, the beam path in the lens becomes increasingly asymmetric for pixels outside the center. Therefore, the MTF also depends on the orientation of the line pairs in the image field. Two perpendicular orientations are selected from the large number of possible orientations, as shown in the adjacent figure.

A converging lens will focus light from a distant source to the point called the focal point. The focusing is illustrated in the figure on the right.

A specific MTF curve is also only valid for a specific point of view. In general, the MTF curves for different image points are different, so a large number of curves would be required to describe the entire image field. Therefore, another representation is used in which the modulation is plotted over the image height, starting from the center of the image, for reasonably selected spatial frequencies. This is the basis of the data sheets.

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In addition, the modulation transfer function depends on the f-number set, the image scale used, and the weighting of the individual spectral components. Therefore, additional MTF curves are needed to characterize the image quality. Insensitivity to changes in scale is also a quality criterion that must be taken into account.

There are two types of lenses: primes, which have a fixed focal length, and zooms, where the focal length is variable. Zooms are super-handy as you often only have to carry one lens around that will be capable of shooting lots of different subjects, from landscapes to portraits, so it’s great for travel. Prime lenses, however, are usually lighter and are often available with larger apertures than zooms.

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You should also bear in mind that focal length translates differently on a DX camera (such as the Nikon Z 30, Z 50 or Z fc) compared to an FX ‘full-frame’ camera because the sensor on a DX camera is 1.5 times smaller than the FX sensor. For example, if you put a 50mm lens on a DX camera, you will actually get the angle of view and magnification similar to an 75mm lens on an FX camera (because 50 x 1.5 =75).