The second oversimplification is that not all of the individual light waves that come from a source are necessarily polarized in the same direction. In fact “natural” light from light bulbs and the sun is “unpolarized,” which comes about because each of the individual light sources (atoms) are aligned in random orientations, and all send out random, unaligned light waves. When such light is passed through a polaroid, half the light gets through. To see why this should be so, break every electric field vector of every wave into components parallel and perpendicular to the polarizing axis. Because the wave polarization directions are randomly-oriented, there is no reason to expect there to be a greater sum of components along one axis than another. By “half the light gets through,” what do we mean? We mean that the intensity drops by one half. We look at the more general case of intensity next.

Fisheyelens

The electric field vector is the amplitude of the light wave, and we are interested in the intensity. As with any other wave, the intensity is proportional to the square of the amplitude, so the relationship between the outgoing intensity \(I\) and incoming intensity \(I_o\) is:

When you’re out shooting in-field, make sure to check the edges of your frame and to give each element enough breathing space for a thoughtful and well-balanced image.

In contrast to wide angle lenses, which can exaggerate leading lines and emphasise subjects with extraordinary sense of depth, telephoto lenses are great for more intimate scenes, where the focus is on shape and form rather than large, far-reaching vistas.

telephoto是什么

Typically in landscape photography with a wide angle lens, the aim is to have everything in focus from foreground through to the back. This often means shooting with smaller apertures – depending on your workflow and the scene, this can from f/8 through to f/16 and often involves taking several images for focus-stacking.

The range of remote shutter releases on the market vary quite markedly in price from cheap to expensive. You can usually find great options made by third-party manufacturers for a fraction of what you would pay if you were to purchase one made by a major camera brand.

where \(n_1\) is the index of refraction of the medium within which the reflection is occurring, and \(n_2\) is the index of refraction of the medium off which the reflection is occurring.

While one of the hallmarks of landscape photography is the use of a wide angle lens to capture the expansive grandeur of nature and to create a sense of depth, there are times when opting for a longer focal length can increase your creativity and lead to better photographs.

As stated previously when discussing the speed of light waves through transparent media, the mechanisms that govern light propagation through media are complicated. There is little we can say about it in this class, except to say that because the light wave is electromagnetic in nature, it interacts with electric charge, which is present in all matter. It so happens that it is possible to construct a solid substance which greatly restricts oscillatory motion of electric charges along a single dimension. The upshot of this is that the charges react to electric fields along one direction (or rather, components of electric fields along one direction), while they don't react along a perpendicular direction.

During our photo tours, we sometimes hear photographers saying that they have trouble with using telephoto lenses, simply because they aren’t able to capture enough of the surrounding landscape. Some photographers find it difficult to make a composition with a telephoto lens, whereas others just don’t know how to use them effectively or even where to even begin.

Check out our top tips for photography using a telephoto lens to make the most out of your landscape photography. Photo by: 'Albert Dros'.

Compressing the scene with a telephoto lens has many uses. You can use it for enchanting forest photography, to capture tendrils of fog and mist in the landscape, as well as to photograph lightning. The possibilities are endless!

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This material can have a dramatic effect on light passing through it. If the light is plane-polarized (see Figure 3.1.1), then its propagation through a medium will be affected by the preferential orientation of charge oscillations. When the light polarization is aligned with what we define as the polarizing axis of the substance, then little of the light is absorbed by the substance (i.e. the substance is transparent to this light), while if the light is polarized perpendicular to the polarizing axis, then virtually all of the light is absorbed. Such a filter is called a polaroid or polarizer.

\[n_1\sin\theta_B = n_2\sin\theta_2 = n_2\sin\left(90^o-\theta_B\right) = n_2\cos\theta_B \;\;\;\Rightarrow\;\;\; \tan\theta_B=\dfrac{n_2}{n_1} \; , \]

This page titled 3.7: Polarization is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by Tom Weideman directly on the LibreTexts platform.

If you don’t have a remote shutter release or if you’re not keen on investing in one, then consider using the shutter release delay function on your camera. Most DSLRs will allow you to set a 2-second delay, meaning that after you press button, there will be a couple of seconds before the shutter is released. This is enough time for your camera to settle from the initial movement introduced by your physical contact, thereby reducing camera shake.

Remote shutter releases may be connected to your camera either wirelessly, by Bluetooth or by using a cable. You can usually stand a small distance away from your camera and trigger the camera’s shutter by pressing the button on the remote.

The aim of such a lens is to magnify subjects at moderate to far distances, so that you’ll invariably be able to take a photo of something that is further away within the landscape.

Unpolarized light enters a series of four polaroids with axes of polarization that are each rotated \(30^o\) clockwise from the previous polaroid, making angles of \(0^o\), \(30^o\), \(60^o\), and \(90^o\) with some common reference point. What fraction of the intensity of the incoming light is the intensity of the outgoing light?

Telephotolens

For the polarized sunglasses to remove all the glare, the angle the light makes with the perpendicular to the ice must be Brewster’s angle, so:

While most natural light is unpolarized and we can polarize it with a polaroid, it turns out that is not the only way it can be polarized. A more “natural” way to create polarized light exists thanks to reflection. As we have said many times, when light (or any wave) strikes an interface between two media, it is partially transmitted and partially reflected. Consider the following scenario: Light polarized in the vertical direction strikes an interface between media such that the reflected ray aligns with the electric field vectors of the transmitted ray. There is an important principle in physics that states that the conditions at the boundary have to work out properly. This means that the electric field vector of the incoming light must add up properly to the electric field after striking the interface. The electric field vector can of course be written in components with the “x-direction” being the electric field direction of the transmitted wave, and the “y-direction” being the direction of the reflected ray (which is perpendicular to the transmitted ray). But the outgoing light cannot have an electric field vector pointing along its direction of motion (light is a transverse wave), so no light reflects!

One interesting application of this phenomenon is 3-D movies. Long ago someone came up with a brilliant idea for making movies projected onto a 2-D screen appear in 3-D. The idea is based on the fact that a large component (but not the only one) of seeing in 3-D is stereo vision. Your right eye sees objects from one perspective, while your left eye sees it from a slightly different perspective. You can see this is true by holding up your finger in a fixed position and alternately opening-and-closing each eye. Your finger’s position appears to change relative to the background. This inventor’s idea was to project not one but two images on the same screen. One image is recorded from the perspective of the right eye, and the other from the perspective of the left eye. Then the trick is to make the right-perspective image invisible to the left eye and the left-perspective image invisible to the right eye, so that each eye sees only its own perspective. The original inventor did this with colors – red lenses obscure red images, and yellow lenses obscure yellow light, so films were recorded from two perspectives, and each perspective was projected in a different color – one red and one yellow. But today we like our movies to be in realistic colors, so someone came up with the idea of projecting the two images with differently-polarized light, and then give viewers glasses that only admit the properly-polarized light into the respective eyes.

\[I = I_o\left(\dfrac{1}{2}\right)\left(\cos^2 30^o\right)^3 = I_o\left(\dfrac{1}{2}\right)\left(\dfrac{3}{4}\right)^3=\dfrac{27}{128}I_o \nonumber\]

Widelens

While it is possible to handhold a telephoto lens when photographing landscapes, you’ll likely have to use a much higher ISO than you would if you were to have your camera on a tripod. This increases the likelihood of introducing more noise into your images, so where possible, use a tripod when shooting with longer focal lengths.

Given that telephoto landscape photography is all about the details, being zoomed in to such long focal lengths will mean that your viewer will be able to see every single aspect of your shots, from the trivial components all the way through to the absolute nitty-gritty points. This will leave you with very little room for error when focusing. In fact, it will be extremely evident even if your subject is only slightly out of focus.

The thing about telephoto lenses is that most of the time, they’re big. Oftentimes, they can also be very heavy. As such, it goes without saying that when shooting telephoto images in-field, the weight of the lens will leave your camera prone to shake. This can affect image quality, so in order to ensure optimum sharpness in your images, the best thing to do is to mount your camera to a tripod.

This feature is particularly useful when shooting handheld with a telephoto lens. It’s also a good idea to switch it on for landscape photography in windy conditions, as the image stabilisation in your telephoto lens can counteract the vibration and movement introduced by the wind hitting your tripod.

This process all comes down to what happens to the electric field vectors. After passing through the first polaroid, all the electric field vectors are aligned with that polaroid's polarizing axis. When those vectors come upon the second polaroid, just the component of the field vector that is aligned with the new axis gets through, resulting in a new vector shorter than the original.

Telephoto lenses may be used to make a distant subject appear closer in your frame, as well as to fill the frame in a meaningful way. They’re great for wildlife photography, for isolating details when out and about in nature, as well as for capturing action, photographing the moon and deep-sky astrophotography when you don’t have access to a telescope.

About the author:  Serena Dzenis is a landscape photographer based in Iceland. You can find more of her work on her website or by following her on Facebook and Instagram.

Resolving the original electric field vector into components parallel and perpendicular to the polarizing axis, and keeping only the parallel part means that the new electric field vector magnitude is:

If your telephoto lens comes with a tripod mount ring, then it is best to use that rather than to mount the camera to the tripod how you normally would. The tripod mount ring will help to balance the lens, meaning there will be less strain upon your tripod head. When unbalanced, a heavy lens can cause your tripod head to fall or to move about when you are lining up for a shot. The result can be extremely annoying, particularly when you lose that perfect frame of composition.

We can use this distance to derive the horizontal distance from the point of reflection to the point on the ice directly above the mammoth:

This is known as Malus's law. Notice that it works exactly as we expect for the cases where the angle happens to be \(0^o\) and \(90^o\).

By using Live View, you’ll be able to magnify your subject so that you can focus more precisely on a certain area. It’s especially useful when the subject is far away, such as with a mountain or a tree in the distance.

The remote shutter release is usually one of the last things on a photographer’s mind when it comes to purchasing accessories. However, it is an invaluable piece of equipment for landscape photography, particularly when using a heavy telephoto lens.

\[\tan\theta = \dfrac{x_1}{6\;ft} \;\;\;\Rightarrow\;\;\; x_1 = \left(1.4\right)\left(6\;ft\right) = 8.4\;ft \nonumber\]

Not convinced yet? Let’s have a look at what a telephoto lens actually is as well as our top ten tips for using one in-field to create stunning landscape images.

Shooting with a telephoto lens is not entirely different. You’ll still want to shoot at the optimum aperture range for your lens to ensure that you’ll end up with the sharpest images. In landscape photography, this is referred to as the ‘sweet spot’ of your lens and with most telephoto lenses, it will fall somewhere between f/8 and f/11. Here’s how to find the sweet spot of your lens if you’ve never done it before.

Primelens

Why? Well, a remote shutter release enables you to trigger your camera’s shutter without the need for you to touch your camera. This reduces the amount of camera shake that you introduce upon physical contact when pressing the shutter release button, which can help you to take much sharper and better landscape images.

Virtually every camera manufacturer has at least one telephoto lens in their line-up, so it isn’t difficult to find one to suit your particular type of camera. Some of the more popular telephoto zoom lenses on the market today include the Canon EF 70-200mm f/4L USM, Sony FE 70-200mm f/2.8 G Master and the Nikon AF-P 70-300mm f/4.5-5.6E ED VR. Even third-party manufacturers produce excellent telephoto lenses to fit full frame cameras of major brands, of which the more notable are Sigma and Tamron.

Opticallens

We can easily write down an expression for the "special angle" at which total polarization occurs (this is known as the Brewster angle), by noting that for this angle the reflected ray makes a right angle with the transmitted ray (because the field vector of the transmitted wave is perpendicular to the transmitted ray and is parallel to the reflected ray). Combining this fact with Snell's law gives the Brewster angle, \(\theta_B\):

Now let's consider what happens if we send the natural light through two polaroids in succession. Clearly when the light reaches the second polaroid it will be plane-polarized from the first one. If the second polaroid is oriented the same as the first, then all the light gets through, and the intensity is unchanged, and if its polarizing axis is at right angles to the first polaroid, then no light will get through it. But now we seek to determine the intensity of the light that passes through the second polaroid if the angle between their polarizing axes is somewhere between \(0^o\) and \(90^o\).

Telephoto lenses most definitely have a place in the world of landscape photography. These highly effective and versatile lenses can have a large impact upon your work, enabling you to improve upon your photography by seeing the world differently – the result being a portfolio of more diverse and unique images.

Due to their weight and general size, telephoto lenses are prone to moving – with your body if you’re shooting handheld and with the wind if you’re using a tripod. Either way, you will no doubt experience some degree of camera shake, including during the moment that you release the shutter, when electronic components move internally within your camera.

A paleontologist is looking for the remains of a wooly mammoth in an unusually clear section of a glacier. The glare off the ice from the sun makes it hard for her to see, so she puts on her polarized sun glasses and is immediately rewarded when, along the line where the glare is cut to zero, she finds what she is looking for. Now she just needs to figure out how deep the carcass is. Fortunately she has a physicist (you) on staff. You measure the height of her eyes above the ice surface to be \(6\;ft\), and you measure the distance from the position where she first saw the beast through the glare, to the point where you can look straight down at it. This distance is \(18.4\;ft\). You estimate the index of refraction of the ice to be 1.4. Find the depth of the wooly mammoth.

One of the benefits of using a telephoto lens is having the ability to compress the perspective of the scene. What does this mean exactly? Well, to put it simply, when you use a telephoto lens to shoot parts of the landscape that are further away from your camera, the result is that they will appear to be bigger and compressed closer to the foreground than they actually are.

The Brewster angle occurs when the reflected light makes a right angle with the transmitted light, and from symmetry (just reverse the direction of the light to see this), that is also true of the incoming glare and the light from the mammoth. Therefore we can use \(x_2\) and the tangent of the angle to get the depth:

Focal length

So whether you are after a mid-range telephoto or a super telephoto zoom lens, there will no doubt be something available out there to fit your needs.

When the unpolarized light passes through the first filter, the intensity is cut in half and comes out polarized at \(0^o\). Then it passes through three successive filters, and applying Malus’s law for each \(30^o\) change of polarization angle brings in a factor of 0.75 for each polaroid. The result is that the final intensity is:

Have you got any other tips for landscape photography with a telephoto lens? What has worked for you and what hasn’t? Leave a comment below!

Not only will you take sharper images with a telephoto lens between these apertures, but you’ll also ensure an adequate depth of field.

We have overly-simplified things here, in a couple of ways. First of all, a light wave does not have to arrive at the polarizer in either a parallel or perpendicular orientation – it could be aligned at any angle with the polarizing axis. What happens then? Well, electric fields are vector fields, which means they can be broken into components, so the component of the electric field that is parallel to the polarizing axis gets through, and the other component is absorbed.

Of course this result is only for vertically-polarized incoming light, so unpolarized light that reflects at this angle will have its vertical component removed, which means that the reflected light is horizontally-polarized. More generally, light that is reflected off a surface at just the right angle will be polarized parallel to that surface. It also happens that if the angle is not just right, then while the light is not entirely polarized, it is partially so (depending upon how close to the correct angle the reflection is). By "partially polarized," we mean that the amplitude of light waves measured (using a polaroid) along one direction is not the same as the amplitude measured along the orthogonal direction. In practice this means that a polaroid aligned parallel to a surface from which the light is reflected will admit more light than a polaroid aligned perpendicular to that surface.

Any movement or shake can and will affect the overall quality of your images so where possible, you should increase your camera’s ISO sensitivity. By shooting at a higher ISO, you’ll be able to capture sharper images with your telephoto lens for better landscape photography.

Last but not least, when using a telephoto lens for landscape photography, it’s important that you don’t frame your shots too tightly. While telephoto lenses are great for excluding unnecessary elements or distractions within your composition, a tight frame can reduce the impact of your images, making objects appear as though they have been cut off at the edges.

A telephoto lens will also give you room to experiment, particularly when there is a messy or lack of interesting foreground in the scene. Rather than capturing a wide angle view of the clutter, you’ll be able to isolate certain elements, to create interest in a different way.

Image stabilisation (also known as vibration reduction) is a function available on most telephoto lenses that reduces the risk of taking blurry images. Basically, these lenses have a floating lens element which moves automatically to compensate for camera shake when the image stabilisation feature is turned on.

To ensure a sharp focus when shooting with a telephoto lens, try focusing with Live View on the back of your camera’s LCD screen. Most digital cameras these days have this function, while some even have LCD monitors that can tilt in different directions, making focusing all the more easier.

This brings us to our next point, which is that when shooting with a telephoto lens, you’ll benefit a lot from increasing the ISO, even when shooting on a tripod.

telephoto lens中文

A nice application of this effect involves polaroid sunglasses. Most glare from sunlight comes off surfaces that are horizontal (roads, lake surfaces, etc.), which means that the light that reflects off such surfaces has a relatively small fraction of its polarization in the vertical direction. This means that if we place polaroids in front of our eyes that are allow only vertically-polarized light to pass, then very little of the horizontally-polarized glare gets through. Of course, only half of the non-glare light gets through as well, but at least one's vision of light of important objects (on coming cars or boats, etc.) does not have to compete with the incoming light from glare.

One might expect that since the first and last polaroids are at right angles to each other, no light at all should emerge from the last polaroid. But when the light passes through a polaroid, it gains a new polarization aligned with that polaroid's polarization axis, and has no "memory" of its previous plane of polarization. Unless two consecutive polaroids are at right angles, some light will always get through each polaroid.

Using a telephoto lens for landscape photography can be a little bit difficult at first as it requires a whole different approach to using a wide angle lens. So to help you make the most out of this piece of equipment, here are our top eight tips on how to use a telephoto lens for landscape photography.

A telephoto zoom is one of the best lenses that you can have in your camera kit for landscape photography. That’s because such a lens will allow you to isolate objects and other details within the landscape, with a much more narrow depth of field. You can zoom in on lines, patterns, layers, textures and even silhouettes for more abstract images or when you are faced with a scene with a lack of foreground interest.

Basically, Live View gives you the option to use the LCD display screen of your camera in place of the small viewfinder, giving you a much larger representation of the scene than you would be able to see with your naked eye.

One such application for this technique is moon photography. By using a telephoto lens, you can make the moon in the background seem extremely large in comparison to your subject in the foreground, such as a mountain, simply by being further away. If you were to shoot the same scene at the same distance with a telephoto lens, then both the moon and the mountain would seem incredibly small.