LANDSCAPE AND TRAVEL PHOTOGRAPHY

LANDSCAPE AND TRAVEL PHOTOGRAPHY These notes are written to complement the material presented in the Nikon School of Photography Landscape and Travel Photography class. Helpful websites: Nikon Learn and Explore Manuals for Nikon products Goals for the Day People have always enjoyed the beauty of the natural world, and photography lets everyone capture it in their own way. By approaching this topic first through light and exposure, then shifting into technique and technology, the class is designed to help you become a more successful and creative landscape photographer. We ll also explore wildlife photography and discuss ways to be more comfortable and productive when traveling. Our class will cover multiple topics, broken down into two main sections: 1 Light and Technique 2 Composition and Travel Photography is as much craft as art, so we ll explore both the creative and the technical sides of it in this seminar. 1

Section 1 Light and Technique There are many components to a successful photograph the right equipment, the right setting, great light and/or interesting weather, and of course, the photographer. The most important part of that process, though, is the creative one going on inside the photographer s head. Without a solid understanding of light, your best photos will come from luck more than skill. Light can be broken down into four primary qualities: Dynamic Range Size Angle Color Dynamic Range The Dyanmic Range of a camera is the difference between the darkest and lightest areas it can record in a particular scene. This play between light and shadow is often what makes a picture interesting. But however pleasing this contrast may be, it can also create problems for a photographer because of the differences between how a camera records a scene and how the human visual system perceives it. On a sunny day, there will be times when areas of the scene you re choosing to photograph will either go totally white (overexposed) or totally black (underexposed). That happens because the camera simply can t capture that entire range of light in one exposure. The range exceeds the range the camera is capable of recording. Sometimes that creates problems, sometimes it doesn t. If our goal is to create images that are realistic, making the viewer feel as if they were there with us, then those images have to feel natural. If areas are overexposed, what we often refer to as blown out, then there s a disconnect between the photo and reality. The image no longer looks like something a person might see, because they never see that way. On the other hand, we re used to seeing areas of blackness (such as a black coat, or heavy shadows), so that feels normal. In digital, if you overexpose your highlights there will be no digital information or details there. It will be a white hole in your image. That s why we like to say, protect your highlights. That means expose for the brightest areas, so you hold detail there. Fortunately, we have two tools today that makes it much easier to do that. 2

Most of today s cameras have the ability to display a histogram. That s a graph that shows you the range of light the camera captured, from black (left side) to white (right side). That graph will go up and down, like mountains, the height simply indicating how many pixels of that density (on a scale from 0 to 255) there are. For photographers, the height of those graphs isn t important it s the spread, from side to side that matters because it s the edges where trouble arises. If the edges of the histogram touch either of the walls, it means there was light in the scene that wasn t recorded. If it hits the left side, there will be pixels in the image that are totally black (no detail recorded). If it hits the right side, there will be pixels that are totally white (no detail, again). As mentioned before, areas going black in a picture can feel natural, but areas going blown-out white won t. And that s why photographers love the histogram. It can tell them if they ve got an exposure problem (hitting either wall), and they can then adjust their exposure to avoid that. It takes time to learn how to read and understand histograms, but it is well worth the effort. There s also a simpler option in your camera s Display menu for warning of overexposed highlights, which is often referred to as a highlight warning or flashing highlights. Turning that on means that if you ve set playback to show Highlights and any areas are flashing, they re indicating part of the scene is overexposed. The highlight alert is easy to see and understand, but you need to remember that it s only an overexposure warning. The biggest range of light challenge that photographers regularly face is when shooting the sun or moon. Their brightness level can be so great that it s well beyond the range of any camera to record both them and any surrounding area. That means you need to find ways to photograph them where the range between their intensity and the surrounding area isn t as great. With the sun, that means photographing it when it s partially obscured or reduced in intensity by something like clouds or fog. The same is true with the moon. It s easiest to photograph in the early morning or early evening, when its luminance is closer to that of the surrounding area, maintaining detail in both. Size Small light sources, like the sun, or spotlights, create hard-edged shadows, and high contrast light, which is called hard light. Large light sources, which is what you have when a cloud obscures the sun, lacks contrast and if there are any shadows, they re soft, thus the term soft light. 3

Angle All light sources illuminate in a direction or angle. It could be front light, side light or back light. In the old days people were told, put the sun behind you, when taking pictures. But front light, like that, is usually less pleasing light, because it can be harsh, and because it s coming from the same direction as the camera. Front light also tends to flatten detail. Back light is the opposite of front light. With the light behind your subject you again have a range of light problem. You can choose to expose for the subject, but then the background will overexpose. Or expose for the background, and leave your subject as a silhouette. Silhouettes can make interesting pictures, but are easily overdone. Side light is what most photographers prefer to have when possible. Light coming in at an angle can bring a subject to life, by helping define shape and showing texture. Color The last quality of light is color. All light has color. With digital cameras, how we capture that color is primarily controlled by the white balance setting. By default, cameras are set to Auto white balance, which means that each time you shoot a picture, the camera analyzes the light it s collected and determines how to process it to make the light white. Over the years cameras have gotten quite good at that, and you may be perfectly happy to leave your camera on Auto white balance. However, to get the most out of your photography, you should start looking at, and at times using, white balance as a creative tool. If you know what the light source is that you re shooting in, why not tell the camera? Cloudy? Then set that. Sunlight? Check. Indoors, are the lights fluorescent or incandescent? Not sure? Shoot some tests; see what looks best, or closest on the LCD. And remember, the goal of Auto white balance is to try to neutralize light. If you re shooting a beautiful sunset, that Auto setting may actually reduce the color. In that case the Sunlight setting, or even Cloudy or Shade, would be a better choice. All four of these qualities of light Range, Size, Direction and Color have a huge impact on us as photographers, especially as landscape photographers. The more you think about them, and start to appreciate what they can do for you, the better your pictures will be. Now let s look at some tools that we have for modifying, or controlling light. 4

Polarizing filter A polarizing filter is still considered by many to be an essential piece of photo gear. That s especially true for landscape photographers. What most people know about polarizing filters is that they can darken a blue sky. But that s not what makes a polarizing filter special. What s great about this filter is the other things it does. Because this filter removes polarized light, its true strength lies in its ability to reduce or remove reflections or glare. In doing this they can also increase color saturation and sometimes cut down on haze. They re great for photographing foliage because they let more of the color show through (they can reduce reflections off the waxy coatings of plants). And sometimes they can also make rainbows appear more intense. Neutral Density (ND) filter While a polarizing filter reduces the light entering the lens by about two stops, its main job is to remove polarized light. For times when you want to intentionally lower the level of light entering the lens, you need a Neutral Density filter. It s simply a dark filter whose only job is to block light. Neutral means it shouldn t change the color, and good quality ones will have a minimal impact on color. The primary use for an ND filter is to allow you to use slower shutter speeds. The normal way to reduce shutter speed is to lower the ISO and close down the aperture. But if that s not enough, then adding an ND filter will do the trick. Most photographers use them to create those silky water shots, but they can also be used to blur other action or to allow very shallow depth of field in bright light. Graduated Neutral Density (Grads) filters These are a twist on regular ND filters, as they change their density gradually from one edge to the other. They re normally used to darken an overly bright area (like a sky) while having less effect on the other part of the scene. In other words, they re tools to reduce the range of light. Grads come in both soft and hard, and in different densities (like regular ND filters). Soft means the gradation happens gradually, hard means that it happens in a very short space. 5

Sharpness Photographers have always been concerned about the sharpness of their images. Digital capture has taken that to a new level, offering a degree of sharpness unknown with film; which has made photographers more aware, and more determined, to achieve that sharpness. That makes understanding the details of sharpness more important than ever. There are four key issues we ll cover that affect sharpness, or perceived sharpness. They are: Stability Lens Choice Depth of Field Resolution Stability Camera movement can cause blur in images, so a key to sharp images is making sure the camera is as stable as possible when the picture is taken. Good technique holding the camera and lens properly, bracing yourself against objects all pay dividends in sharpness. Shutter speed is also a factor. The faster the shutter speed, the less chance of blur caused by camera handling. And tripods are one of the best stability solutions available. Wired, Infrared or radio releases are all good for tripping the shutter, as they don't require the photographer to touch the camera. If you don't have one, you can always use the self-timer. Many cameras allow you to control the countdown time for the self-timer, from two-seconds on up. This can be controlled in the self-timer menu within the Custom Settings Menu. High-resolution cameras add a new twist to the formula for sharpness. They ve now gone well beyond the amount of detail that 35mm film could reproduce. That makes good technique more important than ever, and places more importance on the value of high quality lenses. When Nikon introduced the D800 and D800E, they were the highest resolution 35mm-style cameras made. At the same time, Nikon released a Technical Guide for those cameras, written to help photographers take advantage of that increased resolution. It stressed not only the importance of stability and shutter speed, but discussed diffraction (see below) and recommended a specific group of lenses; which points to the fact that as cameras have increased in their ability to record finer and finer detail, lenses have also been redesigned to achieve that resolution. 6

Any conversation with landscape photographers is going to get around to depth of field. Depth of Field is simply the area in front of and behind the point of focus that also appears in focus. Remember, a lens can only focus in one spot. Closing down the aperture (smaller f/stops) increases depth of field, giving more apparent sharpness around the subject. Staying with depth of field, you d think that the smallest aperture possible would give you the most depth of field. Which is correct. However, as you make that aperture smaller, you re actually decreasing sharpness by a small amount. That s diffraction. As the aperture gets smaller, the angle of light entering the lens increases, and the light waves start interfering with each other. The result is a slight loss of resolution, or detail due to diffraction. Most lenses are at their sharpest two-to-three stops down from their maximum aperture. Sharpness is a topic photographers can (and often will) talk about for hours. It s important to keep in mind, though, at what size and distance the image is going to be viewed at. The smaller it is, the greater the viewing distance, the less critical sharpness matters. And finally, post-process sharpening (via software) can increase apparent sharpness, and is part of most professional workflows. Section 2 Composition and Travel Before we get into composition, let s cover a few technical details. Today most serious photographers have their cameras set to capture RAW (Nikon calls its RAW file format NEF, for Nikon Electronic Format). That means you re able to capture an image and save it with little to no compression or loss of information. Shooting RAW also allows you the flexibility to modify various aspects of the file, like White Balance after it s taken with no damage to image data. There are two big advantages to this over JPEG. First, there s no loss of image quality through compression (which JPEG has). And second, there s more data to work with when editing the file. Every camera must use processing settings that determine things like color, contrast, saturation, sharpening, noise removal and the like. In Nikon cameras it is called Picture Control. The Standard setting is how the camera comes set from the factory. However, you can try the other settings as well, such as Vivid or Neutral, and even adjust those further to create your own unique look. There are two important things to keep in mind about this. First, when shooting JPEG, 7

those changes happen to every image when they re captured. With NEF files, you can change those settings afterward, on the computer to change the processing. And secondly, with NEF files these settings are only recognized by Nikon software. Third-party software, like Adobe or Apple, will ignore in camera settings, applying their own processing parameters when opening the file to view and edit. Composition Composition is perhaps the most important step a photographer takes, perhaps even more so than exposure. Composition is where photographers express their creative vision of how a scene should be viewed, and what s important in it. Here are a few tips to help with composition: Many photographers take pictures of scenes they find interesting, but don't think about how the viewer will see the picture. Not having been there, experiencing that moment with you, will they understand what you want them to see? More simply, will they understand what the subject of your photo is? A classic maxim in photography is get closer. Whether that s accomplished by using a longer lens or physically moving closer, getting closer almost always improves a picture because it makes the subject more obvious. Another common mistake is being so focused (mentally) on the subject that you ignore what else is going on in the frame. Take a moment to look at the edges of that rectangle, and ask yourself, is this what I want people to see? Most pictures have at least a foreground and a background. It s important that photographers realize and understand that, and use them. This is particularly critical when using wide-angle lenses. They can capture such a wide vista that it becomes hard to understand what you re supposed to look at. Having a foreground subject makes it both nearer and larger, giving it more significance in the frame. Photographers should also spend time thinking about where, exactly, they want their subject in the frame. The rule of thirds suggests breaking the frame up into nine rectangles, and thinking about placing the subject at one of the four intersections. Wildlife Photography If you spend much time outdoors, or at zoos, you ll eventually be doing some wildlife photography. The same guidelines of composition apply here, but there are also special considerations as well. 8

With wildlife there s a good chance that the animal will move, and when it does, you probably want it to stay in focus. Nikon offers many, many options for controlling autofocus, and over time you should explore them to find which works best for you and your style of photography. It s easiest to think of autofocus as divided into two sections; AF Area modes and Auto Focus modes 1. Auto Focus Modes These control how your lens responds when you press the shutter button half way. AF-S is Single-servo AF. When the shutter button is depressed half way down, the lens will focus and hold the focus at that distance until the shutter press is completed, or pressure released. This is ideal for stationary subjects. AF-C is Continuousservo AF, and in this mode the camera focuses continuously when the shutter is pressed half way, trying to keep the subject under the active Auto focus point in focus. This is the best option for moving subjects. 2. AF Area Modes These control how the brackets you see in the viewfinder work together to focus on and track your subject. Each camera has several options and you can choose between a single focus point all the way up to all Autofocus brackets being active. The AF Area Mode you choose depends upon your subject, how large they are in the frame and if they will be moving or stationary. Choosing both an AF Mode and an AF Area Mode lets you customize how your camera s autofocus system works. Here are two ways to approach that for moving subjects: Camera chooses where to focus For this, set the Auto Focus Mode to AF-C Continuous (so it will continually adjust focus on a moving subject) and the AF-Area Mode to Auto-area AF. In that mode the camera will choose what to focus on based on the group of AF sensors and what s closest to you. You choose where to focus Again, AF Mode is Continuous (AF-C). But now you ll control what AF point the camera is using (or at least starting with) by setting the AF-Area Mode to Dynamic 21 (or more, up to 153 if your camera allows it). You ll now choose what Autofocus point to use and the camera will engage a group of surrounding points to track the subject and maintain focus. Once you choose an Autofocus point and acquire focus the surrounding 20 points (if using Dynamic 21) will help track the subject as it moves through the frame as long as you continue to maintain pressure on the shutter button (keeping autofocus engaged). You could also try the 3D option, or on the newer cameras (like the D4S, D810, D750, D5, D7500, D850 and 9

D500), the Group area AF option to maintain focus while photographing a moving subject. How can you check to make sure your focus is on? Earlier, we discussed the things that affect sharpness when taking pictures. Now let s look at how to confirm we ve got a sharp picture afterwards. The key here is the idea of one-to-one (1:1). To see if an image is sharp, you have to be at a zoom level where one pixel in the image is being represented by one pixel on screen. That s 100%. With all Nikon DSLRs, you can zoom in to 400% while previewing an image using the LCD. So if you zoom all the way in, then zoom out two steps, you ll be at 100%. Newer Nikon DSLRs make that easier. As you start to zoom in on the LCD, you ll see a bar at the bottom of the image. When it turns green, you re at 100%. Environment is also a key part of wildlife photography. If you re at a zoo or a game park, then you probably want to compose your photos so the setting looks as natural as possible. However, there will also be times where showing that artificial environment will be an important part of the story. And, remember that backgrounds are as important in wildlife photography as in any other. You want clean backgrounds that lack distracting elements that might take the viewer s attention away from the animal. Telephoto lenses are the normal go-to lens for photographing animals, but don t ignore the power of a wide-angle. At those times where you can get close go eye-to-eye with an animal you ll end up with a photo that s more powerful because of its intimacy and uniqueness. Travel Thanks to today s transportation options, the world s gotten a lot smaller in the last hundred years. The internet has made it incredibly easy to do research, not just reading about places to go and see but actually seeing those places, in pictures and video. But travel still involves moving, carrying your gear, and that means making decisions about what to bring and what to leave behind. There are nearly endless combinations of camera gear you could buy and take. Let s look at a few different kits, starting small and going from there. Basic Landscape A DX body with one lens, like the 18-140 or 18-300, or a pair of short to medium zoom DX lenses (perhaps the 10-24mm and 16-85mm) can be a great starting point. That keeps both cost and weight down. 10

Basic Travel Same as above, except now with a short zoom and a long one (out to 200 or 300mm), plus a small Speedlight (like the SB-500 or SB-700). Compact Travel/Wildlife Now the emphasis shifts to two cameras and more of a zoom range. Pairing a DX and an FX body gives you two different sensor sizes to work with, and a wider zoom (perhaps 16-35mm) and longer zoom (80-400mm) give you more reach at both ends. Landscape Photographer s Dream This kit is built around two FX bodies for maximum resolution and features, and three high-quality lenses (16-35mm, 24-120mm and 70-200mm) for maximum sharpness. Maximum Reach Now we re talking about more serious wildlife photography, pairing a DX and FX body for sensor options with a long telephoto (perhaps a 500mm or 600mm), a zoom telephoto (80-400mm or 200-500mm) and wide zoom (16-35mm). Maximum Performance For the fastest autofocus and frame rate, a D5 body, D850 for maximum resolution and three lenses (500mm, 70-200mm and 16-35mm); plus two teleconverters (TC-E14 III and TC-E20 III) and a Speedlight. Any person who travels has to make decisions about luggage, and that s more important for photographers than most people. Since you re already bringing extra weight thanks to your cameras and computer gear, the less personal gear you bring the happier you ll be. A good rule of thumb is to carry with you everything that s most important for your trip. That means not only cameras and lenses, but also battery chargers and personal medications. Just as you try to bring the right photo equipment for where you re going and what you re doing, plan your luggage similarly. Make sure you know the limits on carry-on pieces, both size and weight, for every plane or vehicle you ll be in. Pack, un-pack, re-pack, un-pack Do this several times, asking yourself whether you truly need everything. How many pairs of footwear do you really need? Can you do laundry during the trip? Are you bringing clothing that you can layer if it gets cold, rather than a bulky coat? 11

Most photographers like to travel with a laptop so they can download and review their photos, as well as stay in touch with folks back home. Plus, you can use the travel time to work on photos. Just make sure you have the right electrical plug adapters if you re going to a foreign country. It s also important to be able to maintain your camera gear while traveling. That means wiping down the outside if you ve been out in rain, sand or dust, and keeping your lenses and filters clean too. Don't forget about the sensor. A dirty sensor will create major problems later, so be careful changing lenses, and bring along a small blower for added cleaning. Of course, having enough high-quality memory cards is imperative. Don't expect to be able to buy cards where you re traveling; always have more than you need. And if you re traveling with a laptop, consider having a card recovery software package on it. Card errors can happen, and being able to recover those images, which is likely, will help you sleep better at night. If your plans call for leaving the country, make sure your passport is up-to-date and not expiring soon. Check to see what the entry requirements (Visa?) are for the countries you ll be visiting. Being comfortable, rested, well-fed and hydrated means you re more likely to be happy and creative. So it s important to take good care of yourself when traveling. If you re traveling anywhere that the water or food is suspect, take extra precautions. Drink only bottled drinks that you open. Bringing a water purifier is a good idea. And as for food, if the water s suspect, then the old adage of Boil it, peel it, cook it or forget it is good to remember. Bad weather can make good pictures, if you re prepared for it. Umbrellas are a photographer s best friend in the rain. A gallon-sized clear zipper closure bag big enough for the camera to fit in, and a couple of rubber bands can protect a camera and lens from rain. Dressing warmly in cold weather, having gloves that let you use your fingers, wearing the proper footwear for wet weather, ice or snow all contribute to helping make you a more successful photographer. Finally, there are sure to be times where you d like to share what you re shooting with others, immediately. Rather than make a poor quality snap with your smartphone, try the wireless technology (Wi-Fi or Bluetooth) built into many Nikon cameras. That will allow you to quickly and easily see the photos on your camera from your compatible smartphone (ios and Android TM supported), then download that photo from the camera (no wires needed) so it can be posted right away. And there are even inexpensive adapters the Nikon WU-1a and Nikon WU-1b that 12

add that ability to some of Nikon s cameras that don t have the Wi-Fi built-in. Find out more here. In Closing The only limit a photographer faces in pursuing their craft is time and inspiration. There are an almost infinite number of directions you can take this art, from HDR to Infrared to underwater to close-up to panoramas to lightpainting the list is nearly endless. Learn your equipment, practice and experiment. But most important of all, have fun! If you re looking for more ideas, Nikon s Learn and Explore website is full of information and how-to articles on different directions you can take, and Nikon has a presence on most social media sites as well, offering tips, suggestions and instruction. In addition to those listed below, Nikon also has a Facebook page for people who attend Nikon School, where you ll have a chance to post your own photos for feedback, as well as take part in group discussions. It s at https://www.facebook.com/groups/nikonschool/ Facebook: https://www.facebook.com/nikonusa Twitter: https://twitter.com/nikonusa Instagram: https://instagram.com/nikonusa/ YouTube: https://www.youtube.com/nikonusa Google+: https://plus.google.com/+nikonusa/ Flickr: https://www.flickr.com/groups/nikondigitallearningcenter/https://www.flickr.c om/groups/nikondigitallearningcenter/ Vimeo: https://vimeo.com/groups/nikonusa But wait, there s more One of the great things about photography is that once you understand the basics, the opportunities to explore in different directions are nearly endless. Here are a few that are especially well-suited to landscape photographers: Night Photography Most people don t try night photography because it seems too difficult or complicated. And that's simply not true. As with all photography, it's a matter of figuring out the technical side, and then getting creative. Here are a few things you need to do, or understand, to be successful: 13

First, you'll need a tripod. While it doesn't have to be expensive, you'll be happier if you buy a good one. A good tripod will last a long time and be a pleasure to use. More importantly, it will be sturdy and result in better pictures. For exposure, you'll be more successful with night photos if you shoot in Manual exposure mode, as the wide dynamic range from light to dark makes using an automatic mode nearly impossible. Avoid moving the camera when taking the picture (which would result in blur), so use a cable release (or Infrared oir radio remote trigger) or the camera's self-timer to trip the shutter. It's doubtful the autofocus will work well in the dark, so turn it off and focus manually. Finally, when looking at your photos on the LCD in the dark, remember that the image will look brighter than it really is. You'll probably need an exposure that looks a bit too bright on the LCD, and check the histogram too. Lightpainting Lightpainting is just night photography where you're providing the main light. One great thing about it is that you can do it anytime, anywhere, as long as you've got a room you can make dark. Like night photography, you'll need a tripod and want to shoot in Manual exposure. If it's dark enough, you can trip the shutter by pressing the shutter button, or use a release or self-timer. Again, you'll want to turn the AF off and manually focus. Now let's get to the fun part. The trick in lightpainting is using a little light, not a lot. You want to paint light onto just some areas of the scene. If you light up everything, then you might as well use a flash. A good picture done with lightpainting will look as if multiple light sources were used, or just one but from an interesting angle. If you re working in a small area, like something you've created on a table at home, then a penlight can provide plenty of light. If working outside, painting large objects like trees, then you need something more powerful, like a handheld spotlight. Exposure is all trial and error, but having the LCD makes that pretty easy. HDR (High Dynamic Range) Imaging This is an area that's gained great popularity the last few years thanks to better software. As we discussed earlier in the program, the range of light in many scenes exceeds what our cameras are capable of capturing in one exposure. In HDR photography you shoot the same scene several times, at different exposures, and then combine those photos later in software. Most simply, it's a way to extend the dynamic range of a picture. As with night photography and lightpainting, it's best done on a tripod, though most good software can assemble a hand-held series. It's best to 14

shoot in Aperture Priority, so only shutter speed changes (otherwise the change in depth of field can cause problems). Most of today's cameras have an automatic exposure bracketing feature, so you can use that. You'll need a minimum of three shots, one at the "correct" exposure and two more, one over- and one under-exposed. And finally, while it's possible to manually assemble the photos using layer-based software, it's much easier (and usually better quality) to use one of the third-party HDR packages for that. Time-lapse Time-lapse sequences have become extremely popular, and most Nikon DSLRs today have that capability built into them. Using the Time-lapse movie option in the menu will create a finished time-lapse movie right in the camera. If you want to take more control over how your time-lapse is created, then you d probably choose to use the Interval time shooting menu to capture the individual frames, and use them to create a movie afterwards. Infrared Infrared photography (IR) in the days of film was a very difficult and complicated process. It involved using a filter to block the IR wavelength from entering the camera, and since IR is a longer wavelength of light, focus was difficult. The process of shooting Infrared photography with a digital camera can still be done with a filter, but there s another way as well. If you like the look of IR and choose to dedicate a second camera to shooting Infrared images only, you can have it modified by a third party. Once modified, the camera can no longer be used for regular photography it's an IR-only camera now. There are several companies that can do this conversion, and LifePixel.com is one that several of the instructors have used. In that process the low-pass filter is replaced with a filter that's sensitive to IR. With that new filter in place, the camera captures IR only and exposures are similar to what you'd have in regular situations. * Note that modifying your camera will void the manufacturer s warranty and often cannot be reversed. 15