Resolution

But often you’ll hear someone who has asked you a picture (even an advertising agency!) Say that “I better with 72 points per inch . ” This information is useless. What we have to say is how many pixels you want to take the photo. For example: 1,500 pixels wide or 800 pixels high. This data perfectly defines the resolution of the file that you send. As an example, these pictures have a resolution of 900 x 600 pixels, a size suitable for the Internet.

And the dots per inch?

The question then is, what resolution do I need? Depends on what it is going to use the photographs : for viewing on the monitor or to print ? And here come into play dots per inch (also called dpi or ppi).

In a monitor , the screen resolution is just the number of points that the monitor displays (eg 1024×768) and dot density (measured in dpi) is the number of dots displayed on a monitor inch (2 , 54 cm). For example, the monitor with which I am writing this article is set to a resolution of 1280×1024 pixels screen. Now I take a ruler and see how tall the width of the monitor: 38.1 cm = 15 inches. So the horizontal resolution of my monitor is 85 dpi (1.280/15 = 85 dpi). You see, the famous 72 dpi we have all heard or read (as resolution of a monitor) is not true: depending on monitor size and screen resolution you have set the user (in fact it is the 72 dpi the time of the first Macintosh did have a screen resolution of 72 dpi, but later ceased to be true to evolve monitors).

And to print what resolution I use?

This question has no single answer. Yes we can talk about minimum recommended resolution for each output type. For example, to print a photo with an ink jet printer , a resolution of 150-180 dpi is sufficient. To offset or print (magazines, books, etc..) recommends between 200 and 300 dpi. However, to print a billboard just 50 dpi or less. Again, the myth of the 300 dpi for printing anything is totally false.

Calculate print size resolution knowing

Finally, we calculate what we need resolution file to print a photo to A4 size, with an ink jet printer, 150 dpi:

A4 = 29.8 cm = 11.8 inches wide.

For a density of 150 dpi need the photo is on the long side = 150×11.8 = 1770 pixels

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Instead, the shutter speed of the eye is single (1 / 100 sec.) which has an evolutionary point of view is perfectly adequate, but the camera clearly has more options (such as very fast shutter speeds, which allow you to freeze movement, something the eye can not do, or the opposite extreme, long exposures required to build light and see what is invisible to the eye).

And what about the sensor ? Well that’s where the difference is enormous: it is quite large (like a digital back CCD) and has pixels of similar sizes, but has a resolution equivalent of several hundreds of mega pixels, although this parameter is not exactly comparable: a point, the eye only processes a fraction of the total visible area, the rest remains out of focus black and white!

Let’s see a possible example: The human eye, on a sunny beach, with a shutter speed of 1 / 100 sec. to f11 and an ISO of 12 (and a resolution of, say, 350 Mpix.). The exposure equivalent of a digital SLR camera (of say 12 Mpix.) would be: f16, 1 / 500 sec. and ISO 100. This of course is only a theoretical calculation since all these parameters are not exactly comparable in reality or equivalent …

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Before, we relate the different parts of both: the goal is the combination of the lens and the cornea (which in turn serves as a UV filter as well). The diaphragm is constituted by the combination iris / pupil (which expands or contracts to change the opening), and the sensor is the retina. Finally, the image processor is the brain.

The Human Eye in Figures

There is some controversy regarding the focal length of the human eye: some authors speak of 16 -18 mm although it seems that consensus is another figure: 22-24 mm , whose value depends on several factors such as distance from the eye to the subject, age and health of the individual.

The Diaphragm

The maximum diameter of the pupil depends on the age (this is well know amateur Astronomy and Astro !) in young people come to dilate the pupil to 7 mm, a figure that is reduced from 5-6 mm of 40-45 years. In contrast, the minimum diameter of the pupil is 1.5 mm. With these figures we can calculate the focal ratio (f) of the human eye, from f3.3 (of 4.6 for adults over 45 years) to f16 at its opening minimal, ie, a relatively short range compared with a normal lens ( for example 50 mm f1.8 – f22).

The ISO of the Human Eye

ISO What the human eye? In fact, the human eye has a sensitivity native or base such as digital cameras, but surprisingly adapts to ambient light levels very extreme. In this way it is calculated that the human eye in a bright environment has an effective ISO of about 1 , and change in conditions of very low luminosodad has an equivalent ISO of 800 . However, the contrast ratio detected by the human eye than 10,000:1 , far from what has been achieved by any digital camera (or analog).

Shutter Speed

This parameter is interesting: in fact, the eye has a vision system constantly sends continuous information to the brain for processing. The shutter speed is equivalent aproximadamanete one hundredth of a second (the time interval that the eye is able to distinguish), but under certain conditions is capable of detecting light emissions of only two hundredths of a second long.

The Sensor

The retina has a diameter of approximately 40 mm (if extended to form a flat surface). That is, almost twice the area that a sensor full-frame 35 mm format (which is 24×36 mm) and more similar to the sensors of digital backs. It has about a hundred million light-sensitive receptors, of which 7% are cones, the cells with substances called opsins , separately detect red, green and blue and are insensitive to light (photons require at least 1,000 to activate.) 93% are Poles, cells by rhodopsin , a substance that is most sensitive to green light, are responsible for monochromatic vision and are very sensitive to light intensity (a single photon can he activate). The diameter of the cones is about 6 microns and 2 microns sticks (the photosites of the SLR CCDs have a diameter of between 5 and 8 microns, somewhat higher than the rods and cones similar to).

Quantum Efficiency

A parameter on the CCDs little known but important in this context is the quantum efficiency (CE) : measures the efficiency of a CCD and represents the percentage of photons incident on the CCD that are able to release an electron. For example, a CD of 50% means that for every 100 photons that affect the photosensitive surface of the CCD, it generates 50 electrons. Importantly, the EC varies by wavelength of light (usually maximum toward 550 nm, which corresponds to the green).

By way of comparison, the film has an EC of between 5% and 10%, while CCDs have an EC of between 40% and 90% (green), the human eye has an equivalent EC 15% (green), a value closer to the film to the CCD.

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The Human Eye: An Incredible Machine

First, it should be noted that the functioning of the human eye rests on the most sophisticated and powerful computer that exists on our planet: the brain . What we see is the result of what has caught the eye with what the brain has processed. The analogy in digital photography-relatively speaking-would capture raw (RAW file or data captured by the CCD) and processed image (in Photoshop or JPG file that the camera has been generated from data raw).

Example of this teamwork of the eye and the brain is the fact that the human eye actually sees the world upside down and reversed as in a mirror (like a camera optical bench). It is the brain that is responsible for correcting the image in the two axes. In fact, babies see the world uncorrected (this the the reason why they often look in the opposite direction to the movement trying to follow).

Another example is what happens in Architectural Photography : If you tilt the camera up to photograph a tall building, the vertical lines converge. And the same thing happens to the human eye, only that the brain is responsible for correcting the distortion.

Continuing Vision

What we see is actually a constant flow of changing information that the brain is constantly processing, assembling images to generate a vision of the world around us. It is a very complex and surprising.

For example, although the joint vision of both eyes produces an angular field of about 130 °, in reality the area in which at one time the eye is focusing is only 0.5 °. The rest of the image remains blurred (progressively as we approach the edges ). All this happens quickly and continuously and that is why we have the feeling that this is occurring (imagine a camera with a 90 ° angle covered but only 0.5 ° is focused!).

The Retina: Perfect Sensor

The retina contains about 7 million cones (capture the red, green and blue) and about 120 million rods (extremely sensitive to light level). The distribution of both types of receptors is not homogeneous, since the cones are located at the center of the retina. This implies that the edges of our field of view are always monochrome (including daylight). However, the rods are capable of detecting light levels as low as a single neuron (as a reference point, under normal light, our eyes can recognize about 3,000 neurons per second).

Many animals (especially birds) have a much higher number of cones than humans, allowing them to detect prey at great distances. In contrast, nocturnal animals have a high number of rod to improve night vision.

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Food Photography: The Volumes

Not the same light a steak dish a soup. What is the differentiating factor? The volume . In the first case, usually it’s volume is interesting to note, including the texture of the meat and juicy appearance. In contrast, in the case of soup, raw plate geometry and surface aspet it. Therefore in the first case we use a low angle, usually 45 ° to the horizontal, and if we use a soup encuandre zenith (orthogonal to the plane which supports the plate).

Lighting

Use a framing overhead and side lighting contrasted to highlight surface textures . We also use another flash at 45 °, diffused light (for example, a window of light from at least three or four times the diameter of the dish) which is responsible for lighting smoothly the rest of the dish . This flash is placed between 90 ° and 180 ° to above. In this way, we managed to light up the whole plate at the same time enhances the texture of the cream. Try to imagine how this dish would be if we used a frame at 45 degrees and you will notice the difference.

The Frame

We have seen the camera position and illumination of the dish of cream. Now we have to define the frame : that is, what elements define the object retratato and what not, so that first appear in the frame and the second does not appear. In the present example of the cream, the geometry of the depicted object (in this case, the circular plate) is key to understand the product. Imagine the same picture but with a frame-for example, that only shows square-cream without seeing the plate. Could not understand how the depicted object and lose its strength and appeal.

To the right is another example completely different (see other examples of photos of Food ): we want to highlight the volume and texture in this dish. We use a frame at 45 degrees and light from illuminating the edges of the object, helping to define the profile of it.

The other light source-side diffuse, serves to illuminate the whole at the same time creates soft shadows that define the volume of the object. As for the frame, in this case the target is not necessary to understand the object-is portrayed, it distracts attention from the important, and we use a short frame, with shallow depth of field to focus attention on the object central.

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Food Photography: A Question of Photogenic

But how do we get what looks appetizing photograph? First, like everything in photography, there are foods (products or prepared meals) that are photogenic and others not. Therefore, this factor plays in favor or against us. For example, foods like an orange, a strawberry, a salad, etc.. are inherently photogenic (attractive colors and textures are regular and interesting). Instead dishes such as soups, cooked dish, a stew of meat in gravy, etc.. are nothing photogenic and therefore difficult to photograph well.

Food Photography with Perfect Perfect

Second, we need to get the food that we are photographing perfect (or almost). Not worth a strawberry or orange anyone either. They have to be perfect. There are two ways to do this: go to a regular supermarket and buy several kilos of this product and pray to display a perfect piece, or-more-attend recommended certain grocery stores that are dedicated to this and you can get parts you apply with excellent quality. Obviously this service has a price-and not cheap.

Preparation and Placement: Key Elements

And third is the preparation of food and its placement along with other elements and props (if any). In the case of a gourmet dish of a restaurant, for advertising or for a cookbook, can-and often-Chef prepare himself. However, advertising (packaging mostly) usually hire the services of a (a) stylist (called Home Economist and Food Stylist ) which is responsible for search and buy food (and props) in preparing and then placing them properly to the picture. This is a very important job that we can trust the Home Economist as a specialist and knows how to prepare, mix and place the various elements so that they are visually appealing.

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Gradient Filter Neutral

Curiously enough is a filter unknown (and underutilized) among fans of photography. The most commonly used format is the Cokin , rectangular in shape. At the top has a neutral gray gradient and the bottom is clear. There are different gradient densities (as neutral gray filters) depending on the amount of light you want to block. There is a little-used variant that has a reverse gradient, ie, the gray area in the center of the filter and the gradient occurs both above and below.

Polarizer Filter

The Polarizer filter is another essential for Digital Photography . Light behaves as a wave form that propagates in a straight line and consists of two components: an electric and a magnetic traveling at 90 degrees relative to each other. In certain circumstances (as when the light hits water or glass, or in the upper atmosphere) one of the two components is eliminated in the process. We then say that the light is polarized (one axis or another). Polarizer filter is precisely what makes the other remaining component filter, completely eliminating polarized light.

The visual effect is, as we all know, the elimination of glare on glass, water and some varnishes. It also has a very powerful and at times dramatic on polarized light from the sky and its reflection in all the surrounding objects: the blue of the sky darkens and intensifies, sometimes reversing the relationship of light in heaven and earth. No good, no clutch, removes shine from metallic objects.

The polarization is rarely total and its degree depends on several factors, one of the most important being the sun’s position regarding the photographer: the maximum effect is achieved with the sun high and 90 º of the photographer.

The polarizer in the Study

Finally I wanted to mention another use of the polarizer, less known: their use in Studio Photography . As the light we use in the study is not polarized, so that our filter to affect previously we polarize light : This is achieved by placing a polarizing film in front of all (or some, as appropriate) flashes. As we look to the object whose brightness we remove, we rotate one of the sheets first and then the other, until we notice that the brightness is reduced somewhat. Finally, we turn the polarizing filter that is on the camera lens to achieve partial or complete disappearance of the brightness.

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Aerial Photography from kites (KAP): Introduction

Aerial photography from kites (known in the Anglo world as KAP – Kite Aerial Photography) is performed primarily by hanging a camera from a kite-flying stably, and closing the shutter from the ground using radio control (RC), or by a intervalometer connected to the camera (in this case is usually called self KAP). Therefore we can define two different teams depending on whether land is controlled by RC, or automatically triggered by an intervalometer (auto KAP).

The basic equipment of KAP is as follows:

• A kite . It is not worth anyone. Has to be stable in flight and have sufficient strength to lift the camera equipment. There are two kinds of kites for KAP, with structure and unstructured. They differ among themselves, besides the presence or absence of structure-flight by the angle of each type of characteristic that is committed and the range of wind speeds in which it is able to fly (there is light wind kites and kite High Wind-there is a kite that can fly in winds of 5 km / h in 40 km / h for instance).

• A Framework for the House . In English it is called rig and is a kind of frame with two pieces-usually alunimio U-shaped, one subject over another. The upper part is fastened to a cross-shaped structure (called Picavet, whose function is to stabilize the camera ) from which is threaded a thin rope that passes through the four corners of the cross and that goes to the line of the kite ( normally hangs the camera about 20-40 feet below the kite). In the bottom of the U is holding the camera. In this way the camera can turn left or right ( pan ) or up and down ( tilt ).

• A camera . The most important parameters when choosing a camera for KAP are: 1 Weight, 2nd photo quality, 3rd manual controls, 4 ° Possibility of remote shooting with infrared port or entry remote trigger, 5 th output video in real time. I personally would also second the camera’s ability to save files in RAW format.

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So I put an example which we hope will come to understand this: the relative apparent size of the moon and the great Andromeda Galaxy (also known as M31). The Moon has an angular size of about 31 arc minutes. M31 has an angular size of about 180×60 arc minutes.

In the picture, you can see a photo montage of the two in which you can see the apparent size relative . That is, if M31 had the same luminosity as the moon would look like in heaven. Impression is not it?

This object is immense and that despite its remoteness – 2.5 million light-years its apparent size is huge (in fact, twice the size of the Milky Way).

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(A) In the case of emission and reflection nebulae, many of the best known, and photography have a very large angular size, so focus telescopes are used short to medium (between 200 mm and 1,000 mm overall ). In this case, the aperture (the diameter of the front lens) is very important due to the low luminosity of the object.

(B) The low luminosity of the object involves long exposures (about 3-5 minutes to 30-40 minutes) which has important implications for further processing (noise control) and the equipment used (it takes a ultra precise tracking sidereal to prevent the stars and the object exit calendar – trailing in English).

(C) light pollution (CL) is very important: it determines the contrast between the sky background and the object. The more CL, lower contrast and the worse the quality of the picture. The atmosphere on the other hand – these focus-has very little impact on the quality of the picture.

(D) In ​​the case of objects of smaller apparent size, such as planetary nebulae and most of the galaxies, the approach changes: longer focal lengths are needed (not as much as Planet), the order of 1,500 mm to 3,000 mm. The opening is still very important (more open = more light = shorter exposure time). However, long exposures are kept, and the processing is similar to the large emission nebula.

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