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Objectives Values \u200b\u200bObjectives stabilized

stabilizing system allows a goal off the slight blur that occurs when you take a picture by hand, without support and, when the shutter release, we made a small movement objective. Is often referred to shake or vibration.
This happens usually at shutter speeds below 1/LongitudFocal, for size of full-format sensor. If your size is APS-C sensor, the threshold corresponds to somewhat higher velocities.
To understand the stabilization mechanism, the first thing we do is explain what the target's movement that attempts to compensate. This movement can be decomposed into two components, as shown in the figure.
A vertical component consisting of a complete rotation of the camera and with it the objective "about the axis X. From a practical standpoint, the goal pointing a little towards the sky or a little to the ground.
A horizontal component consisting of a complete rotation of the camera and with it the objective "about the axis Y. From a practical standpoint, the goal pointing slightly to the right or slightly to the left.
Clearly, any rotation around the Z axis, the optical axis, will not have any influence on the image due to the circular symmetry of the targets. From the practical point of view equivalent to slightly raise the right or left of the camera.
Sensors are informed of these movements and sends the data to a microprocessor that after calculating compensation, active engines that move slightly inside the objective lens. This has placed among the rest that make up the group and its sole mission is to reduce vibration. The attached figure is represented this lens, but not the rest of the group.
The stabilization system activation caused by pressing the shutter button halfway, in the same action in which activated autofocus. Naming
blur the issue makes sense, because the situation is somewhat similar to what occurs for points closer or more distant to the focal plane that contained within the limits of the depth of field. That different rays from a single point in the scene converge in a wider area than the circle of confusion and therefore it is blurred in the image.
Here, the process is somewhat different.
Consider, for simplicity that the jitter is only a vertical movement. And let's realize that the goal a little more pointed skyward.
In this case, the rays from any point in the scene belonging to the focal plane impact on the target in different areas and different angles. So some intersect the image plane in an area outside the circle of confusion centered on the image point. In this way we obtain a blurred image of a point, because they belong to the focal plane, should generate the image plane in a circle (formed by all the rays that reach it by following different paths) below the circle of confusion. Obviously, this same reasoning applies to all items included within the limits of the initial depth of field.
The work of the stabilization system, in this case, slightly move the lens correction through the use of vertical motor so that the entire target system do impact the beam at the image in its original position within the circle of confusion.
Through this mechanism can coseguir reduce the shutter speed 3 to 4 steps, without showing the blur caused by vibration. Of course, not all the time.

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ISO

Objective: Nikon 18-200 f3.5-5.6

Focal Length: 135 mm.

Aperture: f5 Shutter Speed \u200b\u200b

: 1 / 125 sec.

ISO: 400

ISO stands for International Organization Stadarization and in the field of photography measures the responsiveness of light-sensitive material to produce a photographic image well exposed. When the ISO setting increases is possible to obtain a correct exposure in the presence of less light.
Increasing ISO is really a process of amplification of the electrical signal generated by the light sensor fotocaptores. An entirely different process to that produced in the field of film photography.
inexorably linked to amplification of the electrical signal is the phenomenon of noise. Thus the main problem to be addressed when using high ISO settings is the management of noise.
We can raise several questions: Under what circumstances
is necessary to raise the ISO?
How can we increase the ISO value, without deterioration is the picture obtained by the appearance of noise? Let
to comment on the second question. Actually the answer depends on the sensor you are using. The base level is usually 100 ISO although some cameras will automatically start at 200 and a few at 50. The mechanism is such that if we raise the ISO value of 100 to 200, we get the same exposure to the light half.
If using as reference a digital camera compact, the sound is already very evident even when we held the first increment of 100 to 200. Therefore, few joys.
for digital SLR cameras, low-end may be possible to raise up to 400. In my Pentax ist DS, which launches the series on 200 ISO beyond 400 the noise starts to be a problem. For semi-professional digital SLR
, values \u200b\u200bof up to 800 ISO is not usually an issue. In my Nikon D200, is what suecede.
In the case of professional SLR is possible to raise the level more. So they say.
In all cases, and it is important to be clear, what is meant by the above paragraphs is that the noise-generation inevitably is easily removed using a photo editing program. Because their intensity is mild.
But there are always a "but" only if the correct exposure at or very close to correct. This means that if you manipulate the image with an image editing program to get the correct exposure, we have not succeeded in capturing, it is likely that we bring out the noise and just ruining the picture. In case of underexposure the problem worsens.
With respect to the first-and still-unanswered question, it is customary to say that the proper context for raising the ISO value is when the scene lighting is poor. When it is dark. For example, in sunsets, interiors, etc. And it's true.
But in my opinion, there are other circumstances more favorable to it in increasing the ISO value. When we try to shoot static subjects not targeted faint in normal lighting conditions. To realize: A flower swaying in the breeze at 11 am. If we use a very bright target such as the Nikon 18-200 f3.5-5.6 is often necessary due to the small size of the flower, use a focal length of about 150 mm. In that case the greatest possible openness is around f5. With these data, the appropriate shutter speed to get correct exposure can be so low that the movement itself flower, swaying in the breeze, lead us to a power of focus. (Notice to mariners: Here the fact that the lens is, as it is, stabilized, adds nothing. Since the mission of stabilization is to correct the movement of camera shake in the hands of the photographer and has no power to act on the flower that is moving. More on this in another article.)
In such cases there is an additional favorable circumstances. Since the lighting conditions are correct, the electrical signal generated is high and therefore the signal to noise ratio is very favorable.Lo which means that the noise is negligible.
Finally, the protocol used is very simple: Set the correct exposure with the lowest ISO value, typically 100. It raises the level to where possible or necessary, then increases the shutter speed in the same number of steps.

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Opening Aperture: f22

Opening Aperture: f45

In the previous article diffraction theory for circular targets, it was established that a separation between the centers of the Airy disks of:

d = 1.22 fλ

guaranteed, according to the Rayleigh criterion, two points of light very close to be resolved as different points in the image and do not constitute a single oval of light, something that obviously hurts their sharpness.

It is time to understand what are the practical implications of this statement.

If we take an APS-C sensor typical 23.6 mm. wide by 15.8 mm. high that contains within it a pattern of 3872 x 2952 fotocaptores of light, is quite simple to calculate what the estimated separation between the captors.

horizontal separation = 23.6 / 3872 = 0.0061 mm.

vertical separation = 15.8 / 2952 = 0.0054 mm.

As these results are merely estimates, we can say that the separation is about 0.006 mm.

If the incident light is predominantly bluish tint, which is most common in outdoor photography, its wavelength is about 0.0004 mm.

With these data we are able to estimate the number f that guarantee the Rayleigh criterion. If we use a value of f11, then:

d = 1.22 x 11 x 0.0004 = 0.0054 mm.

Therefore, with this value for the number f, the distance between the centers of the Airy disk is less than fotocaptores existing between two points ahead and the image is properly solved.

In the heading of the article are two pictures taken at exactly the same conditions using a tripod, remote shutter release and the Tamron 90 mm macro lens. f2.8.

The only difference is that in the first of them has used an f value of 22 and the second a 45. It is clear that, despite being a value significantly steeper than the threshold corresponding to f11, the former is not observable a noticeable loss of sharpness, while the second does. The f values \u200b\u200bfor these numbers are:

d22 = 1.22 x 22 x 0.0004 = 0.011

, D45 = 1.22 x 45 x 0.0004 = 0.022

In the first case the distance is about twice that which exists between two consecutive fotocaptores. The second is four times larger.

Just keep in mind that the above calculations are merely estimates and their only intention is to give a qualitative approach to the problem, without trying to be absolutely accurate.

Finally, it should be noted that the title of the article is related to the fact that these so closed diaphragms are only used in practice photomacrographs.

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photomacrographs Diffraction and Diffraction in photography tripods

When light shines on the corners of an object or through an opening in it, is diffracted, which means that it shows an interference pattern consisting of alternating light areas and shade. In the event that the opening is approximately circular, so as forming the diaphragm, these zones are concentric rings. Yes a size very very small. In our everyday experience diffraction is the cause of that area intemedia in brightness between the parties strongly illuminated by the sun and the darker areas, which sometimes occurs in the corners of buildings.

The figure accompanying this article, we assess the situation in which the infinite light from passing through the lens exposed through an aperture of diameter D. Under these conditions, the camera sensor must be located at a distance F, corresponding to the lens focal length, if we get a sharp image. When light passes
creates inteferencia pattern above, which is a first illuminated circle (called Airy disc) and a series of concentric rings alternating dark and bright concentric rings. The brightness of these rings fell sharply as we go away from the center. Is what the wave shown in the diagram. The theory of Fraunhofer diffraction (Optica. Hecht-Zajac, American Educational Fund, pp.372-375) states that, for circular cracks, the angle θ formed by the lens optical axis and the starting position of the first ring Dark is calculated using the formula: λ

Θ = 1.22 ---

D

where λ is the wavelength of incident light .
If we have two very close light rays, the diffraction patterns will overlap. If they are really close, the two respective Airy Physicians will overlap and two points of light will be indistinguishable in the sensor. Form a continuous oval. The Rayleigh criterion states that for both points of light can be distinguished, the centers of the respective Airy discs should be separate at least by the radius of any of them. (We must remember, as shown in the figure, even within the Airy ring, the luminosity drops sharply as we move away from downtown).
Therefore, the separation d - as also seen in the figure - is expressed by the following formula (Bearing in mind that for very small angles senθ is approximately equal to θ) d = F



Substituting θ in above formula, we find that:

λ F d = 1.22

D ---

But it appears that the ratio F / f D is the number for that opening.
From which we have the exprexión:

d = 1.22 λ f

which allows us to calculate the distance between the centers of the Airy disk, for two rays of light coming so they can be resolved as two distinct and not be mistaken as a single point of light.
In the next article we will the practical consequences of this formula.