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| 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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