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TheJoe.it Into the (open) source

24May/113

Photography: how to use ISO values

canon-eos-20d

In today's article we talk about photography, and precisely on the value of the optimization ISO depending on exposure or aperture.

We begin by saying that the term ISO indicates the standard to which we are referring to indicate the sensitivity of the internal sensor of the digital cameras in relation to light. In other words, by setting a low ISO value we will have a little light-sensitive sensor and a photo darker, vice versa (with the same aperture and exposure times) with very high ISO values ​​we will have a more sensitive sensor and a dramatically clearer picture (with some grain of digital noise in most, but more about that later).

How to begin using the ISO

The ISO, and I speak from amateur, are a very useful tool for those who approach to digital photography for the first time.

We often have to do some night shots, or in closed environments and not to have a flash powerful enough to irradiate the area. In this case the best option is to place the camera, or better to mount it on a tripod (but not always is available) and set an exposure time of a few seconds. Unfortunately, it often happens that is not available a natural support or a tripod, in that case we should take a picture holding the camera in hand. Needless to say, with an exposure of a few seconds the picture will move. The ISO (the sensitivity of the internal sensor) we are meeting in this regard. Depending on the lighting of the environment we set the most suitable value. The ISO is often modified automatically by the camera if there is a built-in light meter, otherwise the standard reference value is 100. We use 100 ISO in bright light, if the environment is dark we will have to increase them. Not always in compact ISO value is editable, but for some years the compact also enjoy the opportunity to set them manually, a great advantage especially for those who are beginners, or not disponde large liquidity.

For the novice photographer trivially just think that the ISO is useful for taking pictures in the dark, without camera shake.

The ISO and the relationship with light

As already said the ISO value should be set taking into account the amount of light from photographing. Actually, this value is a real relationship. For example taking a photo 200 ISO'll need half of the light needed to have the same shutter 100 ISO. To filter half of the light are the two main classical methods: opening time of the diaphragm, amplitude of the diaphragm. I remember that the diaphragm is present only in SLR, will therefore not be possible to set these variables on a compact or a bridge. Usually these last two categories have an adjustable aperture, but it is a digital simulation, nothing mechanical.

Among the menu of the SLR is the ability to set priorities.

Shutter priority:

With these settings, the diaphragm does not change the time of its opening, thus increasing the ISO will increase the width of the opening.

Aperture Priority:

Conversely, with these settings, the diaphragm does not change the width of the opening, thus increasing the ISO will increase the exposure time.

Depending on the light, and the subject to be photographed will be used one or the other method.

The flash: this unknown

With flash always recommend to pay attention, it is a tool that if used wrong can be "lethal". Start by saying that the flash is useful only if we respect the distance table usually on the back of the flash, or whatever in the instructions supplied with. But first of all we see when we do not need the flash:

  • When we want to photograph a square or a monument whose distance is beyond the reach of the flash, no effect,
  • When your subject is beyond a glass, or a reflective surface. The result will be the same flash reflection in the glass (with polarizing filter),
  • When the subject does not need a direct illumination (subject is too close or too far away),
  • When you do not want to create sharp shadows in the background.

When using the flash ISO sensitivity must be set low enough. Depending on the type of flash will then amended.

For shooting landscapes, squares and monuments it is preferable to place the camera on a tripod or place it, set a low ISO and increase the exposure times. However, if you do not have any support, however, the flash does not help, the only solution is to disable the flash and raise the value of the ISO, in the non-professional machine that will inevitably produce digital noise.

The problem of noise

This problem has already been successfully treated a few articles ago, acquaintances "repetita adjuvant". Use a very high ISO value means getting a photo with noise. The noise is colored grain that is obtained often in poor visibility conditions, very common in compact, and is due to several factors, such as a sensor too small, a sensor too hot, a bad compression software inside the camera. To the problem of digital noise there is no solution. If your camera produces a lot of noise the solution is to change camera. But if our disease is likely to be chronic, There are at least of palliative care that could make us feel better without having to change the sensor.

One of these is to rely on photo editing. There are commercial programs specially designed to reduce noise, and exists G'MIC, an advanced software is also available as a plugin for GIMP which has among its filters also allows noise reduction.

Perhaps not everyone will remember the old film cameras. I remember that film existed of different types, the most expensive (to preserve the ones that you had to put in the fridge) were the most sensitive. I remember that it was all very "romantic", and are still fascinated by the film, however, another disadvantage was having to constantly relate to the sensitivity of the roller. Once the film was in its place had to take these photographs, paying attention 12, 24 the 36 times the sensitivity. The difference is that now you can set the sensitivity of the photo and photo.

About

I keep this blog as a hobby by 2009. I am passionate about graphic, technology, software Open Source. Among my articles will be easy to find music, and some personal thoughts, but I prefer the direct line of the blog mainly to technology. For more information contact me.

Comments (3) Trackbacks (0)
  1. Ciao Alex, thanks for the comment. And’ a pleasure to be of assistance.

    To tell the truth I thought it was a little’ poor image, if you have any suggestions on how to improve the content are available.

  2. Have you explained in a simple and clear, is what I was looking, thanks:)

  3. nice tutorial.. You touched very interesting aspects
    for a technical approach to photography.. :-)


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