Wednesday, December 28, 2016

The ISO Value

Sure you have discovered on your camera ever to select "ISO", but never knew quite what this really is good. Now, in addition to aperture and shutter speed, the ISO value is also a big impact on the exposure of the image. It controls the sensitivity of the sensor in the camera. To illustrate this, we face the sensor of the camera time as our eyes. Everyone knows that: if you evenings by disabling the light, it takes a while until your eyes have adjusted to the darkness. If you now stop test the light again, sometimes a harmless table lamp for a short time appear extremely glaring and you have to squint until you become accustomed to his eyes again. The reason is that our optic nerves adjust according to the light sensitivity depending on the brightness. And so it is with the sensor of the camera, only that we can there govern its sensitivity via ISO setting as desired.

The ISO Value
On sunny days, you can easily take pictures with ISO-100
The sensitivity of the "optic nerve of the camera", the sensor is so, it expressed and set in concrete figures. ISO values ​​of 200, 100 or less stand for a low light sensitivity. Such values ​​are ideally suited to take pictures in situations with sufficient light, for example, on a cloudless, sunny day outdoors. But as luck would have it so, pull at once powerful lot of big dark clouds before the sun. To the image can now expose even with ISO 100 correctly, you'd have to either open up the aperture, or possibly adjust the exposure time so long that you need a tripod to get blur-free images. If both is not an option, you can increase the ISO value, in order to counteract the. Because he cares for an extended scope for the setting of different shutter speed and aperture combinations. The higher you let the ISO, the more sensitive the sensor responds to incident light. Values ​​from 400 to 800 are thereby generally used for cloudy days or indoors where not much light is present. Values ​​from 1600 can find their application in low light conditions where flash can not be used or allowed (for example in the event photography at concerts, theaters, etc.).

ISO values ​​and noise
That sounds almost too good to be true: too long shutter speed? ISO value up! Take pictures with the shutter closed in dim light far? ISO value even higher! Unfortunately, the thing as so often but a small hook. Depending on the camera model, the image quality deteriorates in some cases considerably with increasing ISO value. It comes to the so-called image noise and loss of detail in the image. Many compact cameras and older bridge cameras rushing already clearly visible from ISO 400. If you want more shooting under low light without flash, should access to an SLR. Their much larger sensors can record 1600 even halfway usable images even at ISO. Have an acceptable noise performance as the entry-level models Nikon D5300 or Canon EOS 700D. Who has higher claims, but must dig deeper into their pocket and possibly professional models with full-frame sensor access (eg Canon EOS 5D Mark III). But even with SLR, the rule is: less is more! It is always advisable to start only with low ISO values ​​photographing and value only then raise when the required time-aperture combination with the best intentions may not be recoverable. The picture below illustrates the impact of the ISO value to the image noise. While the left photo is almost no noise is visible, you can see on the right clearly the detail and loss of sharpness and image noise. Therefore: go gently with the ISO value to! Your photos will thank you.

100% Sample of the raw data from 4 shots with different ISO values ​​- from left to right: ISO 100, ISO-1600, ISO-2300, ISO-6400th
Using the ISO value - What to do when it gets dark?
Now it can be avoided to handle situations with high ISO value is not always. An example: you are photographing with open aperture at ISO 800 without a tripod and without flash at a party. Therefore you need the shortest possible shutter speed, which should not be less than about 1/40. When the shutter speed should be set so long now that your images from being blurred, brings you nothing less noise. Now you can quietly raise to 1600 or even 3200, and the shutter speed faster again, unlike the ISO value. Better noisy images as totally blurred! Of course you have, depending on the lighting situation try to find the best compromise. And sometimes you also brings the best camera anymore. For where there is no light, no picture can emerge. You remember the comparison with the eye? Where is no light, we can not see anything. In the case one then has no choice than to put away the camera or use a flash.

Digression: ISO and RAW
Some bridge cameras and virtually all SLRs offer you the option of your own photos in raw format to read the so-called RAW format. These RAW data is in other words the "digital negatives" your images. They remain different from the JPEGs produced by your camera completely unprocessed. When converting your images into JPEGs software processed in the camera, the images namely and it is the brightness, contrast and saturation and added noise away with various filters. Unfortunately, the latter often work very hard and image information is irrevocably destroyed. Not so with the RAW format. Thus you have one hand the possibility of subsequent image processing on a computer with special noise filter software to remove significantly more noise and secondly to preserve details and sharpness in the picture. The RAW format still offers other advantages, but is labor intensive and very memory hungry (up to 40MB per image).

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