Hi all…today, the first basic concept of the image…ISO
Some of you might know and remember ISO stands for International Organization for Standardization and they set some standards, namely, ISO12232:2006, for determining sensitivity of a camera sensor, hence the name ISO. Not going into all the technicalities, long story cut short….ISO lets you change the sensitivity of the sensor.
Lower the ISO number (say ISO 100/200, even up to 400 on some cameras) better will be the clarity of the picture, this is kind of a thumb rule. So, why would we want to rise from these numbers at all, set the camera to the lowest ISO and snap away…we always want the sharpest of pictures right? The argument is true, Yes, we do want the sharpest photos but every now and then, we are in situations where we do not have decent amount of light. Bumping up the ISO, lets us deal with this issue. When we are increasing the ISO number, we are increasing the light sensitivity of the digital sensor. The ISO system today, in digital cameras is equivalent to what film speeds were in the film cameras. Remember the numbers written on the film rolls, and how a 400 or a 800 speed film would be pretty costly and hardly be given to us, when we were younger, while the 100 or 80 speed ones were cheaper and more dispensable. Back then, the film speeds reflected how sensitive the film were to low light conditions, more sensitive, more pricey.
But, the sensitivity comes with a trade off too…noise, digital noise. Digital noise is what causes tiny grains to appear on the photos. Sometimes we do put on a film-grain effect on the photo to make it look different, but if they come up in the original photo, it is undesirable. Now, with increase in the sensitivity, the noise also increases. To counter this, the cameras generally have a noise reduction system in them. These systems, take care of the noise till ISO 800 with ease, some take handle it up to ISO 6400 too, but beyond that, the noise overwhelms the anti-noise system and they appear in the photos.
Below are a few photos, which are almost 200% crops of bigger photos, taken of a pillow cover at various ISO to show the difference. Notice that in ISO 100, 400, and also in 800, the strands are pretty much visible separately but once beyond that, they start getting smudged in the photo…this is being caused by noise and in ISO6400 and ISO12800, the details are almost non existent.
The high end DSLRs provide with ranges near ISO204800. Agreed, at that high range, your picture will be noise and noise only, but the sensitivity will allow you to shoot at pitch darkness and your camera will see more than your eye can and give you some outputs, in theory at least…need to try this in practice someday..
Now, even in the entry level DSLRs, the noise reduction system is good enough that on a general viewing, the noise might not be a distraction to the great photo that you have taken. But as and when you start printing them, say at 100%, the noise will show up and believe me, you would want to avoid that.
To avoid the noise from creeping in and ruining your shot, you ll need to handle the aperture ( F stop) and the shutter speed….topics coming up on the next posts..