Hi and welcome back. This week we going to talk about the sensitivity of the camera which is basically the sensitivity of the sensor inside the camera this is also called ISO and you may come across an old term ASA.  All of these are basically talking about the same thing how sensitive to light is a sensor in the camera.

Just so you know the old term ASA means American Standards Association and you’ll come across this ensemble really old books talking about film photography. The other term that was always use around that time is ISO and that someone that we still have today and that means International Standards Organisation. There is another term that you will come across every now and again and this relates to flashcards and that is guide number but don’t worry about that now.

Back to sensitivity, what does it all mean? Well we already know that it’s how sensitive the camera is to the light coming in but is that all that it is, couldn’t maybe have something else that we need to think about happening when we change the sensitivity and even decrease or increase the ISO on the camera. Doesn’t really matter if we let the camera use auto ISO, is it really worth knowing about this and changing to a specific ISO or limiting the range of the automatic ISO? The easy answer all these questions of course is, yes.

Let’s just call it ISO or the rest of the lesson. So cameras have what they call native ISO, all this means is that it is the best ISO normally the lowest that the camera can use to capture the best possible image. Most pocket cameras will use 100 ISO, DSLR is will often be able to go down to 50 ISO or maybe even lower. In the film days the lower the ISO the better the image.

Okay, so why is a lower ISO better than a higher ISO? This all comes down to grain, grains what we used to call
the small spots that make up a photograph because in the old days and fill when you took a photo on the film itself when you are developing at the black parts which are the contrast is with silver sulphate crystals were captured on the cellular and when you then exposed photographic paper those black elements became white and of clear parts of the image became black and in order to get the different shades of black and white which represent colour there were even more or less silver sulphate crystals. So when you expanded that image and zoomed in as we now call it you could actually see the crystals which made up the darker colours until it became of course black. So this is where the term grain comes from. Now we all know in digital photography there is no film, but we still have this strange spots and noise that comes up when we zoom into an image or indeed when we increase the ISO to a higher level. So it is not film, what is it that causes this noise to happen? Well simply put as we try and pull more information out of light the electronics inside the camera trying to resolve more and more detail with less and less information. In the digital noise which often appears as maybe even blue or green or purple splotches on an image is the electronic noise converting the light into electrical signal to be saved on your memory card.

So digital noise is an artefact which often is more visible with the higher ISOs. Now is cameras and sensors get more advanced the level of signal-to-noise ratio which is the electronic noise is getting better on some of the high-end digital DSLR is you can get a clean image over 64,000 ISO but on some older cameras and some of the consumer level cameras you’ll start see noise creeping in a thousand ISO but it all depends on your camera the age of your camera the number of megapixels that is try and be drawn from the sensor in relationship to the size of the sensor all of these things will determine how noisy your images are at higher ISOs. There is no way of fixing this it comes down to your camera your sensor and the technology that was used when the camera was designed and built.

You can of course use noise reduction both in camera and in software. This will help but will not alleviate the digital noise or grain that you will see in your final images. The other thing that helps to determine how much you actually see noise is how much you may zoom into an image, how much you may crop an image, how big you try to view the image, what file format you save the image in and of course the size of a print or just look at it on a computer monitor. There is no one size fits all and no one easy answer to all these things affecting noise, it comes down to the individual, the camera and the use.

So what does ISO mean to us when we taking photos, one of the general rules of thumb when we look at ISO and using? Well, back to the native ISO of the camera some 100 and some are 200 ISO. Some cameras may go down to 50 ISO or lower. But to us, most people are happy to live around 100 ISO the general photography in normal daylight. But that doesn’t mean that you don’t change your ISO, changing the ISO will allow you to create the point of balance between the speed of the image which will discuss next session and the aperture of the image which we looked at last week so to some extent it’s a determining factor in speaking the speed of your shutter and the depth of field and how much like comes through that opening in the lens.

So as a rule of thumb, we have 100 or 200 for normal daylight shooting, late afternoon open shade not directly in sunlight maybe 400 ISO, using flash 400 maybe 800 ISO. The higher ISOs at thousand 1200, 3200, 6400 ISO well they are all useful ranges on modern DSLR’s and as we spoke of before you can go all the way up the scale and still get acceptable images. And akin to all of this is what is acceptable to you, you may be happy with a little bit of digital noise in fact you may want digital noise to help soften hard lines in your image it all comes down to what you are trying to get out of your photograph. So the right ISO is something that you with time will be able to creatively use in balancing the exposure triangle. You will be able to determine if you want to set an ISO and go off for a shoot, or have a camera set to an automatic range of ISO where you will the camera decide the ISO and you will play with the other two sides of exposure triangle to drive your depth of field or drive your shutter speed depending on what you’re trying to capture and use the ISO simply as a base with an allowable range in the automatic mode. But remember you’re smarter than your camera and your creative vision is something that you know and your camera never will.

So before we close let’s just have a quick look at auto ISO. Many cameras will allow you to set a range of ISO the camera to use, what you’ll find on consumer enthusiasts and even some professional cameras is that the automatic range will be from say 100 ISO through to 800 ISO or maybe even up to 6400 ISO. What this means that the camera will use any of those settings based on your chosen aperture and your chosen shutter speed to achieve a correctly lit or exposed image. The sacrifice you make of all of this is that the camera using a higher ISO can introduce more grains your images then you would be expecting now this may not be important to you but if you’re doing a wedding or something in low light or changing light situations it may be of benefit or detriment to. It’s up to you to make that decision and either set your ISO, limit the range of your automatic ISO, all at the camera do everything for you and you’re satisfied with the outcome. Ultimately comes down to what you want from your image and if you really need to or want to understand how to impact your images before you capture them or to control the camera in capturing that image.

For a simple subject such as sensitivity, there can be a lot of goes into. Don’t let this daunt you, if you have a real interest in photography and you want to control your images and create your creative vision it sounds like a lot but once you use it a few times it becomes second nature. Don’t worry about the science just think about how much digital noise you can accept an image and the impact that the ISO setting will have on your shutter speed and your depth of field if you have what you want fantastic you’re well on your way to understanding this capturing the images that you’re after. Until next time, catch you later.