EXPOSURE Pt4: ISOSo here we are at the final chapter in explaining the seperate elements of exposure.
Once I've explained ISO, I can then start to show how the three work together rather than as individual subjects. Everything so far is so that you have an understanding of what each element does, but once you look at all three together, you'll start to see how one always affects the other.
ISO originates from film cameras - ISO is the
sensitivity of the film. The higher the ISO, the more sensitive the film is, so the less light is needed to record an exposure.
When I was younger and had a cheap film camera, I was always told to use 100 ISO film for outdoors/holidays/bright environments. If using the camera indoors or darker environments I should use 400 ISO because it was more sensitive to light and therefore better at capturing shots in lower light (200 ISO for anything inbetween)
I always tended to use 100 ISO because I mainly took photos outdoors, but on the occasional time I took a photo indoors or at dusk, it always came out much darker. This was because the film was less sensitive to light, so wasn't able to fully capture the images in the lower light.
Because I wasn't too bothered about photography, I just didn't bother with having different films with different ISO ratings...whatever was cheapest and 100 ISO. Simple.
Since getting my SLR and learning more about ISO, I have started to appreciate that it plays an important part of the exposure process.
ISO is an industry standard measurement for sensitivity, so all 100 ISO films
should have the same sensitivity. The same with 200 and 400 etc...
Now, since digital cameras don't use films, why is ISO important? Because the digital cameras sensor is able to adjust sensitivity just like replacing film from 100 ISO to 400 ISO on a film camera (except the change is made by the click of a button)
This is an instant change unlike changing film, so you can switch ISO's instantly between any shots. BRILLIANT!
So what is the drawback of ISO? Well, the higher the ISO, the higher the sensitivity to light, but also the lower the quality of the shot. Because the sensor is now more sensitive, it's more suseptible to noise (graininess, unwanted colour, lack of sharpness etc...)
Imagine it like a volume control on a stereo. If you're quite close to the speaker (bright light) you can have the volume fairly low (100 ISO) and the sound is perfect quality. As you walk away from the speaker (less light) you can't hear it quite as well so you have to have the volume up (200 ISO) to be able to hear it better. Move a lot furhter away from the speaker (low light) you need to turn the volume right up to hear it (400 ISO) but at this point the sound is more distorted because the speaker is really having to push hard.
The more voulme you have, the more sound distortion you get. The same with ISO....the more sensitive the sensor becomes (higher ISO) the more 'noise' you introduce to the exposure.
Here are some examples:
Here is a shot I took of the bottom of the speaker on my desk. I took this with my Sony P&S camera at 100 ISO holding it fairly close to the speaker.
I then took the same shot but at 400 ISO so that we can compare the two ISO's side by side. The actual image ^above^ has been reduced a bit from its original size but these two shots are viewing at 100% size (i.e. not reduced, but cropped)
Can you guess which one is 100 ISO and which is 400 ISO? Can you see the noise, the extra graininess etc...
Lets do the same with an SLR, but to an even greater extent...this is like turning the volume
right upHere is the original shot, much reduced in size (the original size is a LOT bigger than the point & shoot image) This was taken with my SLR on a tripod at 100 ISO
I then took two more shots at higher ISO's for comparison. These shots are all showing a part of the picture at 100% original size. On the left is 100 ISO, I then increased the sensitivity a hell of a lot to a massive 3,200 ISO....and the shot on the right was taken at an enormous 6,400 ISO!!
The difference is obvious, but then, there is a massive difference between 100 ISO and 3,200 ISO...let alone 6,400 ISO!
Another comparison...here is another shot (taken on my P&S at 100 ISO)
Here is a 100% shot of it alongside another that I took at 400 ISO
The same again with my SLR - this initial shot showing the overall image (massively reduced)
Now lets view it at 100% alongside three other ISO's (from left to right....100, 400, 3200 and 6,400 ISO)
There is a big gap between the 400 and 3,200 ISO, but I am sure you can work out that the image will just gradually get worse the higher the ISO? You can certainly notice the difference in image quality between even 100 and 400 ISO can't you?
Now for an interesting comparison....here is the difference between an SLR at 400 ISO and a point & shoot at 400 ISO.
You are viewing both those shots at 100% (no reduction or enlargement) and you can very, very clearly see the difference in noise quality even though they are both taken at the same ISO.
Why is this? Well, as I've said from the start, a cheap P&S will take good images, but will never be as capable as a more expensive camera. The sensor on a P&S is nowhere near the quality of a sensor on a decent SLR which is designed to cope better at higher ISO's. A good SLR will be able to handle higher ISO's to a much more acceptable level.
Having said that, you can see that even a high end digital SLR loses quality/gains noise as the ISO increases, but the rate at which it loses that quality is far, far less than cheaper cameras. My previous DSLR had about the same amount of noise at 800 ISO as my new one does at 6,400. It was
waaay better than my P&S (as used above) but was also a long way off the quality of noise handling my new DSLR is capable of.
Higher ISO gives the capability to take shots in lower light, but pretty much
always at the expense of image quality. Something to always bear in mind when thinking of upping the ISO