After 20 years I've decided to kick my 20-a-day smoking habit. This blog is hopefully going to serve to anchor me in my quest and maybe provide some focus for me which will help me quit successfully. I will be giving up using the "Cold Turkey" method.
To understand how ISO ratings affect us in our digital ventures, we also need to understand how ISO ratings affect us in "real film" photography. Those of you that have ever had even a slight brush with photography already appreciate that with "real film" the objective is to focus light onto the film itself. We focus light onto the film for a pre-determined amount of time in order to achieve an "exposure" - or as we all know it - to take a picture.
For the moment, let's take the camera out of the equation. Let's say we have a roll of ISO 400 film (the ISO rating is not important at this point). Imagine the film is in the palm of your hand and you can control the amount of available light that hits the film by opening and closing your hand. I want you to further imagine that you have opened your hand for 1 second and then closed it, thus stopping any more available light from falling onto the film. What you have just done is taken a picture using only your hand and the exposure time was 1 second long. It goes without saying that the picture you've just taken will be a white blur as the available light hasn't been focused using a lens, but you've taken a picture nevertheless.
Okay, now we have a basic understanding of "exposure", let's get down to the real meat of this post. What does the ISO rating actually mean? Put simply, it means the higher the ISO rating the faster the film will react to the light focused on it. For example ... Our 1 second exposure time on our "in-palm" ISO 400 film can also be duplicated using an ISO 800 film and only opening our palm for half a second. If we were to use the ISO 1600 rated film we would only need to open our palm for a quarter of a second. If we were to use a "slower" film - say an ISO 200 - we would need to open our palm for 2 seconds to achieve the same exposure as the ISO 400. This means the higher the ISO rating, the "faster" the film (needs less exposure time). This also means that the lower the ISO rating, the "slower" the film (needs more exposure time).
So why does film have an ISO rating? When and why would I use the different types of ISO rated film? Well, I would use film with an ISO rating of 50-400 when I know the subject is going to be fairly still, such as a portrait. I would use film with an ISO rating between 400-800 if I was going to be outside shooting moving objects. I would use film with an ISO rating between 800-3200 if I was shooting very fast moving action. There is another aspect to choosing which ISO film to use and that is "film grain". Film with a low ISO rating will produce a less "grainy" picture than those of a higher ISO rating, so sometimes choosing an ISO rated film can quite literally be as simple as an artistic choice.
The example image to the left shows the effects of altering the ISO rating on my digital camera, this was the only setting that was changed, the other settings remained constant. The sections of the image - from left to right - correspond to the ISO ratings 100, 200, 400, 800 and 1600. The correctly exposed image was in the middle and the camera was set to ISO 400. As you can see the middle image appears to be the most correctly exposed. On the faster film we are over exposed and on the slower film we are under exposed.
Here's the million dollar question ... "My digital camera doesn't take film, so what possible changes could occur within my digital camera when I change the ISO rating?". Well, from my example image we can see that the exposure changes as I change the ISO rating. The manual for my digital camera says that the image will be grainer in appearance if the ISO rating is increased, but I've seen no evidence of this yet. The manual also says the flash can be used over greater distances if I increase the ISO rating and shorter distances if I lower the ISO rating, but I am yet to test this theory.
The technical aspects of this article are presented as I understand them. If you feel something written here is incorrect, please feel free to add a comment to this post, I would greatly appreciate you taking the time to let me know.
For me this journey will be all about what I can learn on the subject of digital photography. I already have a small understanding of how a camera works and enough knowledge to be able to get myself into trouble, what I truly lack is the experience and the knowledge that will enable me to move forward and take large creative steps. In short, I have an understanding of the toolset, I just don't know how best to use them in unison to create something worthy of a second look.
With each post I shall discuss different aspects of digital photography and share what I have discovered. I hope some of you decide to join me on this quest as I know there are lots of people out there with very expensive camera equipment and haven't a clue how to best use it. This must be true as statistically I cannot be the only one?
I also plan to make this blog a good resource for others that are interested in learning about digital photography.
The technical aspects of this article are presented as I understand them. If you feel something written here is incorrect, please feel free to add a comment to this post, I would greatly appreciate you taking the time to let me know.
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