Saturday, May 24, 2008

A bit about ISO/ASA......

Rather than using my own pictures this time I'm going to be showcasing a few pictures from an e-friend of mine who does a lot of work on movie sets.

Today I'm going to cover ISO/ASA and why you need to understand how to use it effectively. ISO and ASA are the same thing, and so from here on out I'm going to refer to them simply as "ISO".

ISO is a measurement of the sensitivity of the device used to capture the light let in through the lens. That's it. That's ISO in a nutshell.

Now you may be wondering why it matters and where it ties into everything else, which is good because I'm going to tell you.

My general rule for effectively using ISO is this, leave it on it's lowest setting unless you need it to be higher. Why would you need it to be higher? You will always use ISO to give you the right exposure at whatever shutter speed and aperture you need, but never the other way around.

Now for the implementation:
therealmr does a lot of work on movie sets and that doesn't provide him with a lot of light. I'm sure you all know by now that having a slow shutter speed will make your pictures blurry, and you've probably also noticed that the great majority of lenses don't go below f3.5 or f2.8.

So if your aperture won't go lower or you want to maintain your depth of field, and your shutter speed is as low as you can take it without getting blurry pictures, what do you do?

You turn your ISO up.

I wouldn't advise shooting above 200, or really 100 ISO unless you just don't have an option. I will say this however; even with entry level DSLRs, the noise at 1600 ISO is comparable to the amount of grain you might see in some of the 400 ISO film I used to use, so don't take things too seriously.

I'll finish todays post with a few examples of someone using a high ISO constantly, and some of the why.

This is a good example:

In this picture using flash would have destroyed the interesting pattern on the wall, using a slower shutter speed may not have frozen the dancers motion resulting in a blurry picture, and his lens was already at 2.8 which is probably as low as that particular lens can go. All this resulted in him using 800 ISO, to achieve a proper exposure.

Another example:

Here his lens was at f1.4, his shutter speed 1/50 sec, and his ISO was 1600, and his picture is just barely exposed well. Once again, his lens couldn't go to a lower aperture, and his shutter had to be reasonbly fast to reduce camera shake from blurring the picture.

One last example:

ISO 800, 1/160 sec, f2.8

Thanks to therealmr for the permission to use his photos. Please visit him here.

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