a1 Photo Tips

Lately, I have been talking about the Exposure Triangle, and how you need to understand what it is all about to take creative control over your picture making.

In this post I figured I’d demonstrate one of the points of that imaginary triangle - the ISO setting.

Remember what the three points were?

Aperture - size of the light opening into the camera

Shutter Speed - how long time the shutter stays open

ISO Setting - sensitivity setting of the light-recording camera sensor

You may recall that I have told you the image quality gets impaired if you crank up the ISO-setting. OK, now I am going to show it to you, according to the old adage, “One picture is worth 1000 words.”

See the pictures above? Both are shot at the same aperture, but with different ISO-settings. For the one on the left I set my old Canon Powershot digicam at 50 ISO, and right after snapping that picture I changed to 400 ISO and snapped the picture to the right.

Well, in fact both of these are enlarged details of the original pictures; here below you can see what the original pictures looked like (I show the 50 ISO one here, the other looks just about the same).

The enlarged details show very clearly how the image quality gets degraded at high ISO-settings (400 ISO was the highest I could get with my camera, more advanced digicams allow for much higher ISO numbers). The difference is especially evident on perfectly smooth and uniform surfaces, like on cars.

Note how the surface looks quite grainy at 400 ISO.

– Hmmm, I wonder where they use such funny license plates on cars…?

The ISO scale is set so that each doubling of the numbers equals doubling the sensitivity; like ISO 400 is twice as sensitive a setting as ISO 200, which is twice as sensitive as ISO 100 - and so on. In other words, by sacrificing some of the image clarity I have made the camera sensor EIGHT TIMES more sensitive to light!

In low-light situations, this could mean the difference between getting a useable picture or not, like being able to shoot at 1/40 of a second rather than 1/5 - in the latter case it would be very difficult to avoid blur due to camera movement.

You may wonder how this image noise happens? Well, you probably know that a digital image is composed of an array of tiny squares called “pixels“. Each pixel can have its own color, thus forming a mosaic that builds up the total picture. Now imagine there is a tiny goblin sitting at each pixel, with the duty of trying to figure out the nature of the brief light pulse that arrives at that pixel when the picture is snapped.

At low ISO settings the goblin doesn’t need to make up its mind until there is enough light to make a good decision. But if you crank up the ISO-setting, each goblin is forced to decide based on very scanty data - more or less make an educated guess. And therefore the final image will be a bit of a guesswork.

Even if you don’t believe in goblins I’m sure you can follow my reasoning. So what have we learned today? Something like this maybe:

If all else fails, we can crank up the ISO-setting of a digital camera to get a picture where it otherwise wouldn’t have been possible.

In other words: avoid upping the ISO number unless it is really needed - or you don’t really care about the image quality. Note: you can set the ISO value on automatic on probably just about any digicam. If you do, make sure you know what is going on to avoid surprises. The camera may have a low opinion of your ability to hold it steady at slow shutter speeds.

Update: I should mention that advanced users may be interested in testing post-processing software which reduces such image noise as you get at high ISO-settings. Since I haven’t tested these myself I don’t know how good they are at improving the quality of such images, but I’ve seen that some swear by them.

This post ties in with previous ones I have written about how to get creative control; either using the aperture, or using the shutter speed settings. Now I address a special type of situation: You want to capture something, maybe an event, that takes place indoors, and you either are not allowed to use flash or you don’t WANT to use flash.

The event could be a public performance or maybe a wedding ceremony. In either case, using flash may be a no-no. Assuming you have a camera with built-in flash unit and nothing more, the result of a picture snapped with the flash unit as major light source is nothing much to brag about. Sure, you can clearly see what is going on but that’s about it. The light is harsh and ugly, everything close to the camera is very brightly lit and whatever is further away gets gradually darker, disappearing into blackness.

Then there is the fact that firing off a flash may be very distracting and irritating. Like during a wedding ceremony - how romantic is it to have a flash zapped in your face at the exact moment you say “YES”?

If you want to tackle situations like these successfully, getting both beautiful pictures that convey the mood of the event AND remaining friends with people around you - then learn to work in ambient light without any flash!

And again, I bring out the good old Exposure Triangle:

1. Exposure Time = Shutter Speed

2. Aperture = Size of Light Opening

3. ISO Setting = Sensor-sensitivity

These are the main in-camera factors you have to master, to be successful. — Now, would you believe me if I told you the picture above was made with a hand-held camera, without any tripod or such support? Yet I’m told it was. And the only light comes from that candle!

How was that possible? Well, the photographer must have a firm understanding of The Exposure Triangle. To get a picture like this, you have to get as much light into the camera as ever possible, at a short enough time to avoid motion blur. Now look at those three factors. Which one do you use to get as much light as you can into the camera, in short order? Right, number 2; the aperture setting!

So, you set the aperture at the largest opening (ie. the lowest number on the scale) possible. If you are lucky enough to have a digital SLR, you may be able to choose between different lenses, and pick the one with the largest maximum aperture (= the “fastest” lens).

Now, what else can you do to get a clear image with as little light as possible? Correct! - You crank up item number 3, the ISO-setting, as far as it goes! This makes the camera sensor react to smaller amounts of light, at the expense of a somewhat impaired image quality. You get more “noise”. And you may be willing to live with that noise, which won’t be so noticeable if you don’t make the image very large.

Or you can actually get rid of at least most of it using post-processing. I’ve heard there is for instance software called “Noise Ninja”, designed to reduce such image noise.

By using a large aperture and a high ISO-setting we have, hopefully, been able to acieve our goal: To use a shutter speed (ie. exposure time) short enough to get a sharp image without motion blur. And if there still isn’t enough, here is another little photo tip: Deliberately under-expose the image slightly! You can correct that later, using any image-editing software like Photoshop.

Of course, how much light is “enough” varies depending on your ability to hold the camera still using a long exposure like 1/15 of a second or so. I gave you some how-to tips on that in an earlier post: How to Hold Your Digital Camera. And if the subject moves slightly during the exposure, the effect may actually be very interesting - with some luck!

Photo credits: child picture: Ctd 2005; performer picture: reportergimmi