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.

Get your aperture right, and you may get mucho better pictures! Now what is Aperture really? OK, I think I recall there is (or was) even a famous fine-art photo magazine called “Aperture“. So, it seems to be an important concept in the field of Serious Photography.

Wikipedia says: “In optics, an aperture is a hole or an opening through which light is admitted… Obviously, the aperture also determines how many of the incoming rays that are actually admitted and thus how much light that reaches the image plane.”

Well, Wikipedia has got it spot-on, as usual. You use a large aperture, ie. a large hole, and lots of light streams in. You use a small aperture… what do you think happens? Right, less light gets through during a set amount of time! One detail to remember: in your camera, large apertures have small numbers and vice versa, like f=2 is a large aperture and f=8 is a small one. Expensive, “fast” lenses are capable of large apertures. OK, I guess we could stop here and let you figure out the rest yourselves…

Still there? OK, the thing about aperture is to get control over how you use it in your photos. You see, if you use a large aperture, the depth of field is small - and conversely: small aperture equals large depth of field.

This is the important thing to know about aperture. Maybe I should add a few words about what depth of field is. Think of it this way: You focus the camera on something, say a flower in a field. Usually, not only that particular flower will be rendered sharp in the picture, but also some of the flowers closer to the camera as well as some of those further away.

This is the phenomenon called “depth of field”. Just how much of it you will get in each case depends on several factors, but the main ones are your distance to the subject and your aperture setting. Assuming you have already chosen a distance that you like, you can now adjust the depth of field by playing with the aperture setting.

Do you have a somewhat distracting background which you’d rather get rid of? OK, try using a large aperture to put that pesky background out of focus! Since the depth of field is now smaller, everything that is significantly further away from the camera than the subject you’re focusing on will be rendered blurry - and hopefully less distracting.

Obviously, if you use a larger aperture you need to change one or both of the two other points in the Exposure Triangle - shutter speed and ISO-setting. You will need to use a faster shutter speed and/or a lower ISO-setting to avoid having the picture over-exposed to light. Complicated? Not at all - I’m pretty sure there is some setting on your digicam which takes care of this automatically. Like, you set the aperture you prefer and the camera takes care of the rest. If in doubt, consult the manual…

Now, suppose you are snapping a picture of something and you want all of it in focus - what do you do? Right again! - you use a SMALL aperture setting. Like the photo of the spiral staircase here, note how all of it is rendered sharp, even the knob in the lower-right corner which seems quite close to the camera.

This is how you play with aperture to control the depth of field in an image.

Before closing, I like to give you another short photo tip: You need to remember that the camera’s autofocus always thinks whatever is in the center of the picture is also the thing to focus on. This is by NO means always the case, as in the staircase case here. The photographer wouldn’t have managed to get everything sharp if he had put the focus on the most distant part of the picture - which is in the center. Instead, he must have focused on some point about half-way up the stairs, to get this splendid result.

Photo credits: eye by DownTownPictures, staircase by procsilas.

In case you are new to photography, you may feel it is convenient to just put your digital camera on automatic and hope for the best.

If you do, I bet you will soon get a bit frustrated with how your pictures often don’t come out the way you intended, and you sit there wondering what’s going on.

OK, then it is time to take the first steps toward having control over the camera - as opposed to having the camera control YOU!

Take the clown picture here for example. Imagine how dull it would have been if you had taken the picture using automatic settings. The camera would then have fired the built-in flash unit and ruined the mood of the event (and you may also have gotten thrown out for disturbing the act!).

On the contrary, the photographer here had total creative control. He took the picture using the ambient light, and used a very long exposure time. And, yes, the result was motion blur.

However, what do you feel when you see that “blurry” photograph? Personally, I feel it is a great shot! And you could never make a picture like this unless you had creative control over your camera.

The Exposure Triangle

To begin with, there are basically THREE WAYS you can control how the image is exposed in the camera when you press the shutter. You can think of these as the three tips of a triangle; the Exposure Triangle.

1. Exposure Time = Shutter Speed

2. Aperture = Size of Light Opening

3. ISO Setting = Sensor-sensitivity

The exposure time, also known as “shutter speed”, determines how long time the camera sensor is exposed to the light from the subject of interest. Long exposure is another word for slow shutter speed.

The aperture setting determines how big the opening is allowed to be, for the light coming in. And remember that the larger the aperture opening, the lower the number on the aperture scale. Expensive camera lenses usually allow the use of larger apertures, making it easier to work with them in low light.

Finally, the ISO setting determines how high you crank up the light sensitivity of the sensor unit in the camera - the part that transfers incoming light to an electronically stored image. Higher sensitivity means more “noise” in the image. To get the best quality you usually set this to 50 or 100 ISO units.

So, a few words on shutter speed. Generally, if nothing you’re trying to capture is moving much you can use shutter speeds down to maybe 1/60 of a second. With practise, you can use even slower shutter speeds, ie. longer exposures, for non-moving subjects. In case you want to freeze movement, you need a faster shutter speed. For instance, a car driving past you and going fast may require a shutter speed of 1/500 of a second to “freeze” its movement.

The picture of the surfer here was shot at a very fast shutter speed, to “freeze” the movement. Fast movement = fast shutter speed.

To get creative control over the shutter speed point of the Exposure Triangle, you need to consider how you want to use that setting to control the mood of the image. Like, do you PREFER to “freeze” the movement by using a fast shutter speed, or would you rather experiment with a very slow shutter speed to get intentional motion blur, as in the clown picture?

In the case of the clown picture, the low ambient light wouldn’t allow a very fast shutter speed - and neither would it be needed or even desirable in that situation. Conversely, in the surfer photo the light was quite strong which allowed the photographer to snap the picture at a fast shutter speed - likely 1/500 of a second or even faster.

You could have made a very different surfer picture by using a slower shutter speed, to create some motion blur. Then you would have needed to adjust the two other points of the Exposure Triangle accordingly - smaller aperture and/or lower ISO setting, to avoid over-exposing the image.

In conclusion: You use the shutter speed point of the Exposure Triangle to control how you render movement in an image. If the rendering of movement - either by “freezing” it or by using motion blur - is a top priority in a particular situation, then your first priority is to adjust the shutter speed to a setting that fits your intention. The other two settings (aperture and ISO) will take the back seat, so to speak. You simply set them to whatever is needed to get a correct exposure.

Photo credits: clown: Ctd 2005, surfer: abnelphoto.com