ISO? What’s ISO?

ISO is shown in numbers, and is an indication of how sensetive the film or digital sensor is to light.  If you’ve ever bought film, you’ve probably seen numbers like iso 100, 200, 400 and so on.  The higher the ISO, the more sensetive to light the film or sensor is, and the more grain (film) or noise (digital) the image will have.

Because there is more light sensetivity at higher ISO values, one can use higher shutter speeds and/or smaller apertures to perhaps, freeze the subject in low light situations or gain greater depth of field.  Take care with ISO though, the higher you go, the more noise you get.  Software can help reduce or remove this noise, but this has it’s limits.  You may also wish to use use high ISO to take advantage of the creative effect that noise can bring. Experiment with it.

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The images above have had the ISO increased by 1 stop for each. Open them up and see how the noise affects the image.  Take note of the darker portions which is where the noise will generally be more noticeable.

ISO 100 is generally accepted as the norm and will give the cleanest images. Some digital cameras now go down to ISO 50.  Consumer digital cameras have a general range of ISO 100 to around ISO 3200.  Sensor type and size also affects how noisy an image will be a comparitive ISO’s. for instance, a £100 point and shoot camera will most likely be very noisy at ISO 400, whereas the full frame sensor of something like a Canon 5D will produce very clean images at ISO 800 or more.

Most consumers will buy a camera to take snapshots, leaving it in full auto mode. in this mode, the camera will select the ISO that is appropiate (trying to keep as low as possible). Many digital cameras, including the lower end point and shoot types will allow at least some manual control, and thus will allow ISO adjustment.

When choosing which ISO to use, there are a few factors i think of to determine this, these include -

• How bright is the scene?
• Am i using flash?
• Do i want the ambient light to register?
• Am i after a clean image, or would i like to introduce noise/grain for artistic effect?

If there is lots of light, my subject is stationary or fairly slow moving, and i want little to no noise i’ll proably use ISO 100 – 400.

Some situations which may call for increased ISO include the following -

• Indoor events such as a concert or sports event
• Wedding ceremony where there may be a restriction on using flash (which has an added benefit of being able to freeze the subjects motion)
• Art galleries or exhibitions where flash use may be prohibited

Any scene where the mood of the situation is better captured without flash will usually also require pushing the ISO up.

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ISO is as important a tool in photography as shutter speed and aperture. learn it, use it. Experiment and have fun with it.  Go as low and as high as you can go, seeing how it affects your images. Remember, when adjusting ISO, you will need to adjust your shutter speed and/or aperture as well to maintain the exposure you’re after (remember, the correct exposure is not always the creatively correct exposure).

As you know (i hope!), we have discussed shutter speed and ISO and how they affect your images. Today, we will look at the final part of the triangle, Aperture. Without doubt, aperture is the most creative of the 3 with shutter speed coming a very close 2nd. Changing your aperture can turn an image from being flat and dull to full of life, dimension and intrigue.  So, lets look at what aperture is all about.

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Aperture, big or small?

In simple terms, the aperture is the size of the hole in your lens.

When you press the shutter release to take an image, the aperture blades in the lens open up to the size of aperture you have set in your camera. This hole allows light in so the sensor can see the scene or subject you are pointing at.

The smaller the number (e.g. f1.4) the larger the hole and the more light gets in, the larger the number (e.g. f11) the smaller the hole and less light gets in.

Aperture is measured in f stops. Depending on the lens, these can go from f1.0 to around f22. A typical 50mm lens would probably have a range around f1.8 to f22.  Moving 1 full stop up or down either doubles or halves the amount of light entering the lens. For instance, going from f2 to f2.8 would halve the amount of light hitting the sensor.

Be aware that changing your shutter speed 1 stop up or down also doubles or halves the light, as does ISO, so if you adjust one, you would need to adjust one of the others in the opposite direction to keep the same exposure.  Not many photographers i know make a habit of adjusting ISO regularly (generally preferring to set it once to suit the scene) and mostly just use shutter speed and aperture.

Like with guitars, the top string is at the bottom, the low E is at the top, going up the neck is actually going down towards the body..and so on – aperture has it’s numbers backwards.  smaller means bigger.  at first it’s confusing but you will soon get the hang of it.

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Aperture, the creative side

The main ‘creative’ thing that aperture affects when you take an image is something called depth of field.  Depth of field is basically how much of the image is in and out of focus. A small aperture (large F number) will have most, if not all of the image in sharp focus, and a large aperture (small F number) will only have part of the image (wherever you focus on specifically) in focus.  Other factors determine how much or how little is in focus for any given aperture, such as subject distance, more on that later.

In the images below, i shot the same scene 4 times with differing apertures. They go in 2 stop intervals from f1.4 to f11 (f1.4, f2.8, f5.6, f11).

Click each image and notice how the background is more and more in focus as the aperture is decreased (larger f number).  If the background was closer or i had focussed on something further away, then the background would appear much more in focus.

The best way to learn how aperture control can make such an impact to your images is to go out and experiment.  Get yourself in manual control, set the largest aperture your lens has, and shoot something, then shoot it again, reducing your aperture each time. Remember in manual control, you will need to adjust your shutter speed and/or ISO to get the same exposure or you could pop yourself in AV mode – aperture priority – and just adjust aperture, the camera will sort the rest out for you.

Have fun and happy shooting!

When i bought my first DSLR, i admit i was more than a little intimidated by all the settings, icons, knobs and buttons. Now, it’s mostly second nature, and largely, once you know what’s going on one camera, the rest are pretty similar.
Read the rest of this entry »

Hopefully, you will have seen the article on the exposure triangle. In the article, we take a brief look at Shutter speed, ISO and Aperture. In this article, we drill down a little more on shutter speed and how it affects the images you produce. Read the rest of this entry »

The triangle of exposure as seen in the image on the left contains the 3 (hence a triangle!) ingredients used to make a photographic image.

How you use each of these ingredients (and subsequently alter the the others) will give different results (albeit with the same exposure if the ratio is maintained). Read the rest of this entry »