Look on the brighter side of life – ISO photography

ISO is a setting to increase the brightness of a photograph.

Sometimes you have a dilemma when, in low light conditions, you wish to avoid an underexposed image. Let’s say that, even though you have opened your aperture as far as your camera allows in order to retain sharpness, the image is still under-exposed. So then you have set your shutter speed as slow as you can yet still avoid avoid blur, but the image is still under-exposed. If you don’t mind blur – or if you want special effects such as light trails – you could mount your camera on a tripod and take a long exposure. (If you are taking an exposure longer than about 1/50 seconds without a tripod you risk camera shake and undesirable blur.)

In other circumstances, however, in order to increase brightness your only option other than flash is to raise the ISO setting. Unfortunately, if you raise the ISO significantly, you will begin to notice ‘noise’ or ‘graininess’ in your image. You then have to trade off motion blur against graininess – or miss the shot.

I’ve provided here a series of images of the same scene, on the same day, as darkness appears. I took this first one at 20:37 using ISO 100 at f/11 and 1/25 seconds. The focal length was 20 mm for all this series. The image is reasonably sharp and without noise.

This photo was taken 3 minutes later and yet is brighter. I increased the ISO to 200, increased the shutter speed to 1/100 seconds, but retained the aperture of f/11. At ISO 200, there is no noticeable increase in graininess.

By 22:03, I was using ISO 250, a shutter speed of 4 seconds and an aperture on f/3.5 – that’s an increase of 8 aperture stops alone. There is some noise but not much.

By 23:28 I was using ISO 3200, a shutter speed of 25 seconds, and an aperture of f/3.5 – as wide as possible with the lens I was using. There is considerable noise. In the following two images I have cropped section of this image to illustrate the noise or grain.

This is a crop from the middle- left of the picture.

This is a crop from the bottom right.

The shutter speed of 25 seconds was as slow as I could use, with the lens I was using, without causing spot stars to trail as a result of the earth’s rotation relative to the stars.

So, in summary, The ISO setting on a camera can be used to brighten a photo, but start by setting an aperture suitable for your subject. Then set your ISO to its base value – usually 100. Take a test shot and if the preview image indicates motion blur, try a faster shutter speed until you get a sharp test shot. If you still experience blur, increase the ISO but use a faster shutter speed. If after increasing ISO a few times you start getting noise in the image, try opening your aperture.

My featured photo of light trails today illustrates some of the types of trade-off issues. It’s a low light shot for which I wanted sharpness overall ie good front-to-back depth of field for the light trails, and — preferably – a starburst effect from the street lights on the roundabout. My start point was, therefore, a small aperture of f/18. However, I wanted the exposure to be long enough to capture the light trails, so I used a tripod to avoid camera shake and a fairly low ISO of 125. My focal length of 30 mm was wide enough to take in the scene I’d chosen. As the scene became darker I eventually got the shot I wanted with a 30 seconds shutter speed.

I’ve provided a link below to an excellent website that explains ISO in crystal clear terms.


Photography – Aperture Words, words, words I’m so sick of words

Any newcomer to photography, picking up a modern digital camera is immediately confronted with a mystery. On the lens he or she might see something like SMC Pentax DA 1:1.8 50 mm. Turning to the camera – on a dial on the top they might see some of the following – B, M, AV, TV, SV P, AUTO. On the sides and rear of the camera there are acronyms such as AF/MF, RAW Fx1, AF/AE-L, ISO, WB, LV. If they were to ask what these initials mean, they’ll hear words like Aperture, Focal Length, Shutter speed, ISO. Pressed further, their mentor might mutter terms such as Depth of Field or Exposure triangle. As Eliza Dolittle sang to Freddy in the musical ‘My Fair Lady’, ‘Oh, words, words, words, I’m so sick of words…is all that you blighters can do?’

In the next few blog posts, I’ll try to explain just a few of these terms to the best of my ability. But you can find more detail by ‘googling’ any of the terms. Anyway, I’ll start with aperture. Essentially the word ‘aperture’ in photography refers to the hole in the lens through which light reaches the sensor – the bit that actually records your image. The hole in the lens is at the centre of the shutter which opens when you press the button to take a photo and closes when the shot has been taken. The shutter is made of ‘leaves’ that move both to do the opening and closing, but can also be set to change the size of the hole to create different effects.

This is a photo that I took in my garden this morning of a heather plant. I set the opening to create a wide hole – as wide as this lens would allow. Notice how only part of the plant is in focus and everything behind the plant is blurred.

The aperture – or size of hole – that I set for the the photo was f/1.8. Let me simplify that. 1.8 is almost 2 so when you see that f/ it refers to a ratio of 1/2 or half. So if the aperture size were f/16 the ratio would be 1/16. You know from simple arithmetic that 1/16 is much smaller than 1/2 – a sixteenth is smaller than a half. Why did I choose such a big aperture? I wanted only the plant to be in focus – I wanted the background to be blurred. That’s an effect known as a shallow depth of field where sharpness is confined to a very narrow band of depth.

I shot this photo at f/8 – an eighth, so I only allowed in a quarter as much light as in the first image in one way, but the camera compensated by opening the aperture for a shorter time, 1/5 seconds, to provide the same level of exposure.

The image looks different. In a way I’ve let in about the same amount of light, but I’ve changed the recipe for doing so. I used a smaller aperture but the shutter was open for 1/5 seconds whereas in the first photo it was open for 1/100 seconds. Look at the difference between them. In the second photo, the whole of the plant is in focus and the back ground is less blurred. In other words there is a greater depth of field. The field of sharpness extends further forwards and further backwards as well.

In my final photo, the settings are an aperture of f/22 and a shutter speed of 8/5 or one and three fifths seconds. Now look at the depth of field – how sharply the back of the garden has come into focus.

I don’t want to stray much further into depth of field, diffraction, ISO, angle of view and so on. Today’s blog is just to provide a simple introduction to the idea of aperture and the kind of role it plays in photography. I’ll just provide two examples below of deliberately choosing one size of aperture over another to change the depth of field.

I don’t do portraits of people, but that’s a definite area for wide apertures. This is just a handheld photo of my daughter’s dog, Ted. It was taken indoors in low light conditions, so I had to boost the brightness of the photo in camera using the ISO setting – I don’t have flash either. I took the shot at f/3.5 – quite wide with a shutter speed of 1/320. If you were to enlarge this image you’d be able to see that only the dog’s left eye (the one on the right of the photo) is in focus. You can almost see my reflection in the eyeball.

This final example is of a lone tree at Lake Wanaka in the South island of New Zealand. I shot this at f/14 (quite narrow) and 1/80 of a second. See how the image, though handheld, is fairly sharp from the beach to the mountains.

Tomorrow I intend to post about exposure, or more specifically about what sort of shutter speeds you might use for different types of photograph.