Say cheese.

Want to take better photographs? I think one thing that will really help, is to understand a little bit about how a photograph is actually captured by your camera. The way I see it, the process is the same regardless of how fancy – or not – your particular model is, and it basically boils down to this:

Various bits of glass (the lens) let light pass through a variable sized hole (aperture) for a variable amount of time (shutter speed) onto a sensor of variable sensitivity (ISO).

OK, so that’s a lot of variables, and the combination of the different values and settings for each will have an impact on how your photo will turn out.  Don’t be bamboozled – let me try and make things a little clearer….

For those of you who already own, or are considering a DSLR purchase, I’ll come back to the glass bit in a minute. However, whether your camera is a cheap and chearful compact, or the latest and greatest DSLR requiring a second mortgage, the other three elements – aperture, shutter speed and ISO – are all key to achieving perfect exposure. No, we’re not talking about skinny-dipping, or getting your face on the cover of Who? magazine – ‘exposure’ refers to the magic combination of these three elements resulting in the desired image on your memory card.

What the f/*.*?

Aperture – technically the area of your hole (!) – is measured in f numbers. Larger holes let in more light, and have small numbers – like f/1.8 – and conversely, smaller holes have large numbers (e.g. f/22) and don’t let in as much light. Aperture settings affect the depth-of-field in your image, or to put it another way, the area fo your image that is “in focus”. Large apertures give less depth of field (smaller area in focus), and small apertures more depth-of-field (larger area in focus). Don’t let this confuse you – I find the easiest way to remember is: low or small f-numbers for small area of focus,  high or large f-numbers for large area of focus. Simples!

Shallow depth-of-field (large aperture/small f-number….with me?) causes the subject to stand out clearly from the background which will be out of focus. The term ‘bokeh’ (boak – ay) is used to refer to this blurred out of focus area, and has absolutely nothing to do with you not enjoying the packed lunch you brought with you on your photographic expedition. If you want to isolate your subject from the background, as is desirable for portraits, use a small f-number. If you want both near and far subjects to be in focus, choose a large f-number.

When you press the shutter button, the camera opens and closes the shutter to let light pass through the lens so it falls onto the sensor. The shutter may only be open for a fraction of a second, or it could be kept open for a very long time. If you’re looking to photograph a moving subject, it’s most likely you’ll want to use a fast shutter speed to ‘freeze’ the action and avoid catching a dose of the streaks. Of course, you might want streaks in your photo. A slower shutter speed can be used to capture motion in your image – great for that silky smooth ‘water flowing over rocks’ shot, or for streaking car lights heading for the city at dusk. If you’re going to experiment with slow shutter speeds, you’ll need a tripod or other stable surface to lay your camera on, otherwise you’ll end with something very abstract indeed.

Full Stop.

Aperture and shutter speed are very much linked when it comes to achieving correct exposure. You’ve probably already heard about ‘stops’, but what are they? Simple – stops are steps. Have a look at some standard aperture settings – f/2.8 – f/4 – f/5.6 – f/8 – f/11 – f/16. You’ve probably seen these numbers on your camera somewhere, and each of the steps in the sequence is a ‘full stop’. I won’t delve into modern cameras which offer aperture settings in 1/2 or 1/3 stops – which I personally think should be referred to as commas. The process of ‘stopping down’, or reducing the area of the hole by one full stop (going from a setting of f/4 to f/5.6 say), halves the amount of light passing through the lens. Going the other way (e.g. from f/4 to f/2.8) doubles the amount of light getting through.

The exact same principle applies to standard shutter stops (e.g. 1/30, 1/60, 1/125, 1/250….) One step up – 1/60 to 1/125 – lets in half the amount of light, one step down, double. Pretty neat, huh?

So what’s the link I hear you say? Well, let’s say that for a given scene the ‘correct’ exposure is going to be 1/125 at f/8. If we move Mr Shutter one step up to 1/250, and Miss Aperture speed one down to f/4, the exposure is still correct, although the photographic result will be different – the second setting has less depth of field, and more ‘freezing’ of any motion in the scene.

The third element in our little triangle of exposure, is ISO. There’s a pattern here too – ISO 200 is twice as sensitive to light as ISO 100, and only half as sensitive as ISO 400. In the example above, my camera was set to ISO 200, and I’d decided to choose an aperture of f/8, giving a ‘correct’ shutter speed of 1/125. If I change my ISO setting to ISO 400 (twice as sensitive), the correct shutter speed for perfect exposure is going to be 1/250. See the pattern?

Using a low ISO setting will give you the best quality results, where higher settings tend to introduce ‘noise’ or grain to your images, often along with ‘smudging’ and other processing artefacts as your camera works harder to resolve the image. When the ambient light is low and you don’t want to use flash, you’ll need to use high ISO settings, and even so, might still need long exposure times. At high ISO settings (ISO 800 or higher), the quality of your results will vary considerably depending on your camera. DSLRs and ‘premium’ compacts with larger sensors are clear winners, generally producing better low-light/high-ISO results than budget models.

So what..?

Experimenting with your own camera will help put this all into perspective (sorry). I’m particularly keen on indoor photography, and prefer taking hand-held images without using a flashgun where possible. When I first started taking pictures in ‘program’ mode, and the camera stopped making all my decisions for me (and popping up the flash most of the time), most of my indoor shots were blurry. Not good, considering I’d moved from £300 compact – which took great snaps of my kids – to about £1500 of DSLR kit on the persuasion that I’d get “better photographs”….!

It was obvious after about 5 minutes, that because I wasn’t using the flash, my shutter speed needed to be much slower to compensate. “You could have used a larger aperture” I hear you say (well done you!), but at the time, I was using the basic kit lens that had came with the camera, so the largest aperture I could use was f/5.6 – not very fast glass at all.

So how slow a shutter speed can you use, and still get a nice, sharp result?
Well, I later stumbled upon a really useful tip that’s well worth engraving in your brain –

The shutter speed at which the average photographer can hand-hold a shot without introducing camera shake, is 1/focal length.

This basically means that if you’re using an 85mm lens and therefore your focal length is 85mm, you can hand-hold at a shutter speed of 1/90s (‘cos that’s a little bit more than 1/85 which isn’t going to be an option!).

In practice everyone’s mileage is going to be different – some of us are naturally a bit shaky. Personally, I’ve found 1/(2 x focal length) or a bit faster is more like it – so when I’m using my 50mm lens, I’m aiming for a shutter speed of 1/90 (or 1/125) to achieve pin-sharp hand-held images. Modern ‘image stabilisation’ technology helps improve this by as much as 4 stops (remember stops?), and whilst I now have a few more lenses, my 50mm doesn’t have this, so I stick with the maths, and it works! Of course, with image stabilisation – and a steady disposition – you can hand hold shots at very slow shutter speeds.

I now appreciate – and hopefully you do too – that if half-pressing the shutter produces an exposure with a shutter speed of 1/30, in order to achieve 1/125 (and a nice sharp photo), I can either (a) increase the ISO by 2 stops – from 200 to 800 – or (b) increase the aperture, by going from f/5.6 to f/2.8. The overall exposure will still be the same.

Final thoughts

I’ve not talked about lenses yet for all you DSLR buffs, and there’s so much other stuff I’ve not mentioned – like how focal length, and distance from the subject also affects depth-of-field, as does your camera. Yes, bigger is better when it comes to sensors I’m afraid, and there’s no doubt about the benefits gained by using ‘fast’ (large aperture and generally expensive) lenses particularly when working in low-light situations – but understanding your exposure options and thinking about what you’re taking a picture of, before you actually press the shutter, will allow you to really get the most out of your existing kit – guaranteed!

Things to remember:

  • Set your ISO as low as possible for optimal quality
  • Choose ‘aperture priority’ to control depth-of-field
  • Choose ‘shutter priority’ to control movement (or lack thereof)
  • Shutter speeds less than 1/focal length – use a tripod

We don’t all take pictures in ‘controlled conditions’, so most of all, don’t expect miracles and take time to consider the job at hand – trying to take a photograph in a dimly lit room is going to need long exposure, high ISO or a large aperture (and possibly a combination of all three, a tripod and some patience).
If you have time, take it, and get the shot right.

I’m no expert, just an enthusiastic hobbyist, but the above ‘science’ has really helped me understand how my camera works, and helped me take better pictures – hopefully it will help you too!
Happy snapping.


2 thoughts on “Say cheese.”

  1. Good article Alisdair. Noticed one typing error: “Aperture” one step up to 1/250 should be shutter, and “shutter” speed down to f4 should be aperture.

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