Digital Camera Guide Part 3

So from parts 1 and 2 you hopefully now know more about how digital cameras tick then most of the non-specialist shops trying to sell you one. Here I'll detail what all those settings mean, what happens when they are adjusted and hopefully avoid terms like hyperfocal distance and exposure bracketing (or at least try and do a good job of explaining what they mean)

Focusing

With auto-focus (AF) this should be a doddle and occupy no need for thought or worry, but this is the first step in getting shots that you want and the first stage in where shots can go wrong and it's that very helpful auto-focus that can cause all that.

AF systems come in a variety of different flavours and cameras can often have the ability to choose between which one you want to use, they roughly divide into two camps - Multi-point AF or Centre AF.

Multi-point AF systems look at the scene you're trying to take a picture of and supposedly tries to pick out those items it thinks you're trying to focus on. Once it has it adjusts other settings in your camera so that all those points stay in focus. For a quick point and shoot this is fine, but you're rare person if you've never had the AF decide that the far off tree top-right is more interesting than the bush you're really trying to shoot. This is because of how the AF system works.

Focusing is something we don't have to think about when we use our eyes we just do it, but a camera has to determine what's in a scene and how to tell if it's in focus or not. Take a board split black and white and aim a camera at it and the AF will adjust until the dividing line appears sharpest; take a pure white board and the camera can't tell just by looking if it's in focus or not.

Now take that and consider my green bush sitting on green grass with green trees in the background, is it any wonder the AF system has opted for the higher contrast tree-against-sky, it's the only thing it can judge with accuracy if it's focused or not.

This problem also applies to Centre AF, in this instance though the AF is confined to just looking at the the centre point of what you're shooting at so it has a better chance of at least focussing on what you want.

AF can also be weighted, this is all the latest 'fad' of face recognition does. It uses the same Multi-point AF but favours what it thinks of as faces.

Try switching between the settings you have and see which consistently produces the images you expected. If that doesn't work you're going to have to go Manual.

When you opt for manual focusing you will normally gain an enlarged portion of the view, almost always in the centre and you can tweak whatever dial necessary until you judge that what you're looking at is in focus. It's certainly more fiddly and without practice might produce more blurry shots than the AF, but with practice will allow a much greater control over the image. For quick shots you're likely to stick with the AF, but ones where you have time manual may produce something better.

One focus type I've yet to mention is Macro. For the most part if you try to take a shot of something 'in your face' you'll just get a blurry mess; for those cameras offering it Macro AF allows much closer shots. For manual focusing there may be a special macro mode you can tweak or it may just form part of the normal manual focusing ability. Again explore the options you have.

Aperture

One of the big things that gets whittered on about is aperture, f-stops, exposure blah blah blah. The aperture of the camera is the opening through which light is passed to the sensor. It can either be fully open, with all light streaming in; fully closed, and you get a black photo; or some point in-between. Those bits in-between are measured in f-stops and get shown as f2.4 or f8; they should really be marked as f/2.4 and f/8.0, but like most things it gets abbreviated.

The addition of that mark though is important to understand what f-stops mean. Put simply they're a ratio of the diameter to the lens; a ratio because obviously lenses can differ. Keeping it darn simple and not accurately if we imagine a lens 1" in diameter then an f-stop of 8 is an opening 1/8" in diameter, an f-stop of 2 is 1/2" in diameter.

I want to stress that the figures I'm using here aren't accurate as the diameter is tied to the focal length and not the diameter of the lens. However hopefully the point has been made the larger the number of the f-stop the smaller the diameter of the aperture because that's the number you're dividing by.

Changing the aperture size has two consequences, the first should be obvious - a smaller opening means less light getting in to the sensor, a larger one means more. However it has a much deeper result and that's Depth of Field.

Depth of Field

This is where terms like hyperfocal distances get bandied about, but let's ignore that for the moment. The depth of field (DoF) is the distance before and after the point you're focussed on that remains in focus. If you have a big f-stop number, that is a small diameter opening, the DoF is very large; most of what's in front of the focus point and what's behind it will be in focus. If you have a small f-stop number, a large opening, then the DoF is very short and the only things likely to be in focus are at the focus point.

This is why I dealt with focussing first and this is one of the settings that gets changed with AF systems. In order to get everything it wants in focus the AF will set a focal distance and change the f-stop to increase or decrease the DoF.

So with my obviously fascinating bush I use a manual focus on said bush and set my aperture to f2.4. I take my shot and both the bush and most of the foreground and the majority of the background is in focus. Keeping the same focus I switch to f8 and take the same shot. The bush is still in focus, but the foreground and background are blurred.

Almost all cameras even in auto mode will tell you what f-stop they're using, if you have an Aperture Priority mode switch to it and try it out on the same shot with the same focus and see what happens.

However as I mention the first consequence of changing the aperture size is the amount of light that reaches the sensor and to compensate that means dealing with shutter speeds

Shutter Speeds

Fast or slow, this is the measure of the delay between when the shutter opens to take the shot and when it closes. The first obvious difference is that the slower the shutter speed the more chance there is of something in your scene moving and creating a blur. If you want to take a photo of something that is by itself moving then a faster shutter means you can 'freeze' that motion.

In theory therefore unless you're going for that speed-blur effect you want a fast shutter speed, however this comes with a downside similar to the effects of the aperture - namely light levels.

The slower speed means the sensor gets exposed to light for longer, for a bright scene this can lead to overexposure and everything turning up white. Too fast a speed and not enough light hits the sensor so you get a black or dark photo. But hey that might be the very style you wanted, assuming it wasn't though the interplay between shutter speed and aperture is one to watch.

So a small aperture like f16 means less light getting to the lens, which in turn means you need a slower shutter speed, a large aperture will need a faster speed; depending on how much light is about in the first place it's that simple.

So I've got a small aperture to keep everything in focus, I've selected a fast shutter speed to capture a fast moving object and the photo I take comes out pitch black. Time to change the ISO setting.

ISO

I dealt with ISO as a factor for buying a camera in part 1, this is where that pays off. To recap, for a digital camera the ISO setting reflects how sensitive the sensor is to light; the lower the number the more light needed to trigger a reaction.

As with everything so far there is a downside. The more sensitive to light you make the sensor by increasing the ISO level, the greater the chance that the pixels will be triggered by 'phantom' light leading to noise; at a basic level the photos appear grainier the higher the ISO.

So as with my previous example if I want my small aperture and fast shutter speed I need to increase the ISO and get stuck with the graininess, or do I?

Well one way to get around this is to provide more light at the very instant I take my shot and that means using a flash.

Flash

If I've neglected this aspect of cameras it's simply because the flashes that come built in to the majority simply aren't always that good or useful. To be effective a light source needs to be close enough to the subject to provide extra reflection, while not being close enough to bleach the colour. Sadly having the flash attached to the camera can pretty much screw up that balance and is one of the reasons you'll see studios cluttered up with so many extra light boxes and diffusers when they have a perfectly fine built-in flash on their camera.

DSLRs try to get around this by having a pop-up flash, when required the flash rises up on a hinge. This has the result of keeping the camera compact and trying to keep the flash as far away from the camera as possible under these constraints.

If you don't have that option then one you may have is to adjust the flash level itself. This is something that requires practice if the camera doesn't do this automatically. The trick is to provide enough light to allow you to have the small aperture or fast shutter that you want without bleaching the scene and making everything look flat.

Even if the flash adjusts its own level, this is still something to look at as the camera may decide it needs a really strong flash to illuminate the entire scene, when you're just trying to capture the group in front of you - white out.

Conclusions

Hopefully that's given some insight into the most commonly used aspects of a camera's workings and how they all interconnect with each other; saying that I'm sure Dan will spot something I've missed :-)

Next part here