Decent Exposure Part 2

In an earlier post I discussed the various controls available to you for controlling how your camera exposes the scene before you. However, I didn't talk about how to read or wisely adjust what the camera tells you via its light meter, or what decisions it will be taking behind the scenes.

If you're relatively new to the whole camera thing, you're probably using scene modes or even the full auto 'green' mode present on many cameras. The level of control afforded you in these modes varies, but they all have in common that they will tell you what decisions regarding shutter and aperture they have made, but tend not to allow you to change them. Some allow ISO adjustment, some don't. I would therefore argue that one of the best ways to learn how to take pictures is to find out what the scene modes do, then make those decisions or break those rules as you learn.

I should qualify this with one quick note. The actual decisions taken by the camera are way more complicated in many cases than I'm about to suggest. My description is more of an approximation or ultimate simplification of reality. The camera will usually use a clever metering mode, compare its results against a library of saved 'standard' scenes, and choose what it considers to be the best selection of variables. You (I presume) don't have such a library, so you'll be using rules of thumb mostly instead.

Landscapes
The landscape mode will be attempting to get as much in focus as it can. It will therefore be using the smallest aperture it can get away with whilst maintaining a fast enough shutter speed to give some chance of avoiding camera shake. If auto-ISO is enabled, it may increase the sensitivity to achieve the two aims. Some compact cameras lock the focus distance on infinity in landscape mode, then rely on their relatively high depth of field to make the foreground look acceptable too.

Portrait Mode
In many ways this is the opposite of landscape mode. The camera will select a large aperture (small number) and will usually be focussing pretty close. The aim is to blur the background, thus emphasising the subject. ISO will be kept as low as possible, while maintaining hand-holdable shutter speeds. This is easier in this mode due to the wide aperture in use.

Close-Up (macro) Mode
True 'Macro' photography is defined as producing an image on the sensor which is larger than life-size. This requires specialist gear and is not what the 'close up' mode is designed for. However, the principles are the same. This mode will be expecting you to be focusing as close as you can, often using flash to add light and allow the use of small apertures to maximize the extremely shallow depth of field at close range. Shutter speed is considered to be of secondary importance although at this range, any shake at all will make the picture unusable unless the light is bright enough to allow very fast speeds. The camera will therefore play its usual game of compromise and trade some depth of field for a safer shutter speed for handholding.

Night Portrait
Usually shown as a person's outline against a night sky on the mode dial, this is a mode which allows the use of a relatively advanced feature - slow sync flash - within an easy to use 'beginners' mode. The camera will meter so as to expose the dark scene properly, as if the subject person was not present. With this part out of the way, flash will be added so as to give extra emphasis to the subject, lifting them out of the darkness of the scene as a whole. Due to the potential slow shutter speed needed, this mode may well require the use of a tripod. Think of it as landscape mode (maximising depth of field for distant scenes) combined with a blip of flash. This mode will provide the means for you to get snapshots of family or friends or whomever, in front of darkened scenes such as night cityscapes or fairgrounds. Once you move on to manually controlling your slow sync flash, you'll find it's usually quite customisable for more natural results than the 'stuck on' effect that some auto modes create.

Sport/Action
This one is all about shutter speed. The camera will do its usual compromise calculations to work out how to get the fastest possible shutter speed without making the image unusable. It will do this by opening up the aperture as wide as it can, increasing ISO in some cases etc. It will sometimes also affect the focus mode, changing it from 'one-shot' to 'servo' or 'continuous' autofocus, meaning that there is no longer any concept of locking on - the camera will be expecting you to track the action, shooting as you follow. It will therefore follow as best it can by keeping the AF moving with the subject.

DEP and A-DEP modes (canon only)
if you have a canon SLR then you may well have access to one of these modes, and sadly there's a good chance that it will be A-DEP - the less useful of the two. In this mode the camera attempts to choose an aperture and a focus distance which will render the subjects under the closest and furthest focus points (in the viewfinder) sharp within the depth of field available. DEP mode is much more useful (though still hardly an everyday staple in my experience), allowing you to individually select, using the shutter button, the closest and most distant objects you want to be sharp, then allowing you to recompose before the shot is taken.

Not the Length of the Grass...

Yes, with a terrible piece of punnage I'd like to introduce a mini topic worthy of being thrown into the mix at this point, which is Depth of Field. Also known as Depth of Focus, this concerns what I can only really summarize as 'front-to-back' sharpness. Look in any magazine where there are both portraits and scenery shots, and the main difference you will usually see is that in the landscape shots, the whole of the scene will be sharp, from the closest sheep to the distant hills. Look at a portrait and you tend to find that the only sharp part is actually the subject, and the background is thrown out of focus, thus partly or entirely rendering it a blur.

The distance between the closest and furthest elements which are rendered 'acceptably sharp' is described as the depth of field. If you're using a digital compact or small bridge camera then your control over this effect will be limited, and can best be demonstrated when shooting as close as possible to a detailed subject, using the longest setting on the zoom lens. Some may show the effect on the LCD screen before you press the shutter, while on others you will need to compare captured images. If you're using a reasonably well specified SLR camera, whether film or digital, it's much simpler to demonstrate the effect, due mostly to the additional control available over the settings, and the 'depth of field preview' button which I personally regard as essential on any film SLR camera and highly desirable on digital SLRs. The circumstance where the resulting differences will be most noticeable will be the same scenarios as for the digi-compact i.e. close subject, long lens.

So to the demo.

Set your camera or lens to a wide aperture (small number) such as f/4 or as wide as your kit will allow, put the camera on a tripod or beanbag, focus on a nearby subject such as an ornament - something with some front-to-back depth to it. Look through the viewfinder or at the screen. You should see that only a small part of the subject is in focus. At the widest aperture, what you see is what you get. The image will record like this if you fire the shutter. Take the photo.

Now 'stop down' the lens or camera to the smallest (large number) aperture available. This may be anything from f/8 to f/32 depending on your kit. The image in the viewfinder will not change, so if you're shooting film, use of the depth of field preview at this point is your only route to check the result before your prints or slides come back, and it's well worth a look if using a DSLR too. As you press the button or lever the viewfinder will darken significantly. As your eye becomes accustomed to the reduced brightness you should be able to see that much more or all of the scene is now sharp. What the button or lever is doing is closing the lens down to the aperture you selected, allowing you to see what the film or sensor will 'see' when the shutter fires. On a well specified digital compact I would expect the LCD screen to show the result of the change, but many may not and you will have to take the photo to see the difference. The results should be obvious in these circumstances.

Which brings me back to my earlier comment, about depth of field control being limited on digital compacts. DoF is affected by three main variables. The focal length of the lens :- shorter lens = more DoF, the aperture of the lens :- smaller aperture = more DoF, and the size of the recording medium :- smaller size = shorter lenses = more DoF. On a digital compact, the sensor tends to be very small, increasing the depth of field. Due to the small sensor size, lenses tend to be very short, increasing the depth of field again, and the available aperture range is limited, thus having a further limiting effect on your level of control. These factors all conspire to make it difficult to achieve shallow DoF on many digital compacts unless you are very close, zoomed in, and using a wide aperture - using portrait mode will achieve this if your camera does not have aperture controls.

Mini Hint #1 - Caffeine

Avoid caffeine for (at least) two to three days before an important shoot. You'll be amazed by how much steadier your hands become.

Decent Exposure

Exposure is a term that's scattered liberally around any text on photography. It basically stands as a shorthand for all the settings and decisions that enable you to get an image on screen that has the brightness, colour rendition and clarity that matches the natural 'eye' view of the scene, or whatever version of that you have set out to create. Variables in question are shutter speed, aperture and film or sensor speed (ISO). I'll cover each of these in turn as they'll all be useful to you the very moment you start to see your camera as a creative tool.

Shutter speed
This is the amount of time the film or sensor (i'm going to use the term 'image plane' to refer to these two generically) is exposed to the light. Pretty obviously, longer time open equals more light hitting the image plane. Shutter speeds traditionally run on a doubling pattern, but generally the number displayed needs to be considered as a fraction. For example a speed of '1000' displayed means one-thousandth of a second, a relatively fast speed. '1' means one whole second, and inbetween we generally find 2 (half a second), 4 (quarter), 8 etc up to 64, which is then 'almost' doubled to 125, 250 etc up to whatever your camera maker deems necessary. Mine goes to 4000. Some go much faster than this, and many go to much slower speeds than 1 second. A shutter speed of 'B' signifies 'Bulb' exposure - a throwback term which basically means the shutter is held open for as long as you hold the shutter release. sometimes accompanied by a 'T' setting ('Time') which opens the shutter on one press of the release and closes it on a second, these settings can be used for very long exposures lasting several minutes or even hours when shooting star trails etc. Fast shutter speeds freeze action or movement, slow ones blur it. Different subjects will look good at different speeds. For example you may assume that a racing car should be shot at the fastest possible speed, but if that causes the wheels to be frozen too, the car will appear not to be moving. If you want to experiment with the effects of different speeds, find a fountain or fast-moving stream and shoot it at all different speeds. From swirling milky streaks to sparkling droplets, the effects are very different. Shutter speed also has an impact on flash photography. Your camera will have a maximum sync speed, above which the flash cannot be used. On most digital SLRs this is a respectably fast speed above 1/125 sec. On many (specifically Canon) budget film SLRs it was/is much lower, around 1/90 sec, though some flash units can get around this limitation.

Aperture
The Aperture setting controls the amount of light entering the lens in a different way to shutter speed, though the two are related. The aperture is the name for the hole or gap through which light passes on its way to the image plane. The diameter of this hole can be varied using either a ring around the lens barrel, or a setting on the camera body. For all Canon EOS SLRs and lenses and many of the modern budget nixon lenses, this is a camera body setting, if you're on an older camera, especially anything manual focus, the aperture tends to be set from the lens. Settings range on normal lenses from about 1.4 to 32, in numbers which increase by multiplying by approximately root2, thus the range goes 1.4, 2.0, 2.8, 4, 5.6, 8, 11, 16, 22, 32. These numbers are often referred to as 'f-numbers' or 'f-stops' and written as 'f/5.6'. This is because they are expressed as a fraction of the focal length of the lens, and thus the same number can mean the same exposure setting regardless of the lens length. F/32 is thus much smaller than F/2.0, one sixteenth the diameter in fact. The gap between each number in the range is known as a 'stop' and setting your lens to a smaller aperture is known as 'stopping down'. One stop of aperture corresponds to one doubling or halving of shutter speed, an arrangement known as the reciprocity law. If your camera suggests, for example 1/250sec at an aperture of f/11, you could equally shoot with settings of 1/60 @ f/22 or 1/1000 @ f/5.6, and obtain the same exposure, albeit with different effects. We'll come on to aperture and shutter speed related effects in a future entry. For now I'm just concentrating on exposure and as such we can leave aperture there.

ISO (or 'film') speed
This is controlled on film cameras by physically changing the film, or sometimes changing how we choose to treat film. As such it is a 'whole roll' decision that must be lived with for up to 40 frames if we don't wish to waste film. On digital cameras it tends to be much easier, and can be set differently for each and every shot if we so wish. It is a measure of the sensitivity of the recording medium, be that film or sensor. Usually available in doubling hundreds from 100 to typically 800 or 1600, it can be treated as simply another exposure variable, allowing you greater flexibility with your shots and the conditions in which you shoot them, it does have tradeoffs however, which are perhaps not so obvious as those related to shutter speed. Suppose you are set at 1/100sec @ f/4, your lens aperture as wide open as it goes, and your ISO on 400. The light levels drop and you need just one extra stop to expose correctly. Aperture is at maximum so that leaves just shutter speed or ISO. If you reduce the shutter speed (increase the time for which the image plane is exposed) then you risk not being able to hold the camera still. If you take the other option and push the ISO up to 800, your image quality may well be compromised by increased image 'grain' or 'noise' (extra patches or blotches of colour or light where you don't want them) which is a common side effect of higher ISOs. Going one stop higher to 1600 will seriously affect your image usability on all but the highest quality SLRs. It's there to be used, but bear in mind that speeds typically above about 400 ISO will adversely affect your images in some way. One quick addendum for any pedants in the building - the technically correct definition of ISO includes both the European DIN specification and the more familiar numeric American standards. The 200 or 400 or whatever is technically called the ASA rating, but in most publications etc, ISO and ASA are used interchangeably,

This has become something of a monster post, so I'll leave it there for now. Once you've digested the settings, I'll try my best to explain how and why and most importantly when to use them.

Composition: Getting it all where you want it.

Everyone who takes photos does some level of composition - it's one of the few things the camera really can't help you with. We're talking about the act of pointing your camera towards something or someone, thus making it or them your subject. Sometimes you'll change your zoom length or raise or lower the camera to emphasise your subject against a background, sometimes you'll physically move position so as to stop that lampshade looking like it protrudes from your sister's head. All of these actions allow you to change or improve the composition of the image, make it look neater prettier, more dramatic, or even stark and unattractive if that's the effect you're going for. Giving a little thought to composition can make the difference between an uninteresting snapshot, and a picture you print large and hang on your wall.
There are a number of compositional 'rules' that i'll come to later. These give you a conventional starting point when putting together a new image. For now we're just introducing terms so learning, following and most importantly, breaking the rules can wait.

Getting Started - A Camera

Before we go any further I just want to define one common acronym. SLR stands for 'Single Lens Reflex'. This basically means that you look through the viewfinder and you see the image through the lens itself, via a complicated arrangement of mirrors and prisms. What you see is what you shoot. These cameras almost invariably have interchangeable (removeable) lenses and other accessories available. I'm defining the term here as throughout this blog I will be using the term SLR, and it makes more sense to define it here than later on. There are other arrangements found on other camera types, such as the familiar direct viewfinder (little glass window) found on many film and digital compacts, live LCD screens found on most digital compacts and some digital SLRS, and rangefinder and Twin-Lens-Reflex (TLR) viewfinder types found mostly on vintage and professional-level equipment.

So you'll need a camera. You may own a suitable one, or you may be able to borrow or buy one. Most car boot sales will turn up 35mm film SLRs these days for pennies, especially the old manual ones where the old lenses don't fit new equipment, which is true of old canon, minolta, olympus and vintage russian (Zenit etc) stuff, or where the seller has no real interest in photography and just wants rid of their dad's old camera gear en-masse. I would argue that a manual film SLR with slide film is probably the best way to learn about photography in its purest form, just because you are responsible for everything from focus all the way down, the camera won't correct anything for you, and the processing of the film can't compensate for your mistakes as is the case with print film.

Alternatively you might already own a film or digital SLR, or a compact camera with a degree of manual control over the settings. For example, I have two digital compacts. My 'night out' camera is a Nikon Coolpix 4100 which affords manual control over basically nothing. It's very much a point-and-shoot only. The other is a Canon Powershot G5, which is the other end of the scale, affording much the same level of control as my SLRs, and only lacks the interchangeable lenses. This level of compact is often described as a 'Bridge' camera, as it bridges the gap between digital compacts and SLRs for those who want more control (or often, longer lenses) but don't want the added bulk and don't need the flexibility of an SLR. Pretty much any film or digital SLR (there are a few particularly simplistic exceptions) and any digital bridge camera will suffice for a learner.

So is your digital compact suitable for learning photography? Depends what you want to achieve. If you want to learn about photography as an art and a science, understand why shots turn out how they do, and tweak things and push the rules to creative effect, then probably not. If however you just want some basic help to be able to take better pictures, and it has at least a selection of scene modes (landscape, portrait, close-up, night-scene, night-portrait) plus ideally a flash, exposure-compensation and user settable ISO speeds, then yes. Even my Coolpix has all of these settings except the settable ISO, so I suspect if you have a digital compact made within the last four years, you can probably get started with that, and get hold of more complex gear as and when you feel you need it. Camera phones on the whole are probably not suitable due to the dubious image quality returned by most of them, though some of them are changing the rules there - most notably the Sony Cybershot phones.