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Proffessional Photography: Composition, Cropping, Exposure tutorial

Choosing the best digital or film camera

With so many camera models to choose from, at a bewildering range of prices, where do you start? Well, the way I choose any new toy these days is to start at the end. What do you want it to do? Err . . . take pictures. Yes but what kind of pictures and what are you going to do with them? The other burning question is how much are you prepared to learn? And, of course, how much are you prepared to pay?

As you are reading this and have actually made it to paragraph two, I think we can assume that you are prepared to learn at least a little. So what do you want to do? Do you want something that you can keep in your pocket at all times so you can snap the kids? Do you want a camera that will allow you to take pictures in any lighting conditions from any distance (with the right gadget screwed on the front of course)? Is this going to be a hobby or just some quick snaps?
I haven't seen any cameras on sale in recent years that do not have a fully automatic 'point and shoot' mode, most will automatically switch on the flash for you when it is needed so you may wonder why we need all the other manual and semi automatic modes and an instruction book to make your head spin.

The answer is that, although the camera can produce good exposures most of the time, there are times when, to get the results we want, we have to apply a little know-how and select more appropriate settings than the camera would automatically choose.
Before choosing a camera with lots of knobs and dials it is a good idea to consider whether you are ever going to bother to learn what they are all for. I've been around cameras for many years now, and I'm still learning what all the settings on my latest camera actually do. I never bother to learn how to do something until I need to. So there are certain obscure settings that I have yet to find a use for. Of course it would be nice if we could choose just the buttons we need and have each camera custom made for us but in the real world all we can do is choose the level of control based on how much we think we might want to get involved. Generally speaking an SLR will have more knobs, dials and menus than a compact camera which will give you more control over your pictures but will have a much steeper learning curve.


Things you can do with a tripod that you can't do without one
What to look for when buying a tripod
Tips for using your tripod
Buy a good sturdy tripod and use it as often as possible.

Yes, they're heavy, bulky and the last thing you want is more stuff to carry around with you, but they also open up a whole range of techniques you can try that would not be possible without one.

Sometimes I use one just to focus my mind on what I'm doing. Because it's more difficult to move everything around it makes me think more about the camera angle before I line up the shot. When I'm photographing people I don't like anything to slow me down, I think it's very important to get the shots as quickly as possible before the subject gets bored, but when shooting objects it's good sometimes to slow down and think a little more.

Things you can do with a tripod that you can't do without one.

1) Take pictures at slow shutter speeds without getting the dreaded camera shake. This enables you to do lots of interesting things like having some, non-moving, parts of the picture sharp while other, moving, parts are blurred. In the picture on the right the water takes on a cloud like quality due to the slow shutter speed.

Also panning with a moving object, like a car, is easier with a tripod. Panning at a slow shutter speed will render the object (car) sharp and the background as blurred streaks. (see the bicycle picture on Shutter Speeds and Apertures)

2) Use much smaller apertures giving you greater depth of field. Because you can use slower speeds you can shoot at any aperture you like. (see the coffee bean photo on Shutter Speeds and Apertures)

3) Shoot a series of frames that will join up into a panorama more accurately. Although this is possible hand held, the best way to shoot panoramas is to shoot in upright format, take lots of pictures that overlap and use a tripod that has been carefully adjusted to be level with the ground.

4) Shoot a series of frames at different exposures to create a montage like this picture that I shot for a website. I decided that I wanted to shoot the fire on the terrace against a sunset background. I needed to try to shoot the whole thing as one photo rather than compositing two shots together as this would have been tricky to get right, especially behind the glass. By setting up the shot using a sturdy tripod I could shoot different exposures for the different elements of the photo and then layer them together in Photoshop.

Here are the three separate shots that make up the final composition, the top one was exposed for the sunset and is the background in the final image. As you can see, very little of the fire or the flame are visible.

The second shot was taken much later, an hour after the first shot, but exposed for much longer to really bring out the flames. You can see that the sky is much lighter in this shot as a result of the longer exposure, which gives very bright highlights in the glass. This introduced the only really unnatural looking part of the shot, the highlights are too bright for the sky, but I kept them anyway because I just like the look of them. As a bonus I got lights on the hillside as well which adds to the atmosphere of the shot.

The third picture was shot with as flashgun to show the base of the fire, the stones and the table. You can see by the position of the clouds that this picture was shot at about the same time as the first one, but it could have been shot at any time. The flash on camera gives horrible highlights on the glass but that's OK because I wasn't going to use that part of the picture anyway. I did get a nasty highlight on the foot of the base though but manage to dull it down a bit in Photoshop.

Because the three shots were taken with the camera securely fastened to a tripod the composition is exactly the same in each one, so it was easy to drop them on top of each other in Photoshop and then, using layer masks, select the bits I wanted from each photo.

If I had used the camera hand held, each shot would have been slightly different and the montage would not have been possible.

Below is the layer palette from Photoshop showing the three layers. The layers stack on top of each other and the way to reveal some of the layer underneath is to use a layer mask. The black and white smudges to the right of the pictures are the layer masks. The black parts of the layer masks are transparent, grey bits semi-transparent and the white bits are opaque. So you can see which bits of each photo I have selected.

What to look for when buying a tripod.

Don't buy a tiddly little thing just because it will fit into your gadget bag. Most of them are worse than useless. The trick is to get the right balance between weight and strength. It's no good if it's so heavy that you never want to take it anywhere and it's no good if it won't support the camera properly. The manufacturers seem to delight in over estimating what their tripods will support. Buy one that's man enough for the job. Then go to the gym and build up your muscles.

I use a Slik Pro 700DX with my Canon EOS300D. It is quite a heavy beast but it's rock steady even with a longer lens on the camera. It goes up to a decent height and even at almost full height it is still quite steady. Also the good news is it's not too expensive. I have even been known to use it for a bit of video in an emergency although you should really use a fluid damped head for that. The manufacturers say it will support up to 15lbs well, I'll tell you, I think that must have been on a good day. Take that with a pinch of salt but also bear in mind that it will be twice as good as one that says it will support 7lbs.

Using your tripod.

A few quick tips to help you get the best from your tripod.

Always spread the legs fully. Common sense really, it's going to be more stable the further you spread the legs. Some tripods, like mine, allow you to spread the legs past the normal stops to get you out of trouble in tight situations. Only use this facility when it's really necessary.

Use the minimum height you need. Don't go higher than you have to, the higher you go the more wobbly the tripod will be.

Extend the legs rather than the central column. The central column should only be used for fine adjustments, it is not as solid as the legs.

Adjust the height of the legs before spreading them. It's the only way to make sure that the legs are all the same height. This will give you the best chance of the camera being level. However you still need to check it by eye or with a spirit level.

Selecting Photos
This is starting at the end really, but it is also the simplest and most useful tip to improve your photography.

Tip - select only the best of your pictures to show to others and leave the rest in the drawer. Showing someone every picture you have taken dilutes the effect of the best pictures and gets very boring. You may want to show twenty pictures of little Johnny at the park because they are all quite good and you can't decide which are the best but, trust me, you will be better off making that decision and showing only the few good ones.

Hey, you're thinking, I came here looking for a course in photography and I get this, this isn't photography.

Yes it is. Presentation is an essential part of photography and what you don't present is an essential part of presentation. Follow the advice above and you will immediately be promoted from 'photo bore' to someone who looks like they know what they are doing.

Your friends and relatives will beg you to see the rest of the pictures, resist at all costs. If you give in to their demands, you can regret at leisure as you watch their initial enthusiasm lessen with each photo they turn over. You've already shown them the best, what do you expect?

This advice is not just for beginners, although old hands will probably have learned the hard way already. I have taken many tens of thousands of pictures over the years but, if I was asked to mount an exhibition of my best 100 photos, I would be thrown into a blind panic. As each new 'great shot' comes along, it moves the goalposts, and last year's great shots don't look so great any more. That's why this is such a great hobby, there is no finish line, even the best photographer in the world can still aspire to produce a better picture next time. Having said that, some of the shots I took over twenty years ago are still in my pile of favourites. Learning and improvement are not always linear.

Photography - Composition
Placing the elements of your picture within the frame and deciding what to leave out.

In our modern world of automatic cameras, which focus for us and adjust the exposure in an ever more perfect way (most of the time), the biggest difference between a good photograph and a mediocre one is the compositon.

In every photograph we take, we can decide where the boundaries of that photo will be, called the cropping. We can also choose the viewpoint. If we are taking pictures of people or movable objects then, often, we also have the opportunity to arrange them into the shapes we want.

I use the word 'shapes' deliberately as that is what good photography is all about, creating shapes and textures that please you.

If you are shooting landscapes or other immovable objects then you must compose the picture by moving yourself and deciding where to place the point(s) of interest in your picture.

There are various compositional rules (I prefer to think of them as guidelines) to help you. These rules will help you to compose pleasing pictures, however, you will often find that a really striking picture will show a blatant disregard for the rules. Once you are aware of the rules then break them as often as you want but, at least, know you are breaking them and why.

Landscape photographers are particularly fond of this one, but it works well for many types of subjects. The rule of thirds simply says that, instead of placing the main focus of interest in the centre of the frame, which gets a little boring, that you look to position it on an intersection of the thirds. That is to say one third up and one third in or two thirds up and one third in etc.

Here's a 'thirdsy' sort of picture, hold your mouse over the picture to see the grid. Placing the boat near the top of the picture tells the viewer that what they are supposed to be looking at is the reflection.

We could take the boat out altogether, of course, this would focus our attention even more on the reflection but the picture might then be a little too minimalist.

Also the mast is almost exactly on the 'third' line. There is a little space to the right of the bow of the boat which helps to give the impression that, although the boat is not moving, it has somewhere to go.

Although a nice illustration of composing 'on the thirds' this picture falls foul of another 'rule' in that it has very light corners, escpecially at the top right and, coupled with the yellow stripe, the effect is to lead the viewer's eye out of the picture. We'll talk about this more later.

Using Diagonals

Setting your subject matter on a diagonal will almost always make for a more dynamic picture. Even if this is an invisible diagonal that draws your eye between two points. Move around the subject (not too close in the case of my crocodiles) and look for a diagonal.

Photography - Cropping and Framing
What to leave out, what to put in and where to put it.
Tip - One of the easiest ways to improve your photography is with careful attention to framing. Look into the corners of the viewfinder to see what is there. Do you need all that background? Can you get closer to your subject or zoom in? Would the picture look better as an upright or landscape?

The most common mistake people make when taking pictures is not filling the frame with the subject. If it's a photo of granny waving from the doorstep, let's just see granny and the door, not half the houses in the street with a small granny shaped blob in the middle. I think the culprit for this phenomenon is the focusing aid in the centre of the viewfinder. Most cameras have some sort of circle or rectangle etched onto the glass and we are inclined to think, in our less thoughtful moments, that this is the whole picture area. Take a moment to glance around the viewfinder to see what you have got at the edges and especially in the corners. Watch out for clutter in the background, that lamppost growing out of granny's head. Make sure that everything in the viewfinder is there because you want it to be.

Landscape or Portrait?
A lot of people never, ever turn their camera on it's side and shoot an upright picture. Yes, it can be a little awkward to hold until you get used to it but, what a difference it can make to the picture. If you are taking a picture of one person then it is essential to shoot upright, you waste so much of the picture area at the sides if you don't.
The picture on the left is a typical snapshot, two miles of coastline with a pink blob in the middle. Turning the camera on its side and moving in a little closer, as in the picture on the right, gives us a much better picture of the girl and we can still see enough background to get the message that we are on the beach.

For the sake of good layout on the page, I have made these two pictures the same height. In fact they are the same size, if you can imagine them in their original dimensions the girl is ten times bigger in the photo on the right.

Even when you are shooting landscapes, you will find that, sometimes, the picture will look more dynamic with an upright frame.

Always think, with every picture you take, should this be an upright or a horizontal view? Usually the answer is obvious and dictated by the shape of the composition but sometimes, for instance when the composition is square, the best choice is not obvious. In this case take two pictures, one of each.

Can't I leave the cropping 'til later?
If you are printing your own pictures then you get a second chance to get the cropping right but, don't rely on this to make up for sloppy camera technique. If you crop your pictures afterwards in the computer or in the darkroom, you are throwing away quality. You are wasting some of those precious pixels that you paid so much for. What's the point in having a camera with five million pixels if you are only going to use three million of them?

Photography Tutorial
Choosing the best Viewpoint

Selecting your viewpoint, the position from which you photograph the subject, is a very important part of composition and one that some people pay very little attention to. When taking a photo of a group of friends, how often do you move around the group looking for the best angle?

The first, most obvious difference between one viewpoint and another is the background. If you are photographing a subject that cannot easily be moved, the only way to change what is in the background is to choose a different viewpoint.

The subject itself can look quite different viewed from different angles. Photos can be made to take on a whole new dynamic by selecting an extreme angle of view. I shoot a lot of pictures, especially sports shots, laying down, getting the camera as close to the ground as possible.

Also the perspective can change quite drastically, especially with wider angled lenses. If you photograph a person full length with a wide angle lens from a standing position, their head will be too big in proportion to the rest of their body. If, on the other hand, you kneel down and shoot the same picture from waist height, you will see that the whole picture is better proportioned.

When shooting outdoors, the viewpoint you choose also affects how the light from the sun falls on your subject. This is a whole new can of worms which is fully discussed under lighting.

Two full length shots from fairly extreme angles. A moderately wide angle lens gives a certain amount of perspective distortion, the first shot in particular makes her feet look very big in proportion to her head. This distortion enhances the effect of the flared jeans and the big shoes, whereas in the second shot the distortion of the shooting angle is working against the effect of the big shoes and flares balancing the picture. If we use a wider angled lens and shot from even closer, the distorted effect would be even more pronounced.

In both cases you can see that the choice of angle has given us a nice plain background as a bonus.
These two shots were taken from more or less the same position as the first shot but, as we zoom in, the effect of the low angle is lessened. Less distortion but a pleasing angle giving us a slightly 'larger than life' feel to the picture.

When shooting against a bright sky like this you need to pay careful attention to the exposure, the automatic metering system will render the face too dark so you need to compensate for this. Take a few shots with the exposure compensation at different settings or, better still, meter manually taking a reading from close in to the face. The shot on the right metered correctly because the face fills the frame more and is lit by the sun.
These two shots were taken from the same position as the top right and show the same lessening of distortion as we zoom in. What I didn't bargain for until I saw these two pictures side by side was that the apparent height of the camera changes with the angle of the head. I think you'll agree that the picture on the left appears to have been taken from a greater height than the one on the right. Weird!
Photography - Exposure - Getting it right
By 'exposure' we mean the amount of light that falls onto the film, or CCD if you are using a digital camera. In modern cameras the exposure is usually set to automatic by default and, most of the time, it can be left there and will produce beautiful pictures. There are times though, when the lighting conditions are difficult or we want to produce a particular effect and it would be nice to understand what is going on 'under the hood'.

The problem with all types of film and recording media is that they cannot record the entire range of contrast (black to white) that the eye can see. Especially when you take into account that the eye is constantly adjusting to cope with high contrast. On a sunny day if you look into the shadows of a scene then into the bright areas, the iris in your eye will quickly adjust so you can see detail in both.

Faced with the task of recording as much information as possible, the camera will try to average out all the light levels and expose the film accordingly. As burnt out highlights are normally considered uglier than black shadows, the camera, left to it's own devices will normally err on the dark side. Which is no good if you are shooting someone's face against a bright sky. It's the person's face you want to see, and you don't really care if the sky is white.

Auto Exposure
The camera manufacturers have come up with all sorts of ingenious metering systems to try to help, there are now multi mode metering systems, which give you a choice of 'centre weighting', 'spot metering' or 'multi spot metering' on many of the better cameras, but none can guarantee to give you what you want every time.

The temptation to think that your camera 'knows what it's doing' is great, even for more experienced photographers, which is my main complaint against automatic cameras. It's easy to get lulled into a false sense of security, switch your brain to more interesting things and end up with a pile of rubbish.

Click here for an example of a tricky lighting situation

Tip - using auto exposure to your advantage.

If you have a modern camera, the chances are that the default metering system is 'centre weighted average', which means that, although it takes an average reading of the whole scene, it takes more notice of what is in the middle of the frame. Which is good news for us. The other good news is that it takes this reading at the time when you take 'first pressure' on the button to take your picture. When you push it halfway down and it beeps at you, not only is the focus now set (on an auto focus camera) but the exposure reading is taken and the aperture and shutter speed are set. So, if your main point of interest is not in the centre of the frame, it's a good idea to put it there temporarily while you focus and take your light reading, then move the camera whilst still holding the button halfway down and compose the picture the way you want it to be. A common use for this technique is when you are taking a close up shot of two people and there is space between their heads, if you're not careful the camera will focus on the wall or trees behind them. If the background is very dark or very light this can alter the exposure significantly and result in faces that are too dark or too light.

Skin tones are what most meters are set up to consider an 'average tone', they are also usually the part of the picture that we most want to get right. If I am photographing a group of people in difficult circumstances, like bright sunlight for instance, I will often move close in to the group and take a light reading from someone's face or, if we are all standing in the same type of light, I will take a reading from the back of my hand. This is no good, of course, if the subject is in bright sunlight and I am in the shade. Brown parcel paper is also an extraordinarily accurate surface to take a light reading from.

Manual Exposure
Now it's time to turn that dial away from 'programme' mode and have a look at the dreaded 'manual' mode. There are also a bewildering array of other choices such as 'aperture priority', 'shutter priority', 'exposure compensation' etc., but once you understand the basics you will be able to select the most suitable mode.

The amount of light falling on the film is governed by three things.

The amount of light reflected from the scene which, if you are outdoors, you can do very little about.
The 'shutter speed' which is the amount of time the shutter is open, measured in fractions of a second.
The 'aperture setting' which is the size of the hole through which the light enters. If you look at the lens of your camera you will see a diaphragm in the middle of the glass which the camera adjusts according to the light. This does exactly the same job as the iris in your eye. Aperture settings are measured in 'f stops'. For an explanation of 'f stops' click here.
The shutter speed and aperture settings have other quite separate effects on the photograph which we will discuss in another article, but for the purposes of exposure, making the picture darker or lighter, they are interchangeable. Make the hole twice as big and open the shutter for half the time and you will expose the film the same amount.

Why use manual exposure?
The advantage of manual exposure is that the settings do not keep changing as your scene changes. Let's suppose that you are taking close up photos of cars passing by. Some of the cars will be black or dark colours and some will be light colours or white. If you are filling the frame with almost nothing but car, the meter will be trying to render each car as mid grey. Although it will probably not succeed, what you will notice is that the background is a different shade in each photo.

I often have to take portraits of people, some are wearing very dark clothes and some are wearing white. If I am not careful with my light readings the skin tones will be affected by the clothes.

Although it is by no means always necessary to use manual exposure, an understanding of how it all works will save a lot of disappointment.

Camera Shutter Speeds and Apertures
So what's the difference between shutter speed and aperture?
Shutter Speed
Although, as discussed in exposure, the shutter speeds and apertures are interchangeable as far as exposure is concerned, they each have their own unique effect on the picture. Let's take a look at shutter speeds first as their effect is easily understood. We'll look at apertures further down the page.

The shorter the time that the shutter is open the sharper the photo will be.

If you are photographing fast moving objects such as cars or people running you need to select fast shutter speeds to capture the sharpest picture you can. One exception to this is when you are panning the camera with the subject, the object of the exercise here is to render the subject sharply and blur the background, so a careful selection of the right shutter speed to do both is necessary. I often find that a little blur in the right places on a picture gives a greater sense of movement than if everything is pin sharp. This blur, however, must be in the right places, normally we want to see the head and torso rendered sharply but, if the feet and hands are blurred, it can often be a good thing. Blurring the background can also get you out of trouble when there is a lot of clutter that will detract from the main subject. Getting the shutter speed right to render the correct balance of sharpness and blur on any given subject can really only be determined through trial and error. One of the great advantages of the digital camera with it's instant playback is that this learning process can be a lot shorter than it was before. If you have a zoom facility on your playback of pictures, now is the time to get familiar with it. I had my digital camera for quite a while before I realised that I could review my pictures and zoom in to check the sharpness.

Not only moving objects suffer from too slow a shutter speed. If you are holding the camera in your hand rather than having it mounted on a tripod, you will see the telltale signs of 'camera shake' (i.e. the movement of the camera) at shutter speeds longer than 1/125th of a second. A secure pair of hands will be able to get away with 1/60th or even 1/30th of a second but the camera would be better mounted on a tripod. Once again I will say at this point that the difference between a mistake and an effect is usually the degree. A small amount of blur would be considered a mistake, whereas really blurred streaks of light can be an interesting effect. It's all a question of convincing the viewer that you intended to do it.

Tip - When the shutter speed is important as with moving objects, it's a good idea to set the camera to 'Shutter Speed Priority' mode. This is where you select the shutter speed and the camera selects the appropriate aperture according to the light reading.

Of course, if you are taking photos of static objects like houses with a camera mounted on a sturdy tripod, you can leave the shutter open as long as you want without blurring. An interesting by-product of this, if you get to see really old photos taken in the first part of the 19th century, you will see that there are almost no people in the photos at all. That is because the exposure times were so long that the people had walked through the scene without being rendered. For the same reason the really early pictures, in the time of Niépce, the late 1830's, have almost no shadows because the plates took all day to expose and the sun moved across the sky illuminating the scene from both sides.

Click here for an example of using different shutter speeds.

As well as letting more or less light into the camera the size of the aperture you choose governs the 'Depth of Field'. Depth of field means the amount of the picture, from foreground to background, that is in sharp focus. A smaller aperture will give you a greater depth of field and a larger aperture will give you a more restricted depth of field. This characteristic can be used to good effect in many ways.

If you are photographing vast landscapes on a sunny day, the chances are that everything will be in focus and you will not notice this phenomenon at all. Depth of field, or the lack of it, is much more noticeable when taking close-ups. As I mentioned in the section on moving subjects, it is often desirable to render the background of your picture out of focus. This is easy to achieve by selecting a larger aperture to restrict the depth of field.

Conversely, when photographing very small objects (as in the picture opposite) getting everything in focus can be quite a challenge and may require a very slow shutter speed in order to be able to use the smallest aperture available. The focal length of the lens makes a difference to the depth of field available, the longer the lens the more restricted the depth of field. A wide angle lens will give you almost limitless depth of field.

Tip - If depth of field is important to either make sure everything is in focus or to throw some things out of focus, select the 'Aperture Priority' mode on your camera. In this mode you select the aperture and the camera selects the shutter speed according to the available light.

Tip - If you are shooting in bright light and want to restrict the depth of field, use a neutral density filter in front of the lens to reduce the light entering the lens. These are available in different densities, 2x, 4x, 8x etc. each one cutting the light in half, quarter, eighth etc. In extreme circumstances you can screw a couple of them together. Although they are 'neutral density' filters and should not effect the colour balance, if you use two or more together you might need a little colour correction at the printing stage.

Technical Stuff - Shutters Speeds and Apertures
What do the numbers mean?
If you look at the exposure display in your viewfinder you will see two numbers. On a normal sunny day you might see something like '125 16' or '500 5.6'. The first number is the 'shutter speed' and is simply the time that the shutter will be open for, expressed as a fraction of a second. So 125 means that the shutter will be open for 1/125th of a second, and 500 means that it will be open for 1/500th of a second.

The second number, sometimes referred to as the f-stop, tells you the size of the hole (aperture) in the lens. This number is also a fraction. The number represents the focal length of the lens divided by the diameter of the aperture. So an aperture that is 10mm in diameter in an 80mm lens will have an f number of f/8 and the setting f/16 on the same lens will be 5mm across.

From this you can see that if you change the lens to one of, say, 160mm focal length then the size of the f8 aperture will be 20mm. However, because the diaphragm is now twice the distance from the film the same amount of light will reach the film. This is a bit complex but if you have a mathematical bent and you draw it all on paper you will see why (see inverse square law). If not, just take my word for it. Now you can see that a larger 'f' number, say f/16, is actually a smaller hole and lets in less light than f/8.

Large aperture = small f number
Small aperture = larger f number

To make matters even more complicated, modern lenses, sophisticated beasts that they are, are not always physically the same as their focal length. So the good old f-stop acts as a nominal indicator of how much light will reach the film, rather than an accurate measurement of aperture size. This amount of light is independent of the focal length of the lens.

ISO rating for Film Speed
ISO stands for 'International Organization for Standardization' and their film speed ratings are used to indicate the relative amount of light necessary to give a proper exposure. A normal film will be rated at ISO 100. A film rated at ISO 200 will give a proper exposure with only half the amount of light compared to the ISO 100 film, enabling you to shoot in lower light or with a smaller aperture or faster shutter speed. The ISO 200 film would be referred to as a 'faster' film. There are films available that range in speed from ISO 25 to ISO 1600.

So why not use the faster films all the time, what are the advantages of slower films?

The faster films have a more prominent grain structure the individual grains clump together to form spots that are visible to the naked eye, especially when you blow the photo up to A4 or larger from a 35mm negative. In certain circumstances this effect can be used creatively especially in black and white photography but mostly it is undesirable.

How does all this effect digital cameras?

In the digital photography world the phenomenon is called 'noise' not 'grain', the cause of the problem is slightly different. When light levels are low, the sensor has trouble reading the scene properly and pixels of random colour are thrown into the picture. However to us photographers the end result is the same or very similar.

The 'better' digital cameras have, usually hidden away among the manual settings, a sort of simulation of the film speed effect. My camera for instance, a Canon EOS 300D, has an ISO range from 100 to 1600. This feature is not available when you are in fully auto mode but is available in all the other modes. I tend to keep it set to ISO 200 most of the time as the grain structure is not significantly worse than ISO 100 and it gives me that extra f-stop to play with. When I am shooting fast action and I want to freeze the action (not always the case - see shutter speeds and apertures) then I'll select ISO 400 or 800. If the light is very bad ie night time or indoors then a shot at ISO 1600 is often better than a blurred shot caused by using too slow a shutter speed or no shot at all.

Here are two images, you are looking at a small blowup from the centre of each image, the left one was shot at ISO 100 and the right one at ISO 1600. The difference is fairly pronounced at this magnification but (this is at 100% zoom), at more normal sizes the difference is harder to see. The grain becomes most obvious in parts of the picture which are fairly plain, such as the sky. These two shots, of course, were shot in daylight. The effect will be even more obvious in pictures taken in lower light levels.

Reciprocity and Reciprocity Failure - an Explanation
Reciprocity is the interchange of shutter speed and aperture. This rather posh word just means that a combination of a shutter speed of 1/125th of a second with an aperture of f8, which is referred to as an exposure setting of '1/125th at f8', will give the same exposure to the film or digital sensor as 1/250th at f5.6, which is the same as 1/500th at f4 etc. This reciprocity works well, up to a point, but film users will find that, when you have very long exopsure times, several seconds or so, the reciprocity breaks down and extra exposure time is neccessary to compensate. This is known as reciprocity failure.

Reciprocity Failure (film users only)

All colour films suffer from reciprocity failure when exposed for longer than a few seconds. This results in a colour shift as the three layers of the film respond to a different degree. The exact colour will depend on the brand of film you are using. The colour cast can often be corrected at the printing stage so is not a major problem unless you are using slide film. The only real way to avoid the problem is to use a faster shutter speed, which will mean also using a larger aperture and sacrificing some depth of field. If you don't understand the connection between aperture and depth of field read my article on shutter speeds and apertures.

Reciprocity failure will also be a problem with black and white film but in this case all that is required to put things right is to make an even longer exposure. How much extra you need to give is hard to tell, the best solution is to make several exposures at different times. After all your subject is not going to run away, if you are hoping to get a good shot of it with a two or three second exposure, it has to be something that is not going to move.

All you really need to be aware of is that if you are shooting night scenes for instance at very small apertures, you would be well advised to shoot a series of photos at varying exposures, this is called 'bracketing' and is a very useful technique even in these days of digital cameras and instant replay.

Good news for digital camera users

Reciprocity failure is not a problem with digital cameras, however noise can be.

Bad news for digital camera users

Long exposures on digital cameras can produce visible noise, which looks a bit like the grain you see in a fast film image. This noise or grain is usually most noticeable in plain areas of the picture. See my article on ISO Film Speed for some pictures and more information.


Category: Photo Art | Added by: Admin (05.03.2009) | Author: geofflawrence
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