Leading lines

I was browsing through some of the images I brought back from my recent weekend in Paris and it struck me how often I rely on a tried and tested compositional tool. As I looked through my images, it was obvious that my eye is naturally drawn to subjects that benefit from the principle of leading lines. The image below is a classic example of this simple principle. In this image, the eye is naturally drawn to the end of the avenue by the lines formed by the trunks of the poplars and the converging lines formed by the tree tops. It almost doesn't matter what the subject is, by using lines to bring the eye to the desired location always seems to form a pleasing image. In order to exagerate this effect, the end of the avenue also sits in a good compositional position

Leading lines once again perform an important role in the structure and dynamic of the image below. The convergence of the lines of the floor tiles combined with the centres of the arches and their columns, serve to draw the eyes to the statue in the alcove at the end.


Leading lines are a really powerful tool and they don't have to be straight. The image below isn't a favourite by any stretch of the imagination, however it certainly shows how a curved line formed by the bank of the pool provides a strong leading line.


If you take a look at the post before this one, I've even framed the example image to take advantage of strong leading lines. The more images I look at, the more I realise how much i look for this sort of structure unconciously.

Keep a look out for examples when ever you're taking pictures; pathways, fences, piers, coast lines and many other simple structures can provide great lines that really bring an image to life.

Cheating with HDR images

I spent the weekend just passed in Paris and took my wonderful Canon 5D Mk II DSLR with me. Whilst their I was able to visit the astonishing Palace of Versielles and it's amazing gardens. It's difficult to do justice to the magificence of Versielles in a short blog post and a few photos so, if you get the chance, it's a place you must visit!

One of the challenges when capturing images inside buildings like the palace lies in the huge range in tones one encounters. The difference in brightness between the brightest sunlit highlights and the darkest shadows is enormous, way beyond the daynamic range of even the most sophisticated DSLR. This issue not only affects the camera used to capture the image, it also affects the display an image is viewed on or the printer used to record it for posterity. The human eye also has a limited dynamic range (not as limited as our trusty electronics) but the brain plays a remarkable role in seamlessly processing detail in shadows and in the highlights as the eye continuously adjusts the amount of light it admits. cameras, displays and printers clearly cannot do this!

A great approach to dealing with wide dynamic range situations is a techniques called High Dynamic Range (HDR) image creation. An HDR image is really a mixture of three or more images at different exposure levels (optimal exposure, under exposure and over exposure) The idea here is that the underexposed image reveals details in the highlights that would otherwise be lost while the over exposed image reveals hidden detail in the shadows. A piece of software takes these differently exposed images and maps their details into the the dynamic range of a single image. in other words, you end up with a picture that has the best representation of detail right across the dynamic range in the original scene, albeit squashed into the range of darks and lights that can be rendered on your PC's display or with your printer's inks.

There are a number of different tools available for creating HRD images, Photoshop has one built in. I like Photomatix Pro but as I said, there are many available. The standard approach with all of them involves providing three or more differently exposed images. Now the optimium way to do this is to capture three different images using a tripod mounted camera. the problem is, when you're walking around a major landmark with several thousand people, it's not always possible to take the time required to set your equipment up and a single hand held shot is all that is available. Never fear! As long as you shoot RAW, all is not lost and this is where the cheat comes in.


RAW images contain a great deal of detail. As such it's possible to reproduce the effect of over and under exposeure pretty accurately through your RAW conversion programme. I'm using LightRoom but the same process is available in all RAW converters. Simply set the exposure value in the converter to -1.5 stops, 0 stops and +1.5 stops and save these as three separate .tiff files. These files can then be loaded into your favourite HDR image generator and a final image created. I'll cover the actual technique used within the HDR tool in another post but for now, the results can be seen below...

Photoshop's coolest tool

It's been a while since I last blogged, I've found that e-mail, Twitter, Instant messaging and plane old human interaction take up a lot of time. Add to this the need to work 12 hours a day to earn a living and there's not much time for much else! Anyway, as the Autumn nights begin to draw in, I plan to make a real effort to produce more material, including tutorials over the next weeks and months. With that in mind, I'm going to start with a Photoshop tutorial and, in the spirit of extreme laziness, it's not one of mine :-)

The Vanishing point filter introduced in Photoshop CS3 is one of the most powerful tools in Adobe's falagship's already impressive armoury. The Vanishing point filter allows you to manipulate images (adding components, moving objects, removing unwanted distractions) while taking account of the images perspective. As I mentioned, the tutorial is not mine, but this excelent two part submission will give you a great insight into its unique capabilities...

The Canon 5D Mark II and a puppy

For one reason and another my blog has been woefully neglected over the last month or so. The same goes for my beloved 5D Mark II. The arrival of two eight week old Jack Russell puppies gave me an opportunity to give the new body a brief initial test drive. I coupled it to my 70-200mm f2.8 L IS lens and started to get to know this incredible feat of image capture technology.


Now these guys are clearly seriously cute but, squirming puppies make critical focus at wide apertures very tricky...


I love the way the 5D Mark II captures colour and detail. Although these images have been published using Lightroom and Photoshop, this was only in order to provide RAW conversion and cropping. Everything else is pretty much as-shot...


I did notice that my focus was very slightly off when the puppies were static. I have subsequently modified the micro-focus adjustment for this lens on my 5D Mk II body and it is now pin sharp every time.

All together now... AAAAHHHHHHH !!!!

Hot pixels spoilt my day...

Last week I received my much anticipated Canon 5D Mark II camera body. As soon as I had the opportunity I eagerly unpacked the unit, attached my favourite L series lens (70-200 mm f2.8 IS L) and started playing. Let me say before I go any further this camera is simply incredible! the issues I have faced are specific to my unit and just bad luck. So first the good news...

The 5D Mark II is a 21M pixel full frame digital SLR that also supports full HD video capture at 1080p. The latest firmware (version 1.1) offers full manual exposure control over said video so this product now becomes one of the most useful and flexible image capture tools on the market. Now I'm a stills guy, I've never really explored video but the 5D Mark II will almost certainly change all that. From a stills point of view, it is a joy to use. The colour rendition is fantastic with a rich accurate palette, the sensor yields fantastic detail (when coupled with the right optics) and the high ISO noise control is simply incredible.

With my old 5D I would shoot at ISO 800 if the need arose but would never really consider ISO 1600 due to noise and the loss of detail that would always result in post production. With the 5d Mark II I set ISO to 1600, shot a few frames and was simply blown away by the cleanliness and usability of the frames, they were fantastic! I pushed the ISO up to 4000 and found I could still get perfectly usable results requiring very little post processing! This will revolutionise my wedding photography and the ability to capture those all important candids in low light situations. Simply amazing!

Now one check I always perform on a new camera body is the hot pixel check. The HP check is pretty simple, all you do is place the lens cap on your lens in order to exclude all light, set the ISO at a suitable mid point (I chose ISO 800) and take a longish exposure (30 secs). Now look at the captured image at 100% and it should appear uniformly black, at least on the 5D Mark II. On other cameras that don't enjoy the same high ISO performance as the 5D MK II some noise may be visible, this will take the form of faint mutli-coloured mottling but it should be pretty uniform across the frame, this is normal and not an indication of an issue. In my case, I was checking for "hot" pixels. These often result from small manufacturing errors in the production of the camera's sensors but can also indicate other more worrying issues. To my horror, when I examined my hot Pixel frame, I found somewhere between 8 and 15 instances where the pixel was glowing either white, red of blue. These pixels remain "hot" from frame to frame and could be visible on dark areas of an image, especially when attempting astro-photography. They can also be a problem on dark video scenes where the removal would represent a great deal of work. In the image below I have circled some of the most obvious pixels as they won't show up on the compressed image allowed by Blogger.


The Eight examples circled here were the eight brightest, you can see they are distributed uniformly across the frame.

So why should you worry? After all, 8 pixels in 21 million is a very low percentage, what's the problem? Well consider the following...

• this is a £2000 camera body!
  
• On normal daytime shots, these blemishes would be unlikely to show up. On night shots, Astro photography or video footage of dark scenes, they certainly would.
• It's a real pain having to remove blemishes from every frame you ever shoot!
  
• Blemishes of this type suggest a problem in the quality assurance stage from this manufacturing batch, there could be other hidden problems.
  
• Errors in the production of the sensor could be a one-time problem but they could also indicate a sensor with degenerative problems leading to further, significant degradation.
  
• When I contacted Canon to discuss the issue, they felt it was a problem and a replacement would be required

I should be receiving a replacement unit very soon. I believe I was just unlucky this time and can't wait to get my hands on this fantastic camera again soon. Once I have my working body I will publish my thoughts and impressions together with some examples of the miracles this camera is capable of.

The mysteries of exposure

I was asked recently to explain exposure, not in the Antarctic sense you'll understand but photographic exposure. This post will try to take this question on and represent another chapter in the set of photographic how-tos and tutorials I've stumbled happily into writing. This is a big subject and this is a longer post than I intended so please bare with me...

Although many would-be photographers use simple point and shoot compact cameras, more and more now buy one of the many affordable digital SLR cameras on the market. Unfortunately many SLR owners, having gone to the additional expense of buying one, leave it in auto mode and end up with essentially the same shots they could have captured with a simpler system. An understanding of exposure and its control opens up a world of many possibilities and creative opportunities otherwise denied by auto mode. you can find an explanation of the limitations of a camera's auto mode in this earlier post.

So exposure, what does it really mean? As with most things in photography, this question has both a technical and an artistic response, for the rest of this post I'll focus on the control of exposure and come back to its artistic use in another post. The simplest definition of exposure is the process of controling the amount of light that is captured by by a camera's digital sensor or film frame. It's the variations in light and dark (highlights and shadows) that form an image and both digital sensor and film have the capability to capture a certain number of different degrees of light and dark (tones). The range of distinguishable tones that can be captured between the darkest shadows (black) and the lightest highlights (white) is called the dynamic range. All digital camera sensors have a defined dynamic range as does photographic film. The greater the dynamic range, the larger the number of light and dark tones that can be captured and, therefore, the more detail that can be represented.

So that was all very interesting but how does it relate to exposure? For the rest of this discussion I'm going to discuss digital cameras but the principles extend to all photographic equipment including video. The dynamic range of a digital camera's sensor defines the range of tones that can be captured between the darkest shadows and the brightest highlights. If the amount of light captured in part of a scene is brighter or darker than the limits of the sensors dynamic range, that part of the scene will appear as a featureless area of white or black. In this case we say there's no detail in the highlights or shadows respectively and this is often referred to as "clipping".

When we control exposure we are controling where important tones in the image sit within the dynamic range of the camera's sensor. Your camera's histogram, the graph-like image that can be enabled on most cameras, is the best way to visualise the exposure of any image (apart from the image itself).



It gives a view of the pixels in the image plotted against brightness levels. The more pixels to the right of the image, the brighter the overall scene and vice versa when the greater concentration is to the left. For a more detailed explanation of the histogram, take a look at this link. Now there's no such thing as the "perfect" histogram. The distribution of the pixels between tones depends entirely on the nature of the image. Imagine a wide angle photograph of a bride against the dark night sky. Since it's wide angle, the bride would occupy a small percentage of the image. Assuming she's wearing a white dress, and we want to see it against the inky black night sky, the histogram of the shot would show a small group of pixcels to the right (the bride's dress) and a large group of pixels to the left (the night sky) with nothing in the middle. This would be a perfectly acceptable histogram for that scene. The point here is the histogram can be used to quickly and accurately assess if the exposure used actually captured the scene the photographer wanted.

Exposure control means ensuring the things that are highlights, mid tones and shadows are where we would expect them to be in the histogram for any particular image. So what's involved in it's control? Discounting flash for a moment, there are three key elements to exposure control, the photographers's holy trinity if you like - Aperture, Shutter speed and ISO value.

Aperture
The aperture of a lens describes how "open" it is and, therefore, how much light can enter the camera while the shutter is open. Aperture is often expressed as a "f" number e.g f2.8, f4, f5.6 and so on. These curious numbers describe the ratio of the lens' focal length to the width of the opening controlled by the lens diaphragm. In other words a 100mm lens set to f4 will have an aperture opening 25mm wide (100 / 25 = 4). The lower the f number the wider the aperture. It's for this reason that very fast (f4 and above) long lenses used by sports photographers are so large, heavy and expensive. Consider a 600mm lens at f4, it would have to have an opening of at least 15cm (6inches) and this would be the minimum width of the main glass element! Photographers ususally vary the aperture value in order to control the Depth Of Field (DOF) of the image, DOF is explained in detail here...

Shutter Speed
No surprises here, whilst aperture defines the width of the opening, shutter speed determines how long the sensor is exposed to the light entering the lens. The longer the shutter is open the more light can enter. Photographers vary the shutter speed for a range of reasons. very often, in hand held candid shots for example, we try to select the fastest shutter speed we can in order to minimise camera shake. On some occasions, we want a slower shutter speed so the feeling of motion and movement can be introduced. We do this by the deliberate blurring of moving subjects against a sharp stationary background. or by panning with a moving object keeping it sharp whilst blurring the background scene. In these cases a slower shutter speed is required.

ISO
The ISO value determines the sensitivity of the camera's sensor to light. The higher the ISO value, the more sensitive the sensor is to the light falling upon it and the more detail can be captured for a given aperture setting or shutter speed. The ISO value is typically modified in order to preserve a given combination of shutter speed and aperture in lower light situations. Imagine you're taking a wedding shot in a church with subdued lighting. Even with the aperture wide open at say f2.8. you may be left with a shutter speed of 1/15th sec which would risk the introduction of camera shake. Assuming the current ISO value was 100, setting it to 800 would realise a shutterspeed of 1/125th sec as the sensor will be 8 times (3 stops) more sensitive. There is however an important note of caution, increasing the ISO value will increase the amount of "noise" captured in the image. When the ISO value is increased, the sensor, which converts light falling upon it into electrical signals, amplifies those signals. As with all cases of amplification, random noise is amplified with the signal and can become significant (more on this in another post).

Aperture, Shutter speed and ISO are very closely linked. For any given exposure setting, say f5.6 at 1/250th sec at ISO 100, if I vary one of the values up, and another down by the same amount I will maintain the same exposure! Now at this point I need to explain how the width of the opening of a lens and the time it is open or the sensitivity of the sensor can be varied by the "same amount" when they are entirely different parameters. I need to introduce the notion of the "f stop".

Every time I double the amount of light I allow into my camera, I add 1 "stop" to the exposure. Now I can double the amount of light by controling the three values we have just described. If I open the shutter for 1/125th sec instead of 1/250th it is open twice as long so twice as much light enters the camera. I've therefore changed the shutter speed by 1 stop. If I open the aperture wider to f4 (f4 admits twice as much light as f5.6 and an explanation of why can be found here) I have doubled the amount of light that can be collected by the camera for any given shutter speed, I have opened the Aperture by 1 stop. If I double the sensitivity of my sensor say from ISO 100 to 200 I have increased the sensitivity to light by 1 stop. This is pretty cool, I have a single unit of measure that can describe three completely different values. the reality is deceptive, although the parameters are very different, they are all affecting the amount of light captured in an image and it is this value that we are actually varying and measuring. See here for a more complete explanation...

When setting up a shot it is the combination of Aperture, Shutter Speed and ISO values that determine the overall exposure of the image. So how do I decide which settings to use? Firstly, if your camera supports manual override (M) it probably also supports Aperture priority (AV) and Shutter Speed priority (TV). If you set your camera to (M) you probably have a view of your camera's lightmeter in the viewfinder. It's typically the case that the meter represents a good exposure by indicating a point in the middle of a scale. If the meter is pointing to the right of centre, it's suggesting over exposure and if it's to the left, under exposure.

Consider the image of the dragon fly landing on a small, weathered wooden fence. There were a number of considerations driving the choice of settings in this image. firstly, being an unpredictable insect I had to choose a fast shutter speed to stand any chance of capturing a sharp image. Secondly, as I was using a long focal length lens, it has a maximum aperture of f5.6 at full zoom . I therefore had to increase the ISO valuer to 400 in order to get the fast shutter speed I needed for the aperture I was forced to use.


The combination of settings in this image delivers histogram that acurately positions the highlites to the right and the shadows to the left without an clipping (pixels bunched up at the edges) leading to lost detail.

Had I chosen a shutter speed 1 stop slower than the settings above, the image would have been over exposed by 1 stop as in the image below (note the histogram is bunched up to the right hand side with much of the detail beyond the limit of the sensor (clipped) these are the very bright areas of the fence that have no or little detail in them)


If i'd chosen a shutter speed that was too fast, say 1 stop faster, I would have ended up with the under exposed image below. (note how the pixel distribution has shifeted to the left of the histogram indicating darker tones make up the bulk of the image. We are aslo beginning to lose detail in the legs and the body of the Dragon Fly)


This image and the choice of settings demonstrate the linkage between the three exposure parameters. In this case, to get the shutter speed I wanted at the maximum aperture I had available to me I actually modified the ISO value!

This was a long post and I have only scratched the surface of this subject. there will be more to come in future posts. In the meantime, try activating the histogram on your camera and watch the effect of different combinations of settings on the histogram and, more importantly, your images.

Composition, the photographer's secret weapon

Photography is an interesting discipline in that it combines art and technology closely and inextricably. Now I'm a technology guy and in no way would ever be considered an artist of any sort. I'm always looking for tips and tricks to make up for my fundamental lack of artistic talent and I want to share one such technique in this post.

Composition is a crucial component of any shot. Beyond the technical considerations of good exposure etc, it is its composition that determines whether it's a run of the mill snap or a pleasing photographic image. Let's use this image of a tiny Damsel fly taken at some distance in order not to scare it away...


Technically, this shot isn't too bad. The exposure is good, the colour and contrast is strong and there is decent depth of field control. The trouble is this shot is pretty much instantly forgettable, it's subject, the Damsel fly, is small, smack bang in the centre of the frame and lacks impact. You've probably heard that placing the subject of any short in the centre of the frame generally leads to a boring snap. Wouldn't it be great of there was a rule or a formula that could help make that artistic difference? Well there is!

There are a number of tools at the photographers disposal when it comes to improving an image's composition. One most will have heard of is the "rule of thirds", simply stated, the rule of thirds places an imaginary grid over an image where the grid lines divide the scene horizontally and vertically into 9 sections as below.


It just so happens that if the subject of an image is placed on the point these lines cross, a more pleasing composition can be achieved. The rule of thirds is actually an approximation for a better tool based on the amazing "golden ratio", This video gives a great explanation of the ratio and its fascinating properties as does this post.

Now let's apply the golden ratio to this image instead of the rule of thirds, the grid would look something like this.


Now using this grid we can crop the image so the Damsel fly occupies more of the frame. In addition we position the key part of the subject on the intersection of the grid lines...


The result is a dramatic improvement in the feel and aesthetics of the shot. The eye is drawn naturally to the head of the insect, the image below seems somehow more natural, more alive, an intimate view of a living secret world.


The Golden ratio grid also works in portrait view as below...


Cropping in this way brings the same sense of life to the image but changes the feeling of scale...


In these examples I've applied this technique by cropping the image in post processing using Adobe Lightroom. Generally I try and get as close to this type of composition as possible when taking the image in the first place. I do this by trying to imagine where the intersection of the grid lines would be in my viewfinder and positioning the subject accordingly at the point I take the shot. Only small adjustments are then required in post processing preserving as much of the original as possible.

The Golden ratio is a powerful tool, try thinking about it next time you look through your viewfinder. If you find the Golden ratio tricky, try the rule of thirds, it's a good approximation, easier to imagine and usually produces good results. If you have a compact camera and use the screen at the back to compose your images, you could even place small marks on the screen marking the intersection points. If you use these techniques you will see a tremendous improvement in the quality of your shots and everyone will want to know how you do it...

Summer hits London

You know when Summer's here, sunshine, warm sulty breezes and butterflies. I looked out of my window this morning and was greeted by hundreds of Painted Lady butterflies (Vanessa cardui) congregating on some flowering shubs. I grabbed my Canon 40D and my 100-400 mm f4.5-5.6L IS lens and went out to capture some shots in between conference calls!

I chose the 40D rather than the 5D as it as an APS-C sensor which applies a 1.6x crop factor. These butterflies are very skitish and the effective focal length of 640mm at full zoom enabled me to get in nice and tight without causing them to flee.

By the way, I wanted to use the right collective noun for butterflies and found there were a few choices. Flight, flutter and rabble were good, but my favourite was kaleidoscope !

A quick snap

I awoke this morning and casually looked out of my kitchen window (I live in a first floor apartment, that's the second floor if you're reading this in North America!) and noticed this little fox cub playing in the gentle warmth of the early morning sun.

click here to see this image at my Flickr stream

It was one of those "bugger! where's the camera?" moments. I managed to grab my Canon 5D and attach one of my favourite lenses, the superb 100-400mm f4.5-5.6 IS L and fire off a few frames before the cub disappeared back into the undergrowth. I had to take the shot through a window pane as the noise from opening the frame would have scared the little guy away. Unlike most L series zooms it doesn't have constant aperture through the zoom range but, nonetheless it does possess the magic that is Canon L series optics. Now this isn't the finest shot ever taken by a long way but the reasons I like it are as follows :-

• It was taken through window glass (at an angle)
• It was taken from a distance of about 30 meters (100 feet)
• The image above results from a very aggressive crop of the original frame.

Taking the points above into account, it shows just how important good optics are for any shot. I really did crop this very hard (it's less than 20% off the original frame) yet it still retains considerable detail and contrast even though it was taken through a rather grubby pane of glass at a good distance. This really highlights the incredible resolving power of these lenses and ensures the full potential of modern digital sensors can be exploited. These lenses are pricey and the link I've used above takes you to the canon site where the full recommended retail price is quoted; there are, however, numerous sites that offer this lens at a more affordable level. If you're really lucky you may even find a used one but it's unlikely, photogs would give up a limb before giving up an L series lens!

Depth of Field Update

Following on from my recent post describing photographic Depth Of Field I wanted to post a link to David Ziser's Blogg where he discusses the composition of family portraits and the use of DOF in the construction of those shots. David's blog is one of my personal favourites as he shares many pro tips and techniques including some great video tutorials.  Check it out...

What is Depth of Field?

Composition is probably the most important component of a pleasing image. It is composition that sets a piece of photographic art apart from a simple snap. Interestingly enough, composition is defined as much by that which isn't obvious in a shot as those elements that are clearly defined. Depth of field is the term that describes which elements of an image are visible in acceptably sharp focus and which elements are blurred out. Depth of field defines that area of an image that extends in front of and behind the focal point of a particular subject. Typically landscape photography requires very large depth of field, everything from a few inches in front of the camera to infinity has to be in acceptable focus. Look at any examples of the best and there is always something in the foreground, something close, often refered to as foreground interest. Being a landscape shot not only should there be foreground interest but there should be clear focus all the way to the horizon. Candid shots of people and some portrait techniques often call for much narrower depth of field, in some cases only a couple of inches front to back are in sharp focus. I have examples of great candid shots where the subject's eyes are in focus but the tip of their nose and their ears aren't!

Depth of field is a crucially important tool in photographic composition and its skilled control really can add to one's photographic repertoire. It allows the photographer to clearly define the central subject of any image, isolating it from confusing and distracting backgrounds. Consider this first shot; it's quite a nice summery scene and the subject, the brick built bird tower, is visible and obvious. Even though it is the most dominant structure in the picture it blends into the overall scene and doesn't "pop" from the surroundings (by intention in this case).

(Click image to enlarge)

Now consider this second image. Just a single glance reveals the subject clearly, even though it's nothing more than a small group of tiny pink flowers. The reason these tiny little blooms "pop" so evidently is the eye's urge to examine items in sharp focus and ignore less defined components of the scene.

(Click image to enlarge)

The process of using focus in this way relies on appropriate management of Depth Of Field (DOF). Until recently, useful DOF control was only really available on higher end SLR cameras. SLRs, specifically their lenses, enjoy large apertures and long focal lengths and it is the combination of these parameters that provide the narrow DOF effect. This is much more of a challenge on smaller compact cameras due to the physical size limitations enforced by the compact format. More recent compacts do offer the attributes necessary to achieve these desirable results and the Canon Powershot G10 is a good example. The combination of a very short focal length and small maximum aperture explains why most compact cameras defer to providing extensive depth of field ensuring as much of an image is in focus as possible.

OK so far so good, DOF is a great thing, so how do you control it? It's actually pretty simple if your camera has the capabilities. DOF varies depending on the focal length of a lens, its aperture setting and the distance between the camera and the desired subject. if you want to close down the depth of field so only a narrow sliver of the image is in sharp focus, use a lens of 50m focal length or greater and open the aperture as far as you can (f5.6 or wider) while getting relatively close to your subject. If you want to open up the DOF ensuring as much of the field of view is in focus as possible, close down the aperture to say f11 or smaller. If you have the capability, set your camera to AV (aperture value) mode where the camera will adjust the shutter speed automatically. This way all you have to think about is the composition and the desired DOF by varying the aperture. (most pros shoot with manually set values. If they are going to use an automatic mode, it will typically be AV as it gives them creative freedom to adjust DOF). There is a complex equation that enables the calculation of DOF but it is more complicated to explain than the scope of this post permits. Fortunately there are a number of on-line calculators that can help and DOF Master is one of the best. The link offers access to the on-line calculator and its downloadable forms. This site also provides a nicely illustrated description of Depth of field and the various components and considerations that enable its mastery.

Drag that shutter...

Time for another photography post. This one is related to the first ( Using your flash on a sunny day ) where I attempted to show the power of using your camera's exposure settings and flash unit essentially independently.


In this post I'm going to talk about "dragging" the shutter. This technique is usually used in low ambient light situations, night time scenes, sunset shots, shots taken at parties and in night clubs. Dragging the shutter means setting a shutter speed that is long enough to capture light from the background while relying on the short flash burst to capture the foreground. In the first post, we were trying to reduce the amount of ambient light collected by the camera by increasing the shutter speed and using the fast flash pulse to illuminate the subject. We were doing this in order to reduce the impact of the blindingly bright background light, the Sun. This time we are going to reduce the shutter speed to allow as much ambient light in as possible.

So why worry about this at all? Everyone will have seen shots, usually taken at a party or a wedding, where the subjects are brightly illuminated by flash but are captured against a completely dark background. There is no context to the shot, it could have been take anywhere, to all intents and purposes it might as well have been taken in a cave! This happens because the subject is typically close, the background is relatively distant and the flash pulse isn't very powerful. The camera's flash exposure calculation takes over in this situation. The aperture and shutter speed are set by the camera to a standard value (the flash's x-sync speed) and the flash fires in order to expose the close foreground subject. The first image is an example of such a shot (this was deliberately exposed in this way to achieve the desired shot but it does illustrate the point...)

What if we wanted to capture more of the background? What if we wanted to use the background to set the scene, convey something about the occasion or the location? In situations where the light levels are low, we need to take control from the camera as we did in the bright daylight examples in Using your flash on a sunny day. In this case we want to reduce the shutter speed in order to allow much more of that precious available light to enter the camera. As in the other post, we set the flash to expose the subject. This can be achieved by leaving the flash to automatically set it's power setting for a proper foreground exposure (auto mode) or, if you know your flash distances, the flash power can be set manually.

But hang on, doesn't that present a problem? Surely reducing the shutter speed, possibly by a great deal in the case of a dark room, will lead to blurred shaky images? Once again the flash comes to the rescue. The flash pulse is very fast indeed, certainly less than 1/2000 sec. It will freeze in space and time anything it illuminates. Even though the background may be subject to a little shake, it will typically be blurred out by the depth of field of the image (subject of a future post). The foreground subject will be sharp, well illuminated by the short flash burst but set in context.

It's not uncommon to use hand held shutter speeds as low as 1/15 sec with this approach, even lower where where your camera has built in image stabilisation. The second picture, taken within twenty minutes of the first, demonstrates why "dragging" the shutter can make a massive difference to the feel and look of any low light shot when flash is used.

Use your flash on a sunny day...

When I originally decided to start a blog, I set out to tackle two distinct themes, technology and photography. With that in mind I decided today to write a piece attending to the latter. This may turn into a series of the simple tips and tricks I've picked up over the years from my own trial and error and from some great photographers.

There have been so many innovations in photography over the last few years it's hard to keep up. Reading the specs of even the cheapest compact pocket digital camera, one would think all you needed was the ability to stand vertically, point the camera in vaguely the right direction and pow! magic happens. The reality is of course very different. What ever additions or automations appear, what ever surprising applications of digital processing arise, photography remains an art. There are, however a few basic principles and a couple of simple techniques that can turn a dull snap into a decent picture and these techniques apply what ever equipment is at hand.

Photography is about composition and exposure. Both contribute to a photo's ultimate artistic merit but exposure is also driven by technique and a tiny bit of science. On modern digital cameras, exposure control is normally a mystery, hidden by "Auto mode" and left to the supposedly superior intellect of the camera's on-board processor. In reality, that processor, or at least the exposure program it runs, isn't particularly smart.

So what is exposure? Exposure is a term that describes the level of reflected light captured by a camera in order to record an image. In most cases, "correct" exposure means an accurate representation of the scene has been captured where detail is visible in both the highlights (brightest areas) and shadows (darkest areas). In modern digital cameras exposure is controlled by the aperture setting, the shutter speed, the digital sensor sensitivity (ISO value) and, in some circumstances, the flash. At the risk of adding to much complexity, most digital cameras can actually control two different exposure values simultaneously for any given image. The second exposure is controlled by the flash.

All automatic cameras use pretty much the same exposure calculation paradigm. They all attempt to assess a scene and then set the camera's exposure control to achieve an even exposure. In this context, the rather vague and inexact term "even" actually has a numeric translation - 18% grey. An 18% grey card is a tool used by photographers down the years to check exposure. A card that is prepared 18% grey actually reflects light pretty much in the middle of the range between white and black. In other words, your camera's exposure meter aims to make your image look as close to grey as possible! In reality, an image contains a vast range of lights and darks. Your camera tries to find an exposure value that will enable all these different tones to average out at - you've guessed it - grey! So what does this mean in practice? The easiest way to explain this is an experiment. Take your camera, set it to auto and take a shot of a white piece of paper. Look at the result and you will see, instead of a fresh white sheet of paper, you'll have something that looks like it was washed with a pair of dark socks! it will be a washed out grey colour. Ok, now find something jet black, take a shot on auto and...you've guessed it, the black item appears grey and lacking in contrast. In both cases, the camera has set a combination of shutter speed and aperture that achieves a scene that averages to 18% grey. This behaviour has many implications and is the key reason why so many auto-mode snaps end up either looking uninspiring and washed out, or as if they were taken in a cave!

OK, here's the first tip - Use your Flash...
The message here is simple, use your flash when ever you can. Even during the day, in fact especially during the day. Why? You'll have heard it said many times, "never take a shot into the sun" or "always have the sun behind you". While this does provide even illumination of your subject, it also means they are probably squinting. Also, your subjects will look flat and uninteresting, all the contours and definition of their features erased by a solar blast. Finally, you can't always guarantee to have the Sun and your subject where you want them.

Now most people will have taken shots before where the subject is strongly backlit. what typically happens is you end up with a well exposed background and a subject with a featureless face shrouded in total shadow. The reason for this is pretty straightforward, the background light source is dominant, much brighter than your subject's face. The camera attempts to set an exposure that balances the brightness levels in the overall image. It sets a combination of aperture and shutter speed that reduces the amount of light recorded by the sensor to a level defined by the large bright source in the background. Unfortunately, in this situation, the relatively tiny amount of light reflected by the subject cannot compete and the subject is thrown into a dark gloomy shadow.

Now remember earlier I suggested your camera can manage two different exposures simultaneously? The flash unit (built in or external) can come to your rescue. While the camera's main exposure program sets the exposure value for the dominant background, turn on the flash and magic happens. With the flash on, press the trigger and a blindingly fast set of events take place. The camera will launch a pre-flash before the shutter is opened. The intention of the pre-flash is to test the amount of light required to correctly expose the foreground subject. The amount of light is controlled by the duration of the flash burst. Once the amount is computed, the shutter opens for the time required to correctly expose the background and, at the same time, the flash fires for the amount of time required to correctly expose the foreground subject. The end result is an image with a well exposed background and a properly exposed subject, all this happens in the blink of an eye. You see? two different exposure controls applied to a single daytime photo. There are some other desirable outcomes from using daytime flash. The flash helps the skin tones of human subjects to look warm, rich and healthy. Those unsightly shadows under the eyes and chin so typical in sunny day shots will be filled in giving a pleasing, detailed and flattering result. Finally the eyes will benefit from a catchlight, a tiny reflection of the flash pulse in each pupil. The catchlights make the subject look alive and somehow three dimensional.

Both of the images I've included in this post were taken using this technique. Each shot has a low key ambiance yet both were taken in the middle of a field on a bright sunny afternoon. In this case I have used off camera flash and a SLR but similar results could be achieved with a compact. The secret is in managing the two exposures, ambient and flash. In this case, I have reduced the dominance of the natural light by under exposing the ambient light by 1.5 to 2 f-stops. The flash is set to expose the foreground optimally (in this case I used a manual flash power setting, but you could leave the flash on its normal automatic setting and allow it to set its own optimum exposure)

As I said at the top, nearly all cameras have the ability to do this, if you're using a simple point and shoot compact camera, find the control that sets the flash to "always-on" when you're taking your next set of sunny day shots. You'll be surprised by the results and you'll wonder no longer why those frantic press photographers always use flash during the day for those "must-get" publication shots they earn their living from.