Portrait photography in Kent

Our friends' son Julian - a future male model methinks! Look at the eyes...

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Wedding photographers love Curves

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And if you're a digital photographer so should you, since it gives you complete control over the contrast in your images.

Here's a shot of my chum Jack, taken last week, with the corresponding 'Curves' dialogue box in Photoshop. In light grey within the graph is the RGB histogram. To make it simpler to understand what curves can do, let's discard the colour information from the shot by converting it to greyscale.

The horizontal (X) axis runs from 0 (black) to 255 (white), encompassing all shades of grey. It corresponds to the 256 tones being input into the 'Curves' process. The histogram shows the relative number of pixels at all 256 of these tones. The majority are towards the darker end of the scale - the image can be described as 'low key'. The vertical (Y) axis is identical to the horizontal axis except that it represents the tones being output from the 'Curves' process. At the moment our 'Curve' is the line indicated in red. Choose any point on the X-axis, the input tone, travel vertically until reaching the red line or 'Curve', and then travel horizontally left to the Y-axis to see the output tone. At the moment 0 maps to 0, 255 to 255, 127 to 127 etc - the image remains unchanged.

Let's introduce some extreme contrast! The red path now shows the 'Curve' that I've input - look at the affect this has on the image. All input tones from 0 to 130 have been mapped to an output of 0 (black) and all input tones from 131 to 255 have been mapped to an output of 255 (white). The resultant image now contains only black and white - the ultimate in contrast but not so useful as a treatment for our images.

A more pleasing result is seen with the path in red shown above - known as an 'S-curve'. Darker tones have been darkened slightly and lighter tones lightened. The slope of the line in the midtone region has increased leading to a more subtle increase in contrast.

The same process can be applied to colour images but the extreme contrast procedure would make your image look rather odd (which is why I converted to greyscale). In Photoshop curves can be applied to colour channels independently giving great control over colour balance.

Feel free to contact me with questions or comments.

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Capturing light - digital sensors and histograms

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Each pixel in a digital image has a corresponding light-collecting 'photosite' on the sensor of the camera that took it (on the 5D Mark II there are 5616 x 3744, or 21 million, of them!) In the majority of digital cameras each photosite can only record light intensity for one of the primary colours (red, green and blue), assigning it a number between 0-255 (256 values = 2 to the power of 8 = 8-bit). For each photosite information about the other two primary colours is deduced from adjacent photosites using a process known as 'demosaicing'. The Foveon sensor, featured in Sigma's cameras, is the exception - it records the intensity of R,G & B light at each photosite. This information can then be converted and displayed as a digital image or graphically as a histogram.

I took the above 'snap' of my daughter Emily this morning, deliberately including some vibrant primary-coloured objects, to give clear histograms.

Pressing the 'info' button whilst the image is displayed on the LCD of the 5D Mark II gave the above screen which shows a brightness, or luminance, histogram.

Pressing the 'info' button again leads to separate histograms for R, G & B light (the order in which these screens are displayed can be adjusted by a setting in the menus).

In Photoshop the above histograms can be displayed for the image - the 'RGB' and 'colours' histograms are in addition to those that the camera displays.

The horizontal axis on all these histograms represents brightness values which run from 0-255. The vertical axis represents the number, or frequency, of pixels occuring with this brightness value.

It is not always possible to expose a shot so that it is cleanly captured within the brightness range of these histograms - the dynamic range can be too great for the camera (think outdoors on a bright sunny day). In this case some of the tonal detail of the shot will be lost or 'clipped' - it will be either pure black or pure white. One of the benefits of shooting RAW is the greater tonal range that can be captured.

I tend to pay most attention to the brightness, or luminance, histogram as it corresponds most closely to the scene as our eyes see it (the 5D Mark II displays a luminance histogram but many cameras only display the RGB variant). The histogram is calculated by taking a weighted average of the R, G & B light at each pixel, with more emphasis placed upon green light as the eye is most sensitive to this. As a result, notice that the luminance histogram bears most resemblance to the green-only histogram.

The separate colour histograms can be used to see if individual colours have been clipped.

The RGB histogram is purely a summation of the colour histograms and can be used to assess colour clipping - but as a result of this simple maths, 'pixel location information' is lost. The histogram can show strong clipping at the far right of the histogram, due to bright R, G and B pixels at separate locations, without there being any pure white pixels in the image. A white pixel requires values of 255 for all three colours at the same location.

The 'colors' histogram is an overlay of the separate colour histograms and is a convenient way of visualising all three at once - Lightroom displays this.

How this colour and brightness information can be manipulated will be the subject of further posts.

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Lightroom vs Aperture with 5D Mark II RAW files

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I'm a huge fan of Adobe's Lightroom but since upgrading to the Canon EOS 5D Mark II I've become a bit impatient with the length of time it takes to move between shots in the develop module. Obviously Lightroom is having to work hard to render a 21 megapixel RAW file (which can be up to 30Mb in size) but, time is money, and I'm a busy man!

When moving from one file to another it takes Lightroom about 2 seconds to display the new histogram, after which some simple adjustments, such as to brightness and contrast, are possible and 4-6 seconds before the 'Loading' dialogue disappears, after which all adjustments are possible. It doesn't sound like a long time but when processing 500 shots from a wedding I may well move between shots over a 1000 times - this equates to an hour waiting for Lightroom!

This is with a reasonably powerful computer as well. I'm currently using Lightroom 2.3 on an Apple Mac Pro featuring two 2.66GHz Dual-Core Intel Xeon processors, 9Gb RAM, a NVIDIA GeForce 7300 GT graphics card, a 30" Apple Cinema display and running OSX 10.5.6. Not state-of-the-art any longer (the latest Mac Pro behemoth from Apple features two 2.26GHz Quad-Core Intel Xeon "Nehalem" processors) but still a powerful beast nonetheless.

Obviously I could use one of the 5D Mark II's lower resolution settings (sRAW 1 uses 9.9 megapixels with files sizes about 15Mb) but this seems a retrograde step. The extra resolution of the 5D Mark II is a very welcome addition for wedding photography - it gives you much more flexibility in post-processing and allows you to print 'big'.

I read on the internet grapevine that Lightroom, unlike Apple's Aperture, was not able to fully exploit the powers of the Mac Pro so I downloaded a trial version of Aperture 2.1.2.

I found Aperture very accessible and much faster at moving between shots than Lightroom (it takes about a second). The significant drawback, however, is the time lag when applying adjustments, in stark contrast to Lightroom's real time response. I wonder if this is because Aperture is not fully rendering the RAW file initially? Anyway, the bottom line is that there's no way I could work with this limitation and so I'm sticking with Lightroom for the time being.

A couple of further observations regarding Aperture:

1. It displays flash exposure compensation information in the EXIF data. Wonderful! Why doesn't Lightroom?

2. Oddly, some EXIF data is displayed numerically - so rather than displaying 'flash did not fire' you see the number '16'. Not very helpful.

3. Highlight recovery seems better compared to Lightroom.

4. A 'Quick Preview' setting allows you to move between images with no delay. It would be good to see this in the develop module of Lightroom.

If you've got experience of using both pieces of software I'd love to hear your thoughts.

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Kent Wedding Photographer in Uxbridge

We visited some friends in Uxbridge yesterday, and whilst there, subjected them to a very brief portrait session. Jack, wit and raconteur, has a wonderful face for photography. As his daughter described it yesterday, "it's been lived in", but then after 82 years this is how it should be!

Apologies to all those who've requested blog topics and are still waiting - I promise I'll respond to them soon.

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Wedding Photographers in Kent

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Here's a question that I'm sure concerns many wanting to take their first steps in wedding photography:

Hi David,

I'm looking to start out as a wedding photographer. One question remains - Nikon or Canon?

Does Canon have better lenses? Does Nikon focus better and have better Flash performance blah blah.

I'd like your impartial opinion without considering price issues.

A second question - have you played much with the video capabilities of your 5DMk2 - I've not read of any wedding photographers making any use of it.

Thank you!

Alex

Hi Alex,

The bottom line is that you can't go wrong with either.

One of the key factors to base your decision upon is the lenses that you favour. If treated well, they'll be with you for the rest of your working life.

You'll be replacing your camera bodies every 18 months and flash units as required.

I'm not familiar with Nikon kit, and don't spend any time fretting about these matters, but it seems that they have the edge at the moment with camera bodies - the Nikon D3 is very highly regarded. Still it should inspire Canon to greater heights!

All I can say from personal experience is that Canon has a very fine stable of lenses.

I have been using my 5D Mark II at weddings and the results are stunning. The world-renowned wedding photographer Yervant has just posted a clip on his blog.

Yours,

David

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Personal photography

My wedding photography business has been going so well that I've not been finding the time to take shots of the family recently. Also, I rarely appear in the shots when we do find time for a family photo session. On our trip to the park with Emily last weekend, however, we managed to correct both of these deficiencies!

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On learnng

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The most frequent questions I receive are on the subject of flash photography - balancing ambient and flash light, flash exposure compensation etc. People are keen to understand the 'rules' or logic behind the technology so that they can develop their technique in a rational manner. Although I would encourage people to seek out as much information as possible on all photographic subjects (reading widely broadens your horizons), ultimately, for a practical subject such as photography, nothing beats 'doing it'. It's the only way to truly develop a deeper understanding and, with digital cameras, this learning process is aided by the almost instantaneous feedback loop between experiment and results.

The concious competence learning model captures this learning process nicely. It was probably developed by management consultants (it reminds me of Donald Rumsfelds infamous 'known unknowns' quote), as it has that business-ring to the language, but I think it captures an essential truth about learning.

1. You start out 'unconciously incompetent' - you don't know what it is you're unable to do.

2. As you develop an interest in the subject and seek out information you become 'conciously incompetent' - you know what it is you're unable to do. If you only read about the subject you'll be stuck at this stage.

3. As you practise the discipline that interests you, you become 'conciously competent'. You can get the results that you want but it requires a great deal of mental effort.

4. As you practise more and more (apparently 10,000 hours of practice are required to become an expert) you finally become 'unconciously competent'. You're great at the discipline without even having to think about it.

So put your books down, stop browsing the internet, and get out with your camera and flash unit and start learning!

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Depth of field

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I received this question during the week.

David,

I'm struggling with the concept of aperture used at long focal lengths. Close-up I understand how wide apertures demand accurate focusing, but what about at a long distance? It seems much more forgiving. Another layer to my question is how a long focal length will compress the background - does this have an impact on aperture use too?

Thank you!

Matt

This presents a good opportunity to reflect on the factors that affect depth of field (DOF), the distance range from the camera (or more accurately the focal plane, marked on your camera's body by a circle with a single line through it) where subjects appear to be in focus. I shall stick to the headlines in this blog post but, for a more in-depth view on this topic, check out Sean McHugh's fantastic Cambridge in Colour website.

The most important variables in controlling DOF are:

1. The aperture of the lens. As the aperture becomes bigger, the DOF becomes smaller.

2. The magnification of the subject. As the subject increases in size in the image, the DOF becomes smaller. You can easily illustrate this by picking up an object and moving it closer to your face - watch the background blur as your eyes' DOF shrinks. You can increase the magnification of your subject by either moving closer to it (reducing the focal distance) or by using a telephoto lens (increasing the focal length).

The magnification of the subject depends upon the focal distance (distance between subject and the focal plane of the camera) and the focal length of the lens. Note the key difference between focal distance and focal length! It is possible to keep a constant magnification of the subject, and hence DOF, whilst changing the focal length of the lens by making changes to the focal distance. This may seem like nit-picking but it's worth getting your head around.

You can convince yourself that DOF depends on magnification, rather than focal length, by taking a series of shots of a subject at various focal lengths and keeping it the same size in the frame. The DOF appears independent of focal length.

Let's say you're using Canon's 24-105mm f/4.0 L IS zoom lens. You focus on your model at a focal length of 105mm in aperture priority mode at f/4.0. You take your first shot, which with these settings will have a modest DOF. You zoom out 10mm to 95mm, making your subject smaller in the frame, which means you have to move in closer to restore your model to their original size. You repeat this until you're at a focal length of 25mm. If you were to estimate the DOF in each shot by eye you'd say it was constant.

It isin't exactly the same, however. At shorter focal lengths the DOF does increase minimally, even if the subject stays the same size, which means that DOF is not completely independent of focal lengths. The impact of this is small compared to the impact of magnification though.

The following is also worth noting. Most photographers are interested in a shallow DOF for blurring backgrounds. DOF extends in front of and behind the focal distance, but the ratio between the two changes with focal length. At shorter focal lengths the DOF extends approximately 1/3 in front of the focal distance and 2/3 behind. At longer focal lengths this changes to 1/2 in front and 1/2 behind. Therefore longer focal lengths have an advantage for blurring the background.

It's important to note that moving closer to a subject will affect its appearance due to changes in perspective. It is possible to have a blurred background when shooting a model at shorter focal lengths, but the reduced focal distance will distort their features due to the impact on perspective. If you want to shoot people with a blurred background then use a telephoto lens.

To address Matt's comments directly.

1. Using a wide aperture at a greater focal distance gives you a greater DOF and therefore makes accurate focusing easier.

2. A longer focal length will magnify the subject and therefore reduce the DOF. Wider apertures always give less DOF - this is not dependent upon focal distance or focal length.

Questions and comments (due to confusion or errors on my part) are most welcome!

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