Photography Basics – Exposure and Histograms

histogramIn my previous post: Photography 101 – Aperture, Shutter Speed & ISO we explored the basic camera controls, their relationship to each other and their use in both everyday photography and creative photography.

Today I want to look in greater depth at how this relates to the captured image in terms of Exposure and the Histogram.


In simple terms exposure is the amount of light that is allowed to fall on the sensor (or film) when you take a photograph and modern cameras will have a built in exposure meter (or light meter) that will determine the light values of a scene and attempt to return a result that will give a suitable mid tone which equates to 18% grey.

Why 18% grey? Simply, this is the correct value for caucasion skin tones under normal lighting conditions and is considered the standard that meters are set to.

So with our camera set to auto the meter will evaluate the scene and attempt to set the aperture and shutter speed to give an average exposure of 18% grey, which generally will give a reasonable image. The problem with this approach is that we do not always want to photograph average subjects; we may wish to photograph non-Caucasian skin tones, snow and beach scenes, night scenes, high key and low key scenes.

In these situation the light meter will attempt to reproduce the scene to 18% grey which will result in under exposed snow / sand or blacks will look grey or muddy, in these cases we need to make a judgement of what is the most important part of the image to expose for and trick the meter into making the correct settings.

Exposure Meters

Exposure meters fall broadly into two categories; built in (part of the camera) or hand held and can feature several different modes.

Center Weighted Average Metering

In this system 60-80% of the exposure is biased towards the central portion of the viewfinder and gives less importance to the exposure towards the edges. This will generally return acceptable results with portraits and general scenes as it will be less influenced by brighter skies etc.

Average Metering

The exposure is calculated by averaging out the entire scene.

Spot Metering

In this mode metering is based on 1-5% of the viewfinder, typically the very center, variations will enable the photographer to select from different areas of the viewfinder or may offer multi-spot metering, where a series of targets can be selected.

Spot metering is ideal for subjects with high contrast such as back-lit subjects, photographs of the moon or actors / musicians against a dark or light background.

Multi Zone Metering

Also known as ESP, Matrix, evaluative or honeycomb metering. Here, multiple zones are metered and used to determine exposure across the scene, different bias will be given to different areas and this will in some cases be linked to the camera auto-focus to bias the point of focus.

So far we have discussed various metering systems and how they attempt to make the correct exposure, some of their drawbacks and basics of operation, all of which leaves two questions; how do we know if the exposure is right? If it’s wrong how do we correct it?


The histogram is a graph showing the distribution of exposure levels across an image and can normally be found on most image editing software and can normally be enabled to appear on the rear LCD screen of most cameras.

Values to the left of the screen represent blacks and dark tones, to the right light to white tones and the graph will normally show a peak where the exposure is concentrated. If this peak is towards the left, the image will be dark and shadow detail may be lost, if fully to the right the image will be very bright and highlights may burn out. In the majority of situations we would want to expose so that the peak is just to the right of center as shadows can be recovered easier than highlights in post production.

If we need to adjust the exposure when using any of the camera auto modes e.g. program, auto, aperture or shutter priority, then we need to trick the meter by using the exposure compensation control to manually increase or decrease the exposure, use exposure bracketing to take a series of exposures (normally at 0, +1Ev, -1Ev) or use Exposure Lock (AEL) to meter an important part of the scene which is off center before re composing.

Correct use of the Histogram allows us to better understand where the light distribution is within the image and will lead to better captures, with experience and use of the histogram function you will learn to understand how light interacts with the elements of the image and how to better set the camera controls before taking a shot.

Processing Techniques – HDR Workflow

I’ve recently been having an increasing number of conversations on G+ with people who are new to processes such as HDR and wanted some tips and tricks. When I first became interested in HDR Someone was good enough to share their knowledge with me so I thought it was a perfect time to “pass it on”. As a result I will be putting together a few short tutorials on a few photographic techniques, starting with this one: HDR, Using Photomatix.

There are several very good HDR / Tone mapping packages available, I picked Photomatix because I like the interface and results, that’s not to say other packages are not as good, they are but I prefer Photomatix.

HDR Workflow

I tend to use Adobe Bridge for selecting images, note I shoot in RAW almost exclusively and use a tripod for HDR work. Here I have selected 5 RAW files, although the minimum required is 3. I normally shoot at 1EV steps and will take up to 9 RAW’s depending on the light variance and camera histogram. You can use the Photomatix plugin for Lightroom if you have LR and not Photoshop.

Import to Photomatix

Either Drag & Drop  selected files into Photomatix or use the import pictures facility, here you are faced with a couple of pre-processing options and the chance to specify EV values if you have multiple files with the same value. As you can see from the screenshot, you have the ability to select deghosting (manual or automatic), great for windy days and where movement may occur in the image. You can also automatically align images and crop them to match each other, set colour temperature and reduce Chromatic Aberrations and  noise.


If you chose to manually deghost the image (if not why not?) you will be presented with the screen above. The process is simple, use your mouse, tablet pointer etc. to draw around the ghosted areas, as you can see I have selected areas to correspond to the foliage in the foreground and the clouds. Push the Preview Deghosting button to check the effect.

When in preview you can hit the Return to Selection button to add more areas if needed.

When happy with the deghosting hit the OK button to proceed.

Tone Mapping

Hit the button arrowed and the RAW files will be merged by magical pixel pixies into an image ready for Tone Mapping. This is the fun part where the RAW files are analysed and tweaked to produce something approximate to the final image. At this point you will see progress bars on the screen as the images are being processed and combined.

Tone Mapping

Now the real fun starts, along the bottom or side of the screen you are faced with a series of Tone Mapping presets, these are a great starting point and you can select each in turn to see the effect it has. different presets work best on different scenes and to achieve different moods, but as I say they are a starting point. Here I have selected Enhancer Painterly which tends to give a medium amount of processing leaning a little towards grunge.

Also worth noting the pop out Histogram box, I use this all the time to assess how the changes affect the image.

Fine Tune

As I said above, consider the presets as a starting point, the circled control sliders at the left now provide a myriad of options to fine tune the image. You can adjust pretty much any aspect from Saturation & Vibrance to the various lighting effects. Some of the controls I use a lot are Micro Smoothing, white point and detail contrast. Using a combination of these tends to give a more natural looking image whith whites staying white not turning grey, a little POP to the colours and reduction of halos around bright areas. When you are happy with the result, save the file, using File>Save gives the option to save in various formats (I opt for TIFF) and also to automatically export the image to a photo editing suite (in this case Photoshop). It should also be noted that you can save Tone Mapping settings which will be applied as a start point on the next image (great for doing batches taken under the same conditions).

Final Tweaks

Once in Photoshop I tend to make some basic adjustments such as Levels (it’s that histogram again) and localised highlight and shadow control. Dependant on the subject and my mood I may also make some adjustments to sharpness and blur or perhaps tweak saturation or blend in a layer or 2 taken from the initial RAW files.

The Finished Article

Playing with shadows

Playing with shadows

Playing with shadows

Shadows are all around, the harsher the light the more well defined the shadows will be harsh light tends to produce far more compelling photos. Just look around they are everywhere.

Look for shadows that interplay with each other or something that creates a striking contrast. Shadows are ideal subjects for black and white processing, but can create truly compelling pictures even in color.

The tricky part to photograph shadows is to determine the exposure. Using any auto exposure mode will often lead to an overexposed image, this because the cameras light-meter will try to compensate for the dark areas and brighten up the picture and bring out details in the shadows. This is not necessarily desirable, but could not it just be fix in post processing? Sure, but why not expose it correctly in the camera from the start, and reduce the time in the digital dark room. To control the correct exposure, in shadow photography it is best to stick with manual exposure mode or otherwise utilize negative EV exposure, for best result, the histogram should be pushed far to the left.

Personally, I prefer to use negative EV exposure. I believe it is quicker and easier for me to change EV exposure, then switch between different camera modes. This allows me to be ready for the next photo whatever it might be.

Happy Snapping my friends!

Photography Basics – Aperture, Shutter Speed & ISO

1/6th sec @ f22

1/6th sec @ f22

Welcome to the first in a series of Photography tips aimed at beginners to photography and photographers who have a basic understanding but with to improve their creativity.

I decided to write this as a result of comments online that many DSLR owners used their camera as a fancy point and shoot, when I asked around it was apparent that some people who are new to photography may not have an in-depth knowledge of their camera controls or the basics of photography and that a few simple tutorials may help them to achieve their potential.

I’ll start with the basics as they have the most impact on what we all do in general and also have the most creative impact on an image, that is Aperture, Shutter Speed and ISO.


The aperture determines how much light passes through the lens, it is basically a diaphragm that can let in varying amounts of light, similar to the iris in your eye. Fully open and it will let in more light, reducing the aperture size will let in less light, but that is not all the aperture does it also affects the Depth of Field (Dof) in the final image.

DoF is the amount of the image that is in focus on the focal plane, this is basically the point where your sensor (or film) is placed. With the aperture wide open the DoF will be shallow, the portions of the image closer and further away than the main subject will be out of focus and blurred, with the aperture stopped down more of the image will be in focus.

The location of the aperture control on your camera will vary but it will be used to adjust the f-stop or f-number, this number is the ratio of focal length to effective aperture diameter, but a smaller f-number (f3.5) equates to a wider opening and more light / less DoF, a larger number (f16) equates to a smaller opening and greater depth of field.

The actual range of f numbers will vary dependent on the lens in use and you may notice that a zoom lens will have two maximum f numbers i.e. f3.5 – f5.6 which relates to either end of the zoom, finally each change in f-number is one stop or Exposure Value (Ev) in light (remember this it will come up again later).

Shutter Speed

The shutter determines how much light hits the film or sensor, or more accurately, the length of time the sensor or film is exposed to the light entering the camera. On the old wooden plate cameras this was as simple as a wood or metal slide that the photographer would pull out from the film holder and replace after a matter of minutes had passed, as film became more sensitive, the shutter became more advanced offering higher speeds and has now evolved to a series of mechanical blinds in front of the sensor (or film) which open for a fraction of a second to allow light to hit the sensor.

Speeds can range from several seconds to a maximum of several 1000’s of a second i.e 12 s – 1/8000. Shutter speeds also traditionally increase in the following form 1/125, 1/250. 1/500 etc. each increase or decrease in shutter speed related to 1 Ev in light (I said it would come up again).

Again shutter speed has another use, a high shutter speed can be used to freeze motion, that’s great right? We all want the subject to be sharp, right? Well yes, and no. There may be times when you want to convey motion, how do you do this with a subject (or medium) that is static, well by introducing a degree of blur.

Sports photographers will often use a slower shutter speed(1/60th) and pan the camera with the action, when done right this will give a sharp subject but the background will be blurred, a lens can be zoomed during a long exposure to give a creative blur or the motion of a waterfall can be conveyed by turning the appearance of the water into a smooth, silky fog by using exposures longer than 30 seconds.


ISO is traditionally a rating of how sensitive film is to light, different films would have a different rating i.e. ISO 50, ISO 100, ISO 200, ISO 400 the lower the number (ISO 50) the less grain the film has so it produces a sharper image but is less sensitive to light so needs brighter conditions or a tripod, the higher the number (ISO 400 or even ISO 3200) gives a much more grainy image with possible colour shifts  but will allow you to shoot in lower light.

For example taking ISO 100 as standard; an exposure of f8 @ 1/250 at ISO 100 equates to f8 @ 1/125 at ISO 50 or f8 @ 1/4000 at ISO 3200.

So has the advent of digital cameras made ISO irrelevant? No of course not.

Your DSLR will still have an ISO dial, it will vary between ISO 100 to ISO 3200 on average, and guess what? Each step up or down in ISO equates to 1 Ev (you were paying attention to that – right?).

So what does this mean? Well, in general the Lower the ISO the better. A digital sensor works by converting the light that hits its surface into a digital signal, increasing the ISO increases the sensitivity of the sensor by increasing the electric charge across it, whilst this will allow the camera to work in darker environments it will also introduce noise (or grain) into the image, which can result in a degeneration of image quality. Sometimes, however you may need to sacrifice a little bit of image sharpness to get the shot, indoors at a concert or sporting event the lighting may not be bright enough without increasing the ISO, or you may want to use grain creatively.

The Exposure Triangle

Now, if you remember what I wrote earlier there is a common point: each increase or decrease of Aperture, Shutter Speed and ISO increases or decreases the Ev by one stop, therefore a combination of these values will give a correctly exposed photo but with varying effects. If you want just a small part of the image in focus a wide aperture will achieve that but will require a high speed, if you want more of the image in focus use a smaller aperture but you will need a slower speed, this is the basics of making a manual exposure (that funny M symbol on the camera settings).

Most Cameras will have at least a program (auto) mode, Aperture Priority mode and Shutter Priority Mode. Program will do a decent job at getting a well exposed image, but use the other modes and play. Taking a portrait? Open the aperture a bit (to f3.5 for example) and throw the background out of focus. Shooting a landscape? Close the aperture down more (to f11 or f16) and pack the frame with front to back sharpness. At a sports event? Set the camera to Shutter Priority and use a high speed (1/500th ) to freeze motion or use a slower Shutter Speed and deliberately add blur to emphasise movement.

Photography, as in life has rules; rules to get the right exposure, to freeze motion, to obtain the most pleasing composition. I would urge everyone to learn the rules and learn when to apply them for best effect, in this way the technical aspects of photography becomes second nature and will allow the photographer to concentrate on the creative aspect of photography. But just as importantly, or more importantly, knowing the rules means that when you deliberately break them, you know why you have done so, you will have done so for a creative reason, but you will also know how to reproduce the effect when you need to.