The metering modes of your Pentax SLR explained.
Posted: 08/02/2013 - 14:26
Your Pentax digital SLR camera, and all the Pentax autofocus film SLRs before it, has a choice of metering modes. Choosing the most appropriate mode for the subject you shoot can speed up your picture taking process and ensure you get better results first time, but even though these are auto measuring modes it pays to know what the system is doing so you can interfere and make minor adjustments to ensure even better photos.The popular metering modes are centre weighted (also known as average), multi pattern (also know as matrix or segment metering) and spot. Some cameras have partial metering option which is a less precise version of spot. The modes are shown as icons and in the camera dial close up below are, from left to right, spot, centre-weighted and multi-pattern.
Centre weighted metering
Centre weighted is the pattern Pentax chose to include in their 1960s Spotmatic cameras and was the same system adopted by most manufacturers. It's the most straightforward and takes a general average meter reading from a large proportion of the recording area. It's an oval shape and sensitivity increases towards the centre, so if it was viewed as a graph it would look a bit like a mountain. This metering pattern was designed with a landscape format in mind, placing a slight bias towards the ground to avoid the bright sky causing underexposure. It's the setting that most cameras are set to as default.
Centre weighted is good for average scenes where there's no challenges for the camera to cope with. General landscapes, especially with a small amount of sky, evenly lit interiors, building shots and people pictures where the background is a similar tone are fine for the basic centre weighted pattern.
Spot metering
Then Spot metering came along. This has a much smaller measurement area so precise readings can be taken. It's best for use in extreme lighting conditions, such as a person against a bright sky or a light flower against dark foliage. Spot metering can be pointed at the specific area of interest and a more accurate reading taken.
Spot metering is good for stage lit subjects, wildlife photography, sports and other genres where the main subjects is either in spotlight with a dark background or surrounded by a much brighter background.
Multi-pattern metering
As computer technology evolved, camera manufacturers became more concerned about providing more accurate metering and in 1983 Nikon introduce the first camera with multi-pattern metering called the FA. This was to change the way we used cameras.
Multi-pattern has the screen split up into a matrix of regions, each taking a meter reading and then evaluating the result using the camera's micro processor to assess the kind of photo you're taking and adjust exposure to suit.
Multi-pattern metering is good for most kinds of photography, giving similar results to centre weighted in average situations while providing more accurate results in complex scenes.
The poppy illustration above is from a 16 segment meter of an older Pentax SLR.
The illustration to the right is the latest and most advanced 77 segment grid used in the Pentax K-5.
While it's certainly the best as it can tell when a subject is back lit or a small part that you're focusing on is darker than the rest, it still makes mistakes.
And that's true of all modes. Auto exposure, no matter how sophisticated, can still be fooled. And here's why.
A meter no matter how sophisticated is designed to convert what it measure into an average tone. So any reading is automatically adjusted so the camera records an 18% grey neutral tone.If the subject is predominately white such as snow or bride in wedding dress, the meter will try to make them grey. Likewise, if the subject is dark such as a black cat on a dark sofa or a Welsh slate mine in the rain, it will try to make them grey.
Take the snow scene below. It's a point and shoot photograph taken using each of the three metering modes.
Centre-weighted
Multi-pattern
Spot reading from dark area (trees)
Spot reading from light area (snow)
Notice how all but the spot reading taken from the trees has resulted in dark snow. And the spot reading from the trees has resulted in the trees being slightly over exposed with bright snow that lacks detail. Three types of metering and all failed to give the perfect exposure in this scene. Fortunately with digital photography, if your exposure is close you can tweak the levels, brightness & contrast, highlights & shadows or curves using image editing software and end up with a better photograph. Below is a slightly tweaked multi-pattern shot that's lightened the snow just enough to hold detail, while keeping the trees naturally darker than the spot reading.
To get the scene right in camera you have to override the meter to ensure the subject is recorded faithfully. That's why you may have read that snow needs more exposure - nearly two stops! The good thing about digital is you can shoot and view the result on your LCD screen and if it's too dark or too light, adjust the exposure using the manual settings or exposure compensation dial.
Members photos with related tags: Snow
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