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February 06, 2008
[ HELP, MY CAMERA IS AN IDIOT–PART 2 ]
CAMERA AUTOMATION has reached some sort of loony extreme with the introduction of Smile Shutter – the setting that allows you to depress the shutter, wait for the subject to smile and then the camera fires itself. Henri Cartier Bresson can eat his heart out over this innovation. From now on the camera will choose the “decisive moment”.
On one level it is all harmless gimmickry, but on another these extravagant automations raise the customer’s expectations of what cameras can do without intelligent human input. We have already covered the unreasonable expectations of automatic focussing systems, and the other day an email came from a reader who is disappointed with her automatic exposures.
L writes: “Having previously had two Pentax cameras I had faith in buying my first digital SLR – the Pentax K100D. But I have found the default settings a problem when photographing scenes and landscapes with sky. The sky tends to get bleached into over exposed white. A lot of photos seem to come out over exposed. I would really appreciate any ideas or tips on how to alter the settings to improve results.”
We expect too much from the automatic exposure system in a digital camera. Take the case of the over exposed sky.
There is usually foreground underneath the sky. So what is the camera going to "see" as the photographer's priority area? The dark foreground or the bright sky? The dynamic range between the darkest and lightest areas of the picture is huge -- in fact much greater than a digital sensor can cope with. So you have to make a choice -- expose for the sky or for the foreground?
If you want a rich blue sky with big fluffy clouds then you will have to over-ride the auto exposure and underexpose the picture. But if you want detail in the foreground -- say in a subject's face or the detail of a building or the landscape -- then you will have to over expose the sky.
Or, set Spot metering, take a reading from the sky and another from the foreground and then set the exposure manually to an in-between setting.
Digital cameras, like L’s Pentax, all have an Exposure Compensation button. Using exposure compensation you can experiment with different settings, usually between two stops under- and two stops over-exposed. A digital picture is free, so you just keep taking them until you get it right.
Back-lit photos are particularly difficult for cameras to judge. The camera tries to preserve detail in the bright light behind the subject, but this then seriously under-exposes the subject. A back-lit head will have a face in deep shadow if the camera is left to make the decision. In this situation set the camera to spot metering and take a reading from the subject’s face.
Open shade is also difficult for automatic exposure systems. The tendency is to over expose a subject in shadows. Wind the exposure compensation down 1 EV and the camera will do better.
The eye is much more tolerant of wide dynamic ranges of light and dark than a camera sensor. The eye can perceive detail simultaneously in deep shadows and bright highlights that a digital sensor cannot “see”. Sensors have double the dynamic range of film but only half that of the eye – in other words they need intelligent assistance.
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Posted by terry at February 6, 2008 09:55 PM
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