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May 10, 2007
[ THE CURSE OF THE LAGGING SHUTTER ]
DPEXPERT'S EARLY EXPERIENCES with digital cameras did not inspire confidence in the new technology.
One of the first digicams to come our way for review was the Nikon Coolpix 5700, one of the early super zoom pseudo SLRs. This type of camera has an electronic viewfinder rather than the mirror and prism optics of a true single lens reflex. We took one look at the 5700 and wanted it. And then we used it.
We were perplexed. Why could we never capture in the photograph what we were seeing in the viewfinder? Why had the subject disappeared in the short time between pressing the button and capturing the image on the sensor? It was our introduction to shutter lag.
Canon had the same problem with their Powershot Pro 1. Fuji and Konica Minolta were not doing any better. What was going on?
There was a suggestion that the problem could be cured by using the technique of half-depressing the shutter release to lock focus and exposure and then, when the moment was right, pressing the button all the way. But on some cameras the image in the viewfinder froze for a fraction of a second and when it unfroze the subject had moved. That was no solution.
It was also suggested that pre-setting the focus, white balance and exposure manually and using the digicam as though it were an old film camera would do the trick. Why bother?
One chap with a Fuji pseudo SLR keeps the camera on burst mode, figuring that if he takes enough shots when he presses the button one will turn out well.
While shutter lag was once a particular problem on these long zoom cameras with electronic viewfinders – most recent models are more responsive – it has also plagued ordinary digital compacts. The delay – which is only a fraction of a second – is caused by the time that it takes for the camera to set focus, exposure and white balance and to send a corrected image to the LCD screen before switching the sensor off and on to capture the picture. True single lens reflex digital cameras (with a couple of exceptions) do not display the image on the LCD in preview mode and therefore do not need to pre-process the picture. They also do not use the sensor as a light meter and their autofocus lenses are faster, all of which reduces shutter lag. The mechanical shutter in an SLR may also be faster than the electronic shutter in a compact, although there is some argument about this.
All compact digital cameras have some shutter lag and it can be measured. The best objective reviews report lag in fractions of a second. There is a useful comparison table for a range of cameras at this British photo magazine site.
However, the testers typically measure the lag after the button has been half depressed. This is misleading. With the Ricoh, for instance, there is no lag after the button is half depressed, the problem occurs when the button is pressed to the detent. The image on the LCD freezes and when it unfreezes the child or bird has moved. When assessing a camera in the shop that is the phenomenon to look for.
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Posted by terry at May 10, 2007 12:40 AM
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