Tuesday 30 June 2015

Why is the battery required to manually focus through the viewfinder?



Is it normal that I can't manual focus any of my lenses on my 5D MK iii without having a battery inserted? I can focus on an object, and while looking through the view finder, remove the battery and instantly the image will get darker and blurrier.


Is this normal behavior? If so what's going on here?



Answer



Yes, it's normal behavior. The reason you're having problems is that the 5DMkIII has an LCD overlay in the viewfinder. This overlay is used to give you grid lines you can turn on and off and different AF point displays. Without power, the LCD becomes opaque. This behavior is identical in Nikon cameras with an LCD overlay in the viewfinder, and has long been noted.


From the Canon Learning Center's article on the 1DX's & 5DMkIII's intelligent viewfinder display:



The LCD overlay does require a tiny amount of electrical power to operate. This is obviously no concern when the camera is turned on, but if the battery is removed the transmissive LCD suddenly loses a lot of brightness and contrast. This is perfectly normal and will return to full brightness once a battery is reinstalled in the camera (the camera doesn't have to be turned on; it only requires a functioning battery pack to draw power for proper viewfinder operation).



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