# Canon 5D III and Zeiss lenses: focusing screen?



## Niels123 (Jan 27, 2015)

Since a couple of days I own the Carl Zeiss Apo Sonnar 135mm f/2  
	

	
	
		
		

		
			





Wonderful lens, but focusing at f/2.0 is extremely difficult, even when using the green focus confirmation dot in the bottom of the viewfinder. Focusing using live view is cumbersome and quite slow.

1) Is it more accurate / easier to focus using a focusing screen?
2) Which type of focusing screen would you recommend?
3) What is the best place to order this? Officially, it is not supported by Canon to change the screen for the 5D III (only for the 5D II), but there is screens available including installation instructions, for instance here: Focusing Screen with installation instructions here: Canon EOS 5D Mark III  Focusing Screen Installation Instruction

Experciences, suggestions, help, ideas and thougths are greatly appreciated!  
	

	
	
		
		

		
		
	


	




Niels


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## TCampbell (Jan 27, 2015)

My 5D III has the stock screen.  My 5D II has the super-fine focusing screen.  There are a couple of issues when swapping screens.

First and foremost... changing the screen changes how much light can pass through the screen and THAT changes the metering in the camera.  Canon compensates for this on the 5D II by providing a Custom Function to let the camera know which focus screen is installed so that you continue to get accurate metering.  As the 5D III wasn't intended to have user-swapped focus screens, it has no custom function to let you change it.  You might want to look into that a bit... because I suspect you may get inaccurate metering once you change the focus screen.

Second... Canon's superfine focus screen (which works extremely well on my 5D II) is intended only for lenses which are f/2.8 and faster.  This means you when you take that nice Zeiss f/2 glass of your camera and attach something else... will it still be an f/2.8 or faster lens?


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## Niels123 (Jan 27, 2015)

Thanx for you fast reply Tim. All my lenses except the 24-105 f/4 L are 2.8 or faster. All, except this one... f/4 is still not that bad, do you really need f/2.8 or is f/4 also okayish for the superfine focus screen?

How much light do you loose on the superfine focus screen? Is it a full stop, half a stop or less? Do you really notice this on f/1.4 canon glass (with autofocus) when you look through the viewfinder in dim lid situations (e.g. in a night club)?


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