On Mon, 29 Jun 2009 18:05:50 +0200, Darren New <dne### [at] sanrrcom> wrote:
> Fredrik Eriksson wrote:
>> It means there is a mirror in there.
>
> Fair enough. One has to wonder why there's still a mirror in there. :-)
>
> My Sony lets the light hit the sensor, then puts the display in the  
> eyepiece.

Your D90 can do this too, though the image is displayed on the back LCD  
instead of in the viewfinder.



> You don't have to screw around with a whole bunch of internal mechanics,  
> waiting for the mirror to get out of the way, trying to draw fancy stuff  
> on the viewfinder without having to do things screwy. :-) No left-overs  
> from mechanical days.

The main drawbacks of not having a mirror are that you cannot have a  
through-the-lens optical viewfinder or phase-detect autofocus.



> I'm still not sure how the thing autofocuses without interrupting the  
> light. I can only guess it's using a half-silvered mirror, and hence the  
> prohibition against linear polarizers.

Actually, there are two mirrors. The big one is indeed semi-transparent.  
Most of the light is reflected up towards the viewfinder and exposure  
meter, and the rest goes to the smaller mirror which reflects the light  
down towards the autofocus sensor. Linear polarisers can mess with  
exposure because they can alter the proportion of light that reaches the  
exposure sensor.



-- 
FE

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