How do I clear or brighten the optical viewfinder?
My Canon EOS 70D has a dim optical viewfinder. It is so dim that the exposure metering in the viewfinder overexposes by nearly three stops. I can compensate with exposure compensation, but the optical viewfinder is still dim. I would rather fix the problem than patch it over.
I have reset all of the camera’s settings and updated to the 1.1.3 firmware. The battery is fresh.
Nothing in the optical viewfinder looks or sounds loose. Both mirrors in the mirror box are present and unobstructed—nothing there looks or sounds loose. The focusing screen looks correct and properly seated. Nothing looks out of place when looking through the optical viewfinder to compose a shot.
Each metering mode produces the same overexposure.
Live View works fine. The same lens, with the same focusing distance and the same aperture produces correctly exposed images. There does not appear to be any problem with the lens. There does not appear to be any problem with the main sensor.
It looks like the problem is entirely inside the optical viewfinder.
I am wondering whether a focusing screen from another model of camera could have been put inside, since only the focusing screen and the mirrors affect how much light gets bounced up into the viewfinder.