I've often wondered if the E-M5 (or any other camera with an EVF) would experience viewfinder light leak during a longish exposure. While not having the mirror box of a conventional DSLR, would the camera somehow absorb enough light to affect the image through the EVF viewfinder window? I've just attended a seminar where the lecturer adamantly insisted that the viewfinder window on ALL camera's should be covered. I ask this because covering the window is one thing which I consistently forget to do although (I think) my images look fine anyway. Are there any optical engineers out there that can answer this question? Thank you in advance, John
There is no optical path to the viewfinder in a mirrorless camera so they shouldn't be affected by viewfinder light leaks.
I would seriously doubt the validity of the lecturer if they don't understand that an EVF has no direct light path to the sensor. The only "light leak" i've ever heard of in a mirrorless camera was the Fuji X-T1, where the accessory port panel could allow light into the camera body if you had the cover panel off for whatever reason(AUX power or remote trigger).
"I would seriously doubt the validity of the lecturer if they don't understand that an EVF has no direct light path to the sensor." Absolutely - scary what some people putting themselves out as "experts" know or don't know about m43....
Actually true, all OPTICAL viewfinders on dSLR cameras should be blocked *IF* you take your eye away from the viewfinder! That's because the sensor for measuring light is located usually above the optical viewfinder...if you look at the following cutaway of the E-400, you can see a second lens that goes to a circuit board: {} EVFs don't have this issue as the light reading is taken from the imaging sensor as there's no light path from the lens to the electronic view finder, it's electronic.
Yeah but that second prism sensor only operates when the mirror is down. It's completely disabled during exposure. It measured the light off the ground-glass. The problem is not what occurs DURING exposure, it's what occurs when metering while your eyeball is not pressed up against the viewfinder. Light coming into the viewfinder during metering would affect the chosen exposure. Nearly all of my cameras worked that way all the way back to my old Spotmatic. That sensor is not used once the mirror flips up. Minolta had something called CRC where the prism meter could detect the difference between the light in the prism and the mirror box and compensate. Everyone else used a viewfinder shutter. You only need to cover that viewfinder if you've got the camera on a tripod, or support of some sort, and you're metering a scene to take a photo, and you do not have your eye up to the viewfinder.
