I'm a fiend for low light photos. It's really striking to me how much light is wasted in a DSLR by bouncing it off the primary mirror into the viewfinder. I mean, obviously, you need to see what's going on, but I'd happily trade off something like a 50% dimmer viewfinder for 50% more ability to focus in low light. I wonder if there would be any possible way to take the mirror box out of a DSLR, use either some kind of chemical or mechanical process to strip off some of the reflective coating, and then put it back into the camera, resulting in a modified camera that has amazing low light focusing abilities. Or, perhaps just replace the primary mirror with a custom made piece of glass that has a lower reflectivity.
I guess the obvious drawback is now you have a camera that has a dimmer viewfinder but is modified to perform in the exact kind of conditions when you would WANT a bright viewfinder. I should probably just trust that Canon has already figured out the perfect reflectivity of the primary mirror to get both adequate viewfinder brightness but to leave enough light to get adequate autofocus.
I was also thinking about some kind of hypothetical super low light focusing mode where there's no modification to the mirror, but when autofocus on the camera begins, it flips only the primary mirror up, allowing all of the available light to reach the secondary mirror and focusing sensor. Then, as soon as focus is achieved, the focus point still blinks red, albeit on a totally black viewfinder, and you can snap the photo. This is probably way too much viewfinder blackout time for most people, especially in those crucial few seconds leading up to the moment a photo is taken. But honestly sometimes I'd take this sort of situation over having a viewfinder that I can see the entire time, but the camera just hunts and hunts for focus... It would be kind of a last-ditch effort autofocus mode for very low light situations.
I guess the obvious drawback is now you have a camera that has a dimmer viewfinder but is modified to perform in the exact kind of conditions when you would WANT a bright viewfinder. I should probably just trust that Canon has already figured out the perfect reflectivity of the primary mirror to get both adequate viewfinder brightness but to leave enough light to get adequate autofocus.
I was also thinking about some kind of hypothetical super low light focusing mode where there's no modification to the mirror, but when autofocus on the camera begins, it flips only the primary mirror up, allowing all of the available light to reach the secondary mirror and focusing sensor. Then, as soon as focus is achieved, the focus point still blinks red, albeit on a totally black viewfinder, and you can snap the photo. This is probably way too much viewfinder blackout time for most people, especially in those crucial few seconds leading up to the moment a photo is taken. But honestly sometimes I'd take this sort of situation over having a viewfinder that I can see the entire time, but the camera just hunts and hunts for focus... It would be kind of a last-ditch effort autofocus mode for very low light situations.