As a hobbyist photographer owning a DSLR camera, I’ve been asking myself every now and then why there is a moving mirror inside my camera. You know, the one that gives the camera its name (SLR stands for Single-Lens Reflex camera). I mean, I understand why they put the mirror in film cameras, but not why it’s still there in digital cameras.
After all, the whole point of SLR was to present the frame precisely as it will be captured on film through the real lens, as opposed to having a separate viewfinder. This way, the photographer can adjust the focus and sees the image change for real, and also how zoom affects the frame. In short, the mirror’s job was to send the actual image up to the viewfinder.
And then came the digital sensor. All of the sudden, every cheap point-and-shoot camera shows the wannabe-photographer the image exactly as it’s going to be captured on an LCD screen.
So here comes the question: Why is this old-fashioned mirror still there in professional cameras? Why aren’t camera manufacturers putting a small but high-end LCD screen inside the viewfinder, as they do with these semi-DSLR cameras (except for a small niche of cameras)? The use and feel would be exactly the same, only you’re watching a rendered image instead of a direct optical link.
It’s not like somebody does the focus manually, and needs to see “a sharp image” in the viewfinder (except for a few who install those split prisms). Let’s face it, focusing manually based upon the sharpness in the viewfinder alone is a recipe for a blurry result.
Let’s see how an LCD-viewfinder on high-end cameras change things:
- Reliability and durability: It’s well-known that mechanical parts, and moving mechanical parts in particular, are the weakest link in any electronic device. With the mirror removed, it’s possible to design a significantly more reliable camera with no moving parts in the camera body.
- Dust on sensor: The mirror moves and creates dust which accumulates on the sensor’s surface. Without the mirror, it would be possible to install a protective glass window so that the sensor would reside in an isolated environment.
- Focus: Today’s DSLR cameras have these special focus points, which are essentially small image sensors feeding an image processor, which in turn determines how sharp the image is. In an LCD-viewfinder arrangement, the real sensor would be exposed all the time, so there wouldn’t be any need for special focus sensors, and focusing could be done on any spot (as opposed to a limited number of points).
- Price: An LCD screen is cheaper than the optics, motor, mirror and focus sensors necessary to maintain the SLR arrangement.
- The critical moment: With an LCD viewfinder you don’t loose touch at the moment of shooting. On the contrary, the camera may even show you a quick snapshot of the captured image, which is very helpful when using external flashes (did all of them fire?) or when the subject is moving quickly.
- Night photography: When shooting at night (long exposure or with flash), it’s pretty common that one sees nothing in the viewfinder. With an LCD viewfinder this doesn’t happen, as we know from cheaper cameras: The camera responds to the low light with a longer exposure time and/or amplification, resulting in a low-quality image in the viewfinder, but good enough to work with.
- Vibration during shooting: In some cases, the small vibrations caused by the mirror’s motion may have an adverse effect on the image’s quality.
- Overhead photography: Sometimes there’s no choice but to shoot with the camera away from you. Journalists raising their camera over a crowd, for example. The irony is that some semi-DSLR cameras have an adjustable LCD screen, so you can point the screen towards yourself allowing precise aiming and focusing even when the camera is above your head. DSLR cameras, on the other hand, may sometimes support a live view on the LCD screen, but it’s clearly not intended for serious shooting. And an adjustable LCD screen is not something one could think about, even though journalists would surely find it useful.
So all in all, there are several substantial advantages to removing this mirror and putting an LCD screen in the viewfinder instead. Apparently, there is no disadvantage in doing this. So why isn’t this the mainstream trend?
I suppose the answer lies in this post’s title. Camera manufacturers know their market. “SLR” stands for quality and professionalism, regardless of being an obsolete technology. It’s mixed with high-end optics, the ability to control the shooting parameters and switching lenses. And the fact that it makes the camera more expensive and harder to reach for amateurs is not necessarily a disadvantage.