Why is Live View so noisy and unlike mirrorless shooting?

Question

Why I enter "Live View" on my Nikon D5100, the mirror is locked up and I see a live view of whatever the CCD is seeing on the articulated screen just like a mirrorless system.

But when I go to take a picture, suddenly the screen shuts off, and I hear four separate noises. It sounds like the mirror is being lowered, then the shutter which has a kind of double "chaching" sound, and then another mirror which sounds like the mirror being lifted again.

But this makes no sense to me! The mirror has to be lifted to enter live view, as well as to take a picture. The shutter already has to be open for the sensor to capture light to be displayed on the screen. The image is already hitting the CCD as seems evident by the fact that it is being displayed on the screen. So why do I need to hear any noises at all? It's needlessly loud and delays the shot a bit. It seems like it should just record the shot. If I record a video it just does it without any extra delays or noise.

I looked in the manual and it says the screen will go off while the shot is being taken, but there wasn't any mention of this other nonsense. Why is this happening and how do I make it stop?

Answer 1

It's because on a (Nikon) DSLR, live view is part of the video stream with rolling shutter. This stream is usually not in a raw format and is typically reduced resolution. Some Nikon's have a "silent live view photography" menu option that allows recording a video frame w/o switching into still mode (mirror/shutter fixed).

In order to switch back to full resolution stills mode (w/o rolling shutter) the sensor has to be cleared, recharged, and then re-exposed to the light; the shutter typically closes in order to block the sensor from light during this sequence. And the shutter/mirror typically cycle together with the same input signal... because they normally should. On older/lower models the mirror also has to cycle in order for the lens to stop down (e.g. if the aperture was changed while in live view)... these cameras do not have live view exposure preview capability (for the same reason). Later models only cycle the shutter (e.g. my D850).

But this doesn't have to happen exactly this way... the Nikon D850 is the first Nikon DSLR that allowed full resolution raw stills w/ silent photography (live view video stills). This is really a result of more advanced video capabilities and it still involves the rolling shutter. I think the D4 allowed full resolution stills in jpeg format... I don't know all of the specifics, but it's safe to say you'll probably have less capability with older/lower models.

And I used to tape the mirror up on my D300 to prevent the mirror cycling/slap during live view photography; but I can't really recommend someone do the same.

Answer 2

On a DSLR, when you use the viewfinder, the mirror is lowered, and a secondary mirror reflects some of the light to phase-based AF and exposure sensors at the bottom of the camera. These are accurate and fast.

When you use live view, the AF is contrast-based AF (the camera lens hunts until it find a position that maximizes contrast). This is slow (in your camera, likely much too slow for a moving object) and not too accurate.

So, when you take the picture, it can make sense to shortly lower the mirror again to use the faster and more accurate phase-AF sensors (and possibly the exposure sensors).

More recent cameras can have a better AF that uses the main sensor alone (for instance, the Canon cameras have "dual pixel" sensors that act as phase-based AF sensors), and may not need to switch to the external sensors.

Answer 3

Because in the Nikon D3x00 and D5x00 series, as well as many previous entry level Nikon DSLRS and pretty much all Nikon 35mm film SLRs, the same mechanical motion actuates the mirror assembly and the aperture linkage. Once the mirror is up, the aperture can not be changed from the body. This worked fine when the mirror was always down until just before a photo was captured.

With the advent of Live View shooting, it's proved to be not quite as elegant a design.

If the aperture needs to be changed from what the camera is using for Live View, the mirror must cycle to change the aperture. Just one of several legacies from the pre-autofocus era that remained in Nikon AF film SLR bodies and digital SLRs for many generations of products in an attempt to keep all legacy F-mount lenses compatible with the newer cameras.

Only within the last half decade has Nikon started to adopt in earnest new ways of controlling the aperture electronically instead of mechanically. This has come at the cost of some newer bodies not being compatible with older F-mount legacy lenses. They straddled the fence for many years with their upper tier bodies by separating the mechanical actuators for the mirror from the actuators for the aperture, but continued to use the legacy design for the lower tier bodies such as the D3x00 and D5x00 series.

Answer 4

It sounds like you might be leaving a critical piece of information out: Under low-light conditions?

I've never owned a Nikon DSLR but it's probably because the live view has to refresh often (e.g. at least 24fps if not faster), so it boosts the ISO very high to be able to get shorter samples. Hence noise. It's probably also skipping any post-shot processing, but that's probably inconsequential next to the ISO issue.

But when it takes the actual photo, it's leaving the shutter open long enough to get a lower-ISO shot.

As to why all the extra noises, I can't actually answer that specifically for that camera, but can address it more generally. SLRs are evolving. The early Sony a7 series, for example, could be set up to take pictures while only engaging half of the shutter (front or rear curtain, user choice). This eliminated half of the noise. But you also lost some other capabilities. With newer a7 models, you can disable the shutter curtains entirely, relying 100% on "electronic curtain", which is essentially silent. (The a7 is also mirrorless, so it doesn't have that noise anyway.) Currently there are some inherent limitations with lack of shutters, but those are likely to be resolved in the future.

Personally I like the mirror "thunk", though it does add vibration. I also like the shutter noise when I'm shooting alone and noise isn't an issue. (Otherwise I prefer to be less conspicuous and moment-interrupting.) But the industry seems to be evolving away from both, or at least a physical shutter. Many cameras currently are in an in-between place.