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I like to use live preview mostly but when I use the viewfinder, the shutter clicks considerably faster. I think is has something to do with the SLR technology, not just settings. Why slow performance in live preview?

EDIT: I am aware of the slower auto-focus in live-preview but even in manual focus mode, there is a considerable difference in operation. Feels like the shutter takes longer to "start taking the photo".

PS: I've a Nikon D5100.

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2 Answers 2

up vote 15 down vote accepted

There is more shutter lag because the shutter has to close first before opening again to expose the shot. When you turn on live view, the mirror is raised and the shutter is opened, so the image formed by the sensor can be fed constantly to the LCD. When you take a shot in live view, the shutter closes again to 'reset' the sensor before the actual exposure is made.

When shooting with the viewfinder, the process (simplified) is:

Press button -> mirror lifts -> shutter opens -> light hits sensor which registers it -> shutter closes

When shooting with Live View, the process is:

Press button -> shutter closes -> sensor 'resets to 0' -> shutter opens -> light hits sensor -> shutter closes

Essentially, the mirror lifting is a quicker process than the shutter closing and the sensor 'resetting'.

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1  
OK. What I make of it is this, and correct me if I'm wrong: when I'm using live view, the sensor is being used even before taking the picture, to show the preview on the screen. The camera is essentially taking a photo and showing it on the screen [around] 30 times a sec. When I ask it to click a photo, it first has to clear the sensor whereas in viewfinder, the sensor wasn't in use at all! so no need to clear it. –  BlueFlame May 6 at 8:55
    
@BlueFlame precisely correct. –  Philip Kendall May 6 at 10:00
    
Correct. I'll clarify that in my answer, actually. –  ElendilTheTall May 6 at 12:57

It's probably mostly about the autofocus. The live preview mode uses the same kind of contrast detection autofocus as almost all compact cameras; this can be considerably slower than the phase detection autofocus system used with the optical viewfinder. If you switch to manual focus, you should see an almost-instant shutter delay in both modes.

For more information, you might want to take a look at the following questions:

What is the practical difference between phase-detect and contrast-based autofocus?

What are the technical differences between using a DSLR viewfinder and live view?

Using the viewfinder has also other advantages in addition to fast autofocus; perhaps most importantly, it gives the camera another point of support (your head), reducing camera shake.

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Edited the ques. it's not the autofocus. –  BlueFlame May 6 at 8:46

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