It should be at infinity?
I've always used a tripod and remote shutter release, I assume its manual focus in live view with the magnifier you're referring to right? What do you mean by mirror up?
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What I meant by "mirror up" is to select the setting where the mirror goes up and there is a delay before the shutter opens. This prevents the vibration of the mirror from ruining the sharpness of the shot, or, from another point of view helps to get a sharper shot.