Use mirror lock-up for astro shots
WHEN YOU LOOK THROUGH YOUR viewfinder, the light you see has passed through the lens and reflected off the camera’s mirror up to your eye. On pressing the shutter button, the mirror has to briefly flick up out of the way to allow light onto the sensor – that’s why the viewfinder momentarily goes black. The problem is, this mirror movement sends tiny vibrations through the camera, which can lead to a lack of sharpness in images. In normal day-to-day shooting, these vibrations have no practical impact at all, but they can be an issue when using shutter speeds slower than 1/20sec. This means astro, macro and landscape photographers need to take measures to combat the problem.
On most cameras there are now two ways you can do this. The first is mirror lock-up, a function that allows you to flick the mirror up before you take the shot, giving any vibrations time to die down. On a Canon, activate mirror lock-up in the menu, press the shutter button once to flick the mirror, wait a second, then press it again to take the shot. On a Nikon, mirror lock-up is sometimes in the menu, and sometimes on the Release Mode dial, marked MUP.
The second option is to shoot in Live View, and combine it with the Quiet/Silent Shutter function, the latter of which tends to be slightly better as it uses an electronic first curtain, so there’s no movement of the shutter mechanism. Live View is a bigger drain on battery life, but both options will slow down your shooting speed, so aren’t ideal for day-to-day shooting.
Above Mirror lock-up or Live View with Silent Mode will help reduce internal vibrations that could cause blur.