You can either use a star tracker with very long shutter speeds to capture a lot of light and thus a high signal to noise ratio, or you can use star stacking, a method of capturing multiple photos with shorter shutter speeds that are then aligned and averaged in software to reduce noise. Noise reduction tools these days are great, but they can’t fix everything all the time.įortunately there are ways to capture both pinpoint stars and achieve low noise. If you try shooting with a short enough shutter speed to capture completely motionless stars, the noise level can be so high (depending on your camera and lens f-stop) that the exposure is either unusable or needs a ridiculous amount of noise reduction, resulting in large size prints that can look very grainy or blocky due noise or noise reduction. The result is that you’re usually shooting with a shutter speed that captures enough light for tolerable noise, but it’s also probably long enough that the stars trail in the frame. So you’re stuck using a shutter speed that isn’t long enough to capture enough light for a high signal, and having to use a high ISO as well to boost the signal to a usable level, which can add additional noise to the image (although how much depends on your camera).
However, when shooting the Milky Way you’re usually going for short star trails, or completely pinpoint (trail-less) stars, which means you’re limited in how long you can expose before the stars appear to move too much in the frame. A higher signal will result in less noise even with a high ISO (depending on your camera, modern sensors are much better). If you exposure for a longer period of time, you’ll capture more light, and have a higher signal to noise ratio, meaning less noise. But the noise isn’t all just from the high ISO. If you’ve done any night photography, then you’re likely very familiar with the noise of exposures in low light using a high ISO. The green color in the sky is from airglow. The Milky Way rises over a fairly intimate canyon view in Canyonlands National Park in Utah.
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