![]() This comparison is intended for reducing noise before you do anything else to it in order to retain faint stars and nebulae. What we are doing in this step, is called pre-processing: creating a single file which you can work with in your favorite image editor. We will work with Adobe Lightroom as a hub to find, compare, and eventually process the image. We'll eventually compare stars in a dark area, a nebula-rich area in the Milky Way, and in the foreground with high contrast to the light polluted sky. That keeps the light-polluted horizon well within the histogram and certainly works wonders for noise reduction purposes. Let’s say we don’t bump the ISO all the way to 12,800, but settle for a stop less at 6,400. The maximum setting on the D750 will overexpose the city lights on the horizon (light pollution), so we avoided maxing out the camera. Above that range, the signal will be amplified once it's been recorded by the sensor. At any lower setting than 100, that signal is attenuated. The camera used to capture an image to test the capabilities of noise reduction software was the Nikon D750, with a native ISO range of 100-12,800. ![]() While both record a value of 30%, neither of those will ever reach 100%, because of Earth’s day and night cycle. Now, consider that at the end of the exposure, our planet has rotated and the sky seemingly shifted one pixel. Let’s say a pixel recorded about 30% of its capacity. The electric charge recorded over the exposure time multiplied by the ISO-setting is a measure for how bright that star actually is. A photodiode, a piece of a pixel on a camera sensor, translates the brightness of that star into an electric charge. As it progresses along the night sky, its image is projected upon the camera sensor. Think of a star that at the beginning of the exposure is in one place. The 500-rule is a better rule of thumb, but for the sake of the argument, think more along the lines of a 300-rule if the Milky Way is the subject for your full-frame. Even a shutter speed of 20 seconds with a 14mm lens on a full-frame body is really pushing it in terms of preventing star trails. While this may be the case when your composition includes either celestial pole, it is definitely not the case when you capture the galactic core of the Milky Way. So, if I shoot at 14mm, this “rule” will tell me that I can expose for up to 43 seconds until the stars appear to trail. The rule of thumb is the 600-rule, which states that if you divide 600 by your focal length on a full-frame camera, the maximum shutter speed in seconds pops out at the other end of the equation. Just skip to ISO and we’ll catch up there. If you can follow along, this next part may appeal to you. To make a long and complicated story short: An increased exposure doesn’t necessarily mean more and brighter stars. To avoid star trails, there’s a rule of thumb going around the internet, but I’ll warn in advance that there’s more to it. But we can’t expose for the stars any longer, since the rotation of the Earth will stretch them from pinpricks to streaks across the sky. We want to increase the signal-to-noise ratio. ![]() In which other genre do you max out the ISO as well as the shutter speed for almost every shot? Anyway, raw converters and Photoshop plugins will help to reduce noise, but what we really want is to increase the exposure of the stars in these nightscapes without increasing the noise. I'm choosing to compare those tools on a nightscape image, because its typical usage scenario is almost always the same. There are many tricks and tools available to enhance the quality of our images, about as many as there are genres in photography. In fact, I would love to learn which current software reduces noise the best myself. I’m just a regular landscape photographer who happens to shoot Nikon. Methodįull disclosure: I’m not affiliated with any brand or software developer. “Expanse of the Night.” Shot with a Nikon D750 with a Samyang 14mm f/2.8 IF ED UMC Aspherical Nikon AE (Rokinon, Bower, Walimex: they’re all the same, just rebranded).
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