Astrophotography 101 - Critical Aspects of Nightscape Photography - Cameras

In terms of cameras, if you own a camera made in the last 5-8 years you have a perfectly capable piece of equipment. These days there are very minimal differences between manufacturers when it comes to producing cameras which deliver high quality Nightscape results, there is absolutely ZERO reason to break the bank on a camera body in 2020. Even APS-C cameras made in that time are absolutely solid performers, some of my favorite images in the last 2 years have come from a used $300 Nikon D5300 paired with a relatively cheap (but absolutely awesome) Sigma Art 18-35mm f1.8 lens. The bulk of your budget should be spent on a higher quality lens vs a more costly camera body.


People will give you terms to consider when it comes to buying a camera, things like Dynamic Range (DR) and read noise are the most common. Let’s consider these elements and how your camera settings will impact them:

Dynamic Range: This is the range of light that any given composition has, from the very brightest element to the very dimmest element in a scene. If you point your camera outside on a sunny day, away from the sun, you will have a very standard DR. If you take a picture of a hillside on a cloudy day you will have a very small dynamic range. If you point your camera towards a setting sun you will have a very large DR, the range of light going from the very very bright sun to the very very dim foreground. Likewise, Nightscape images have the most extreme DR possible, stars and other interstellar objects are EXTREMELY bright objects buried within a VERY dark background and chances are your foreground is very dim. In any given exposure you are very likely to clip highlights (meaning you cannot recover the color information from a bright light source) and clip shadows (meaning you never collected signal and can’t recover shadows). So when someone talks about the DR of your camera what they are talking about is the ability of the camera to collect signal from the very brightest light sources to the very dimmest objects and not clip/lose information. More DR means that the camera gives you the opportunity to execute an exposure without losing either highlight or shadow information. As you increase the camera’s digital gain (ISO) you decrease the DR of the camera, what this means is that as you increase ISO you have to be more careful with your exposure settings in order to not clip highlights or shadows. I refer to this as your “window of opportunity”.


Having a large DR (by virtue of shooting at a lower ISO) does not mean you are guaranteed a great, noise free image. It just means that you have a larger “window of opportunity” to execute an exposure without losing information. At a higher ISO setting you will have a smaller DR, you can still collect the maximum amount of dynamic range from a composition (such as the colors of bright stars and dim shadows detail) without clipping, but your leeway in terms of exposure length is much shorter. At ISO 10,000 you may only have a few second exposure range to work within, 10 seconds might be perfect for capturing the entire dynamic range of the composition while 12 seconds is too long (thus clipping highlights) and 8 seconds is too short (thus clipping shadows). At ISO 1600 your exposure window will be substantially wider, a 10 second exposure might be perfect for capturing the entire dynamic range while 18 seconds is too long and 2 seconds is too short.


So the easy thing to say is “shoot at the lowest ISO” to maximize DR, right? Well, it’s not that easy, the other factors to consider are sources of noise caused by the sensor technology in your camera. Some sources of noise come from converting the analog signal (photons of light) into digital information, generally this noise increases as you increase ISO. Another source of noise, read noise, can be variable across the ISO range, sensor based read noise in some sensors is HIGHER at lower ISO levels and drops as you increase ISO. In other sensors the read noise remains relatively constant across portions or all of the ISO range, these sensors are called “ISO Invariant”.


ISO invariance is a source of confusion and debate for many, the fundamental aspect of ISO invariance is simple: at a certain ISO level the read noise of your camera sensor remains (relatively) constant no matter how much higher your raise the ISO beyond that point. What this means, in terms of “exposure”, is that there is zero perceivable difference between taking a picture at ISO 6400 vs taking a picture at ISO 1600 and then later on raising “exposure” +2 in post processing software. There are caveats that come with this, of course, but the basic thing to understand is that with some cameras you should always shoot at the ISO invariance point and develop exposure, brightness, and contrast to “taste” in post-processing. The main thing to understand, however, is that you still need to execute an exposure that gathers enough signal to swamp all possible sources of noise, whether that noise is generated by the sensor or your post processing later on. Remember, the brightness of the scene will look the same in an ISO 6400 shot vs an ISO 1600 (+2 Exp) shot, but so will the noise. So getting good SNR with a proper exposure at the time the photograph is taken is paramount. What shooting at the lower ISO and boosting exposure in post processing does is give you is more “window of opportunity”, as described earlier, by virtue of having a higher DR.


Realistically there are far too many different cameras and sensors and lens combinations to give a “one size fits all” type of recommendation in terms of settings. I highly recommend reading about your camera’s testing results at a place like Bill Claff’s website (www.photonstophotos.net). There are some broad generalizations that can be made in a few regards, however:


1)  Canon sensors are not ISO invariant, for the vast majority of Canon cameras the sensor will deliver best results at ISO 1600 or 3200, going lower than that will dramatically increase sensor read noise and during shadow recovery you will experience worse noise than if you had shot at the higher ISO. The “break even” point in terms of good DR and lower read noise for most Canon cameras happens around ISO 1600 or 3200.

2) Sony sensors (which are almost universally found in Nikon, Fuji, and Pentax cameras these days and obviously Sony cameras) almost always have an invariance point and should be shot at that point. Some modern Sony sensors have what is called dual gain, mean they actually have two ISO invariance points, my Nikon Z7 for instance is ISO invariant from ISO 64 to 350 and then invariant from ISO 400 up to the maximum ISO. Consulting Bill Claff’s website is the easiest way to find your camera’s invariance point if it has one.


So, the TL;DR of this story so far: Find a high quality lens, with an aperture in the f1.4 to f2.8 range which is mostly free of Coma, LoCA, and decentering while being as sharp as possible.