Starry Skies Auto Focus Guide for Mirrorless Cameras

Starry Skies Autofocus Techniques with Olympus Mirrorless Cameras

There’s a lot of excitement surrounding the debut of the successor to the OM-D E-M1 Mark II body from Olympus and much of that excitement has to do with a feature unique to the world of digital photography; namely, the ability to autofocus effortlessly on stars in the sky even hand held. This is a wonderful feature in light of the fact that any number of accomplished astrophotographers will say that the most often heard question they receive deals with how to get sharp focus in the dark on tiny stars barely visible to the naked eye. The new Olympus OM-D E-M1 Mark III, representing the latest flagship camera model in the OM-D lineup since it’s first iteration in 2014, offers several features brought over from the larger E-M1X professional action camera introduced last year including this brand new feature: starry skies auto focus, and is the first camera to offer such a feature. A quick glance through youtube videos for photographing the night sky repeatedly presents topics related to getting good focus so we can assume this is a major hurdle. Kudos to Olympus for once again bringing a feature that tames yet another tedious process, as they did previously with Live Composite, Live Capture, Focus Stacking, and a long list of features some of you have forgotten ( TTL flash photography?)

The purpose of this article is not to draw attention to the camera you don’t yet own, but to explain how you might already have a camera that can readily autofocus on starry skies with but a little less convenience. That’s right. I’m saying you may already own a camera that you can, with proper settings, point to the sky and hand hold to take a perfectly exposed, pin-sharp focused, night sky. Want to know how? Let’s begin.

First let me begin by explaining what cameras I use and can verify these techniques work well with. You may have other models with similar capabilities but I’ll leave it up to you to figure out how to transfer the settings and techniques I mention here to those cameras. I have two Olympus OM-D E-M1 Mark II bodies and one OM-D E-M1X body. I’ve used these techniques successfully to do astrophotography with the following lenses: mZuiko Zooms: 7-14mm f/2.8 Pro, 12-40mm f/2.8 Pro, 12-100mm f/4 Pro, 40-150mm f/2.8 Pro; Primes: 8mm f/1.8 Pro, 17mm f/1.2 Pro, 45mm f/1.2 Pro, 75mm f/1.8, 300mm f/4 Pro.

Overview of what we’re going to do: we’re going to for the moment ignore everything you’ve learned regarding getting good quality clean photos of the Milky Way or tracking mounts for deep space objects and simply focus on how to set up the camera to see in the dark. Basically that ‘s what the new feature for the E-M1 Mark III does if you’re watching the videos. It’s doing automatically what we’re going to learn to do step by step. Obviously the camera has some advantages if it can do this pre-programmed compared to our stumbling through this in the dark, literally, but we can do a fairly good job of replicating what the starry skies AF mode does, with some limitations.

 

 

With the E-M1 Mark II I have assigned a custom set, C3, to be my base set for landscapes and nightscapes. Looking at the SCP we can observe it’s in Manual mode, C3, ISO200, 1/250, f/5.6 in RAW capture and sunny white balance (good for night skies since the sky if full of billions of suns). I will import this custom set into the PASM settings by turning the mode dial to M and then pressing the Menu button to access the Camera 1 menu, first item: Reset / Custom Modes, and select Recall from Custom Mode, slide to the right and scroll down to Custom Mode C3, press OK, and Yes.

Now I’ll make some settings adjustments and anything I change now will be ‘sticky’ meaning I can change modes, switch the camera off and on, and these settings remain until I change them. First I will adjust the ISO to 25,600. Then set shutter to 1” and the aperture to wide open for the lens that’s mounted. In this example I have the 8mm f/1.8 Pro fisheye lens attached so the widest aperture is f/1.8

Now for some other notes on how my cameras are configured. When I’m doing landscapes and astrophotography projects, basically any of the more tedious and methodical kinds of photography, I use back button focus so that there is no issue with the shutter button half press changing what I’ve set up carefully for focus. I’m using the lever AEL/AFL button be the autofocus button and the lever is set to be in SAF+M in position 1 and PreMF in position 2.

Photo of mode 2

Photo of A1 menu

My C3 custom set is stored with Preset MF distance set to 999.9 meters which tells the camera to set the lens to infinity when that lever is engaged. In addition I have the MF Assist turned on both Magnify and Peaking on. Both of these settings are in the A4 gear menu.

photo of A4 menu

Photo of button function

A couple of other notes: I have the Fn2 button assigned on all my cameras to the digital tele-converter. I also have the two buttons beside the lens mount on the front of the camera set to toggle Magnify and Peaking though we will hardly need them here, but fyi. I’ll be using the focus ring on the lens to activate Magnify if and when needed, to check focus.

photo of focus points

One last change: my C3 setup that I imported uses a single AF point for SAF+M, usually about 1/3 of the way up the screen because for landscapes it’s a good starting point for AF and depth of field issues. But here I want all points activated both in SAF+M and when the lever is switched to PreMF as well because the AEL/AFL Lever button will be able to override the PreMF setting if I want.

In this example I have the 8mm f/1.8 Pro attached and it is the most difficult lens to autofocus on stars mainly because it has the widest field of view of any native m43 lens with autofocus capability and it also doesn’t obtain sharpest focus with the PreMF setting as it overshoots infinity by a measurable margin and so it is paramount that the user follow some additional steps to ensure sharp stars.

The first thing to do is switch the lever to position 2 to engage PreMF and then point the camera to the sky and press the AEL/AFL Lever button to activate AF and for every lens but this one, it generally works and you’ll see one of the small green rectangles somewhere on your screen or in the EVF that the camera has placed over a star. If you grab the focus ring it should immediately zoom into that point and you may test to see if it’s at the sharpest point or needs a slight adjustment. Once you find the sharpest focus, you can release the focus ring and the lens is now ready.

You can then return the shutter speed and ISO to more reasonable settings and adjust the aperture if you want a smaller aperture for some reason.

As I noted above, this might not work with the 8mm. It is the only one I have that doesn’t consistently autofocus on deep sky stars even at ISO25600. Maybe a 2 second exposure would help but actually there a simpler way to handle this. Instead of pressing the lever button to engage AF, once you’ve switched the lever to PreMF, the camera lens is pretty closely focused on stars and so in this case I’ll engage the Magnify button on the front as well as peaking (I have it set to red light, which helps me see stars as they show up as red specks when focus is achieved) and with that magnify engaged, usually at 10-14x, I will slowly pan the brightest area of stars until one comes into view and it’s usually a fairly distinct orb but with some adjustment to focus, usually back in a bit, the orb will become a very distinct point of light.

With all the primes I noted above, except the 8mm, it seems that PreMF achieves perfect focus at least in these cold temps I work in. But I always check to be sure as it’s so easy when I hit the AF button and a green box shows up where the camera has selected a star to focus on, to grab the focus ring and instantly be taken to a magnified view of that star region where I can then check the focus accuracy. For this practice I usually hold the camera to my eye and use the EVF rather than the screen since it’s easier for me to hold the camera steady in one place and once I’ve gotten AF on a point I can tweak by grabbing the focus ring.

Zoom lenses are generally going to give most accurate PreMF at the wide end of the zoom but at the tele end you will find they generally overshoot the mark slightly and need to be dialed back with the focus ring just a tiny bit. This will actually vary with the ambient temps so what you find is the case in January may be different in July.

The newest primes, like the F/1.2 primes and the 300/4 seem to be able to nail AF whether in SAF+M or in PreMF. For one thing, they have narrower fields of view so the stars are larger. For the larger lenses like the 300/4, I still do this hand held but it’s also something I do when they are mounted on a star tracker during long sessions. Between a set of 100 takes I’ll reset ISO to 12,800 or 25,600 depending on the aperture, and a 1 or 2 second exposure and try and AF after switching the lever back to 1 and then to 2 to activate PreMF. I can always press the Fn2 button also, to activate the digital teleconverter and get a good look at things through the screen or EVF. At that magnification, it’s very easy to see the stars or nebula I’m trying to photograph and pulling the focus ring will zoom in so I can get perfect tweaked sharpness. Then I reset the ISO and shutter speed (and aperture as needed) for the photo session I’m conducting.

This may seem very tedious with so many words to explain how to do something so simple based on what the Visionaries have described with the new Starry Skies AF on the E-M1 Mark III as simply “well you point the camera at the sky after selecting that mode and press the shutter and once it achieves focus, it takes the pictures, and it’s accurate every single time.” However, in actual practice, this is nearly as fast, once you get the camera set up in the first place. And you have to remember to go back after focusing the lens to reset ISO and shutter for the image taking.

Summary steps:

  1. set camera for all points AF, PreMF to infinity, back button focus, MF activates magnify
  2. adjust shutter to 1 second approx. and ISO: 6400 for f/1.2, 12,800 for f/1.8-2, or 25,600 for f/2.8-4.
  3. If normal SAF doesn’t quickly hit focus (it will for most lenses) use the PreMF to get prefocus so stars are sharp and then manual focus to check or fine tune as needed.

I suspect this works best with pro lenses because of their acuity. I have not tested with non pro lenses other than the 75/1.8 which, while not a pro lens, is arguably the sharpest lens ever produced. Good luck and dark skies!

 

Here are two out of camera shots imported via Oi Share to the iPad and posted here to show examples using this technique last evening, February 14, 2020.

OLYMPUS DIGITAL CAMERA
OLYMPUS DIGITAL CAMERA

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