Shooting Stars

The Lyrids meteor shower got me interested in shooting stars again. I wanted to catch a meteor! I've been through somewhat of a learning curve, although I've shot stars before. I thought I would save some of you some hassle, and give you some ideas at the same time. These are some random thoughts on the subject, some quick answers and some pitfalls to avoid.

Click on any image to blow it up. I made them all about 1200 pixels wide.

We'll talk about how I captured and made these three images, totally different techniques.

Nikon D600, Nikkor 17-35mm lens at 17mm, 30 seconds at f/2.8, ISO 2500

Nikon D800, Nikkor 17-35mm lens at 17mm, 30 seconds at f/2.8, ISO 800.

Same exposure: Nikon D800, Nikkor 17-35mm lens at 17mm, 30 seconds at f/2.8, ISO 800. But I merged over 50 frames in StarStaX.

First of all, what equipment do you need? A camera with an appropriate lens, a tripod, and optionally but really important (especially for the 3rd shot), a remote cable release that locks. At the risk of restating the obvious, here's what you need to do:

• Find a spot where you have a relatively unobstructed view of the sky and where it's dark
• Dark means, well, DARK. In all three of those pictures, less so in the first one, there's light pollution in the sky. No, folks, that's not the vestiges of the sunset, those last two pictures were shot after midnight and the light in the sky is from the little town of Minden, Ontario, more than 10 km away.
• Put the camera on the tripod. Before you do, focus it to infinity (it's best to know in advance where infinity really is, in relation to that "∞" mark on your lens). Make sure you turn off autofocusing, VR or IS or whatever your camera maker calls it, and switch to Manual exposure. Turn OFF "Long Exposure Noise Reduction" (Lightroom, Photoshop and a myriad of plug-ins do it better). Point it at the sky.
• Attach your cable release. If you don't have one, you'll want to use the self timer in the camera to give it time to settle down before taking the shot. That won't work for the third shot above.
• Crank your ISO up to 4000 or so, shutter speed to about 10 seconds and aperture as big as your lens allows, and shoot a test shot. This isn't a keeper, it's a quick way to see if you've focused correctly, if the camera is level (the D800 has a built-in artificial horizon that really helps!) and if the composition is what you want. Move it around until you're happy.

If you want to shoot a static star field like the first image, you need to remember that, well, the earth moves. The distance that the star moves in your picture depends on how long the shutter is open and the focal length of your lens. The longer the telephoto, the more it seems to move. So a wide angle works best.

There's a little magic formula, called the "Rule of 600". Divide 600 by your focal length: example, a 50mm lens will give you "12" as the answer. But remember that if you have a cropped sensor, you need to divide that by the crop factor (around 1.5?) so that means 8 seconds. If your shutter is open longer than that, when you blow up the picture you will see star trails.

It's good to have something in the foreground. Here I painted the trees with a small flashlight while the shutter was open. I think the bright star is Venus, and the cluster above it is the Pleiades (did you know the Subaru logo is based on them?). D300, 12mm, 30 seconds at f/4, ISO 1600.

If you don't have a big aperture lens, here's where you're going to get in trouble: you're going to have to crank that ISO up really high to get a good exposure! Here's a starting point:

Aperture = f/2.8, Shutter Speed = 30 seconds, ISO = 1600. I'm sure you can do the arithmetic for your combination. See why that f/5.6, 55-105mm lens is going to get you in trouble?

I underexposed the second shot because I didn't want as many stars. Also there was more ambient light in that direction.

If you want to catch a meteor, you need infinite patience (or incredible luck!).

Here's what you need that locking cable release for. Whatever shutter speed you select, click the cable release and lock it. It will keep shooting pictures, one after another, until you unlock it. Go inside where it's warm, pour yourself a coffee (or a scotch), relax and come back later.

I set up the camera behind the house for about 40 minutes, doing a sequence of 30 second exposures which I later blended together in Photoshop (the technique is to stack multiple layers with "Lighten" blend mode. I did it in batches of 10 until I got all 74 images done). No meteors. But I did see 3 things in the images:

This image is 2 frames merged together. According to what I read, this matches the profile of a satellite. The middle is brighter because the sun reflected off a brighter part of the rotating satellite at that point. I was pointing roughly NorthEast which is consistent with the sun setting behind me. The image was shot at 9:53 pm, about 2 hours after sunset.

There are 4 merged frames in this image. The big streak is clearly an airplane, you can see the regular red flashing light and it's a dual trace. There's another really fine trace that I think was possibly another satellite. 

Here's what happens when you merge those images together.

This is the full merge of all 74 images. Pretty, but not what I was hoping for. Too many stars. You can't even see the second satellite. 

Trying to solve the "too many stars" issue. I first reduced the exposure of the individual frames by one full stop, then dragged down the highlights and blacks even more. I exported the images as jpegs (6000px wide) and used StarStaX* to combine them. Still not enough, I opened it in Photoshop and used Topaz Simplify.  This is a "work in process". As soon as I find the right formula, I'll share it.

* StarStax is a freestanding program that works on all platforms. It's job is to automate stacking those images to make star trail shots. You could do a lot of it in Photoshop manually (as I did at the beginning) but StarStaX has some utilities to smooth the transition by filling in gaps (haven't figured that out yet!). It's FREEWARE and you can get it at http://www.markus-enzweiler.de/software/software.html. Besides, after you export the images to Jpeg, it's a couple of keystrokes to do the comp, all at once, unlike the 45 minutes I took to do it in Photoshop earlier.

Here's a shot that failed.

Same settings, but only 30 exposures. I got tired, and wanted to do the car shot at the top, so I interrupted the sequence. 15 minutes is not enough with a wide angle lens. PS: when I go back to redo this, I'm going vertical. Imagine the reflections of the stars in the water!

The other way of doing star trails is one long exposure. But noise is generated by your sensor when it's under power (especially when it's hot), so the quality seems to be better by merging shorter exposures. That said, you can control the exposure more traditionally.

D300, 12mm lens at f/5.6, ISO 100, 6,130 seconds (102 minutes).

D800, 1850 seconds (30 minutes) at f/2.8, 17mm, ISO 100 

The second shot at the top? OK, I'll admit it. The meteor was created in Photoshop.

Use a black layer and a small soft brush loaded with white. Click where the tail should be, hold "Shift" and click where the head should be (keep it horizontal, you can rotate it later). This works best with a Wacom tablet, make it pressure sensitive. Now double the size of the brush, turn the opacity down to half, and paint in the head. Add a touch of Gaussian Blur or it'll just look like a Q-tip! Practice makes perfect!

Now the third shot: the car. I did all the things I said above; several quick test shots at high ISO to evaluate the focus and composition, one of the test shots showed an ugly shadow on the ground (the light on the car was from a mercury vapour street light about 400 m away, the only light around! But the camera/tripod cast an ugly shadow), so I had to recompose. I got into the car after setting things in motion, in order to trigger the interior lights for a frame or 2. Too bright. So I edited those out in the computer and turned on my iPhone while I was in the car.

Here's the picture again. It'll blow up if you click on it. 

To prepare the images for StarStaX, I opened one in Lightroom, took the exposure down a full stop (too many stars), added highlights and darkened the blacks, added contrast and clarity. then synced all of the changes to the other images. I edited about 12 of the 54 images in Photoshop to get rid of two airplanes and three passing cars (the airplanes were easy: healing brush. The cars were tougher, big soft layer masks, 'darken' blend mode). Then I exported the 54 jpegs to a folder and dragged them into StarStaX.

I'm new to StarStaX so I haven't figured the "gap fill mode" properly yet. But when I omitted the bad frames (cars) it left gaps in the star trails, so I fixed them and put them back in. I ticked "comet mode" which is really cool. Once done: too many stars! So I added a layer of Topaz Simplify BuzSim at about 50% opacity to control how many stars in the image.

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So the above was a rambling mess. I threw all kinds of random stuff at you. But if you go back and read it again, I'll bet it'll save you some time in your star-shooting learning curve!

If you want to do a workshop on this, I'm happy to oblige. We'll spend some time going over the theory, get you set up, then go out and shoot. Then we can come back (next day, not the same night!) and do some computer magic. Very reasonable price. Contact me!

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