So! you've planned your shot and you've been watching the weather and the stars are (literally) aligning for you to go out and shoot the Milkyway. Time to head out and shoot!
Now, one of the key points I should have mentioned in the last post is that if you are unfamiliar with your location, arrive early. OR, even better, scout the location during daylight hours if you can first. Google Maps and Photopills, while brilliant - sometimes don't tell the full story of the spot and you might find that it doesn't work exactly how you planned, or there might turn out to be a better composition than you originally thought which will require some on the fly planning.
Case and point; The Tarawera shoot back in March (Geez its MAY!!) The jetty shot turned out okay, but there were three other photographers there and I didn't want to hog it, so went for a wander and found the branch in the lake - which turned out to be on of my favourite shots so far this year!
The Jetty while okay, had a lot of light pollution spilling on to it and I think distracts from the Milkyway itself
The branch however, I think its just that little cherry on the top as you can see it faintly extending underwater towards where the MW (I'm going to abbreviate "MilkyWay" to "MW" from now on) is on the horizon.
Now! Once you've settled on your spot and are starting to line up your composition its important to start taking some test shots in order to ensure you have your framing just right. Sometimes cropping to adjust composition is a necessary evil, but we should avoid it where we can. If its already dark, start firing off some shots at wide open aperture, at max ISO and some 30 sec shutter speeds just so you can get a bright exposure to make sure you're in the right spot. These shots will look fucking terrible, which is okay! All we're doing here is making sure our composition is exactly where we want it. If you've arrived during daylight hours, or the blue hour and can line up you comp without doing this congrats! You have saved yourself some memory card space. Win.
So Jarred, what settings to we need to use for the actual shots!?
Now, the aperture and ISO will be the easier settings to come to. Aperture: Wide open, if you're using your kit lens at 18mm, that'll probably be f/3.5. ISO will be higher than you're used to shooting at and does depend on your cameras performance to an extent, along with your own personal taste as to how much noise you can live with. We'll start at ISO 3200. The shutter speed is going to require some maths I'm afraid, (Sorry!) because we're on a tiny lil blue marble in this giant universe, that is spinning as you read this. That's right, the earths rotation is a factor we're going to have to bring into things. You see, the earths rotation will cause the stars to appear as little streaks if your exposure time is too long. That's the catch-22 of MW photography, we want a nice long exposure to let in all the light we can capture, but we have to limit it to avoid the stars streaking.
Above is a four minute exposure I took at the Tongaririo crossing earlier this month. This was a foreground image to blend with a separate exposure for the sky (A future blog post for intermediate users). As you can see, the stars have left little streaks or "trails" in the sky as the earth has rotated during the four minutes the shutter was open. This can be a creative decision of course, star trails is a popular thing to shoot - but an entirely different process to what we're taking about here today.
Without getting into stacking (Another blog post coming for more advanced users), basic MW exposures often start with the "500" rule, that is, if we take 500, and divide it by our focal length, that gives us our maximum exposure time before the earths rotation comes into play. The wider the focal length, the longer our shutter can be open before the trails become apparent - there's some science as to why - better left to someone who understands that better than me. Anyway, there's a bit of a caveat here: Most of us at the beginner level have more entry level to mid range cameras with what we call "APS-C" sized image sensors in our cameras. The 500 Rule was developed for "Full frame" or 35mm sensors, so we need to adjust the math slightly to suit our setup. Some use the "300" rule instead, others will use the crop factor of their particular camera manufacturer. All of these techniques will give slightly different numbers and it'll require some trial and error on your behalf to land on a specific method that suits you best. An easy way to do this is use the Milkyway Exposure Calculator over at LonelySpeck.com which is an incredible resource for astrophotography - well worth a read! For me, I typically use the Lonely Speck to figure out my base exposure and go from there.
The "NPF" Rule is another alternative out there, but again is for more advanced shooters and features more complicated maths: (35 x aperture + 30 x pixel pitch) ÷ focal length = shutter speed in seconds. Pixel pitch = the camera sensor’s physical width in millimeters ÷ number of pixels in width x 1000 to measure it in microns. Lets not worry about that one at this stage. Its really designed for people with cameras with high resolution image sensors and for people who want to print BIG.
Lets run some quick numbers, assuming you're on a Canon 80D with 18-55mm kit lens. Canons crop factor is 1.6x for the record. If you have a different camera/lens combo, you will have to adjust the focal length, maximum aperture and crop to suit
500 rule with crop factor: 500/(18x1.6) = 500/28.8 = 17.4sec
300 rule: 300/18 = 16.6sec
Lonely Speck: 19sec.
I suspect the lonely speck is using a variant of our first equation, but assuming a 1.5x crop like on a lot of Nikon, Sony and Fujifilm cameras. 500/(18x1.5) = 500/27 = 18.5sec
Its at this point you have to decide exactly how much trailing you can deal with, bearing in mind it will be more pronounced at the edges of the frame (this is a wide angle lens thing). The temptation here is to set your shutter to 20sec and accept some trails, personally I'd rather err on the side of sharper stars and aim for 15secs. That 5secs is about a 1/4 stop of light and not even the equivalent of bumping your ISO from 3200 to 4000 - probably better to take the small amount of extra noise ISO 4000 will give if a 15sec exposure is too dark for your liking. But, these are your shots, don't let me tell you what to do!
So there we are, we have settled on our base exposure of 15sec, f/3.5 and ISO 3200. I say "base" because this is our starting point, I'm going to say it again, trial and error plays a part in this and its mostly down to your own personal taste. The key is, to experiment with altering these settings while shooting so you have some options to bring back to Lightroom and Photoshop (Lr and Ps). Try some higher ISO shots, adjust your shutter speed to and fro from our base exposure. Because most cameras limit how much adjustment you get between shutter speeds (my Fuji for example only allows 5" adjustments from 15-30"). But, if you have a remote shutter release like I mentioned in Part I, you can really get precise with your shutter speeds and try 16secs, 18secs or even 14secs and see if they are to your liking.
Part IIIA will be a short video for Patrons only explaining how to focus at night, or cheat during the day if your lens allows.
If you have any questions about the stuff covered here, let me know!