Long Exposure Star Trails Guide

Moderator (rovhazman) note eddyizm kindly agreed to share with us his method for long exposure star trails, as some of us might remember few examples posted here in the past. You can also read the article on his blog post. Thank you eddyizm!

Ok, so every time I post star trail shots I tend to get a lot of questions about settings, workflow, and just a basic “How did you do that?”. There’s a couple of decisions you need to make about what you want your final product to be which will determine which method will work best.

Gear used

• Camera – Sony Alpha a700 (over 5 years old now)
  
• Lens – Sony SAL-16F28 16mm f/2.8
  
• Tripod – Manfrotto tripod legs and head (It’s in my trunk so I’ll have to update this later)
  
• Intervalometer - generic after market. A lot of new cameras today have them built in. But you need one with manual control in order to get exposures past the 30 second standard and into BULB mode.
  

Settings

I went for a 5 minute exposure after trying a 20 minute exposure but the moon was too bright. I started with ISO 100 and it worked out pretty good as the moon was *that* bright. I set the f-stop to 4.0 but this lens is sharp as hell even wide open. Focus is set to infinity and should be in manual zoom. You’re not shooting a soccer ball playing across the sky even though the stars move pretty fast, their relative distance doesn’t change much. I turn off all noise reduction in any form on the body. In case it wasn’t clear, I shot this in Manual mode. You need the control. The camera works for you!


settings for the visually inclined
Intervalometer – I hadn’t used it in a while so even though I knew what I wanted to do, I was having a hell of a time trying to do it because basically I had forgotten. There’s 4 settings you need to set.

• Delay – This is how long before the intervalometer waits before sending the command. I set mine to ZERO in this set up because I added a 2 second mirror delay on the camera.
  
• Exposure – (Mine shows BU for this function which I assume is supposed to correspond to BULB on the camera but who knows) I set it at 5 minutes. Depending on your night conditions, you will need to experiment. Different locations, the moon, and how near or far you are from light pollution will determine what the best length is.
  
• Interval – This is important. It had been months since I used it and this is what took me over 1 hour to remember after trying and failing over and over again, which took 5 or 20 minutes on every attempt before figuring out what the hell I was doing wrong. This needs to be set to the exposure time you selected, 5 minutes in my case, PLUS any additional time you have added, ie. the 2 second delay I added on the body. So I set mine to 5 minutes and 3 seconds. In total, there would be roughly a 5 second delay between shots. If you make this delay too long you will have space between your frames. I did this the first time and it came out pretty cool! Of course, I am biased. I am very biased and very awesome.
  
• Frames – This is labeled differently on most gear but basically means how many shots you want to take. Mine will go from 1 to 399 along with a “–” which is the infinity setting that will continue until the battery dies. I set mine to infinity after composing the shot and went to hang out by the camp fire for about an hour and a half.

Post Processing

I got about 20 some images and ended up using about 18.


The interesting thing here was with all the moonlight and the fact that I was exposing for over an hour, the actual light of the moon was able to illuminate all sides of the rock formations, adding a very nice and even exposure to all of it. There’s usually some editing required at this point. Normally it’s some noise removal and exposure levels but since this was done with ISO 100, noise was not an issue. You need to remember that you will be stacking these images so the cumulative light may be much brighter. Generally, you will need to one or two frames for the foreground and composite the star trailed sky back into it. I tend to shy away from this because I’m simply not very skilled with photoshop. Depending on the light, I tend to lower the exposure a stop or so and remove any frames that are too bright in the hopes that I don’t blow out the foreground. The only thing I will always do is play with the sky, making sure that it is dark enough, blue enough and the stars look good. Doing some of this before stacking them goes a long way into making a good image. After they are stacked you have less say in the image than before hand. It’s like being able to change the ingredients to a recipe before you cook it.

Next, I export big 16-bit TIFF FILES for the stacking process. When I first starting doing this, I scoured the net for different ways to stacking images and the best and EASIEST one I found was this photoshop action. Hands down, simple, efficient and free. Of course, this means you have to have photoshop. Do a search and you will find several. Find one that works for you and learn how to use it. They all do the same thing in the end it’s just which one you find easier to pick up.

Stack them up, go for a run or whatever it is you do and then come back with a final image. Do any final editing either in PS, Lightroom or your choice of software. Your first attempt will vary. The key will be knowing if it was your work out in the field capturing images was the culprit or your processing. Once you take that many frames, I believe it is worth playing with the processing for a few runs as you could almost *always* salvage something you like even if it is not what you originally intended. Of course, I am biased. Biased and awesome.

See more from Alabama Hills Night Photography



Edited by rovhazman - 25 March 2014 at 16:41

What a wonderful explanation. Thanks very much Eddy.

Good write up Eddy. Can't wait to go out and shoot with you.

Nice article. Thanks. I love astrophotography, but I haven't done as much of it as I like. You've given me a reason to try this out when the weather gets a bit warmer.

mikey2000, @Jetsplace, MichelvA, rickztahone, ifreedman - Thanks!

GJK - Thanks! The a700 has served me well. The sensor is scratched but I still use it :-)

utcreeper - Thanks. I normally start with a high iso, like 3200 as you mentioned, and open up the lens all the way. But it depends what I'm trying to do. In the example above, I already knew a iso 3200/30 secondexposure would leave me with a extremely bright, day time looking image, which I did not want. I usually go with that method on dark nights while trying to capture some milky way images. I actually was trying to do something different and get a cleaner image so I started with this approach that is written above. I have done hours of 30 second exposures when my goal was a timelapse video, as opposed to simply one static star trail print. Hopefully that makes sense.

Eddy - Thanks for the further explanation, and yes it makes sense.   

Thanks for this article Eddy, very informative I'll bookmark it so I can try it myself!