long exposure

Stacking for Star Trails

Ever wonder how images like the above were made? There are two main ways: 1)one VERY long exposure, or 2) stacking several long exposures.  In this tutorial post, I'll go through the planing, strategy, and technique of the second option - stacking. 

First up is planning (see my post on that here). After you determine the location, the right night, ascertain whether or not you have do-able weather, and select where to place your camera, then comes the fun part - guessing the exposure length, aperture, and ISO, and subsequently figuring out how many you need to take. Looking at your sensor size + lens combo should give you a good idea of how many frames of a particular length you need to make if your goal is a star circle (facing N to Polaris). I have a  whole separate post on this here. In this post, I want to focus on the post-processing portion of making an image like the above. 

So you have your frames, and (hopefully) your "plate" exposure that you shot for the foreground. Now what?

Step 1: get organized by placing all frames in  your stack in a unique Lightroom Collection. 

Step2: Synchronize ALL develop settings across EACH star trail frame so they are exactly the same.

Step3: Separately develop your "plate" frame to taste. 

Step 4: Select all frames in your stack in Lightroom's filmstrip along the bottom of the screen. Right-click on one of the photos, and choose "Edit In / Open as Layers in Photoshop"

Step 5: In Photoshop, drag the plate layer to the bottom of your layers, if it's not there already. 

Step 6: In the layers panel, select ALL star trails layers, and change the Layer Blending Mode to either "Lighten" or "Screen." Choose one based on which looks better - if shot on a moonless night with dark sky and bring star trails, I find "Lighten" to work better. This should allow all the trails to add up and create your finished blend OF THE SKY ONLY. 

Step 7: Merge all the star trail layers together via the "Merge Layers" command

Step 8: Add a layer mask to the merged star rails layer. Use regular mask-painting techniques with different brushes, hardnesses, opacity, etc. to cover over the foreground of the star trails layer with black paint (remember: white reveals, black conceals). The black paint on the mask will "conceal" or cover up the part of that layer, allowing the part of the next-lowest layer (in this case your foreground plate) to come through to the top in your photograph. Take care to make the blend look realistic. 

If you find gaps in your trails, they will need to be dealt with. Stephen Christensen of the Star Cricle Academy has an excellent post on how to manage this scenario - here

That's it in a nutshell! Any questions, feel free to leave a comment or shoot me an email. 


Comet Lovejoy (Part 2)


You may recall an image I made of Comet Lovejoy in 2011 seen at dawn on the beach at Bribie Island, Australia:


I thought Comet Lovejoy had made it's pass through our part of the solar system and headed back out into the Oort cloud in deep space to regroup, never to return again for many thousands of years.

Imagine my surprise when a friend called me the other day and said "are you going out to shoot comet Lovejoy next week?" At first I thought my friend was nuts, until I looked into it a bit further and saw in Sky and Telescope that sure enough, Comet Lovejoy was back. Only, this time it was a completely different comet...discovered by the same person in Australia.

This comet is amazing the fifth comet discovered by amateur Australian astronomer Terry Lovejoy. Can you imagine discovering five comets? I can't. I can barely remember to take the trash out.

I went out last night on a client sunset timelapse shoot, and on the way home I dipped into the meadow at Squaw Valley while it was still dusk, and had a go at seeing if I could find the new and improved Comet Lovejoy (2014Q2 so as to not be confused with the "old" one from 2011).

Sure enough, I pointed my camera to the west of Orion's belt, and there it was. Here's a view of the comet (greenish looking blob about the same size as the nearby stars towards the top of the image about halfway across):


And here's a closeup view fro a crop shot with my 70-200mm at 200:



Supposedly the comet has already passed as close to earth as it will come on it's current orbit (it won't return for 8,000 years). But, it may get a touch brighter as it gets closer to the sun.

Here's a chart from S&T showing where to find it:

Look for Orion to rise right at sunset in the East. Happy hunting!