I recently made my first attempt at stacking a Perseids Meteor shower photo in Photoshop (PS) and after posting my image I had a few people contact me about how I edited the photo. This tutorial only covers the portion of processing for meteor stacking from multiple shots into one image. In order to keep this tutorial short and manageable I will assume the reader has basic PS skills. I currently use Lightroom (LR) CC and PS CC to edit all my photos so there may be some differences with older software versions.
If anyone knows of more efficient ways to do what I’ve done, I’d love to hear it. I came up with this method based on techniques I’ve used for stacking star trails, blending exposures and my desire to make repetitive editing steps as quick as possible.
When I started this image I took ten photos from LR and opened them as layers in PS – this way they all end up as one file. I had also decided which image I wanted to use as my reference or base layer. The reason we need a reference is that we are going to be rotating our subsequent layers around (approximately) the North Star/Polaris. In the image below the radiant point of the Perseids is just above the top of the barn at the front. I wanted the meteors I captured to radiate from a point above the top of the barn so my base image had the radiant roughly in that spot. If you’re shooting for an extended period of time, the radiant can move into the desired position for the composition spot at any time during your shoot. Then you adjust your layers accordingly later.
To make things look less busy I have loaded in my almost complete image and two extra layers with meteors I want to add in. The layers are currently invisible (click off the eye next to the layer).
Add layer masks to the layers on top of the base image.
Make one layer visible at a time. In this case I will select Meteors1.
Select the brush tool and make sure you have the black color selected. Black is to erase, white is to add in. Size your brush to just a bit wider than the width of your meteor streak using the [ and ] keys. Erase your meteor. You do not have to be very exact and I’ll explain why later (this is for the speed factor with repetitive steps I mentioned). Do the same for all subsequent layers.
Turn off the visibility of the layers when you’ve erased all the meteors from all your layers.
The arrow in the image below shows roughly where polaris is in my photo. The stars rotate around this point so we want to rotate our layers around this point.
Use the custom shape tool to select the object that looks like a bulls eye. Place the bulls eye (i’ve made it fairly large so its easy to see in the screenshots) at roughly where Polaris is (Polaris actually moves around a bit).
Because of lens distortion, everything may not line up exactly and that’s okay for what we are doing here. Once the bulls eye is in place the layers are ready to be rotated.
Select one layer, make it visible again and change the opacity to 50%. Select the transform tool (cmd-t, ctlr-t).
If you do not adjust the anchor point image will just rotate around the centre. We need to move the anchor point over to our bulls eye (click on it and move it with your mouse) the.
Then we can rotate the layer around Polaris. I used the little dipper as a common point to line up – notice the little dipper doesn’t line up exactly.
Change the opacity back to 100%, invert your layer mask (click on the layer mask, cmd-I, ctrl-I).
Change the mode to lighten (blend mode is next to the opacity setting). Using lighten is why we don’t have to be very exact in the erasing of the meteor in the initial steps. Unless the brightness of your sky has changed a lot (you’ll have to be more exact when erasing in this case) the lighten mode will only bring through the very bright streak of the meteor. In the photo above you can see that the meteor we were adding is already visible but again if the sky was slightly different we would see a halo around the meteor because we weren’t exact with erasing.
Turn off the visibility of this layer and repeat with as many others as is necessary. You may want to zoom in on the meteors and check for halos too and use the paint brush to refine the edge.
If you’re interested in learning more about night photography and/or processing check out my customizable workshops.