Photography Asked on November 28, 2020
I plan shooting the Perseids meteor shower this August. It is my first time photographing a meteor shower.
This is the gear I will be using
I have already some experience shooting wide-angle starscapes and the milky way. To reduce noise, I usually stack multiple exposures in Sequator (it automatically detects the ground, so you do not have to do any manual compositing).
The problem is that things such as airplanes, satellites and meteors are more or less removed during stacking. So how can I stack photos but keep the meteors visible?
I am (at least a bit) familiar with Lightroom, Photoshop, Sequator and Deep Sky Stacker.
So after some further research, I've come up with a solution by myself. I will try to explain the procedure here.
Create your base image
Take all your photos and stack them in software such as Sequator or DeepSkyStacker. When using DSS, you will have to create two stacks - one for the stars and one for the foreground - and blend them together in software such as Photoshop.
The meteors won't be visible in thie base image.
Find images with Meteors
Browse through all your images (e.g. in Adobe Bridge or Lightroom - but your standard photo viewing app should also be fine if it supports RAW images). Somehow mark the images with meteors that you would like to include in your final composite.
Open the meteor images and your base image in Photoshop (or other software, like Gimp).
Aligning the base and meteor photos
You will have to align the meteor images to your base image (if you used a star tracker, they already might be aligned). Do so by setting the blending mode of your meteor images to Lighten - this will only show the stars and meteors.
It is best if you have your celestial pole in frame - in the northern hemisphere, this is Polaris. For each meteor image layer, enter transform mode (Crtl+T) and set the anchor point to Polaris (If you cannot see it, Alt+Click). Rotate the image until it properly aligns with the base image (due to lens distortion, we will not get a perfectly aligned image. But this is not too important).
If the celestial pole is not in the frame, it is a bit harder to align the images. You will have to do some guesswork and it will take more time.
Blending the images
Once all the meteor images are aligned to the ground layer, hide all meteor images except for one. Create a negative layer mask (Alt+Click on the layer mask button; this will create a layer mask filled with black) and select the brush tool (you could also use the pen tool). Then, paint white (on the layer mask) over the area where the meteor(s) are visible in this image. You should take some time and make sure that only the meteor is selected and no additional stars. Do this for every meteor image.
You can now do some further post-processing.
The process of blending meteor images is also explained in this tutorial - the only difference is that there is no base images stacked for noise reduction.
Correct answer by Jonas on November 28, 2020
So how can I stack photos but keep the meteors visible?
Use only frames with meteors in them. If you shoot about 500 or so 15 second frames, you might have a half dozen to a dozen frames with meteors. You might have two or three that are "good" meteors. Stack one meteor frame with one dark frame. That's about it.
Seriously, stacking isn't much of a thing with meteors. It's kind of the opposite of what you need to do to show meteors in the same frame with stars. The key to effective meteor photos is to maximize the brightness of the meteors moving across many of your camera's pixels in a very short time period relative to the fixed stars that stay over the same pixels for much longer periods of time. The phrase "time on pixels" is the thing to consider. Stars stay on the same pixels for quite a while, even without a tracker. Meteors can cross half your frame in just 2-5 seconds and spend very little time on any single pixel or tight group of pixels.
Stacking essentially takes a bunch of short exposures and gives you the equivalent of one long exposure. This will make your stars much brighter than they are relative to a meteor's brightness for the few seconds it is visible. In order to give the meteors a fair shake, you need to make your exposures fairly short. I'd recommend no longer than fifteen seconds, thirty at the outside. If you can find an opportunity to use a faster lens than your 18-55/3.5-5.6, you should use it. Open the aperture all the way up, crank up the ISO, and set the camera to shoot continuously for long intervals. Make sure you have plenty of batteries and memory cards. If you have a wired cable release, plug it in, lock the button down and enjoy the meteor show. Take a few dark frames periodically to subtract from your individual frames if you want to do anything special to reduce the effect of noise.
For more about the relative brightness of stars and meteors in long(er) exposure photography, please see: Are meteors dim?
Answered by Michael C on November 28, 2020
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