ajamesmccarthy
patreon
Horrific weather right now... reprocessed a shot from a year ago when conditions were better, as well as a technical writeup on how this sort of thing is captured.
🕑 Added 2021-01-29 06:03:52 +0000 UTCSince I can't bring you fresh original content right now, I thought I'd do a patreon- only write-up of the more technical details behind a shot like this.
This is the pinwheel galaxy, one of the galaxies in our local group. This image was captured over many nights from my light polluted skies to bring out the faint spiral structure within it. If you are subbed to my astrophotography tier this is the data labelled "M101- LRGB + HA". That means it was captured using 5 filters: Luminance, Red, Green, Blue, and Hydrogen Alpha. Many captures were captured with each filter, and stacked to improve the quality of the image within each respective color channel.
I'll give you a quick explanation of what these mean, but also a quick bit of camera trivia for context. ALL camera sensors are technically monochrome- but use filters to give you color. Within your phone is a small sensor that essentially just counts how many photons hit it. These sensors have pixels arranged in a 2x2 grid- with different colored filters over each pixel, usually 1 red, two green, and one blue. That allows the camera to generate 3 monochrome images (one for each color) and combine and color balance them to give you a color image. When I do astrophotography, that process is simply done manually instead of automatically. That allows me to spend tons of time using just a luminance filter (basically unfiltered but with some IR and UV blocking) to maximize the amount of light I can gather, and less time shooting filters where much of the light is blocked. This means a faint galaxy can be captured in much less time using my monochrome camera and changing filters manually than with an ordinary camera. If I had dark skies, this wouldn't be as important, because the galaxy would have much more contrast.
The "Hydrogen Alpha" filter is used JUST to capture the bits of nebula that come off the galaxy, those pink blobs you see. This is how the galaxy looks just using that filter:
So in summary, the color you see in galaxy photos are real. But thanks to the limitations of my skies, the technology, and how faint the object is, capturing them isn't point-and-shoot. It requires hours of exposures, stacking and calibrating, and processing to separate the image from the horrible light pollution. If you were floating out in space and had a regular camera and snapped a long exposure of this object, it would look very similar to my final picture, depending on how good your optics were.
Feel free to ask me any questions about this stuff!
Comments
Attached! Although fair warning, it doesn't look very pretty up close ;)
Very interesting, thank you for the information!
Cerity
Hi Andrew π this is great. Can I make a request though, the inline image for whatever reason doesnβt save on the app. Usually you attach images I think, could you do that to the monochrome β thanks for the dort of step by strpπ€― this really is an incremental art β€οΈ
