If the light source is not approximately Planckian, or if multiple illuminants have different temperatures, a white point is not defined.
Hmm... astrophotographers do not use cameras with UV-IR cut filters at all. For example, I owned a few of these:
https://www.zwoastro.com/product-category/cameras/dso_cooled...
They also generally do not use sensors that have Bayer filters. This also screws things up.
Instead they use monochromatic sensors with narrowband filters (either one band or multiple) over them keyed to specific celestial emissions. The reason for this is that it gets rid of light pollution that is extensive and bumps up the signal to noise for the celestial items, especially the small faint details. Stuff like this:
https://telescopescanada.ca/products/zwo-4-piece-31mm-ha-sii...
https://telescopescanada.ca/products/zwo-duo-band-filter
Often these are combined with a true color capture (or individual RGBL narrowband) just to get the stars coloured properly.
Almost everything you see in high end astrophotography is false color because they map these individual narrowband captures on the monochrome sensors to interesting colours and often spending a lot of time manipulating the individual channels.
This is done at the medium to high end using the PixInsight software - including by NASA for the recent James Webb images: https://www.pbs.org/video/new-eye-on-the-universe-zvzqn1/
The James Web telescope has a set of 29 narrowband filters for its main sensor: https://jwst-docs.stsci.edu/jwst-near-infrared-camera/nircam...
Hubble pictures were famously coloured in a particular way that it has a formal name:
https://www.astronomymark.com/hubble_palette.htm
(My shots: https://app.astrobin.com/u/bhouston#gallery)
> astrophotographers do not use cameras with UV-IR cut filters at all
Then there are things like the Nikon D810A, which remove the UV-IR filter from the factory (but IIRC retain the Bayer filter).
A high end DSLR is a huge waste of money in astrophotography. Spend the same amount on a dedicated astrophotography camera and you’ll do much better.
Particularly high praise in astronomy!
The vast majority of hobby astrophotography is done pretty much as the webpage describes it, with a single camera. You can even buy high-end Canon cameras with IR filters factory-removed specifically for astrophotography. It's big enough of a market that the camera manufacturer accommodates it.
Sort of. The telescope used for the Dumbbell nebula captures featured in the article was at worth around $1000 and his mount is probably $500. A beginner cooled monochrome astrophotography camera is around $700 and if you want filters and a controller another $500.
There are quite a few people in the world doing this, upwards of 100K:
https://app.astrobin.com/search
Various PixInsight videos have +100K views: https://youtu.be/XCotRiUIWtg?si=RpkU-sECLusPM1j-&utm_source=...
Intro to narrowband also has 100K+ views: https://youtu.be/0Fp2SlhlprU?si=oqWrATDDwhmMguIl&utm_source=...
Today you can find very affordable monochromatic astrophotography cameras, and you can also modify cheap DSLR cameras or even compact cameras to remove its IR/UV/low pass filters. You can even insert a different semi permanent internal filter after that (like a IR or UV band pass)
I've done a Nikon D70 DSLR and a Canon Ixus/Elph compact.
Some cameras are very easy, some very difficult, so better check first some tutorials before buying a camera. And there are companies doing the conversion for you for a bunch of hundred dollars (probably 300 or 400).
Some deep-space astronomy pictures are in completely made-up color, often because they're taken at wavelengths different than visible light and then color-mapped to look pretty.
But the point here is even if you're taking images with a regular camera pointed at the sky, it's pretty much impossible to match "reality".
Many observations come from scientific cameras rather than actual visible spectrum cameras discussed in TFA. They are not artist's impression like the first case. They will have a completely different view of the object so any visible-light predictions will have some guessing in it but the final picture will be not 100% you would see.
When you see "artist's impression" in a news article about space, what you're looking at is a painting or drawing created from whole cloth by an artist.
This article is about how sensors turned signals into images. When you take pictures with a 'normal' camera, we've designed them so that if you take certain steps, the image on your screen looks the same as what it would look like in real life with no camera or monitor. This article is stating that with the cameras and filters they use for telescopes, that same process doesn't really work. We use special filters to measure specific spectral properties about an astronomical object. This gives good scientific information, however, it means that in many cases it's impossible to reconstruct what an astronomical object would really look like if our eyes were more sensitive and we looked at it.
Did you have the number memorized or did you do a fact check on each of the numbers?
But I didn't know whether Ha was actually highly visible or just had a different wavelength. I didn't know 683lm/W either, and I wasn't exactly sure that 555nm was the peak, but I knew it was somewhere in the mid-500s. If I'd been less of a lazy bitch I would have fact-checked that statement to see where the error was.
POC already out...
Human S cone channel = sum over bands of (intensity in that band) * (human S-cone sensitivity in that channel)
and similarly for M and L cone channels, which goes to the integral representing true color in the limit.
Are the bands too wide for this to work?
For wideband filters used for stars and galaxies, yes. Sometimes the filters are wider then the entire visible spectrum.
For narrowband filters used to isolate emission from a particular element, no. If you have just the Oxygen-III signal isolated from everything else, you can composite it as a perfect turquoise color.
https://www.adept.net.au/news/newsletter/202001-jan/pushbroo...
Hyperspectral imaging is a really fun space. You can do a lot with some pretty basic filters and temporal trickery. However, once you’re out of hot mirror territory (near IR and IR filtering done on most cameras), things have to get pretty specialized.
But grab a cold mirror (visible light cutting IR filter) and a nighvision camera for a real party on the cheap.
Scientific sensors want as "square" a spectral response as possible. That's quite different than human eye response. Getting a realistic RGB visualization from a sensor is very much an artform.
Retr0id•5h ago
jofer•5h ago
embedded_hiker•4h ago
https://airandspace.si.edu/collection-objects/gnomon-lunar-a...
shagie•4h ago
JNRowe•10m ago
One of the great gifts Pillinger² had was being able to shake up public interest via pop culture; there was also call sign by Blur for Beagle 2.
¹ https://www.researchgate.net/figure/Spot-Painting-Beagle-2-C...
² https://en.wikipedia.org/wiki/Colin_Pillinger
pgreenwood•4h ago
https://tothemoon.im-ldi.com/data_a70/AS17/extra/AS17-137-20...