Comment by bhouston | Hacker News Reader

Comment by bhouston | Hacker News Reader

> Many other cameras, particularly those with aggressive UV-IR cut filters, underespond to H-a, resulting in dim and blueish nebula. Often people rip out those filters (astro-modification), but this usually results in the camera overresponding instead.

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)

What you're describing is the domain of a very, very small number of hobbyists with very deep pockets (plus various govt-funded entities).

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.

> What you're describing is the domain of a very, very small number of hobbyists with very deep pockets

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=...

Some even scratch of the bayer pattern of old cameras.

And the entire earth observation industry, which doesn't look the same way but uses the same base tech stack.

You don't need very big pockets for that.

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).

You can even do the conversion diy.

Yep. I did both myself, as I was using old cameras that I had hanging around and if I sent them for conversion it would be more expensive than the cost of the camera.

Conversions done in places like Kolari or Spencer run about $300-500 depending on the camera model.

If I were to buy a brand new A7 IV or something like that, I would of course ask one of those shops to do it for me.

    > astrophotographers do not use cameras with UV-IR cut filters at all

I'll be pedantic here and say that the author's probably talking to people who use DSLRs with adapter rings for telescopes. I've been interested in doing this for a while (just unable to financially justify it), and I think this is actually something people in this niche do.

Then there are things like the Nikon D810A, which remove the UV-IR filter from the factory (but IIRC retain the Bayer filter).

My recommendation, as someone who started with a DSLR and then modded it to remove the UV-IR filter, I would have been better to just skip to a beginner cooled mono astrophotography camera, like the ASI533MM Pro. It is night and day difference in terms of quality and roughly the same cost and it automates better much better.

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.

How do you recover colour from a mono astro camera? Just run it for 3 exposures behind a gel of each of the R/G/B colours, then comp?

Yes, and you would almost certainly want to automate it with a filter wheel that changes the filters for you on a schedule. However, a key advantage of a mono camera is that you don't have to limit yourself to RGB filters. You can use some other set of filters better suited for the object you are capturing and map them back to RGB in software. This is most commonly done with narrowband filters for Hydrogen, Sulfur and Oxygen which allow you to see more detail in many deep space objects and cut out most of the light pollution that would otherwise get in your way.

> How do you recover colour from a mono astro camera? Just run it for 3 exposures behind a gel of each of the R/G/B colours, then comp?

Essentially yes. To get faint details in astrophotography, you actually will capture a series of images of each filter with long exposure times like 3 minutes per capture with a total capture time per filter measured in hours. You then star align everything, then you integrate the captures for each filter into a single frame to remove noise and boost signal, then you comp them together.

> It is night and day difference

Particularly high praise in astronomy!

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