The Sun on 2024-09-13, around the CaH line, also touching Hydrogen epsilon. Pixel shifts range from -36 pixels (blue wing) to +40 pixels (red wing), meaning somewhere around -2..+2 Å in total, give or take.
The Sun in CaK, etalon+shg, on 2024-06-02
I combined some spectroheliograph data with the etalon, Sol’Ex at 62/400 with Lunt CaK B1800 at 102/1100.
The Spectral Composer
I’ve been photographing the Sun for more than two years now almost each and every day, in a bit of a hackish way: using all kinds of filters beyond the 540nm continuum – hydrogen alpha – near UV calcium triad. However, as I advanced, I discovered that this knowledge is simply not common in the community, and not just that, it’s also a bit hard to come by while googling around. Also, to better explain double stacking, off banding and similar stuff, articles like this one Altair Astro’s 3nm CaK Ultra filter: testing, comparison, review are maybe rare.
So I put together an interactive tool to play around with spectra, in a way amateur astronomers find it interesting. The Spectral Composer.
Altair Astro’s 3nm CaK Ultra filter: testing, comparison, review
Solar disk in Altair Astro’s 3nm CaK Ultra filter, enhanced contrast
I got a new filter to pudding-test: Altair Astro’s 3nm Calcium K Ultra, stated to have 3nm FWHM and a very high transmission. Let’s see how it performs.
Before we jump in, let me also present some information I compiled along the way, and some theory and links fellow amateur astronomers may find useful.
Important note: this article is not sponsored by the vendor, and the vendor has not influenced the conclusions presented below in any way.
Contents
- market overview: what’s available to amateurs, around the Calcium K line
- theory and practice: about the filters, the Sun and its spectrum
- first impressions, unboxing
- the tests themselves
- further (reference) images
- conclusions
The Sun on 2024-01-05
With a front ERF, Altair Astro’s Triband, 115mm, Tecnosky 102/1100 refractor, Lunt’s CaK B1800 and the ASI 533MM camera, I obtained the following:
CaK, 2.4Å
CaK 2.4Å, colorized
With a Tecnosky 102/1100 refractor, Herschel prism, ND 0.96, a filterwheel and the ASI 533MM camera, I obtained the following:
Antlia 3nm hydrogen alpha. The disk is clearly continuum, but the prominences were obvious even on the live view
Altair Astro’s G-band filter, 2nm fwhm at around 430nm cwl
Calcium K Sun on 2023-12-31
Using a fairly new setup, as they were in the light train: Altair Astro Triband D-ERF 115mm, Tecnosky 102/1100 ED refractor, Lunt CaK B1800, ASI 533MM, along with my EQ3 with the home built controller, I captured the following frames.
full disk, linear light
full disk, paraboloid gamma curve
detail from the full disk
same, colorized
The Sun on 2023-08-05
Using the good old 150/750 tube, with a ND3.8 film in front, I obtained the following frames.
Antlia CaK 3nm:
For reference, a Lunt CaK image, colorized and mono
And the infrared cwl 850nm, fwhm 20nm filter showing the active regions
The Sun on 2023-06-01
ASI 178MM (cooled), IR850nm 20nm fwhm, Skywatcher 72/420 ED-APO, ND5, mountpusher, EQ3-mod — I believe this image shows the Calcium Triplet
For comparison, here’s the Baader CaK 5nm image (tovább…)
The Sun’s active regions, in Calcium K and other wavelengths, filters’ comparison
Testing Baader’s solar filters, in the ersatz-obsi
As you know, due to various reasons, lately I’ve been doing solar imaging almost exclusively, focusing on full disk observations. Of the many filters I have turned towards the Sun — some dedicated solar filters, some more in a hacker spirit –, the Calcium K wavelength is one of my favorites, obviously. Now that Baader started selling its generation ii CaK filter, I figured I’d test it against itself, the first generation, and against Lunt’s Calcium module.
UPDATE 2024: in the meanwhile I tested Altair Astro’s early bird sample of Calcium K 3nm, against Antlia’s 3nm CaK, and got a B1800 Lunt CaK (btw fuck Bresser for wasting my time, for the second time in a row regarding Lunt products), to deploy in a long, f/11 tube and protected by a full aperture ERF (from Altair), to do full disk solar with chromosphere and all.
As you also know, I record images as a hobby, without any specific scientific goal, I just like the rigor and if some aesthetics can arise from it, in the form of nice solar disk images in this case.
TLDR0: not much difference, but still.
TLDR1: if doing full disk, if you have the old CaK and like it — keep it and your setup the way it is, the new filter is nice, the profile is standard, but overall, doesn’t show anything new nor better than the old one. Both are that good. Obviously not as good as Lunt’s CaK, but they are a fair competition, given the price range.
TLDR2: if you have the Venus U filter, do use it. It’s not as good for the Sun’s active regions as the CaK, but still pretty good. Also, give the dark blue a chance. Or basically any filter you own.
TLDR3: for Venus, the new filter may yield better images, due to it letting through about two times more light (half the expo time). I like very much the CaK images I obtained of Venus, in the 2020 epic season.
Venus, on 2020-04-05, using Baader’s CaK (gen1), as a false bi-color image with a green filter, mapped to cyan and orange respectively, with a N150/750 tube.
