Fibrills are significantly better seen in Ca-H vs Ca-K. I have noticed that even the very small wavelength difference between K and H creates a different focus (with my APO triplet), and my sense is that the optics focuses a little better at H and K (since H is 35 angstrom more to the red). This mi...

The spectral resolution, based on geometric calculation, is 0.21 angstrom. The spatial resolution, based on Rayleigh criterion, is 1.39 arcsec.

The fine spiral details on the Sun today look nice in close up, and the similarities between H-alpha and Ca-H are intriguing. These are 100% crops of the full disk images posted here: https://solarchatforum.com/viewtopic.php?t=42646 . Click on the images to see at full resolution . 210923-Ha-2-106mm...

The fine spiral details on the Sun today look nice in close up, and the similarities between H-alpha and Ca-H are intriguing. These are 100% crops of the full disk images posted here: https://solarchatforum.com/viewtopic.php?t=42646 . Click on the images to see at full resolution; use the arrow keys...

The morning was cool and damp with intermittent clouds. The seeing conditions were actually quite good, but the clouds made imaging difficult. I could not capture many Calcium scans (and could only stack 8). The H-alpha showed lots of fine and complex details. The images are worth opening in a new t...

Nice Calcium prominences!

https://www.science.org/content/article/peak-solar-activity-arriving-sooner-expected-reaching-levels-not-seen-20-years In 2019, as the Sun approached a minimum in its 11-year cycle of magnetic activity, a dozen scientists assembled for a traditional exercise: forecasting the next peak. Now, a few y...

I saw Pedro's images here https://solarchatforum.com/viewtopic.php?t=42550 and thought they made a nice side-by-side comparison to some CaK 0.1 angstrom SHG data I took around the same time https://solarchatforum.com/viewtopic.php?t=42554 . At very narrow bandwidths, in this case 0.1 angstrom, CaK s...

To verify that the bandwidth is close to 0.10 angstrom, I used the Pixel Offset Live feature of our SHG v4.3 beta software. By taking a 500 pixel wide ROI (vs 150 pixel for the images above), I could see that lines around 0.1 angstrom apart could be resolved, as shown below. The auto dispersion func...

It was recently suggested to me by Valery that a very narrow bandwidth of 0.1 angstrom, a CaK image would show almost pure chromosphere emission. After doing some calculations, I realised that using a 3600 l/mm grating would enable my spectroheliograph to achieve 0.10 angstrom resolution, vs 0.21 an...

I know what you mean, when I use mine as part of my 'travelling kit' it adds excess weight and throws balance... I found some cotton bags on Amazon UK "Bronta Mill Plain black 100% cotton eco friendly drawstring/stuff bags". I found the small one made a nice front lens cover for the 80ED ...

That is a very interesting, and I think quite unique, comparison of using narrowband filters and diffraction grating techniques. Just to add some details about the SHG data: I was asked by Christian V. on the morning of Sept 7 if I could do an image in CaK that day (to coincide with his measurements...

marktownley wrote: ↑Tue Sep 12, 2023 9:47 pm The 150mm f6 is an Altair Astro 'bobby no-name' cheapo frac

I bet that's a main reason for the resolution difference. The contrast difference is probably the f-ratio at the etalon. A good APO triplet like the LZOS is just sharper, especially at funny wavelengths like H-alpha.

marktownley wrote: ↑Tue Sep 12, 2023 8:38 pm I think the images with the 100mm are better. I think there is a few things going on.

The LZOS 100/800 objective might also just be a better lens. It's famously good. What is the 150mm f/6 ?

Hi Mark, that's some really nice H-alpha with the Solar Spectrum filter. Is it my imagination or is the 100mm image of AR 13423 better than the 150mm? Is it just because of the higher focal ratio? Or seeing effects with the larger aperture?

pedro wrote: ↑Mon Sep 11, 2023 8:13 pm I'm waiting for my Sol'Ex.

Which telescope do you plan to use with it? I know you have many to chose from.

solarGain wrote: ↑Mon Sep 11, 2023 5:02 pm The collimator is the 2nd piece that has been focused

How was the camera lens focused? It should be focused to infinity first in order to properly collimate the collimator.

Hi John, one minor point: you should rotate the camera so that the spectral line is along the long axis of the camera sensor. This will help later on when you use a narrow ROI. The camera will read much faster if the line is orientated parallel to the long edge. It's not clear from you description i...

Approximately the same cropped region in H-alpha but inverted. Spectral resolution approximately 0.15 angstrom , spatial resolution potentially as high as 1.6 arcsec. Click on the image to see at full resolution and use the left and right arrows to toggle between images. 090923-Ha-106mm-inverted-cro...

As it's unusual to get both very narrow bandwidth and reasonably high spatial resolution in Ca-K, I present here a cropped version of the Ca-K full disk image above. I used slightly more unsharp mask and adjusted the levels for the surface features rather than to show the prominences. The spectral r...

With regards to SHG images in this wavelength range: it is fairly easy to get 0.2 angstrom spectral resolution. But to get the best spatial resolution, a Newtonian should be used for the telescope (as is being done here with the narrow band filters). My guess is this would then push the limits of th...

With regards to SHG images in this wavelength range: it is fairly easy to get 0.2 angstrom spectral resolution. But to get the best spatial resolution, a Newtonian should be used for the telescope (as is being done here with the narrow band filters). My guess is this would then push the limits of th...

For night time star work, the instrument can be much smaller since you only need to a very small image circle (to capture a star, planet, nebula). To make an attractive image of the sun's full disk necessitates the use of longish focal length lenses. I would also suggest that if you use a short fast...

SHG was new to me so I had a little look around and found something from Ken a couple of years ago. Very interesting and from all accounts this is a near perfect example. Thanks for bringing that to my attention. Ken Harrison and the late Peter Zetner have been posting SHG images for the last decad...

How is the quality of the images when not covering the rear end. Does stray light cause problems? If the end is totally open to the sky, then there is too much direct light at the camera lens. At a minimum, it needs some kind of "tent" to shield the camera and the grating from direct ligh...