Author: MatP

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Effect of temperature tuning a Fabry-Perot Etalon solar H-alpha filter

Since the first days I could observe the sun through a narrow band solar H-alpha filter, I was wondering what the tuning effect of such a filter would be. It does not matter whether the filter is pressure, tilt or temperature tuned. The effect of slightly shifting the filter central line is the same. With the temperature tuned filter, I have at hands, a comparable test series is easy to achieve.

I know from previous observations that the filter performs best at 58.0C. Therefore I set the test points at 5 degrees steps across the range of possible temperatures. Only close to the 58C I added 2.5C halve interval steps.
Each individual image was recorded with a set of 100 frames, from which the 20 best frames were stacked. At each temperature I recorded 2 sets at different exposure settings: one for the surface (granulation, … – unfortunately no sunspots were active) and the other for prominences (only minor activity here as well).

As is obvious from the result, the low temperature settings yield close to no interesting view. Between 55.5C and 63.0C the filter delivers good contrast. Beginning at 63.0C contrast degrades again.

Imaging setup:
Telescope: 102mm refractor
Camera: QHY183M @ -20C
Filter: Solar Spectrum – Solar Observer Series 1.5, 0.5A solar H-alpha filter

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Viennese rolls (Handsemmeln) made at home

Baking at home is a regular task for me. I enjoy having a fresh, crunchy and lovely tasting loaf of bread and the house full of this bakery smell 🙂 I am quite confident and pleased with the bread I bake. But when it comes to Handsemmeln, I struggle.

It is common saying, that one needs to fold 10000 Handsemmeln to get them symmetrical and right. OK. I accept that my rolls wont be perfectly shaped (though they look quite nice to me) for the next century ;-). What bothers me is, that my rolls won’t end up with sufficient volume. Compared to the wonderful fluffy inside and hard crust outside rolls from local bakeries, my rolls fall really short at 60% volume and a crust, by far not so crunchy and hard.

Perhaps I am lucky and an experienced baker reads these lines. I would really appreciate comments here!

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Happy New Year (light painting in the starry night)

Light painting is a fascinating way to communicate a message. If the background and light is right, it is only up to your imagination what you add to your photo…

Here is how to create a light painting (how I created this New Years greeting):

  • Find the right scene:
    you need sufficient space to move
    you need a sufficiently dark background to “write on”
  • Set up your camera on a tripod
  • use a wide-angle lens. With a tele lens you have to stand quite far away from the camera
  • use a timer remote or have a friend operate the camera. Otherwise you will have a workout running back and forth 😉
  • prepare a flashlight, which is not too strong. A red or otherwise colored flashlight creates beautiful effects! You may cover your white light with colored filter foil as well!
  • wear dark, non reflecting clothes! Or you will appear like a ghost beneath the text in the image
  • try to memorize, which message you want to write
  • find the right spot where you will write, so that the text is at the right location in your image (take test shots to verify!)
  • find the right size to write your letters. The text has to be readable and within the bounds of your scene or camera frame
  • determine, wheter you will write in single strokes, or multiple strokes. This depends on the intensity of your flashlight and the desired effect, how the letters should look like. Single strokes look quite clean, whereas multiple strokes create a bit fuzzy look, which is often more appealing. Though multiple strokes are more difficult to make, as you write in thin air and have no reference, where you put the previous line.
    Therefore keep in mind: you only move your hand when writing one letter. Move your body only when advancing to the next letter or word!
  • test, how long you need for the message to write. This defines the minimum exposure length!
  • Set the right ISO value and aperture for the desired exposure time. Test the exposure to not over-expose. If you choose a too low ISO / too high aperture, you dim the flashlight. This makes the text you write hard to read
  • Now for the tricky part:
    The text you will write has to be written mirrored! It is the camera who “wants to read” the message, not you!
    Memorize your message in mirrored letters, written from right to left. It helps to close your eyes and just move your hand writing the mirrored text a couple times. Don’t get too frustrated when you make errors! Depending on the letters, I need several attemts to have everything right as well 😉
  • Now you are all set. Get in position, switch on your flashlight. Trigger your camera and start writing!
  • Tips:
    – cover the flashlight with your hand when advancing to the next letter / word!
    – move brisk but fluently
    – direct the flashlight to the camera
    – make equally spaced steps between the letters or words
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Jupiter & Saturn conjunction (handheld with smartphone and pocket telescope)

Winter has just begun and the days as well as nights are already annoyingly full of clouds or high layers of fog. So there is no way to see stars or planets for days or weeks. This situation is especially annoying, if there is a special celestial event like the greatest conjunction of Jupiter and Saturn in years. Jupiter and Saturn were a mere 6 arc-minutes apart from each other on December 21.

On December 26 I did not expect anything better when beeing out a bit. Though this evening, clouds opened up for a couple of minutes to show Jupiter and Saturn very low above the horizon. Jupiter and Saturn had a angular separation of 33.5 arc-minutes.

I had my smartphone and a 50mm pocket telescope with 15-45x magnification at hand. Not much for high-res images. Even worse, I did not have a tripod or anything else to stabilize the hand held setup. Though I could capture the moment. And judging the shaky hand-held setup (telescope in one hand, leaning against a wall, smartphone in the other), it is really beautiful! Fortunately, I captured a burst of 40 frames, so that I could reduce noise significantly (see the raw and processed image below).
For this kind of setup I am really amazed, that the four big Jovian moons as well as a 7.78mag Star can be discerned (see labelled image)!

Acquisition details:
Telescope: no-name 50mm, 15x-45x extendable pocket telescope
Camera: Huawei P30 lite
Location: Graz, Austria
Time: 2020-12-26 16:12 UTC
40 frames (burst capture), manually aligned and stacked in Photoshop (neither PixInsight, Deep-Sky-Stacker nor AutoStakkert were able to align!)

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Sunspots 12785, 12786, 12788 from 2020-11-29

The prolongued quiet phase of the transition from solar cycle 24 to 25 hasn’t have much to show off. But now, the sun has several sunspots as well as prominences to marvel on!
It is really fascinating, that the sun burst into activity within only a few days.

I was lucky to get a brief period of cloud free late morning to image the sunspots 12785 (the spot to the right), 12786 (the large whale-shaped spot to the right, including the tiny spots left to it) and 12788 (the group of tiny spots to the south-east of 12786) in a 2-tile mosaic.
On the limb, there is quite some activity too! See the 2 parts with prominences here:

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Prominence timelapse from 2020-11-22

On November 22 on the south-eastern limb of the sun, a stable prominence was visible. The prominence seems to consist of three different prominences (one flame type, one fan type and one arch type). They all seem to origin from sunspots 12785 and 12786. Whereas I assume, that the arch type prominence to the right is most likely from 12786.

The timelapse shows the activity of the prominences from 09:45-12:30 UTC. The clip has 342 individual images. Each image was stacked from 12 frames out of bursts of 300 frames. Post processing and colorization in PixInsight.

These 2 images from beginning and end of sequence show the beautiful structur as well as the changes within.

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150 Megapixel mosaic of the sun

My solar imaging setup has a quite high magnification. Even though I use a 20 Megapixel QHY183 camera, I may only frame less than a third of the disk diameter at once. This is really neat for prominences and sunspots. But I may not record the whole solar disk. Therefore my only way to go is a panorama or mosaic.

The tricky part of recording a mosaic of the sun is, that you don’t have too much time to complete. First, the sun rotates (even the 25 days period may cause defects at high resolution imaging). Second, some features like granulation or prominences may change within minutes.
For high quality results, the lucky imaging approach has to be used. Meaning, each individual recording for a tile should consist of as many images (lets call them frames, as the data is recorded as a video) as possible. In post processing, only the best frames will be selected and combined for low noise results.

Last weekend I ran the first real test for a giant mosaic image of the sun in H-alpha. I recorded each individual tile with SharpCap. I had to use the seeing filter due to a rather slow USB connected drive. Each tile consists of a set of only 100 out of 2000. From these 100 selected images, only 4 were used to create the final image tiles (which proofed to be a wrong decision, as noise levels remained quite high).

To record the complete surface, I needed to capture 12 tiles. So I ended up using 48 individual frames out of 24.000. After crunching through the 30+GB of data recorded on disk (which was only 5% of the images captured) for several hours, I finally have a stunning picture of the sun in high resolution 🙂

Processing steps:
1) Stacking in AutoStakkert!3
2) Stitching in Photoshop (manually, as neither Photoshop, nor Hugin were able to align the tiles)
3) Gradient removal in Photoshop
4) Wavelet sharpening in PixInsight
5) Histogram optimization in PixInsight
6) Cleaning of edges and border of image in Photoshop
7) Colorization in Photoshop

If you want to fully enjoy this image, here is the 7500×7500 pixel version.

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Satellite transits Mars

On Thursday 2020-10-22 in the evening, I captured image sequences of Mars (see seperate post). During one of the infrared test sequences (I wanted to compare noise levels at +2C vs. -20C) I saw a brief dark shadow passing the disk of Mars. First out, I thought it might have been a bat. But later on, when I analyzed the video, I found out, that the shadow was a satellite transiting Mars 🙂

The transit started at 2020-10-22 18:27:45.498 UT. The satellite left the disk of Mars at 18:27:45.687. So the duration was a very brief 190 Milliseconds! As I recorded with 178 frames/second, I could capture 27 individual images of the transit.

I definitively was very lucky to have registered the shadow during capture time. Otherwise I would never have seen this event in post processing…

Optics used: 10″ f/5 Newton with 2.5x Barlow (effective focal length was 3125mm)
Recorded with IR-650nm pass filter on QHY183M camera at +2C with 178 fps

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Comet C/2020 M3 ATLAS – Nucleus movement

Saturday night (2020-11-21) I recorded LRGB data of comet C/2020 M3 ATLAS. Upon inspecting the image data, I detected a spinning movement of the comets nucleus. To show the movement, I combined the 34 individual LRGB images (240 seconds each) to one stack with the comet forming a curving trail.
During the course of 142 minutes, the comet moved 470 arcseconds (3.3 arcseconds per second).

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