Public outreach for astronomy in Frauental

Last night our astronomy club (www.stav.at) organized a curbside astronomy afternoon and night in Frauental. We had perfect weather conditions to present several celetial wonders to the public. In the afternoon, the sun could be observed in white light and through hydrogen alpha filter. Meanwhile kids could enjoy different activities. When darkness fell, Saturn was obviousely the great “star” to get a lot of a’s and o’s. Several visitors were in disbelief, that a mobile phone would be able to capture a prominence or Saturn / Jupiter. So I shot the 2 images below keeping the visitors baffled. A few tried their own luck by holding their smartphone to the telescope eyepiece. Most of them couldn’t believe, that their *own* phone could do that πŸ™‚

The evening passed by so quickly, but it was a lot of fun and inspiring to talk to all the folks stopping by πŸ™‚

Circular pattern from Newton coma corrector in light polluted locations

As I am imaging in a rather severe light polluted location, where the landlords have installed significantly stronger light fixtures, I am plagued with strong gradients and a circular pattern in my images. These gradients won’t calibrate out with bias, flat and dark frames. I tried several approaches to get rid of them. I added a dew shield with no significant improvement. I added a light blocking hood to the back of my Newton scope with only marginal changes. I created flat frame images in different combinations (with or without dew shield, high and low exposure target, vertical or angled scope position, …). All with no significant changes.

Then I located several light leaks in my imaging train. The worst leaks were at the focuser base, the Off-Axis Guider and the mounting adapter between camera and filter wheel. After closing all the gaps, the results improved. But still the gradients were clearly visible in moderately stretched images.

Focuser base has no light shielding
Quite intense light leak made visible by flash light pointed at focuser base
Light shining through at camera flange
Core of imaging train, showing Off-Axis Guider cover to block light

So in all the past 3 years using this setup, my only chance to create acceptable images was to reduce as much of the gradients as possible in post processing. To accomplish this I had to set several hundred calibration points for background elimination in Pixinsight (loosing any chance to process weak background nebulosity or the like). This was a tedious work, as all calibration points had to be set manually (you may not have any stars or parts of nebulosity, a galaxy within the calibration point rectangle). And still there remained some residue if the gradients. So the results were not of the quality I strived for.

Typical raw image before calibration, stretched
Image after calibration, stretched, showing gradient and ring pattern
Image crowded with 800+ calibration markers for background elimination
Example of M100 after final processing (including background elimination)

Finally, I technically analyzed my scope and imaging train to check for defects like vignetting. I could not find anything, causing such a pattern. So I concluded, the only culprit possible could be the coma corrector.

History:
After several years using an economic GSO corrector, where stars have never been perfectly small and round in my setup, I switched to the Gyulai Pal designed TS-GPU corrector. Images have been really nice. But back then, I used a camera with an IMX183 sensor (15.8mm diagonal). A bit later, I switched to the IMX571 sensor, which has a significantly larger active area with a 28.3mm diagonal. Initially, I could capture images, which calibrated well. Though at this time, the street lights were far less bright and not LED based. So the filters could get rid of the stray light and light pollution. Now, with the close to 4x stronger LED street lights, everything changed.

As I (hopefully) closed all the gaps where light may enter, the front of my telescope should be the only place where light should enter my imaging train. Even with a dew shield it might be possible that light may shine to the front element of the TS-GPU corrector. Either direct or by reflection of the inside wall of the dew shield (which is not the deepest and blackest black possible), the corrector may pick up some stray light. To rule this possibility out, I attached a 10mm extension tube to the front of the corrector.
But unfortunately, there was no change in resulting images.

I could borrow 2 types of coma corrector from astronomy club fellows to test my assumption. So to test, I have one of each corrector: my TS-GPU, a Baader MPCC III and a TeleVue Paracorr. During the last weeks I captured M16 with all 3 coma correctors in L(RGB) and H-alpha from my home with the identical setup.

After calibration and stacking, I applied a background neutralization with only 8-10 calibration points to remove the large scale gradients from light pollution. Then I simply stretched the histogram of the images with automatic screen transfer function in Pixinsight and placed the 3 images of each filter set side by side for comparison. Well – I think, there is not much to say. Only the GPU coma corrector leads to the image defects.

Comparison of M16 in luminance with TeleVue Paracorr, Baader MPCC III and TS-GPU coma correctors
Comparison of M16 in H-alpha with TeleVue Paracorr, Baader MPCC III and TS-GPU coma correctors

Observations:

  • the TS-GPU corrector is with 10cm quite long.
  • the focus position of the TS-GPU corrector lies just a few millimeters above the inner limit of my focuser
  • the TS-GPU corrector protrudes in the tube by 2.5cm (1 inch)
  • both of the other correctors (TeleVue and Baader) require the focuser at the outside limit or even beyond (using extension tubes).
  • the TeleVue Paracorr is 7cm long- the Baader MPCC measures less than 3cm- At focus, the Baader and TeleVue have their front lens element way inside the focuser tube. Therefore, no stray light may enter the corrector

Conclusion:

In light polluted skies, especially with nearby (street)lights, which possibly shine in the telescope, you have to be extra careful. Any stray light may cause severe trouble in astro photography. Locating the light leaks may get intensive and very time consuming. But it is well worth it to spend the time. Your efforts will pay off in post processing and final image results!If you suffer from effects comparable to mine, you should not only hunt down the obvious light leaks (using a strong flash light or even sunlight). You should also check each and every optical component, if at some point stray light may enter your optical train. Try to close gaps and holes and shield your system as good as possible!

ISS Transit in front of the sun

On Sunday, May 1st, I was lucky to have the ISS transit the sun only a few kilometers away. Weather played with my plans as well. So i packed my solar scope and drove to a place right in the center of the transit line.
The transit itself is a very brief event. This particular one lasted for less than 2 seconds. So everything hat to be well set up before the clock reached 08:24:22 CEST.

This image is a combination of 15 individual images captured in 1.02 seconds. The solar surface was further enhanced by a stack of 880 frames adjacent to the transit itself.

M90 Galaxy

This is my first image of Messier 90. It is not yet as good as I would like it to be. Which is due to bad weather preventing further imaging. As the moon is already too bright, I will have to postpone further imaging at least to the next new-moon phase.
Nevertheless, this image shows already a beautiful spiral galaxy with its companion.

Image data:
Date: 2021-04-15 – 2021-04-16
Location: Graz, Austria
Telescope: 10β€³ f/5 Newtonian with GPU corrector (1250mm focal length)
Camera: QHY183M @ -20C
Filters: Optolong RGB + Baader UV-IR-Cut
Guiding: MGEN-II with off-axis guider
Exposures:
UV-IR-Cut: 45x120s, Gain 0, Offset 15
R 30x120s, G 25x120s, B 23x120s, Gain 10, Offset 15

NGC 3628 – Galaxy in Leo Triplet

This is the third and dimmest galaxy of the Leo Triplet. The other two galaxies M65 and M66 are quite close, but did not fit in the image. They seem to be not only close in our view. The three galaxies might interact in gravitational forces.

The dust band in front of the edge on view of the galaxy render it a very interesting and beautiful deep sky target.

Image data:
Date: 2021-04-04 – 2021-04-08
Location: Graz, Austria
Telescope: 10β€³ f/5 Newtonian with GPU corrector (1250mm focal length)
Camera: QHY183M @ -20C
Filters: Optolong RGB + Baader UV-IR-Cut
Guiding: MGEN-II with off-axis guider
Exposures:
UV-IR-Cut: 60x120s, Gain 0, Offset 15
R, G, B: 30x120s, Gain 10, Offset 15

M104 – The Sombrero Galaxy

M104 is one of the deep sky objects, I could capture during the past week of clear nights. M104 is a rather difficult target for my balcony imaging, as it stays quite low. So the influence of the air movements cauesed by the city, I am looking over, is significantly increasing stars and reducing detail in the galaxy.
Apart from detail level – this 4 hours worth of imaging goes deep enough to clearly show at least 4 small and faint galaxies around M104. The faintest being at 17.9mag.

Image data:
Date: 2021-04-04 – 2021-04-08
Location: Graz, Austria
Telescope: 10β€³ f/5 Newtonian with GPU corrector (1250mm focal length)
Camera: QHY183M @ -20C
Filters: Optolong RGB + Baader UV-IR-Cut
Guiding: MGEN-II with off-axis guider
Exposures:
UV-IR-Cut: 58x120s, Gain 0, Offset 15
R, G, B: 20x120s, Gain 10, Offset 15

Project: Messier catalog from Bortle 6 home

After several months struggle with my 10 inch Newtonian telescope, I got all configured properly. Camera, Auto-Guider, APT, etc. are well tuned to produce nice and round stars, even in several minutes long exposures.
I am unable to view or image the whole sky from my balcony setup. I may only point to an area within 80 to 220 degrees azimuth (south-east to west-south-west) and an altitude from 12 degrees to at most 70 degrees. In several occasions, this is truly a very limited view, when objects are only visible for short periods. But still, my view is facing south. So over the course of one year, the majority of the well known deep sky objects are passing by. And for the rest of the sky, I will find opportunities to drive an hour to one of my mountain observing spots with Bortle 3-4 skies πŸ™‚
Living on the northern edge of a city with a south-facing view is by far not a good combination for astronomy or astro-photography. Fortunately, the city I live in, is not too large. Therefore, my average night (if the sky is free from clouds), provides a Bortle 5-6 sky (most of the time 19.3 to 19.5 magnitues per square arc second). Visually, I have a hard time enjoying anything apart from the brightest objects. But imaging delivers really pleasing results.
During the last weeks of testing and imaging, I grew the idea to create my own Messier Object images catalog, where almost all images are recorded from this one location, with all its drawbacks. By pursuing this project, I want to show, that astronomy as well as astro-photography are still possible, even though light pollution gives us a hard time…

See the results, as I progress here: My Messier catalog from Bortle 6 suburban home

M48 and M65+M66 – finally with round stars

The past months I had trouble with my 10 inch scope. I was not able to image with nice round stars. So i kept imaging with my smaller refractor, as stars were rendered round. After some investigation and chat with fellow astronomy club members, I could nail down the cause of the elongated and triangular stars: the auto-guider as well as a too short settle time after dithering were messing up. So, to achieve the round stars everyone is after, I had to increase the settle time after dithering (otherwise, I got double-images due to the offset) as well as the guiding parameters in MGEN. My settings for off-axis guiding on 1250mm focal length are: Threshold: 0.1, Aggressivness: 100% in RA and 80% in DEC and 2×2 binning.

The first test target was M48 with 50% aggressiveness. Stars were not yet fine. The second target was M65 together with M66. Stars are fine!

Image data:
Date: 2021-03-31
Location: Graz, Austria
Telescope: 10β€³ f/5 Newtonian with GPU corrector (1250mm focal length)
Camera: QHY183M @ -20C
Filters: Optolong RGB
Guiding: MGEN-II with off-axis guider
Exposures:
M48: 83x10s L, 46x20s R, 30x20s G, 30x20s B
M65+M66: 48x60s L, 39x60s R, 32x60s G, 20x60s B

M42 with short 2 second exposures

It is amazing what modern cameras are capable of! Intreagued by learning how to improve the quality of deep sky astro photography, I stumbled upon Dr. Robin Glovers talk and essay on picking the correct exposure settings. Dr. Robin Glover is the creator of SharpCap, which is one of the best recording tools for planetary imaging.
A head full with new wisdom, I tested for myself, how true the statements according image aquisition were. Therefore I selected the core of M42 – around the trapezium – to set all parameters to. Using my 10″ f/5 newtonian telescope, I could set only a mind buggling 2 second exposure length, before saturating the 4 stars. I expected to gain a little bit of nebulosity, as the area around the trapezium is really bright. But what I could gain in post processing the 300 individual exposures is simply fantastic! Compare the 2 images attached – the nearly black one is one of the individual frames used to create the colorful result!

Image data:
Date: 2021-03-25
Location: Graz, Austria
Telescope: 10″ f/5 Newtonian with GPU corrector (1250mm focal length)
Camera: QHY183M @ -20C
Filters: Optolong RGB
Guiding: MGEN-II with off-axis guider
Exposures:
100x2s R, 100x2s G, 100x2s B

M51 and IC434/NGC2023

Saturday night, the sky was a spectacular sight. I had the chance to go out to one of my favorite places for observing. The sky was so full of stars – it was really a treat! A bit of “discomfort” posed the low temperatures, which were around -10C all night long.

As I arrived later than I hoped for, I immediately set my scope up. Scope and camera setup were up and ready for imaging soon. But then – a series of technical problems began. The scope did not fulfill GoTo commands properly. After solving this, the auto-guider could not calibrate well. I thought, it should be well enough. But upon inspecting the data back home, I had to discard more than 60% of the data due to elongated or totally ruined images. And finally, at around 2am my primary battery gave up (being only discharged 25%) due to the low temperatures. So I called it a night and went home.

The results I could gather are not as i was looking for. This is primarily due to the very low amound of data. But still, I add them here for the records…

Image data:
Date: 2021-03-06
Location: Gaberl, Austria (RGB) + Graz, Austria (H-alpha)
Telescope: 102mm f/7 APO with 0.79x flattener (equals to 564mm focal length)
Camera: QHY183C @ -20C (RGB) + QHY183M @ -30C
Filters: Baader UV-IR-Cut, Baader H-alpha
Guiding: MGEN-II with off-axis guider
Exposures:
IC434: 24x300s H-alpha, 19x60s RGB
M51: 19x60s RGB

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