… in my world, there is Photography, Astronomy, Electronics, Software Engineering, 3d printing and much more
This eveneing I tested the capabilities of live-stacking in SharpCap and compared the results to a set of longer exposures. The results of the extremely short live-stacking are stunning!
Live-Stacking: 19×2.7s = 51s
Normal stacking: 25x30s = 750s
Imaging with narrow band H-alpha filters for solar imaging (prominences and chromosphere) requires the light beam to be almost parallel before entering the special interference filter called Etalon filter. This is achieved by i.e. telecentric systems, also extending the focal length by a factor of 2-4x. The sensor protection glass and anti-reflection glass of the camera create reflections with each other and the filter surface. Due to the parallel light beam, these reflections create interference patterns, noticable as so called Newton’s rings in the image. It depends on several different factors like sensor construction (micro lenses, …), exact angle of sensor in optical path, angle between sensor and filter / protection glass, … how strong the Newton’s rings influence the resulting images.
It is possible to reduce or eliminate this in post processing. But any minor shift in the imaging train will make it almost impossible to compensate with flat-field images.
Fortunately, there is one alternative option: tilting the camera by a few degrees (usually up to 5 degrees), to widen the distance of the Newton’s rings, where they are no longer disturbing.
As these tilt adapters have a quite steep price tag, I constructed and printed one myself. I had to create several versions, until I had achieved a proper stability as well as stray light protection. But finally, I have a working tool 🙂
If you are interested in the design, you find the 3D files and description here: https://www.thingiverse.com/thing:4301757
See how much the tilt changes the resulting image!
Hints to the images:
– The blurry look in the image with Newton’s rings results from the alignment algorithm locking on the Newton’s rings instead of surface features
– the adapter attached to the filter is a prototype without stray light protection. Hence a strip of black insulation tape was used for shade
Last night I spent near my home town – a short 25 minutes drive – to a place I frequently used years back for astronomy. It is a quite dark spot, though the light pollution is still obvious. Nevertheless I tried to go for some deep sky objects, getting as much observation / camera time as possible in the short nights of June.
My list of objects was not too short. All of them were well placed in the sky and really nice to see :-). So here you go:
1) Hercules cluster M13 (Sony A99ii, 800mm f4, 2xTC, 27x120s, ISO3200)
2) Virgo galaxies M60, M87, M90, M100 (Sony A6000mod, 70-200mmf2.8 @ 200mm f4.5, 22x300s, ISO3200)
3) Virgo galaxy M90 – though I intended M87 😉
4) Whirlpool galaxy M51 (Sony A99ii, 800mm f4, 2xTC, 6x360s, ISO3200)
5) Andromeda galaxy M31 (Sony A6000mod, 70-200mm f2.8 @ 200mm f4.5, 5x30s, ISO3200) – I made an error in exposure time, so instead of 5×300 I ended up with 5x30s 🙁
6) Jupiter (I did not pack my planetary imaging camera – so I used the same setup with Sony A99ii and 800mm scope at 1600mm)
7) Saturn (same as Jupiter)
And far too late (at 01:30) I set up my timelapse camera for a night-to-day movie. The milkyway was beautifully placed just above the pasture. The resulting video clip is below.
Finally a couple of cloud free evenings are here! So lets see, what is to see from the city…
From a balcony facing south across a city, there usually is not too much to expect. This time, I chose the star cluster M5, which is quite bright an was not too hard to see in the scope. Sure, it does not hold to a darker spot away from light polluted city skies. But hey, there is still a lot to see:
Image properties: 75x 40s, 800mm f/4, Sony A99ii @ ISO 1600
After the completely washed away telescope meeting in the beginning of May, I tried to meet up with a few enthusiasts with quite promising weather prospects. Unfortunately the cloud cover did not vanish all the way. Even though there was quite a lot of clouds passing over, I could manage to snap some light frames from M51 – the Whirlpool Galaxy.
Image properties: 16x 180s, 714mm f/7, Alpha 6000 modified
It was fun chatting and also delicious being hosted with creole food 🙂 which compensates for almost any cloudy night!
It is always frustrating to see good weather pass without the opportunity to do some photography – especially astro-photography. So even if time does not permit a trip to the darker spots in reasonable distance from my home, it is worth a try to setup the telescope on the balcony.
This time, clouds cleared throughout the day (and happend to reappear before midnight). So I had to take the chance to spot Comet C/2018 Y1 Iwamoto. Unfortunately, I was unable to spot the comet through the eyepiece. The sky was far too bright (approximately 18mpss) watching straight over the citys light dome and having a 60% illuminated moon shining bright. Fortunately, through the camera I could make out a smudge, being brighter than the sky.
Processing the 180s subs with 1 hour total exposure time, I could achieve this result (compare to the unprocessed image!):
Image is a composite of 2 stacks (one aligned on stars, second aligned on comet). The comet moved more than 1.5 degrees during the 1 hour capturing time!
Above the comet: NGC 2903 (mag 9 galaxy)
At left: NGC 2916 (mag 12.1 galaxy)
Imaging setup: 800mm f/4.0 Newton, Sony A6000 full spectrum modified, UV/IR block filter, UHC filter, coma corrector (at wrong distance).
20x 180s @ ISO800, darks and flats
Conditions: +2°C, 60% moon, 18-18.5mpss sky in suburban location (with ample street light)
After 2 weeks of thick cloud coverage, I had the chance to spend the evening at the observatory. Actually I jumped in to hold the guided tour this evening…
As there was almost full moon and some cloud coverage (which got steadily thinner) I played a bit around with the setup. I thought – deep sky at full moon is a waste of time. But how about the comets 46/P Wirtanen and 38/P Stephan-Oterma? How brigth are the comets still? Would they shine through the moon lit sky?
Well… I could not make out Stephen-Oterma. But Wirtanen was barely (in)visible. I had some other tasks to do, so I attached the camera to the scope and let it run to see, what may be gathered under these conditions.
Despite of the Moon and the corona of Moon, a little bit of the comets was still possible to process from 90 minutes of total exposure time each:
The following timelapses show, how much angular distance the comet 46/P Wirtanen makes, when closest to earth. From my data I see approximately a stunning 1° during 4 hours!
Timelapse 1:
85mm photo lens with 1.5x crop sensor
93 exposures, each 60 seconds long (93 min total)
Timelapse 2:
200mm photo lens with full frame sensor
160 exposures, each 90 seconds long (240 min total)
Timelapse 3:
715mm/f7 APO with 1.5x crop sensor
71 exposures, 30 and 60 seconds over 80 min
After several days with clouds, there has finally been a window of a few hours with stars visible. Unfortunately I had no chance to reach acceptable dark skies. So I had to deal with a more or less 5.5mag sky and some clouds passing by in eastern Austria. This image shows a bit more detail of Comet 46/P Wirtanen, as I used a 200mm telephoto lens. The result is not yet the image I am looking for. So I hope that clouds will clear up the next days for a better and longer imaging session…
Finally the full moon is over. The first chance to properly see some fainter objects like the comet 46/P Wirtanen. Comet 46/P Wirtanen started to rise more and more from the horizon. At November 10 the comet reached only 10° above the horizon. Now it is at approximately 20°. As for one day on November 28 the sticky clouds opened up above Austria. So I packed my gear and headed to the mountains. I ended up at a snow covered mountain top near Lachtal at 1857m a.s.l. At -8°C seeing, transparency and sky darknes were exceptionally! A really treat to observe 🙂
I set up my camera with a 85mm lens and captured 90 minutes of data until the moon rose. I chose the 85mm as I expected to see a tail extending from the comet. But as it seems, the tail is not extening sideways (seen from Earth) at the moment.
I am really pleased with the results and hope for another chance of good weather within the next few days…
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