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 🙂
The evening passed by so quickly, but it was a lot of fun and inspiring to talk to all the folks stopping by 🙂
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 shieldingQuite intense light leak made visible by flash light pointed at focuser baseLight shining through at camera flangeCore 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, stretchedImage after calibration, stretched, showing gradient and ring patternImage crowded with 800+ calibration markers for background eliminationExample 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 correctorsComparison 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!
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!)
I like to observe or image through my 10 inch Newtonian and 102mm APO telescopes. Both have quite long tubes. When slewing to high altitude objects, you risk to collide with the tripod legs. There is only one way to avoid such situations. You have to raise the mount head from the tripod by means of pier extensions. When ordering an off-the-shelf pier extension, one would assume, it would be designed properly and provide a solid construction. With the SkyWatcher pier extension I was proven wrong – unfortunately. Here is why:
A few days ago I received the SkyWatcher pier extension I intended to use with my AZ-EQ6 mount. The pier extension basically consists of 3 parts: – A black base plate, connecting to the tripod – A “pipe” like part with white finish – A top mounting plate, where your mount will be attached. To attach the pier extension, one has to remove the Azimuth bolt from the tripod first. The Azimuth bolt has to be attached to the top mounting plate for fine adjusting the mount head. Next, one has to unscrew the 3 locking screws of the black or white base plate. Either one is OK, but with the white top plate it is easier to place the mount on top. The top mounting plate includes the M10 threaded rod with knurled wheel to attach the mount to. You have to securely tighten the M10 bolt to the mount, as you will not be able to tighten it more, once it is all set up. Finally, you place the mount head on top of the base plate / base plate plus extension (if you unscrewed the top plate alone) and add and tighten the locking screws.
Now that the mount is set up, you will soon discover the design flaws I refer to:
pier extension is not stiff enough As the pier extension consists of 3 parts, which are held in place by M4 screws, you don’t get a solid built like when the parts would have been welded together. As I have seen with other comparable products, an opening to one side would have provided access to the M10 bolt with a rock solid quality. A combination of AZ-EQ6 and 10 inch Newtonian is far too much! A small(er) scope and mount might be OK though.
No Azimuth locking bolt on the base plate This is a show-stopper to me! The whole setup from the tripot up to the scope turns on the slightes touch to the telescope! Any polar alignment will be lost upon changing eyepieces or the like!
I considered, drilling a hole to the base plate to add an azimuth bolt. Though as the whole thing was not stiff enough, I returned the pier extension (thank you Teleskop-Express for accepting a no questions return!). If SkyWatcher would re-design this pier extension or release one with significantly improved design, I would immediately buy one. But up to this point, I have to avoid high altitude objects (or use a smaller telescope)…
After working through all the data collected from the solar eclipse in August, I combined the wide angle images (8mm lens) and the images captured through my 600mm travel telescope to timelapses. The wide-angle video is the result of more than 800 single exposures, covering the day from around 6am till 5pm. The most interresting part around totality is significantly slowed down, as totality would be over in a blink. During partial phase, I was so busy trying to fix my automated triggering system, that I did not realize the clouds until post processing. So it was really pleasing to see all the clouds above my site vanish moments before totality began. On the other hand, the remaining clouds increased the view of the shadow of the moon passing over, which is just amazing!
The inlay in the wide angle video is derived from the high res video.
I am really pleased with the results, but check for yourself!
Several years ago I purchased my first telescope. The telescope had an EQ2 mount included. The EQ2 is an entry level mount, with an all in one mount and tripod base. The EQ2 served me for some time, until I got frustrated with the instability and bad and worn gears in my unit. So one day I replaced it with a goto mount. The last time I used it was for the 2006 solar eclipse in Turkey. Since then the whole thing had to sit and wait for a long time in the basement.
Several years passed until I added a Sky-Watcher Star Adventurer to my collection of gear (I am really happy with this little travel mount!). To use the Star Adventurer in its full extent, a sturdy tripod is required.
None of my photo tripods (neither aluminium nor carbon fiber) could provide a rigid platform to hold against the vibrations of wind or camera mirror flip. After reading several comments on tripods for the Star Adventurer, the direction was obvious to use a wooden tripod. I was already scanning the market for proper tripods, when I remembered the EQ2, which had quite a nice wooden tripod. The only problem to solve was, to replace the EQ2 head with a flat base. The base should provide a stable means to attach the Star Adventurer with one UNC 3/8 screw…
The design was straight forward: The construction exists of 2 parts. A 3-prongue base to attach to the tripod legs and a raised platform for the Star Adventurer. As I didn’t have a large enough piece of beech wood for the base, I used a 40mmx40mm beech wood block. The block was cut in 3 equal parts. These are mitered at 60°. On the other side, I rounded the top part (a rather aestetical finish) and drilled the hole for the bolt attaching the tripod leg.
The platform consists of one round disc of 40mm thick beech wood, which I cut out with a 100mm circular drill. The 4 parts were then glued together with 2 wooden pins joining each leg part, to enhance mechanical strength.
After drilling the required hole for the UNC 3/8 screw and the recessed hole for the screw head with washer, the whole part was sanded, cleaned and finished with hard oil. The platform top face received a rubber coating for a better hold of the Star Adventurer.
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