Updates

2023-09-20: Flake event

See the detail of the Flake event here.

2023-07-14: Chasing tilt – wide field scope

I have been working on the wide field refractor set to replace Moana during her overhaul. However there is some tilt in the new wide field system. I believe the tilt is mostly between the rotator and the scope, with possible low residual tilt after the rotator (sensor tilt) and low to very low miss collimation of the triplet. To be definitive on the triplet collimation I need to use my Takahashi collimating scope, but the adapter for it (Tak S coupling to 2″) has been out of stack for 2 years and there is no sign it will be produced any time soon (I called Tak America), so I eventually bought the Rap adapter instead, which is much cheaper and can connect to M48 thread. Once I get that, I shall answer the triplet collimation question with a high degree of certainty (hopefully).

On the focuser tilt, I have been using stars and Nina’s aberration inspector, from my back yard in the big city, in the midst of light pollution. That requires stars (obviously), so good weather, and staying up pretty late as it is summer and I do not get darkness before past 10pm. Of course, before I work the tilt I first need to align and all that good stuff, delaying the actual useful work even more. So progress has been very slow, as I have other things to do at night, like running Moana or sleeping. If somebody knows a better way to chase focuser tilt, feel free to pm me on Astrobin.

Moana has been performing OK, the electronic box is running warm in the desert heat, so I am cooling it using the exhaust fan, which kicks a lot of dust in the observatory (the floor there is super dusty, as there has been many visitors going in and out, and seemingly all ignoring the door mat). So Moana’s optics are getting dirty, and I should be doing new flats to fix that, but I am slightly worried that if I remotely put the scope head down looking at the flat panel, I may experience movement of the primary mirror again (hanging by the clips in its cell) and mess up the collimation. So, at this point I just keep going and monitor the situation. This is for sure an interesting chain of un-intended consequences.

Last, weather has been pretty cloudy at DSO and the summer nights are shorts. So less frames per night, and a lot of the acquired frames did not pass the bar due to atmospheric nebulosity. An then of course we just had full moon.

None the less, I managed to add RGB to M27 and NGC 6995 and shoot a few star clusters. I will update that soon.

2023-06-16: preparing a trip to DSO

I plan to get to the observatory during the next full moon, unmount MOANA and bring her back for a complete cleaning and overall. In particular: new vanes to reduce diffraction spikes, new carbon fiber primary cell to increase mirror stability without pinching the mirror, so I can get rid of that pesky astigmatism at last, new main camera to enter the modern era (overdue), and new guide camera. Possibly a remote dust cap/light panel and a Pegasus box V3. I want to take my time to test the upgraded setup, and the new mirror cell is still just a concept on the drawing board (but I have been thinking about it for 2 years now). So Moana will be out for some time, at least the whole summer, maybe more.

Meanwhile I will have a wide field refractor on the mount, so I do not miss a beat. Of course I still plan to continue distributing the data, till I run out of storage here, and hopefully beyond.

2023-05-24: A photogenic supernova in a nearby galaxy

This year (2023) has been particularly good for transient events: a great comet (E3 ZTF) reaching magnitude 8, and now a bright (magnitude 10) supernova, 2023ixf, in a nearby photogenic galaxy, M101, well positioned for Northern Hemisphere observing. I had waited for that for almost 10 years! As soon as the weather cleared I updated my sequences to image M101. The SN is so bright it even has diffraction spikes! See a raw frame below, which will be part of an upcoming RGB imaging dataset. The SN is outlined in red.

2023-04-25: Camera cooling properly after all

Well, last night the camera did cool without a hitch. Not sure what was going on. I will keep an eye on it. On the imaging side, I finished M94 and started acquiring luminance on M104, to see if it improves my usual RGB workflow.

2023-04-23: Camera not cooling properly

I have a feeling the fan on the main camera quit working, as cooling is very slow and the sensor does not reach -20C as it should. The good news is I finally got the QHY 268M camera, intended to replace the current camera. I have to see how I’ll go about this one. I may bring Moana back home and put a wide field setting on the pier, although it is a little earlier than I anticipated to do the switch: the milky way does not rise before 3am.

2023-04-19: Accumulating data

I have slowed down the rate of data posting. First because there was quiet a bit of bad weather in the last 2 months. Second because spring being “galaxy season” I am doing less narrow band and more RGB, becoming less tolerant to moon glow. Third because I want to focus on quality: deeper datasets (ideally 30 hours per target), image taken only very close to transit (so no more than a few hours of imaging per object per night), and discarding more of the questionable frames (gradients, soft focus/bad seeing, high clouds, tracking perturbed by wind). And Fourth the nights are just getting shorter.

In the meantime I just posted a photometric dataset for Haumea, which is at opposition about now (April 20, 2023).

2023-02-27: Bad weather streak, some imaging

The weather in West Texas has been horrendous, with clouds, rain and winds up to 60mph!! Only 3 nights of imaging in 3 weeks. The new moon has basically been wasted! But here are some updates:

• Guiding has improved incredibly with the added mass on the counterweight. I was surprised to see such a measurable improvement. When seeing is good I am now below 1 arc second RMS consistently, on every session. I said it below, but I guess I have to say it again. This was a very welcome surprise.

• Collimation is holding well. I stopped parking the telescope head down: although it is better to avoid collecting dust on the primary, I think the mirror, not being glued, does not like too much being suspended by its edges and possibly its clips. This leads to the mirror moving in its cell and decollimation. I am working on a new cell, made of carbone fiber to better match the thermal expansion of the borosilicate. The mirror will be glued on it.

• Looking at the corner of my images, it is pretty good, but I think it is possible to improve. My guess is that the primary is slightly pinched in its cell.
• Still some slight astigmatism when out of focus, small, but very consistent. Not sure if it is the primary being pinched, or the secondary, or some misalignment.

2023-02-16: Star test and imaging

Clear sky at last! Star tested Moana, resumed imaging. Tested Mico and started imaging. It is great to have 2 NINA instances running and 2 cameras churning images in parallel.

Also managed to run LRGBLRGB… on NINA without triggering autofocus, which is the correct way to image comets.

The added weight to the mount (18lbs) to decrease the inertial moment arm must be working wonders: for the first time (ever!) I started guiding below 1 arc second RMS in both RA and Dec! The low wind and good seeing were also helping.

2023-02-12: Upgrades and collimation

The following updates were performed:

• Added counterweight 18lbs.
• Fixed the light panel PWM power supply.
• Added a second 12v bus for the piggy back imager.
• Routed a new 12v power line through the mount for the piggyback electrical bus. For that I had to remove the scope and disassemble the top of the mount. I also checked that the USB and the main 12v line were not twisted. They were not: after 4 months of remote operations including 1 mount lost + manual remote recovery, I had no twists!
• Turned the camera so the sensor frame is squared with the spider. Also turned the scope in its ring so the camera is closest to the equatorial axis to reduce the moment of inertia.
• Installed a color camera on the piggyback, for dual imaging. The piggy back is a 200mm Borg 55FL Fluorite (some kind of Petzval Refractor from Borg in Japan), with an APSC color camera (ASI 071). The Borg is OK for 4/3 sensors, but exhibits coma for anything bigger, so this system is far from perfect, but since I have the camera and refractor, I may as well use them. I decided to nickname the Mini Color system “MiCo”. The Borg will eventually go and be replaced by a Canon-compatible telephoto lens (maybe the Sigma 180) with an Astromechanic focuser.
• Disassembled secondary and primary, dry cleaned them all (as well as the coma corrector), reassembled, and collimated with Catseyes autocollimator. This should have been easy, quick and smooth. But it was at the end of a very long day after driving 9 hours and working on the scope for another 6 hours, and somehow I botched the collimation. The scope started to exhibit terrible astigmatism. I initially tough the astigmatism was due to a pinched primary, or a pinched secondary or both. This seemed plausible, as I had just tightened the primary cell vigorously. So now I had a bad collimation and a bad diagnostic. I finally went to bed, and the mystery was not resolved until the following morning, with daylight, some coffee and a clear brain. The astigmatism was due to focuser axial error -with the daylight I saw the focuser axial shift clearly in the Telecat. Having found a likely cause I could precisely research my predicament, and found the following, in Vic Menard’s words, talking about Newtonians. “An oblique optical axis may indeed deliver an astigmatic image (ref.: Amateur Astronomer’s Handbook, J.B.Sidgwick). Furthermore, the aberration is more pronounced in larger apertures. (page 79, Astigmatism and Field Curvature). In the field, I’ve noted astigmatic defects caused by errors in both axes (focuser and primary) that smear the entire field of view unless the eye is very carefully centered on the exit pupil. The astigmatism was most pronounced with a significant focuser axial error combined with a minimal primary mirror axial error. The aberrations can be resolved with proper axial collimation, and the sensitivity of the pupil disappears as well.” With this new knowledge, I eventually fixed the problem to a good autocollimator read. Then, of course, the clouds rolled in. Although I was pretty sure the problem was solved, I could not star test. So I had to eventually leave DSO without the certainty I had solved my astigmatism problem.
• Last but not least, I saw one of the wild donkey who inhabits the Davis Mountain. Pretty cool!

2023-02-03: decollimation

Collimation had started to drift slightly in the previous months, so I knew something in the optical train was not stable. Some time ago, tracking low on the Western horizon I experienced a defocusing and decollimating event, which I strongly suspect was due to the primary starting to have some play in its cell: while tracking low, the primary is on its side, and not supported by the whiffle tree. The event felt akin to an SCT mirror flop. I remotely moved the telescope vertical (looking at the zenith) then leaning Eastward, and managed to unflop the mirror, but from hereon I knew I was due to a road trip. The only question was: could I keep it together a couple weeks until I received the new camera I have to install and do only 1 road trip for all the fixes and upgrades or … was it game over already?

Well, today I had another flop event, and from this one I did not recover. I managed to refocus (and therefore measure the mirror movement on axis by converting focus steps to microns), but I did not managed to unflop the mirror and the scope is out of collimation. I did not try too hard to unflop either: the right thing to do is to go to the observatory, tighten the mirror cell, carefully collimate and do the other upgrades.

Upgrades todo list. Those are my notes for the first trip back to the observatory since installation 4 months ago. I added a few comments & explanation as some people (considering remote imaging) may find it useful.

• Mark focus position on focuser, mark scope position in its rings.
• Remove the primary, clean it, secure it in the cell. Possibly glue it to the pads.
• Clean the secondary.
• Reassemble the system, recollimate. Follow the Vic Menard collimation book. Use the Glatter laser to get in the ballpark quickly, but finely collimate with the catseye tools (autocollimator). If time allows during day, investigate why the Takahashi collimating scope gives results so different from the other tools for centering the center of the primary. At night, star test & fine tune collimatin with the x4 Powermate. Once the scope is collimated and the Powermate still on, indulge some planetary imaging if the night is long enough. Put the coma corrector back and check the camera tilt with NINA, ASTAP and CDD inspector – should all be the same, but who knows!
• See if coma corrector and filters need blowing.
• Mark focus position. Calibrate the zero position of the feather touch focuser to the almost fully racked position. This will allow large defocus for the Pixinsight wave front analyzer (or the Innovation Foresight wave front analyzer). If time allows record the defocused images and check collimation with the wave front analyzer.
• Connect the secondary heater and add a an electrical fuse to protect it.
• Remove the Guide Scope piggy back: I never use it, as 100% of operations have been Off Axis Guided. That will reduce weight on the scope side, reduce overall inertial moment arm and reduce electrical load on the 12v bus. Possibly add a weight to preserve Dec balance. If rebalancing Dec by moving the scope in its ring redo the meridian limit procedure. Here and here.
• Add a new 18lbs counterweight to the shaft. The goal is to increase weight on the counterweight side, so the weights can ride closer to the polar axis and thus decrease inertial moment arm. You can read this if you need the full explanation. The second goal is to increase the frequency of the mount’s harmonic oscillations. This should help guiding in high wind (above 12mph). Follow AP’s recommendation: “we recommend a slightly heavy RA balance towards the counterweights and a slightly heavy Dec balance toward the back end of the scope when imaging.”
• Rise the flat panel.
• Change the flat panel power supply to the Pegasus Pocket box to have functional variable illumination of the panel using PWM.
• Change the power supply of the exhaust fan of the electronic cabinet to the Pegasus Box, so I can remote control the fan according to temperature inside the electronic cabinet, rather than having a thermostat-only activated fan.
• Add a new 12v power supply and power bus, route additional 12v cable through mount. Check any twisting of cables already in the mount. This is installed in prevision of a future wide field piggy back.
• Remove the network switch and direct connect to computer instead.
• Install the new camera if I get it by then. If not, redo the dark and flat library for current camera. Add 3mn darks. Also add higher gain.
• Redo the flats as collimation has changed.
• Square camera sensor to diffraction pattern for esthetic reasons. Achieve by rotating the coma corrector (and the rest of the imaging train attached to it). Recalibrate guider after rotation.

2023-01-28

I checked the images from the telescope icing night, and they look just fine. Maybe just a bit soft at the coldest point of the night, just before dawn. But I do not think I had any significant icing on the primary, secondary, corrector or sensor. That’s good as I imagine it could not be positive for the coating of those various surfaces!

2023-01-26

This morning I check the observatory cameras before doing the usual mount park, with the instrument head down (to protect from dust accumulation in the tube & mirrors). I found the telescope was marbled with frost , at least on the outside. Low temperature combined with 80% humidity resulted in the formation of a thin ice layer on the carbon fiber tube. The electronic, camera and mount still worked perfectly. I will look at the pictures and see if the ice affected the optics.