Three Quarks for Muster Mark!
6/26/2023. And one for me. A Daystar Chromosphere Quark arrived today, "used once," by David Tandy of AG Composites and offered on Astromart. Works like a charm. I put it behind the TMB92 with a 50mm extension tube to minimize the extension (and potential sag) of the focuser, turned on its internal heater, and collected some videos. I put the Baader 7nm Ha on the end of the A-P diagonal as an ERF (said to be needed above 80mm of aperture, which this outfit barely is).
Visually, it's not much different from the single-stacked Lunt 60THa, but photographically, the field is far more evenly illuminated. At first, I didn't bother with flats, then tried a defocused flat (for dust on the sensor) and promptly lost control of the mount. I was using the SWSA and simply forgot that it has a dec slow-motion control built in. Instead, I kept fiddling with the alt and az knobs on its polar alignment wedge and kept loosening and retightening the dec lock to make adjustments -- this was "sub optimal" in so many ways. So the day was promising but a bit of a clown show. I am out of practice.
A few notes: at first I used a cell phone charger to power the Quark's heater. This worked fine as long as the Quark was drawing power while heating up. Once it reached equilibrium, the power draw fell below minimums, and the charger cut off and did not turn back on. It only took a few minutes for the filter to fall noticeably off band. I plugged it into one of the USB ports on the 12v battery pack I use to power everything astronomique, and all is well. (If I powered both the mount and the Quark from the charger, would the combination keep working? We'll find out in an upcoming episode.)
I got a couple of decent photos. Much better are to come.
- Try with a barlow on the snout of the Quark to raise the F-ratio from the slightly too-fast F24 (=4.3x5.5) used today. Be careful not to touch the diagonal's mirror. (6/27: The small barlow available here produced way too much magnification, at least for today's conditions. More experiments...)
- Check the optical train to be sure the Antares compressor is / isn't in the mix and try it the other way. (It was, and removing it was worthwhile; so is putting it at the end of the snout for a wider field.)
- Explore other click-stops on the Quark's heater once you settle on the mechanical details of mounting the filter, diagonal, and extender. (See below!)
6/27/2023. Something throttled the frame rate down from the 50-90 fps range (full frame vs 2000x1300) to just 8-12. Overheating is always a concern, especially under a fierce Sun. The camera heated up to 53C, and the computer was very hot to the touch. Try some aluminum foil. In the meantime: no to the barlow (except maybe under exceptional seeing), yes to removing the compressor. Make a solar finder.
The Williams Optics alt-az mount developed some slack. I disassembled it, found four loose bolts holding the uprights to its base, tightened them, and put it back together. Some LokTite will be in order if it happens again.
6/28/2023. "C" is for "Simmering" which is what this sunspot group did all day. It's grown dramatically since yesterday, and today between my first visit to it and my second five minutes later, it blew this huge bubble of a flare. The blast faded away over the next 15 minutes or so. This is the show near its peak:
Them what watch such things say it delivered 6 microwatts of x-ray energy to every square meter of the Earth, which doesn't sound like a lot until you convert 1AU to meters and do that Gaussian surfaces thing. Then it turns out that that bubble is shining with about 17 billion billion watts at x-ray wavelengths.
Seeing was pretty poor. A heat shield made of aluminum foil did not keep the sensor much cooler than yesterday (50.5C today vs 53.0C yesterday). As the sensor temperature passed about 48C, the capture rate dropped from 53 to 23fps (which is much better than the reduced rate I saw yesterday). Keep watching that and think about what could be done about it. I used defocused flats for today's clips. The Quark was set to top dead center for band control. Another question is whether it is possible to get a wide enough field for one- or two-part full disk images. I have my doubts that the ASI178MM can do that behind the TMB92SS, no matter what. I've got a 1.25-inch EOS prime-focus adapter on the way because I don't really want to disassemble any of the adapters I've got dedicated to this and that, but I do want to try a larger sensor behind this outfit. The 50D, the 6D, or the R6 may come through. And if not, well the adapter was cheap, and it's bound to be useful for something else.
6/29/2023. Getting to know the Quark continues. I did a series of exposures of an active sunspot as the filter came on band. Last night, I put myself to sleep working out the simplest of solar finders. I settled on a strip of 1/8-inch aluminum (an old yardstick) bent at both ends with a 3/32 hole drilled in one end and mounted on an Arca plate near the middle.
The shadow of the drilled end and the pinhole of sunlight fall on the opposite bent end. The strip was a total of 12 inches long and the "throw" from pinhole to screen is about 9.5 inches. At first I wondered how to aim it, then realized that "aiming" amounts to finding the Sun in the telescope and then marking where the projected image falls (shoot your arrow first, then draw a bullseye where it sticks). I attached the bent strip where a finder or a guide scope would otherwise clamp to the rings of the TMB92SS. Works great!
The air is smoky and very stable today. The Sun is not so fiercely hot on my skin. The camera continued to download at full speed as the sensor temperature climbed to 48C. I again used a loose aluminum foil tent, because why not?
I tried the Antares compressor on the snout of the ASI178MM and got a decently wide view. It would still take more than a couple (maybe 6) frames for a full disk. I'll try a longer extension (but I will not be surprised to run out of in-travel). The same compressor on the nose of a 20mm TV Plossl does not deliver a full-disk view, either, but it does deliver well over half the Sun at a time. Photos are more rewarding than the visual experience.
While the Quark was warming up today, I shot a series of ten brief clips (500 frames each), starting when I switched the heater on and ending when the filter signaled "ready." The process took almost exactly 8 minutes. Then I stacked the best 50 frames from each clip and refined each stack using identical settings and software. My subjective, eyeballs-only impression was that the 7th and 8th frames were marginally but noticeably better than the 9th and 10th (more contrast and more detail) which suggested that I had overshot the best filter temperature. Those two frames were captured 2 and 3 minutes prior to the filter declaring itself ready, that is, when it was somewhat cooler than specified. I cropped the last six images (all the ones that were plausibly "on band") to remove edge artifacts, reformatted them to 8-bit, and then stored them as JPEGs with quality 9. Sure enough, the files for the 7th and 8th frames came out about 5% larger than the others; I'm pretty sure that JPEG file size serves as a proxy for their total information content. That result is probably subject to all sorts of uncontrolled variables, but just the same, try turning the heater just a little lower next time out, one or two notches counter-clockwise from straight-up noon on the knob.
6/30/2023. Fifty years ago today: totality in the Sahara.
In the backyard, I tried the Antares compressor on the tip of a shorty barlow housing into which I inserted the the ASI178MM's 1.25-inch snout. This reduced the image scale more than enough to fit a full disk image on the ASI178MM.
I can reach focus easily by removing the 2-inch extension between the focuser and the diagonal, which as it happens still allows me to focus without the compressor. So that much works out well. I am less thrilled with the bandwidth of the compressed image which seems very broad, but the sky was hazy and that may have made a difference. Let's say this option is still in the works; I could do with quite a bit less extension between the compressor and the sensor. The compressor may be symmetric, which opens up some options. Too much hand-waving! More when I know more.
7/1/2023. I tried the compressor reversed and mounted closer to the sensor; I was not happy. Then I tried a shorter extension, but it was not quite extension enough. Under clear skies, the images can be quite good, so this is probably the way to get full-disk images. Eventually. Add a couple of filter rings to the Antares telecompressor to produce just the right extension, then work on flatfielding, bandwidth, and sharpness. Simple, eh?
As the day wore on, the reported camera temperature rose above 48 or 49C at which point throttling became pronounced. By 51C it was much worse. Today is a 90F day, with a somewhat brutal Sun. I've seen worse, but it's bad enough.
I shaded the camera with a loose aluminum shield; nothing changed, except the camera kept keating up. I pointed the telescope away from the Sun, and again, nothing changed. That was good news: the overheating is not coming from focused energy. The camera topped out at about 53C.
I tried a low-tech experiment: I held an ice cube against the back of the ZWO's case. The reported temperature dropped quickly to 38C. After restarting the camera, throttling was very much improved. I've ordered some heat radiators of the sort that attach to CPU, GPU, and other hot and busy chips. The back part of the camera is already mostly radiator, so this may or may not do the trick. If it does work, great; it's a $5 solution. I can imagine rigging up an ice bucket, but let's try this first. Others add fans and Peltier coolers, but they're mostly seeking low noise and longer exposures. I just want a few degrees of cooling on a hot summer day to keep frame rates up in a useful range, without vibration and no complexity.
Yesterday and today, I set the Quark's heater one notch shy of noon. Seems good. Jen Winters of Daystar says in a video that one notch of the tuning filter corresponds to moving the central wavelength by "1/12000 the diameter of a covid-19 virus" which is about 100nm, so 0.08 Angstroms more or less. Try this video
around the 48 minute mark, plus or minus. Heating moves the band redward, tilting moves it blueward. See also ATM Book 3 for people who were insane enough to try to make these things.
My solar images beginning in June 2023 are made using a Daystar Quark Chromosphere filter on a TMB92SS refractor. A 2" Baader 7nm Ha filter and an A-P dielectric diagonal provide extra IR protection. The camera (~2021 et seq) is a ZWO ASI178MM chosen for its tiny pixels and fast capture rate. It is notorious for a nasty pattern noise which can be avoided with careful exposure or removed using FFT-based processing. I capture
data using FireCapture, stack using AS!3, deconvolve and perform initial histogram adjustments using IMPPG, and polish in Photoshop. The solar kit is mounted on a Skywatcher Star Adventurer "tracking platform."
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