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inFINNity Deck

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    Optical instruments, history of science
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    Castricum, the Netherlands

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  1. Ok, that is interesting. The tilt can be checked by placing a Cheshire eyepiece in the focuser and brightly illuminate it while the lens-cap is on. If the lens-cell is tilted you will not see concentric reflections of the Cheshire's reflector. Nicolàs
  2. Hi Dan, indeed it is quite curious why these artefacts are not point symmetrical. Did you check the front of the lens-cell to see of the are any small uneven spots along its circumference? Do you also see the artefacts in each and every sub? Nicolàs
  3. Hi PottyMonster (is that your real name?), the effect you see could be an uneven spot along the edge of the aperture, although I would expect it to be symmetrical, which it is not in your case. The same for pinched optics, these should be symmetrical as well. The Tak FSQ85 indeed has these dark spikes, which are always oriented perpendicular to the centre of the image. Most likely cause is an unfortunate lens spacing in combination with the type of coating of the lenses and that they are the result of physical amplification and extinction of the light. More information on imaging artefacts in a white paper on my web-site: https://www.dehilster.info/astronomy/imaging_artefacts.php Nicolàs
  4. If this photo is the pin in your focuser, then that is not the original one. The pin should be smooth, only having a smooth thinner section where the large balls run against. The original pins are made of hardened steel, not sure if the dowels you found are made of it as well. If not, they will be too soft. cheers, Nicolàs
  5. Hi Giles, that cage should indeed be properly filled as otherwise the pressure of the ring-nut does not get properly and evenly distributed. And replace all balls, so that they all have the same size. Then when tightening do it in steps and test whether it holds enough load. When overtightened the central pin may get dented at which stage the focuser gets beyond repair (unless you can source another pin). Nicolàs
  6. Hi Giles, see fig.3 on my webpage about my SkyWatcher Esprit 150ED: https://www.dehilster.info/astronomy/skywatcher_esprit_150ed.php The tiny balls, 18 in my FeatherTouch focuser, should fill the whole bearing. The purpose of the large balls is to create friction between the central thin pin and the conic outer bearing cage. This friction is created by tightening the large brass ring-nut, which pulls the three balls down in the conic cage, and to avoid that this causes too much friction between the gear housing and that nut a bearing with small balls is placed between them. As I wanted zero slippage I replaced the whole friction planetary gear by teethed planetary gear from a electro-motor gearbox (see above page). Nicolàs
  7. Hi Andro, I have written software (FITSalize) to do sub arc-second level deformation measurements using a stationary scope and plate-solving. During development, based on the algorithms in J. Meeus, Astronomical Algorithms, (Richmond (VA), 2005), I tested my software against Stellarium and soon found out that Stellarium corrects for precession and nutation, but not for aberration (the phenomenon where celestial objects exhibit an apparent motion about their true positions based on the velocity of the observer). Precession and nutation are accurately corrected for, I could not find significant differences with my software. In order to be still able to compare the results with Stellarium I made the aberration optional. Nicolàs
  8. Hi Alan, I just saw this thread last evening, so a bit late to chime in. I built my own dome six years ago of corten steel (base ring), pine (rafters), plywood (first layer of cladding), and zinc (final cladding), the construction of which can be found on my website: https://www.dehilster.info/astronomy/building-an-observatory.php Regarding your questions: Wind: it is a very good wind breaker, I have been imaging and observing quite often in conditions that seemed to be unfavourable. If you are going to build your own dome you need to avoid any openings larger than 10 millimetres that cannot be closed as the wind will blow in rain, hail and snow. Size: my dome has an inner diameter of 2.8 metres, which is fine when I am alone or only with my wife, but not suitable for more than four adults. I'd recommend a diameter of at least 3 metres (yes, 0.2m already makes a difference), but preferably at least 3.5 metres, that will easily accommodate around 8 adults. Move house: why, if you have an observatory? More seriously: you are moving to a new home and already considering selling it? In other words: do not live on fears! My wife and I hope to move from our current home with our feet forward first. In case future decides otherwise we probably have bigger concerns than an observatory on the roof of our house. A motor for controlling the dome azimuth is a must, for controlling the shutters is nice to have, but so far I am doing without and I have not missed it yet (for my azimuth-motor solution, see https://www.dehilster.info/astronomy/dome_automation.php). Main advantage of a dome is that you can do maintenance and test-runs while the weather is poor, most ROR domes do not allow for the mount to turn when closed. Domes also do have a downside: whilst very comfortable under windy/cold conditions, the capacity of a dome to provide this also results in what is called dome-seeing. Especially when doing solar (but at times also planetary) imaging the dome seeing can have a significant effect of the quality of the collected data. One way to overcome this, is to have the option to open a door or large window opposite or below the slit to allow a steady airflow (in our case the observatory is 7 metres above ground level and we can have all doors open, creating a chimney effect that brings cool air). Looking forward to your progress on this! Nicolàs
  9. I use an ADC to get rid of the Newton rings. It has the added advantage that you can move the solar disc into the sweet-spot with it. Nicolàs
  10. Those four bolts (six in my pier) are also referred to as a "rat-cage" (or "rat-box" as you called it yourself) of which is said that it would ruin the stability of your set-up. My rat-cage is very low, but friends of mine have 'decent' rat-cages and no issues at all. As long as the bolts are thick enough and the set-up properly balanced, the rat-cages are fine (IMHO that is). Nicolàs
  11. Hi Vox24 (is that your real name?), both have some wisdom and truth in it. I am a hydrographic/land surveyor for 35 years now and know a fair bit about setting up all kinds of optical instruments on tripods, piers, etc. In addition I built my own domed observatory six years ago. Setting-up instruments on a level base is always easier than on a non-level base. But as mentioned, there is no need for the base to be level. In astronomy doing a polar alignment is easier on a level base simply because when the base is level the altitude of the mount does not change when the azimuth of the mount is changed. On a non-level base the altitude will change and as a result doing polar alignment may require a few more iterations in that case. So, for convenience, it is good to have the base level, but that is all there is to it. Nicolàs
  12. Nice to also see the Jovian moons that clearly in above image! Nicolàs
  13. Yesterday I had another chance, this time it stayed long enough clear to shoot 20 x 15s subs in RGB and 60 x 15s luminance. Processing was thus now done with luminance instead of the blue channel as luminance. Capturing done between 19:35UTC and 20:08UTC with the SkyWatcher Esprit 80ED and ZWO ASI1600MM Pro Cool. Unguided tracking on the comet. P12/Pons-Brooks was at that time just south of Hamal in the constellation Aries at a distance of 241 million kilometres from Earth (1.611AU). The bright star in the end of its tail is HIP10657, the one at the left is HIP10795. Nicolàs
  14. Here are two nice resources related to solar activity and sunspots: http://haso.unex.es/haso/index.php/on-line-archive/ https://svalgaard.leif.org/ A recent work that I would recommend is C. de Jager, S. Duhau, A.C.T. Nieuwenhuizen, Solar Magnetic Variability and Climate, (Alkmaar, 2020). Kees the Jager was a renowned Dutch solar astronomer and published this work when he was 99 years of age! Weather permitting I do sunspot observations daily both for a project led by Leif Svalgaard and for SILSO. My data is archived at HASO, hence above two links Nicolàs
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