Rusted

I am a martyr to spicules, Dad.

Thanks. The formaldehyde warning came from a general polyester hate site. No poly-cotton bedding is safe, etc.

The morning cloud cleared to blue skies but the seeing was a bit "thermally." Late in the afternoon it settled a bit so I grabbed some videos in W/L and H-a just before the trees intervened. My first ever attempt at merging two images in PhotoFiltre. I'm afraid I got a bit greedy and pushed the prom too far at the expense of the surface detail in the final image. 150/8 CR150 working at 120/10. 90mm internal D-ERF + PST + ZWO 120MC + 2x Barlow nose in SharpCap. I promise to do much better next time.

Excellent! Truly remarkable! A bit more detail on your methods would be most helpful for we plagiarists.

No!

Thank you both. Very reassuring. We lost the local dealer of blackboard paint. So I thought I'd try "something completely different." The gardening "material" has a slight sheen but no worse than some matt black paints I have tried. Not is it likely to flake and coat my optics with sticky bits like the last pot of blackboard paint. Now I am off to paint the shiny new staples with a very small paint brush. Though I'm going to try to cheat first and try a Magic Marker.

Thanks Andrew. Probably pure coincidence but I had a couple of asthmatic moments in the last two days. Normally I'm not asthmatic [at all] except when spraying WD40 in a headwind. Thought I'd better check before it kills me.

Hi, As an alternative to the usual matt black paint I have hung weed control fabric on the wooden framework inside my plywood dome. I reasoned that the cloth is highly breathable. So may help to reduce condensation inside the dome. Now I am wondering if this stuff is suitable for a semi-closed environment? Though the dome is well ventilated. Could it off-gas [say] formaldehyde? The "cloth" seems to be a heavy, non-woven polyester. 100g/m2. Not unlike disposable boiler suits and J-cloths in appearance but almost black, heavier and stiffer. It burns reluctantly when lit with a match and burning drops fall as the material melts into a much smaller, black mass. Not much chance of a fire in the dome so I am not too worried about that aspect. Perhaps I'd better buy a fire extinguisher? Or take the cloth down again and paint the dome.

Thank you, all. I have been using the tiny buttons on the red case to focus. It's all very HiTec around here. I have the latest SharpCap 3.2.6086. No mention of 64 bit unless deliberately chosen and downloaded.

Thanks. There is considerable confusion over model numbers and matching software/drivers. The DC Focus V2 is NOT the ADDITIONAL FOCUS2 for those who need to run TWO DC FOCUS UNITS simultaneously. I can only find images of the original, black cased FOCUS2. No red cased V2 Focus2's appear to exist online. The V2 is the later casing of the original unit with a "proper" power cable instead of a cigarette lighter.

As am I. The HitechAstro DC Focuser crashes SharpCap so badly I have to restart the laptop to undo the total lock-up, with all that entails. I'm now setting the hardware to ASCOM simulation. But, of course, that doesn't actually move the focuser. There is nothing on the support section of HitechAstro's website about the 64 bit catastrophe. Nor mention of any coming updates. Nor did they bother to make it clear on the support page which of the similarly named softwares is essential not to break anything. I even sent them a handy page grab with added explanatory text but they were obviously far too busy with the 64 bit driver to respond. I'd send it back to the retailer for a refund but for the international postage and all the hassle of finding a real DC focus motor controller.

A world authority on the highest precision ever achieved in astronomical horology too? Including the genius of "Woody" Harrison, of Longitude fame? No. Not the US, comic actor of a similar name, but close. A multi-train, precision drive system, including serial spur gears bolted onto a plywood, altaz construction? Reversible synchronous or DC motor? Please keep those pictures coming! We are all here to learn!

Er-um-er.. "upside down" is not considered best practice for telescopes around these parts. Getting back to basics: One should never be afraid to borrow proven methods from other disciplines. Amateur astronomers always tend to think of equatorials in terms of heavy axles in bearings in solid castings. An engineering cul-de-sac inappropriate to the larger task in question here. Clock makers have used axles restrained by two or three radial bearings in a cage-like ring for centuries. So you can use very large diameter, lightweight, hollow shafts like tubular aluminium] or even local rings. Supported by three wheels set 120° apart around the circumference. The shaft rotates very freely. Which is why clockmakers used the device in both ultra heavy and in high precision clocks. The shaft is tightly constrained radially by the wheels. I use the term "wheels" deliberately to show that they need not be small rollers. Small rollers assume very high levels of precision in roundness and hardened surfaces. Wheels can roll over rougher surfaces without hindrance. In some of the heaviest and largest public clocks ever built, once per century between services was achieved. Plain bearings [bronze or brass on steel] were simply not up to the task because of very heavy, highly cantilevered loads. Literally tons dangling on the far end of the shaft and subject to weather, icing and massive wind loads. Now imagine your lightweight but bulkier equatorial mounting, so built. Large diameter, concentric, tubular, structural forms with radial wheel bearings separating the two at distinct points along the length. But, not nearly so bulky as a horseshoe or fork mounting. Nor with the problematic, high friction of Formica & PTFE in larger Dobsonian sizes. Both inner and outer structures can be open and cage-like for lightness but employing rings and wheels as radial bearings at critical points. Apologies for rushed image not having external rollers set 120° apart.

Back in the 1980s I needed an equatorial mount for my newly finished 16" f/5 mirror. I thought of railway wheels on steel rails. So I tried a 24"Ø x 1" thick machined iron disk. Resting on 4" steel edge rollers fitted with ball bearings and a stumpy PA. Too heavy to slew by hand! Grr! Then I made an 18" diameter PVC tube into a right angle joint and another joint at 50° for the PA. Think giant plumbing joints. I fitted the straight sections with 3/4" ply disk and glassed [GRP] the joints inside for extra rigidity. I imagined I'd use [Dobsonian] PTFE/Formica disk bearings but the friction was far too high. The idea of using very large diameter tubing for a mounting may have practical applications these day with foam cored, carbon fiber. It just needs a low friction bearing at the disk contact faces. Multiple journal bearings on edge set in a ring? Skate bearings are cheap and cheerful these days. Not back then. Precision of axes and surfaces could be arranged by longitudinal threaded rods like simple mirror cells. The finished items was hugely [sic] impressive and the accuracy of the fit between the tubes was truly remarkable. I thought myself a bit of a genius for a while [or a **** artist] until the bearing friction problem reared its ugly head. Cantilevered structures require high linear pressures to retain bearing contact. No doubt a lightweight equatorial fork could be assembled using foam cored carbon fiber. Just as we built stressed skin, lightweight plywood forks back then. No need for heavy steel sections and welding and solid shafts as thick as your arm. They can be built one handed by those impoverished enough. Or daft enough to try.

If one expects to have copiests of this project then it assumes you are pushing the boundaries and greatly reducing costs. The first requires that you manage to go well beyond the bleeding edge of current best practice. Which requires a thorough knowledge of the latest PROVEN trends of well heeled and highly skilled builders. Reducing optical costs must include obtaining the same very high quality for much less money than existing commercial sources. Making short focal length optics is very hard compared with average focal lengths. To expect others to follow you must offer repeatable excellence in all areas available to all who can match, undercut or exceed your own budget. Otherwise, why bother? Do you have a mechanical genius with a gift for really innovative design? Access to organic AI? It is now decades since Dobson popularized crude but workable, large aperture telescopes. The biggest were a real struggle or dangerously tall for a wobbly stepladder ladder in the dark. He bypassed centuries of heavy engineering but at the huge cost of poor drives for photography and imaging. Nobody {as far as I am aware] has yet pulled off a similarly affordable and repeatable equatorial mounting for large apertures built from dumpster diving. Though there is certainly plenty of rusting scrap metal hiding away in amateur's back gardens.

Thickness increases not only weight but thermal mass. Hours spent waiting for the thick mirror to cool soon wears thin. Forced air fans can help scrub surface thermal current but wont help the optical figure. It will still lag in a typically cooling regime where the blank is thick. As will a massive, metal, primary cell. Does the blank vendor guarantee precision annealing? What is the LE substrate material of choice? Can your optician work at or below f/4 in such apertures with guaranteed results to allow a practical sized instrument? Fast mirrors have serious coma. For which they invented Paracorr SIPS and Starlight Instruments. Search - paracorr Support for a large mirror is critical to its figure and much more easily achieved, using modern methods, in an altazimuth. Mirror cells by JP Astrocraft A well proven, tracking, equatorial platform is an off-the-shelf purchase. No need for a massive equatorial and crane hire to lift each separate component. Equatorial Platforms: Home Page Here is an example of a fast, modern Dobsonian. Just one of many in an expanding, global market, for mobile, large aperture telescopes. Observing with Webster 28" f/2.7 | Astromart Do an image search for Lockwood Dobsonian for more examples of large, fast, PRACTICAL telescopes. No personal commercial interest in any of the posted links.

Do a search for equatorial platform.

You could try asking Mike Lockwood how much he charges for such a pre-formed, 800mm F3 mirror. Think of the savings in time, weight, OTA size and money in getting it right the first time. Lockwood Custom Optics - In Stock & Standard Sizes Difficulty of support, handling and figuring rises as the square of aperture. Thermal issues alone make a thin & shaped mirror essential. 8 strut Dobsonian with all the latest and best US practices in primary and secondary cell design and altazimuth OTA structures/support/bearing systems. Mr Lockwood is a global resource and discusses all of these factors on his commercial website with constant updates. Successful telescope designers and builders run in parallel with his optical work. Note that the mechanical and optical frontiers move constantly forwards. As some of the brightest minds apply themselves to fast, large aperture telescope, PRACTICAL designs for those who can afford them. The compact instrument would be mounted on a well proven, commercial, equatorial platform. At a site where the average seeing and average cloud cover and security are actually worth investing in such a large and expensive project. Or you could spend years/decades building a white elephant at enormous cost in wasted time and resources like everybody else.

I have the Lacerta 2" and like the optical performance and relatively modest heat sink temperatures. I can get mine unpleasantly warm after hours of tracking the high summer sun with my 7". Lacerta fixed 2" ND3 in the base. Having a single polarizer in the rotating eyepiece base is a practical comfort touch. I added a [2"] UV/IR blocker as extra insurance due to my 7" [180mm] aperture refractor. You shouldn't need one with a smaller instrument and 1.25" wedge. I'm still moving a 1.25" Baader SC from eyepiece to eyepiece and to camera and to binoviewer and back again. Endlessly, so it must be really worth having to put up with all the hassle. A 2" SC would make much better sense for me but it is rather pricey. The 1.25" SC is well worth having for the smaller prism if it is still within your budget. One other thing worth consideration in your solar prism choice is the viewing angle of the eyepiece around lunch time in high summer. The Lacerta uses the 67° Brewster Angle and can make for some odd viewing angles when the sun is high. While in the other three seasons the 67° actually makes much better, comfort sense than the normal 90° IMO. This viewing angle factor will also depend on the size and mounted height of the instrument. And also on whether you want to use a binoviewer. In this case you may need to raise the instrument in high summer for greater comfort. Now what was the question again?

I hope you didn't forget the release agent?

I like the Baader Solar Continuum too and it does noticeably reduce the brightness. Not sure about its ability to protect against excessive UV/IR though. I don't think it should be considered a safety device. Not remotely cheap either!

I'll wear a tinfoil pirate hat. Just to be on the safe side.

If the image is too bright then rotating one polarizing filter against another will allow fine adjustment of brightness. Or you can use an ND [Neutral Density] filter. The real question is: Why does the image seem too bright? It shouldn't. Have you used the [wrong type] of photo solar foil instead of the standard visual type? Have you checked the filter for pinholes or damage without the telescope? Just hold it up and use the tiny sun to test the filter as you move it around in front of your face. Any damage will show as local brightening or glare from pinholes. Which solar protection filter film did you use?

For those of us still enjoying this newfangled wireless "thingy" I have discovered the orientation of my laptop matters. End-on to the distant router seems to be favourite for maximum speed on the Ookla straights. GM

I just checked. There is Frederiksberg Astro Society. https://astronomisk.dk/wieth-knudsen-observatoriet/ Astronomisk Selskab - Danmarks landsdækkende forening for astronomi They have a 150mm solar telescope! A real one! https://astronomisk.dk/?p=103 Not like my home made one.