Rusted

They look strong enough if you remember to set them without fail. The two legged vermin would struggle to lift the roof off too. I prefer permanent hooks or plates riding over the moving parts. Though it may not always be possible with some roof designs.

Thanks Merlin. I thought it was a bit too easy. Hope all is well in your area Down Under? The fires have been dominating the global headlines.

Well done! Like the recycling, design and workmanship. Make sure you have plenty of strong roof restraints in case of gales. Preferably something which works without needing to be set every time you close up. An arched roof may produce lift if the wind is in the right direction.

There seems to be some variation in user's experiences here. Can I try to expand the discussion slightly? Are there alternatives to these "dedicated" diagonals + blocking filters to obtain considerably more, clear filter aperture? I'm thinking of 1.25" or 2" filters which can be placed further upstream. A Baader D-ERF energy rejection filter is assumed as standard up front. UV and IR blockers like the Baader H-alpha 35nm and Beloptik's IR KG3? About 250 Euros for the pair in 2" ahead of the etalon. Could use multiples of each and stacked in series for greater reduction outside the nominal passband? How much more blocking is needed for visual [or imaging] H-alpha beyond these three filters?

Aha! But think of the advantages of not having to strain one's last few remaining brain cells when an app is available at the mere brush of a key? There was a time I would write software to calculate and depict the spherical, chromatic and other aberrations of five colours of light at the focus of doublets and triplets. Back then, offences against the Sin condition would roll off my tongue like a snake oil salesman at a village fairground. Now they have OSLO. So those new-fangled floppy disks and thermal printers are as out of date as a horse a buggy. Pick a card. Any punched card! I'll get my [white] coat.

Hej Lars, Yes that is the correct filter. It is used to remove much of the sun's energy before it reaches the etalon and later filters. I am sorry for the loss of your friend. He seemed very dedicated. I can read some Swedish thanks to being able to read quite a lot Danish. The advantage of eyepiece projection was the precision of spot placement on the solar disk drawing. Most people use solar foil for visual solar observing now. So they would need to transfer what they see onto a scale drawing of the disk. The PolCor2 Debris Finder seems similar to a folded, mechanical spectrohelioscope [or rather spectroheliograph?] in some respects. Very interesting but looks horribly complex to make and align such a thing and then get it to work as expected.

Hi Lars, Your app does indeed work with longer telescopes and much more distant filters. Using manual overwrite entries. I use a 90mm internal D-ERF filter half way inside the main tube of a 150mm f/8 modified PST, H-alpha, solar telescope with a ASI174MM camera. [~11x7 sensor] I haven't checked the actual distance to the filter with a tape measure [yet] but your app's figures look close enough. Many thanks for your useful resources.

Thanks Lars. May I ask why you limited the distance between the sensor and filter to 150mm? For some solar H-alpha applications, energy rejection filters are sometimes placed up to midway between the objective and camera sensor. Where these distances might well be up to 1000mm, or even more, with a longer focal length lens. I have used the bright, tapering light cone to decide on best filter placement to avoid vignetting but this is very fiddly in a long, closed tube.

I managed 16" at f/5 on a full thickness plate glass blank but when I decided to regrind to F/4 I ran out of patience. The F/5 went surprisingly quickly. A low expansion blank is far easier to work with than plate or float glass. No endless waiting for testing. A thin mirror probably needs to be mounted on a multi-point supporting cell and rotated regularly to avoid astigmatism. That's how I worked mine on a 24" lathe faceplate, face up and driven on its edge by a long v-belt from a gearbox motor. I almost always worked by DIY reciprocating machines. Hand work is far quicker and arguably provides a smoother surface. Machines can cause rings and zones from repeating exactly the same length of stroke without care. With handwork, no two strokes are the same but you have to avoid the heat of your hands affecting the glass. Machines have the advantage that you can provide more power and relax during wets but are not compulsory. Mike Lockwood suggests that thicker blanks take such a long time to cool that they should be avoided in all sizes. Not just for the change of figure, when cooling, but the thermal currents rising from the surface. Fans can break up thermal currents and force more rapid cooling or equalization. But need power and may cause vibration.

Cons: Sheer size, weight of literally everything involved, sheer bulk, viewing height, danger of falling, bad back, covering the beast, recovering the beast after another storm, moving it about, number of clear nights, planning permission for a barn conversion, etc. etc. Ready made? Don't forget to add the cost of the air fair for the forklift driver's seat for the primary alone. Or cost of borrowing one at each end. Making a 24" mirror starting from zero? Nah. Several years minimum. Even if you are a "natural." Practice at the dinky sizes doesn't scale well, IME. Mr Lockwood himself recently mentioned lots of interest in using "light amplification" even on on his larger apertures. Bingo!

Some chainsaw suppliers will sharpen any saw chain for you. Only takes a couple of minutes with the right machine. Handy for saws with odd-sized chains or discontinued models. Small, narrow chains don't have the stamina and soon blunt. I spent years sawing and splitting logs for home firewood. Until I started valuing my own labour and limited free time. It's a mug's game.

The DeWalt 54V 9A rechargeable chainsaw is ridiculously powerful without the motor racket. I used it to clear huge birch stumps left by the lazy tree feller. Which meant cutting into very dirty wood and gritty soil on a bank. Like butter! It needs the same respect for safety as any powerful, motor saw. But doesn't exhaust you with the weight, constant noise and endless restarting.

A bit harsh? Texas sunshine? Probably a bit fiercer than sun-baked Surrey? I think Stu's eye shields do offer rather more than mere light exclusion. They also provide some useful, distance-related, eye relief control. I had similar excess eye-relief problems with my 40mm Meade 4000 Plossls on my TE binoviewers for H-a. Never used them again! Had I really wanted to, I'd probably just add a couple of black "funky foam" eye tubes. The 40mm "tunnel vision" view was very disappointing when I was hoping for a 32mm but with extra low power on steroids.

I've been using barbel weights for years on my old Fullerscopes mountings. Aldi did a nice set in a box with loads of smaller weights up to 1.5kg. Very handy! I used the cheapest and smallest diameter 5kg weights I could find online on my big mounting. At 9" Ø they only just fitted in my lathe to smooth the rim on the rather rough castings. These weights were sold as "Olympic standard" bore but were rather loose on my 50mm stainless steel shafts. I eventually painted them white to avoid them attacking me in the dark. It didn't work. They weren't properly "house trained" before I got them.

Judge them by their driving behaviour. They cannot risk easy discovery. If they can drive well then they are quite clearly alien. Though probably not transparent.

Only when they stare back at you! Spooky!

The enemy of handheld [or rested on walls] telescopes is magnification. The "wobbles" putting it in rather technical terms. With increasing aperture, the weight and length soon get out of hand. [A deliberate pun.] In the absence of commercial sky hooks you then have a problem of seeing anything! [At all!] Just take my word for it. There is a space race for larger spotting scopes for birders, hunters and wildlife voyeurs. The lenses and bodies get heavier with each increase in lens size. Which means a heavier tripod. Which needs a friend, Sherpa or slave to carry it all for you. Binoculars are available in many different sizes but nobody ever wants to carry them far above [say] a 40mm aperture and 8x. The sweet spot! Be very careful what you wish for. I have spent decades looking at laterally reversed images but I still couldn't eat a whole one. A "proper" terrestrial prism is essential to the full enjoyment and remaining sanity of the observer using any portable telescope. These prisms have n even longer glass path length than a common star diagonal. So choose your telescope carefully and wisely! Or be prepared to saw big chunks off your end. With advice from your fiends on SGL of course. 😉

For all our faults [well yours, not mine] we have been fabulously lucky to have survived this long. Big, fast, falling objects, too near to astronomical cataclysms, misogyny, pandemics, childbirth, advertising super-saturation, mass superstition, THE 1%, survivable temperatures, radiation, vulcanism, war, earthquakes, drugs and alcohol, volcanoes, inbreeding and interbreeding, climate change, starvation, flat feet, nuclear armaments, dirty water, tin pot dictators, dyslexia, exercise avoidance, UV, genetic defects, monarchy, race extinction, pop culture, obesity, trash foods and drinks, daytime TV, predators, AI, LBGT, Disney, gerrymandering, etc. the list is endless and I have hardly scraped the bottom of the barrel. There is bound to be more to come that we can hardly imagine yet with our myopic superstitions filtering every thought. Somehow we survived with compound interest. We are now so numerous that we are wrecking our only trailer home as we surround ourselves in toxic disposable garbage and take potshots at passing planets. All to satisfy the ego of billionaires, Dumb and Dumber to help their ratings on Junior Twatter. Every single organism in the universe has to overcome the same list and far more and survive to tell the tale in a recognisable language which allows learning from silly mistakes and to achieve iterative progress. Despite the absolute proof that we and they haven't a clue what we or they are really doing. And do so again and again and again and again at every single extinction hurdle which presents itself. Having survived into sufficient numbers to manage really large projects. They must develop FTL or [far more likely] astral projection to spread their own religion of crop circles delivered by black cheese wedges and silly, flying saucers. Well, I don't know about you, but I really don't fancy the look of yours! Don't you have anything with fur and pointy teeth? I could really do with a nice change.

A child proof pier? Whatever next?

There's nowt wrong with Cleethorpes! Mind you, when I were a lad on the herring fleets we'd set sail for Greenland whether we needed to, or not. 🥶

What Peter and Gina said. Choose a deep, rectangular cross section for a bent pier. NOT an I-beam or U-beam which both twist far too easily unless physically restrained. A deep box helps by increasing the moment of the beam perpendicular to the applied loads. Stiffness increases as the square of the depth of the beam or hollow rectangular tube. Which is why floor and roof joists are always set on edge. Not laid flat. Nor made square. Which is wasteful. Round tubes and poles are far more "springy" because they have so little resistance to bending. Moreover, the "leverage" of any offset telescope mass is always trying to pull the pier [or tripod] over at ground level.

I have some direct experience in this matter. My 10' dome is raised on a timber building to second storey height. The massive, pyramidal timber pier is almost immune to vibration. I even had my computer desk directly mounted on it for a while. I have just removed my 7" f/12 refractor from the massive GEM mounting. This was because it was catching the wind through the observation slit in winter. Not even a dewshield to act as a spinnaker and the cell was a couple of feet inside the dome surface. Just the bare objective cell on a long, smooth, 8" Ø metal tube. Early morning solar imaging in the three warmer months avoids the prevailing south westerlies. As the day progressed the slit and telescopes move steadily westwards. Beyond lunchtime was usually a problem despite the meridian flip. [When the telescopes were now pointing into the wind instead of sideways on.] The solar seeing conditions in windy weather are rarely much good anyway. But the general lack of sunshine means I like to try whenever it is shining. A bent pier is just one-legged tuning fork. A perpendicular dropped from the centre of mass must pass down through the pier into the ground. With a GEM that is the crossing point of both axes. Even an offset mass, like a typical fork mounting and hefty OTA [SCT?] will place serious asymmetric loads on a vertical pier. Asymmetry means easily induced vibration to every touch, footfall or breeze.

Hi, We had a sunny day on Saturday 4th Jan. Just before lunch the violent, thermal shaking calmed a little, but not completely. Still struggling with the new version of iMPPG followed by PhotoFiltre7. The usual 6" f/8, internal D-ERF, GPC, PST mods, ASI174. The ring of filaments above the bright AR is interesting. I was seeing similar detail on the monitor at the time.

I liked BBC Basic. You knew where you were with that. It was great fun finding typos and errors in formulae and worked examples in optical, ray tracing, classical text books by the "Great Masters." And false starts in astro magazines where the writer changed the exotic glass and prescription between printed articles. On which glorious careers later depended. All done with countless, nested brackets. No matter how much you doubted your own software it always proved right in the end. Who needed OSLO when you had Basic? Now where's that smug smiley with the long white beard?

Software gremlins may eventually be our only defence against AI and The Terminator. Not theirs. Ours! I have determined that the imaging learning curve is overhanging, covered in dark matter and completely without foot or handholds. Every time you fall off you have to spend twice as much, as before, just to get back to where you last fell off. Meanwhile, the experts not only started with several lifetimes of natural skills and sheer genius, but are pulling ahead at just above light speed.