Rusted

Thanks Dave. I'm suffering from asymmetric glare in the image at the moment. I have a tilt plate but it seems to do nothing at all visible up to its [say] 5mm max. So I'm trying to eliminate the glare by trial and error elsewhere. I'm temped to run adjusting rods to the internal Baader 90mm D-ERF to try tilting that. Or make a door and manually shove it about. Poor summer seeing isn't helping. Early morning seeing just won't stretch to a full day.

Nope! It was inches of sag. 2m long x 35 cm Ø circles carrying eight 16mm dowels.

The problem with any beam begins when you rotate it on its axis. Beams do not function well when the loads are across the minimum dimension. An equatorially mounted beam OTA will soon find the weak dimension. My twin profile beam was 4"x4" but hopelessly weak in torsion. I could have put my whole weight on the centre of the beam when "upright." Not having a laser handy I used a light but stiff crossbar. This easily indicated the OTA's own twist as I moved it around on the GEM. Square beams are not as stiff in torsion as round ones. The absolute worst OTA I ever made was with eight, parallel 16mm dowels arranged around eight plywood rings. It could not even support its own weight without sagging several inches at either end. I hope your new OTA works simply as a result of increasing its dimensions. Previously it had a very similar profile to a rainwater gutter. Which must be the absolute worst possible profile for resisting torsion.

You mean to say there are other planets above the clouds? I always thought it was an old myth. To go with "tridents" and things. How I wish I had an aeroplane, like you lot, so I could see them too. I'll have to look at FLightOptics website about booking a ticket.

It is not usual to have to clean between the glass elements of an objective. So leave it assembled and clean only the front [and back] if necessary! Blower first and then only drape a lens tissue in gentle, radial movements. Never rub hard! No matter how disgusting you have let the precious lens become. There is a considerable risk to any lens removal and replacement from its cell. The problem is the lens getting out of square and jamming fast in its cell. So just tipping the lens out of its cell is the worst possible thing to do! This error is likely to lead to a scallop of glass being cracked away from the lens surface. Usually from the softer and weaker flint. There is a simple method to lens removal and replacement which helps to keep the lens square to its cell. It involves a suitably sized short, drinking glass with a piece of cloth or several tissues placed on the rim to protect the lens. The short glass having already been placed on a firm table at which you are sitting comfortably. Swab please, Nurse? Now send her out of the room. You don't want any distractions! First you unscrew the retaining ring and place it safely aside on the table. Then you lower the cell with its objective over the drinking glass while keeping the cell horizontal. So that the lens is left behind, lying on top of the protected glass. With the cell now resting safely down on the table around the glass. Now carefully check the lens for edge marks or arrows. There should be pencil lines across both elements. The lens must be reassembled so that the marks match their original position and orientation. To do otherwise may result in serious optical problems or damage. Photograph the lens maker's marks if you can. Or make a drawing and keep it safe from marauding kids or negligent wives!! Send them on holiday first! Or take a day off work while they are at finishing school. This will help to ensure the lenses are re-assembled in the correct order and orientation. Reversing the procedure involves placing the lens sky face down onto the protected drinking glass. With the objective cell already lying on the table, the same way up as before, around the glass. You then LIFT the cell slowly and carefully around the lens until it rests safely inside the cell. Lower the cell again at the slightest sign of jamming and be more careful with your levelling of the cell. Once insertion is achieved, the cell and its objective are laid down on the table. Ready for for the retaining ring to be replaced. DO NOT PUT IT BACK DOWN ON TOP OF THE GLASS! NEVER TIGHTEN THE RETAINING RING TOO TIGHTLY! There should always be the slightest rattle in an assembled objective Unless, of course, a compression ring is part of the design. Remember where the ring went! Front or back? In between? Any spacer rings? YOU MADE NOTES or took photographs, or both didn't you? The sky face of the lens will always be facing downwards before re-assembly. Those of nervous disposition may like to start with the supporting glass half full of whiskey. [Or a spirit of your own choosing.] Which may ONLY be consumed afterwards as a reward for success! Or ONLY afterwards to drown your sorrows for abject failure. Probably leading to a nasty flake being gashed from the surface... of the priceless, historical and utterly irreplaceable, 24" Zeiss, Triplet, APO objective.

Chriske> You really are seriously multi-talented!

Convex facing the sky.

Stop glaring at me!

Food, eh? Who needs it?

That seems like a lot of concrete for such a tiny pier?

Lucky you weren't given an H-Bomb. You could have turned into a despot.

Roll off roof?

Buy two observatories get one free! Whatever happened to discount for bulk?

Really struggling with cloud, wind, seeing conditions and all round, ingrained incompetence over here. Tried the tilt plate without obvious change. The Internal D-ERF cell might be worth adjustable tilt. I don't even have a focuser for H-a since the short TS helical fell in half. It looks as if I might finally have to swap a kidney for the longer Borg helical.

Very even and natural results. Well done!

They always want to be lead guitar. Never just rhythm. The mass offset of the secondary arrangements are absolutely tiny compared with the massive primary. The short distance between the cradle and the mirror cell fixing allowed the OTA to twist on mine.

Congratulations on your truly impressive build. No need for the hideously expensive Starlight motor focus system. The cheapest Skywatcher clone DC motor focuser easily drives the 3.5" Starlight FT focuser via one of the black motion knobs via a timing belt and 10T pulley. It will vertically lift the weight of the Lacerta 2" solar prism and ZWO camera or binoviewer. Even more if you drive the golden slow motion knob. You won't want nor like the cheapo paddle in the kit though. Remote motor focusing is a huge bonus even if you are right beside the telescope. Particularly when focusing via a big monitor. The difference in whether you are in exact focus or completely out is absolutely microscopic even on my 7" f/12 refractor. You wouldn't know this until you stopped using manual focusing.

My wife suggested you were about to play "Stairway To Heaven" on that thing. I tried 4" wide builder's straight edge profiles for a beam OTA for my 10" f/8 mirror. It was fine "up and down" for an altaz but had awful torsion problems on an equatorial. The offset mass of the mirror twisted the whole OTA so that collimation became impossible. I hope your straight tubes can resist such torsion.

I am surprised that it is only 2 x 0.75mm^2. I use 2 x 2.5mm^2 stranded speaker cable when I want something with a bit of "welly" for my DIY subwoofers. Inexpensive in long rolls from discount car spares outlets. Clear with a blue coloured line for polarity. How do you tell a Genuine Arduino Nano from a "Dolly?" You can't. They all look exactly alike until they die young.

Set two OTAs side by side and have binocular finders?

I should us a fixed electric router attached to a sturdy centre support to ensure an accurate circumference. Move the "Pacmen" against the cutter. Not with the cutter. Any play [at all] between the router base and the geometric centre will make the exercise worthless. A simple plank between the two may not offer enough stiffness. A thick and stiff triangle is much safer. I speak as one who has struggled with cutting large, accurate curves in laminated birch plywood while building my dome. The router cutter [bit] will "dig in" if you give it half a chance. Causing a rippled surface at the very least. Small depths of cut, increasing steadily in fixed steps, using a sharp cutter. Some swear by up-twist solid carbide bits. I only had access to straight cut, normal carbide bits.

A modest collection of immodest telescopes. Check out the drives on the first example.

Thank you all for your continuing encouragement.

The strange smells in the ancient and mysterious, chemistry lab of my first senior school should have fired an interest. Had anyone survived the tyrant who was supposed to be an educator but chose sadism as his second subject. There were a lot of the "old school" types around back then. Supposedly, highly qualified academically, absolutely hopeless teachers. Most used parrot learning instead of inspiring already gifted youth onto greater things. This was certainly no Hogwarts. All were "bent" on corporal punishment. Probably terrified of the oncoming tide of teenage emancipation before they could safely retire. Insubordination remained a capital crime until my final release onto a totally unprepared world. Just finding a cottage, where one was still allowed to dig up the floor, was an insurmountable hurdle to freelance pyrotechnics by then. Most had been "gentrified" with faux, concrete pavers or herringbone brickwork.

Thanks, but is there an English version?