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About Rusted

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    ATM, imaging, Solar system, photography, blogging, cycling.
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    Darkest rural Denmark
  1. Lunt LS50THa unpackaging

    Rm [£GBP]cx * Ap[m] <= ∞ [The radius of cloud cover [in statute miles] is directly proportional to the expenditure on astronomical optical equipment [in Gravely Blighted Pounds] multiplied by the aperture in meters.] So stop doing it now!! Enjoy!
  2. Hi The new Maier ITF has arrived with an O-ring but no instructions where to put it. Should the O-ring go in first? Or on top of the filter under the lock ring? Thanks
  3. 6" PST Stage II progress.

    Ooh-er? My Maier ITF replacement has arrived in the post. Truly excellent service from yet another company has considerably hastened my H-alpha progress. But! I've got an O-ring in the package. No O-ring fitted with the original Coronado ITF. No instructions. I know the shiny green side goes towards the sun/objective. Red towards the EP. So what about the O-ring? I've searched online but come up completely dry. Bung the O-ring in first.. then the filter on top? Or filter first with the O-ring on top? Eany meany miney....?
  4. 6" PST Stage II progress.

    Hi Peter All thanks to your and Merlin's expert advice and experience. Still waiting for my new ITF but it's all coming together. I wasn't sure anybody else was using a 2" star diagonal. Even though the PST filters have rather small apertures. It just made so much sense I decided it was worth using the 2" Plus, the 2" fittings are so much stiffer when joined together in series. I also get a free push-pull 'focuser' by sliding the filter stack in the adapter. If I counter-bore the adapter I can increase the focusing range to about an inch without moving the etalon.
  5. 6" PST Stage II progress.

    Hi I have just taken delivery of a set of AOKSwiss' excellent PST etalon adapters. Building the optical train with correctly spaced PST components becomes much easier now. Looking at the ITF/BF5 assembly I noticed it has a parallel 36mm waist when both are screwed together. This could easily be accommodated in a standard 2" to 1.25" focuser adapter. It just needs to be bored out a couple of mm from 31.8 to 36mm. The filter's 'waist' allows 3/4" of 'focusing' in the bored out adapter. The filter stack then plugs into the top of a 2" star diagonal to maintain its original spacing. I have also built a dirt cheap D-ERF filter holder from a vintage, stainless steel, P.O. damp sponge holder. Bored out both faces in the lathe and lined and ringed it with cork to hold the filter. Then simply screwed it to the middle Celestron 6" refractor baffle with the same aperture as the 90mm D-ERF holder. It just needs to be shoved in on edge and then turned square to the optical axis to jam it in place.
  6. The 8.75" f/6.7 Mirror Grind

    Try an online secondhand book search website. Antiquarian, antiquariat, or whatever it's called these days. I never owned my own copies but borrowed them from the library on and off for decades. When I finally decided to buy a set they were listed secondhand online for quite a modest sum.
  7. Thickness of 90mm Baader D-ERF?

    Thanks, Peter. Mine has arrived in the post and left me wanting a bit of a discount to save my last kidney. I'd been chain drilling a nice piece of 10mm alu. all morning prior to nose dripping on the lathe. Now I can use something a little less 'deliberate' and save on tissues. BTW: Another dollop of praise for Teleskop-Express!
  8. Hi Quick question on thickness of Baader's 90mm D-ERF: I read online somewhere that they had standardized all filter sizes on 8mm glass. Baader's own website clearly says 6mm. An independent sales website says 5.5mm. The box clearly states 5mm which is confirmed with vernier calipers. I've spent the morning preparing a 10mm thick aluminium adapter ring based on false information. Anyone have a 90mm D-ERF with the same thickness as any of the above?
  9. I can see their design problem. They want it to look pretty and the rings to remain light in appearance. They have a problem with ring clearance around fatter guide scopes. So there isn't much room for added lugs or crescent options. Ask them for a new set of rings with countersunk non-threaded holes. Just to see what they say.
  10. Oh dear, indeed! Totally unforgivable fail on the first day of kindergarten engineering! A possible answer is a thick, wedge shaped washer or spacer under each [much longer] hex socket head screw. Even that would need a radius on the bottom to push the crushing forces [almost] perpendicularly into the ring casting. But, that wedge-shaped, curved washer would still slip sideways as the screws were tightened! The screws ought to be much longer and BOLTS to boot. [See below] As you have pointed out: The ring holes should be plain and not threaded. The manufacturer ought to be providing a complete flat topped, crescent shaped piece to fill the arc for adequate strength. The lateral [skewed] forces would then balance out. Or they should cast one in with a flat top into the ring! Or, provide local lugs for the screw heads to rest perpendicularly on the material to be fastened. A flat surface for a bolt or screw head to rest on is the most basic engineering at early caveman level. Cheddar Man would have known about the huge skewed forces involved in non-perpendicular bolt fixing beds! Interestingly [?] Orion UK's rolled tube rings suffer from exactly the same, appalling, design geometry. Advanced CAD blindness one presumes. From somebody who never made anything from scratch in their entire lives. Hint For The Day: Machine screws are threaded almost up to the underside of the head. Bolts always have a plain length of shank and a shorter thread length. The plain shank provides greater tensile strength and offers far better lateral location in correctly sized holes. Both are measured from the tip to the underside of the head regardless of thread length or head form. Second Edit: Having looked at the design again I have a possible solution. The manufacturer should have countersunk plain holes and used matching countersunk, socket head, stainless steel screws. The ring is very thin at these critical attachment points so the ring castings would probably need beefing up. This is NOT a DIY option because the countersinking tool is attacking the metal at an angle on a radius! It would need a stiff right angled drive to get the cutting bit inside the small ring! So it really needs a very special milling machine to do it right. In summary: I wouldn't start from here.
  11. Corroded ITF PST Mod

    Managed to get the etalon off my PST housing after an hour of cranking uselessly. Now I can do Stage II. I added a bit of plumbing PVC to make the Boa handle more comfortable and add a little extra leverage. It also trapped the rubber strap more securely than by hand. New ITF and D-ERF are in the post along with a set of Beat Kohler's PST etalon adapters at AOKSwiss. Not a great picture but you can see what is happening. It might help somebody who is on the verge of giving up.
  12. Just joined the H alpha club.

    Do you think he's teasing us?
  13. Corroded ITF PST Mod

    Hi and thanks, I am modding my old 6" f/8 Celestron refractor for H-alpha. It will go on my Old Fullerscopes MkIV. A nice bit of daytime observing will keep me off the streets. Used PST? Check. Boa strap wrench? Check. Rusty ITF? Grrr! D-ERF? Ouch! And so it goes on. What really surprised me, apart from the cost, is the extreme violence required to dismantle the PST! PST modification is certainly not for the feint hearted. Nor peace loving hippies. Well, not unless they built serious muscles 'hugging trees' and have their own ear defenders.
  14. Corroded ITF PST Mod

    Just me talking to myself as usual: PST dismantling Pt. 365. By sheer luck I found an old stock 'Constrictor' strap wrench in a rural timber yard. With the prism removed I could clamp the PST body down flat on the B&D bench with a plastic padded Bessey F-clamp. Don't forget some packing underneath to protect the finish of the prism housing if you still value it. Remember not to compress the tuning ring when clamping the PST housing down. It needs the gap in the workbench to avoid the tuning/etalon being crushed. The gold tube needs padded protective support at the objective end as well. This is to avoid bending the tube at the thread end as you lean hard onto the BOA strap wrench. Your weight would otherwise be cantilevered by the thin, gold tube, which isn't very kind. It feels incredibly violent as the parts unscrew in noisy jerks. With lots of very loud creaks, as the thread literally fights every degree of movement. I now have the gold tube free along with both sections of the eyepiece holder. The gold tube would not shift until I tried the old trick of tightening it first. Only then would it give under loud protest and lots of hard pressing on the BOA! The now naked threads are left with a powdery red residue. Red Loctite? With the workshop a nose dripping minus something I've brought the almost bare housing indoors to warm up the rubber tuning ring. At the moment the tuning ring looks and feels like very hard, shiny plastic. I need to get the tuning ring off, to get at the tiny screw, which drives the inner tuning ring. Try tapping your hand on the tail of the BOA lever while still leaning on it if your tube pretends it won't unscrew. Keep the BOA's rubber strap as tight as possible. It will work just like a ratchet so doesn't need to be re-wrapped each time. I'll post some pictures when I have managed to get the etalon free.
  15. Corroded ITF PST Mod

    Better late than never? Image attached of PST ITF from recent purchase. 101xxx Removed the prism and then put a small mirror at 45° in the housing for a "head-on" flash photo of ITF. ITF front surface flawless blue coating by reflection yet looks orange from most angles. The focuser spring is retained with a circlip, next to the black ring and can be pushed off sideways with a small screwdriver. Replacement ITF 656 /17 duly ordered from Maeir Photonics. Is the "glue" on the eyepiece holder a slow heavy drag? Or does it need a good wallop to break the thread locking agent? Is there such a thing as a PST "Locktight" solvent which might help remove difficult fittings? More images of disemboweled PST on my blog. 13+ ?