Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.


  • Content Count

  • Joined

  • Last visited

Everything posted by Alan64

  1. With longer-focus doublets, it can be difficult to tell which convex side is steeper. All one has to do is to install the crown, take it out to test, then flip the crown and test again. The correct side will make itself known, even that of an f/15, I've found. However, the correct side of an f/8.3 should be a good bit easier to identify, and to where there would be no need to flip the crown; an f6 or f/5 being most easily determined.
  2. Be certain to note the order of the doublet... The crown lens is convex on both sides. The side with the steeper curve faces the concave surface of the flint.
  3. I could probably get those locally in zinc-plated steel, but not in stainless. Then, the undersides of the heads of these screws do conform to the shape of the slots' wells, although not perfectly as though the two were one. I did go out the next afternoon; glamour shot... Ever so lovely they are. Would that I had had them right after that one had flown into space. I'd be done with it already.
  4. I have one like that. It's a just a bit shorter, yet a 70mm like that one. It just arrived, last week... It doesn't have a finder, but then it doesn't really need one, as it's a finder in its own right. You may wish to get a star-diagonal to use with it at night. The included diagonal is for use during the day, for terrestrial targets. https://www.amazon.co.uk/Diagonal-Adapter-Refracting-Telescope-Eyepiece/dp/B07GPMX7BN/ref=sr_1_2?keywords=svbony+diagonal&qid=1574104670&sr=8-2 An extra eyepiece or two will enhance the experience. You might even want a barlow... https://www.amazon.co.uk/Svbony-Multi-coated-M42X0-75mm-interface-Astronomy-green/dp/B01ET5BNHA/ref=sr_1_1_sspa?keywords=1.25"+2x+barlow&qid=1574104839&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyWFFWMzJaRkM5R05OJmVuY3J5cHRlZElkPUEwODQzNDMyMktNMjZYMlJTWExJSyZlbmNyeXB0ZWRBZElkPUEwNDU1MTAzMjBKUFRUVjNNUThVRyZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU= Those are just examples of what's out there, and to make the most of it. eBay is another source.
  5. The base has long, open slots in line with the holes of the tube... There is that. It is what it is. I suppose one could tap holes perpendicular to the slots, but then they'd have to drill two more holes into the tube, and precisely, in two directions. The only area I'd really want to tap is the side opposite of where that thumbscrew is, and then to place the thumbscrew there, away from the focusser; the stuff of dreams. But then, I don't have a tap-and-die set, either metric or standard. I've seen them at the hardware, and aluminum is not that difficult to do. By the by, very early this morning I had the second screw cut, but it was a hair too long, so I clamped the head of the screw into my vise-grips and began filing the tip down. All of the sudden, the grips snapped open and the screw flew off into oblivion. I spent almost an hour searching for it, but to no avail. So, today I'm going out to my local hardware and get a couple more... ...or should I get three?
  6. I felt the need to reduce the thickness of the M4 nuts by half, transforming them into jack-nuts. This will ensure that the combined thickness of the two washers and nut, each, will not jut into the light-path... Next will be to determine the final length of the screws, and then to roughen and matte-blacken the components.
  7. I have the new finder-base positioned here... Isn't it lovely? If you don't think that it is, but dead-common instead, please reply to that effect. Those screws are too long. I'll need to saw them down a bit. I don't know the mil, the thickness of the tube's wall, but I suspect that it's the same as that of many of my other larger and smaller entry-level telescopes. Given that, I don't see the need in adding a reinforcement plate on the inside for the base. The tube is not that flexible, at that diameter, just shy of 115mm. I think that in this instance a flat-washer and a lock-washer before each nut will be adequate. Yes, indeed, this type of base is going to be a bit over-kill, but I will be looking to swapping between a 5x24 optical or a red-dot, so it will serve for at least that versatility. I can't see attaching a 6x30, let alone an 8x50.
  8. The telescope is beginning to look like its old self again, and with its focusser installed... To ensure that the tips of the new screws would not jut into the light path, I combined #6 stainless-steel flat-washers with the screws on the outside, for a bit of lift. They also allow for a greater area of plastic to be spanned so as to reduce cracking or splitting in future... On the inside, indeed, the tips of the screws barely extend past the nuts... Afterwards, the tips were matte-blackened... The focusser is completed. The materials used for the focusser's flange improve the seating of same onto the tube, and with less flexing and tension, of and on the plastic. The materials also serve as a shield against dust when the telescope is stored... Now to move on to the finder-base...
  9. It's a bit warmer today, with the cold-snap over the last week having finally subsided. The nuts and lock-washers are now blackened, hence the focusser is ready to install... It's difficult doing this sort of work during the winter.
  10. I don't really know how I ended up with a fourth nut, painted satin-black at the factory. It may have come from another kit, but it was in the bag where I dumped the screws and what-not for this telescope. In any event, I have a spare in case I lose one. The nuts and lock-washers for securing the focusser to the tube have been sanded and washed... ...and next to be matte-blackened. It's cold outside, and I don't want to spray paint indoors...
  11. You could make a pipe-type alt-azimuth mount-head for one of your tripods, and from plumbing/gas supplies... https://www.cloudynights.com/topic/582383-show-us-your-pipe-mount/
  12. Utilising mostly craft-foam and a bit of flocking, the flange of the focusser is now complete... Craft-foam is made of EVA(ethylene-vinyl acetate), as are the mid-soles of athletic, running shoes, so that should be quite durable. With those materials added, I will need to go to my local hardware and get three slightly-longer M4 screws to compensate. I suppose I can tend to the last two aspects until then: the finder-base and the dust-cap.
  13. First off, yours is a 200mm f/6 Newtonian-Dobson; my apologies for thinking that it was the 200P OTA, and at f/5. The secondary off-setting for an f/6 will not be as "wild" as you saw within my images of an an f/5 and f/4, but there is an off-set nonetheless, just not as noticeable. However, within your first image, it appears as an f/4 even, hence my thinking that it was an f/5. The off-setting should not be that drastic for an f/6. The small, lighter circle should appear more centred over the larger, black circle compared to the f/5 and f/4, although not close to being perfectly centred. Here's a mock-up I made with the scene from my 150mm f/5... If I had a 150mm f/6, the scene would appear as that on the right. The secondary-mirror(black circle) would be smaller, and the underside of the Cheshire or collimation-cap(smaller, grey circle) would be more centred within the black, but again, not perfectly centred. You may not be able to see the primary-mirror's clips due to the focal-length of the telescope, and at 1200mm. You can try to draw the Cheshire back away from the secondary-mirror, but then the tool may not be held within the drawtube as securely. It may wobble, depending on how far you draw it away. A collimation-cap is, reputedly, easier to use over a Cheshire, but I do love my sight-tube with its cross-hairs. I would suggest getting a cap... https://www.firstlightoptics.com/other-collimation-tools/rigel-aline-collimation-cap.html You can also make one, and with the dust-cap from a 1.25" focusser, or from the 1.25" adaptor for the 2" focusser of your kit. You would drill a 2mm hole precisely as possible in the centre of the cap, then line the underside with a circle of aluminum-foil, the dull or shiny side; try both. This is my own collimation-cap, and that came with my 150mm f/5... That's a 2mm-diameter peep-hole there. You may find that easier to use, in the beginning. Incidentally, the faster and shorter the Newtonian, the larger the secondary-mirror and the greater its off-setting. The reason the mirror has to be larger with a shorter instrument is due to the fatter tip of the light-cone from the primary-mirror once it reaches the secondary-mirror... See what happened when I shortened the tube. Look at that monstrous tip of light heading towards that now too-tiny secondary-mirror. You can't get past the ol' physics, else I would have a 200mm f/2, and for those bright, ultra low-power and ultra-wide views of the galaxy in Andromeda... That's not happening, I'm afraid. Know your Newtonian; its innards... It's the secondary-assembly and -mirror that gives the most fits. Master it; you will, in time.
  14. Yours is a 200mm f/5, my own is a 150mm f/5; here's the collimation-cap scene of my own... At f/5, the secondary-mirror is off-set. Note that the lighter circle is not centred within the black circle. That's the off-setting, and it's correct and normal. Here's the cross-hair(sight-tube) scene of my 127mm f3.3 or f/4... Note that the smaller circle is definitely not centred within the larger. Faster, shorter Newtonians have off-set secondary-mirrors, and the off-setting occurs automatically as you collimate, thank goodness. Both of those are well-collimated. Use them as a guide if you wish.
  15. Here, I've bolted the focusser onto the tube... ...but only as a test-fitting. Much improved it is, very little if any teeter-tottering, and over the condition in which it had arrived. I could just leave it at that. The focusser appears true and square, and with very little deformation of its flange. This type of plastic is rather stiff; not flexible at all. It needs a bit of dust-proofing, and some lock-washers. Now, the angle at which I had taken that photo is by no means true and square.
  16. The focusser teeter-tottered side to side, like a see-saw, but no more since I installed those shims. An aerial view, and after they were trimmed... To those I need to add something...cushiony, like craft-foam, felt, or flocking, or all three.
  17. The tube simply has a steeper curve compared to the shallower curve of the focusser's flange. It was not matched well, at all, at the factory overseas. It would better fit a 130mm or even a 150mm tube.
  18. 5-minute epoxy was used to attach the shims. The epoxy set up quite fast, and a credit to its type. The surfaces to be joined were scored, but for some reason I didn't sand them beforehand. I don't think they'll pop off however... After a bit, I'll trim them flush. I only wanted to build up the surface, one step at a time. This is just the first layer of material.
  19. I've had these black-plastic sheets for a while. Shims they will serve as, and to compensate for the gaps. I'll be going inward with them almost halfway from the edge, but not quite as the flange is curved.... Any fine-tuning required, and in getting the focusser, the drawtube specifically, true and square to the optical-tube, can be accomplished with other materials that I have at my disposal.
  20. Are you saying that the resolution per eye would receive that of a 4.25"?
  21. Regarding resolution per inch of aperture, would you get that of a 6" for each eye, or that of a 3" still?
  22. The gaps when test-fitting the focusser onto the optical-tube... How would you go about rectifying that? Where there's a will, there's a way.
  23. Those are for making fine side-to-side adjustments when aiming the mount-head, the RA-axis, towards Polaris. You rotate the mount and tripod side to side roughly to line up with Polaris as close as you can with your eyes, then you use those knobs to fine-tune whilst looking through the polar-scope. You may have to slightly loosen the clamp that attaches the mount-head to the tripod for it to work. If so, then once you're aligned you tighten the clamp. Oh, one more thing: with the "Star Discovery", only short timed-exposures are possible with the camera. With an equatorial, and how accurately aligned you are with the NCP via Polaris, you can take much longer exposures, and in gathering that much more light at one time.
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.