Alan64

Yes, but then I'd have to notch out that side for the finders' alignment-tabs... ...which I can do, easily, but then the thumbscrew would be forward, and would not batten down at the stalks entry-point, if that matters really, I do not know. In any event, for me, it's more of an aesthetic concern rather than one of practicality. I have relatively small hands, so it's of no real consequence. I do have this finder-base... ...but that one is for my Maksutov. It's not notched, however I just may notch it out before its installation.

I had gone to all of this trouble... ...and for naught, as the combined jack-nuts and lock-washers are just a bit too thick, and would intrude into the incoming light-path towards the primary-mirror. I then thought I might get by with the original screws... ...but two of the plastic, threaded holes of the cowling; one is totally stripped-out, and the other nigh to that, so there went that idea. Good thing too, as I really didn't want to use them after all. I went out earlier today to my local hardware, and got just the thing, or things rather... The black-oiled screws, with their shallow heads, will be inserted from the inside of the tube, and with the stainless-steel hardware on the outside. The lock-washers will be sandwiched in between the acorn-nuts and the flat-washers. Oh Julian; yoo hoo! You were prophetic, sir. A prophet in your own right... Even though I did not utilise your method for the finder-base, I am to employ it for securing the cowling. Thank you for mentioning it, as it undoubtedly influenced the outcome.

The telescopes attached onto these Dobson-type alt-azimuth mounts are Newtonians. Newtonians afford the largest aperture per pound spent. But there's a catch: Newtonians require routine collimation, more so than any other design of telescope. The procedure can be difficult at first, but then becomes easier; learning by doing, keeping at it. The shorter the Newtonian, the more difficult it is to collimate; the more exacting, the more precise the collimation needs to be, and for sharp and pleasing images, particularly at the higher powers. Note the focal-ratio when selecting a Newtonian or Newtonian-Dobson, and generally from f/4 to f/8. An f/4 is more difficult than an f/8. An f/5 is the shortest that I recommend and suggest. An f/4 Newtonian is configured primarily for photographic applications, although they are used visually, with eyepieces, as well. The longer the Newtonian, the easier it is to reach the higher powers, and where "Wow!" and "Look at that!" exist. But an object zips out of the field-of-view of the eyepiece faster at the higher powers; with a manual mount, without motorised tracking. The shorter the Newtonian, the higher the degree of coma is made manifest. At the edges of the views round stars become streaks, lines, particularly at the lower powers. No doubt the shorter Newtonians are most attractive, as they are more compact, ergonomic; easier to carry, handle and stow away. A 130mm or 150mm f/5 Newtonian is a compromise, and an acceptable one. You get a shorter tube, being more difficult to collimate, and more difficult in reaching the higher powers, but 2x and 3x barlows are available to ramp up the magnification. Never consider any Newtonian shorter than f/5, for visual use. After all, telescopes are all about seeing faraway objects up close. Else, use your eyes or a pair of binoculars. At a 1200mm focal-length, a 150mm f/8 Newtonian-Dobson is a bit long. My 150mm f/5 Newtonian, with a focal-length of 750mm, is a bit short... ...with the 650mm focal-length of a 130mm f/5, even shorter. Yet both, again, are an acceptable compromise between ergonomics and optical performance. A 150mm f/10, with a 1500mm focal-length, is a bit too long... A focal-length of 900mm is seemingly the ideal, the sweet-spot, and that exists within this one... https://www.amazon.co.uk/TS-Optics-150mm-Newtonian-Telescope-Gsn1509ota/dp/B00IN7EBFW With that being the ideal compromise, albeit without a mount.

Next up, the installation of the cowling with its secondary-stalk and -mirror...

The hardware has been filed and sanded, roughened, for the paint...

I had gotten a Thousand Oaks solar-film filter many years ago, and for my 102mm refractor only... The image is yellow-orange. The Baader solar-film is said to be superior, and the image bluish-white. In any event, that TO filter is quite dated. I'd be reluctant to use it again. I've had this sheet of the Baader film for a few years, but I haven't made a filter with it yet... When making and observing with a solar-filter, observe all precautions. Research others' experiences with the film online, thoroughly, and prior to making your own. You cannot be too safe in that regard. When installing the film into a home-made frame, the film must not be stretched in the least. It must be allowed to lay onto the glue or double-sided tape, used to secure it, under its own weight. It will have a wrinkled appearance, which is normal... https://www.firstlightoptics.com/solar-filters/astrozap-baader-solar-filter.html ...but the wrinkling will not affect the view in the slightest. You don't want it doubled over itself, nor stretched taut. A stretched film will distort the view. Avoid black-polymer filters and materials.

Oh Julian; yoo hoo... ...and both assemblies at 4mm in thickness; therefore no intrusion into the light-path. It turned out that the shorter-length screws that I had bypassed initially, there at the left, were the perfect length after all. Oh well, all's well that ends well.

In this instance, the spacing between the inner wall of the tube and the edge of the primary-mirror is at least 5mm, all round. Not a great deal, but enough to conceal the hardware that I'm utilising, and at a total thickness of 4mm.

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.

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.

Is that what you use?

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.

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.

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?

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.

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.

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...

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.

http://www.andysshotglass.com/wilcox_rotating_rings.html

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...

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/

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.

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.