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I now have three 80mm scopes (may those who want only one telescope cast the first stone!), an achromat, a semi-apo and an apo. I needed a solar filter that would match them securely, luckily it's easy enough thanks to the dewshields having almost the same diameter. A filter with fixed attachments wouldn't do, and a filter with sliding attachments would be tedious, so I made one that fits several sizes by itself, by means of a spring shaped like a crown. Since it never leaves the house it doesn't require a shockproof or dewproof case; a very humble cardboard box is it home: The filter's frame is a sandwich of two mousepad layers with the Baader Astro Solar film in-between. Double-side tape and a screw plus plug assembly keep them together. In order to pinch the dewshield the plugs are slanted toward the inside in a V-shape: Superglued rubber O-rings make the filter sticky and prevent scratches. The plugs have slots that proved convenient to slide the flat spring inside of them. The extra layers of rubber (electric cable skin) at the rear make the filter adaptable to several diameters. With a rigid frame only the rear or front set of O-rings would touch the dewshield, but the soft mousepad frame yields under the spring's tension, so all rubber pads always make contact. This in turn is allowed by the Astro Solar film's plyability. The steel spring pushes the plugs against the dewshield, ensuring tight contact: On the front side screws sold with the plugs keep them in place and improve on the double-side tape assembly. This is my f/7.5 achro with added centering screws on the front lens, the rear one is neatly paralyzed by shims. When I got this scope it was badly decentered; plastic screws recovered from finders do the job and do not pinch the glass like metal would. In order to work the spring has to be split, but out of prudence I didn't want to let metal tips in the proximity of lenses, two pieces of heat-shrink tubing cover them, and make for a more finished look, while I notice on this close-up that some rubber parts were not cut too cleanly: Will have to rectify that later . What matters is the filter is safe, and the foam can be pressed against the dewshield tight without marring it. Plus, the black foam kills all stray light for maximal contrast. I wasn't sure what length to use, and the steel spring cannot be stretched if it's cut too short, so I made a trial with a steel insert from a windshield wiper, made of regular rust-prone alloy: Then I used another windshield wiper insert to make the real thing, but this one is rust-proof alloy, looks shinier and will never degrade. I shaped it overall with my fingers, and did the detail work with pliers. The filter locks tight on the semi-apo like it does on the achro, no problem, the dewshields have the same girth; I could swap their caps: (The white thing is a temporary dovetail bar made from hard maple wood that saved the day in another project. It could be used permanently for very lightweight and cheap telescopes). My triplet's dewshield has this rim making it three or four millimeters wider than the other 80mm scopes, the adaptable filter comes in handy: The front piles of O-rings are placed so they pinch the rim for extra safety. The flexible quality of the mousepad material and steel spring make it simple to stretch the assembly over the rim when installing or removing the filter, which has an 83mm or 84mm clear aperture to respect the light cone, by the way. This design may not be transferable on all other scopes but I hope you can pick ideas from this.
I wouldn't want to miss observing the Sun in a full-size 300mm filter, the detail compared to smaller instruments is such a joy to see. I do have an off-axis mask for my 300mm dob but not all the time. If daytime seeing is too bad for such a large scope, I'll switch to a smaller one, but the extra resolution and ease of spotting micro-detail thanks to the brightness is something I can't do without. A sheet of 500mm wide Baader fillm allowed me to craft this. I had enough left to cut several smaller filters. To protect it I made a storage box from cardboard of obvious origin. The box had to be custom-made to save space in my dwelling, and it also hosts a bahtinov mask for nighttime. At f/5 fine focus is not too hard with the smooth single-speed focuser, but in order to enjoy moments of clarity immediately at high power, I pre-focus with the bahtinov, which sees through turbulence, what a nice invention, and simply wait for calmer air. No need to rush to fine focus and waste precious moments. This mask needs to be copied in some sort of plastic, the cardboard trial proved the number and width of the slits are fine. The rear of the filter shows the four clips mating the four button screw heads outside the tube. And this lateral view shows the sandwiching. A rigid backing plus two layers of lightweight neoprene foam cut from a cheap mat in tiger-stripe deco, its poor taste matching its 7€ price. The bottom sheet used to be a shower booth panel, my neighbor had in its garage. Hey, do you need that? No? Okay, thanks! The Baader film is held between the neoprene sheets by staples and many strips of tape. The neoprene is held to the shower booth sheet by little collars, and its edges are sewn together for a finished look. Oversize 10mm stitches didn't take too long to do, and the foam layers can be separated for replacing the film, something glue would prevent. Holes in the neoprene allow to check that the clips' bolts are always tight. Close-up of a clip. They are made of a material whose name I forgot, I only remember it is made in the UK (thanks, guys!). This is a PVC foam that's much easier to cut, drill and sand than full-density PVC, and it's much lighter (thanks, air bubbles!), which is essential for an item that's at the front of a scope where leverage is maximal. My GSO dob has four of these screw heads, one for each spider vane. They proved very convenient for attaching the filter. The black knob is an add-on to move the scope without having to grab the large tube with both hands. Pretty obvious what we're seeing here. Note the clip is flush with the tube, and pressed hard against the scope's metal rim for a very secure and tight fit. Only four clips but eight attachment points, really. Building this with tight tolerances was more lengthy but more reassuring. It is impossible to disengage a clip by accident because tolerances are too narrow, and the shower booth plastic tough spring action doesn't allow it. But should it happen three clips would hold the filter safely. All three layers of frame material are flexible, so, to remove the filter from the tube you just bend it at a corner while you lift the clip, and the clip disengages. I already rebalanced the dob by pulling the 7-kilo mirror to the rear thanks to shorter and tougher cell springs but I'm working on a sliding counterweight made of pliable steel ribbon. Adhesive felt pads protect the paint. Thanks to the large hole the 300mm filter is not too heavy (and it's used without the finder) but the off-axis mask has only a 115mm hole, so it's heavier and may require this. While I study the combinations of heavy or lightweight eyepieces, finder/no finder, mask, filter, I can change the experimental counterweight by cutting off or adding pieces of steel ribbon. Little mounting nuts and bolts through the many holes, there's always one at the right place. Ever hated to feel the Sun while loving to watch it? If you have no sunshield you did. Heat is a discomfort on the head, and light kills off contrast. So I cut a plastic folder in this weird pattern to allow sliding it between the shower booth plastic and the neoprene mat. When it's stuck there it makes quite a large area of shadow, that's such a relief. But that's also only a prototype that wants to be made again with a better material. Has to be opaque, quite thin, very lightweight, but rigid enough. I'll stumble upon the right material sooner or later.