Telescope Restoration - John Dobson used THIS
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- Опубліковано 12 гру 2024
- This giant 14.5 inch Dobsonian telescope has a mysterious problem. The owners have given me permission to investigate the collimation issue and perform a mild upgrade and service. It was an honor to work on a telescope that John Dobson himself has used!
#telescope #restoration #collimation
What could be wrong? Watch and find out!
//Mirror Cleaning Video: • How To Clean A Telesco...
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#restorationvideos #orion #astronomy #Dobsonian
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#reflector
#reflactor
@reflactor
john dobson's dobsonian being the best dobsonian
Absolutely.
I built my 12.5" truss Dob in 2002, and in 2004 or 2005 we had John Dobson at our club to present at a couple of meetings. I got him to autograph my mirror cover. That's one scope that's staying in the family for a long time.
I'm very jealous. I never got to meet the guy. Would've loved to talk shop with him.
Back in the 80s Testors made a flat black spray paint for "stealth" model aircraft. It had a slight texture that absorbed light. A paint like that would have been an excellent choice for your sheet metal, if they still made it. I can not thank you enough for your solar projector video about how to observe the 2024 eclipse. It has been very fun to share the solar storms with friends, neighbors and family. 🌞
i wonder if they have vanta black spray paint
Right now the best solution is Rustoleum's Camouflage Black paint. It's an extremely matte black enamel. So it's tough. I have some Mousou black which is ludicrously black, but very fragile. The Rustoleum can be bought cheap at Walmart. The Mousou comes in tiny bottles from Japan for big money. I'm glad the solar projectors are working out for you. I was using them a week or two ago to see the big sunspots. I also hope your physical challenges are getting easier. Stay strong.
Good question. Vanta Black not a paint, but a vapor deposition method owned by (I believe) the UK government - only one guy is licensed to use it for commercial/art purposes. They did make a black spray paint that they call Vanta Black, but it's not nearly as dark. Mousou black is still the darkest commercially available paint that I know of. I have a tiny bottle of it, bought from Japan. It's insanely light absorbing.
Thanks John for sharing your the king of fixing telescopes
Haha, thank you. Since I only buy broken telescopes, I had to learn quickly.
@@AstronomyGarage well that’s OK that’s why people like your channel because you show them how to repair it how to fix it and a lot of people need that knowledge
Spectacular video. Always fun watching things be restored to their full glory.
Thanks! This was a fun one to work on. :)
You do a great job educating newbies like myself so thanks for all your content🤙🏻
Thank you for the kind words, and thank you for watching.
Sorry for a second comment. 1: GREAT idea on the milk jug material fix! 2: Knowing it’s not your scope, but if it was.. would you think about adding a fan to the back of the mirror box? Would have to cut an opening in that vinyl piece, but would help with cooling the mirror.
Great questions! My original plan involved painting the entire inside black and adding cooling fans, but my research showed that most of the Sky Designs telescopes out there don't have either. So, just to maintain the historical aspect of that telescope, I left it the same.
A friend is gifting me their used XT8 Intelliscope that I helped them refurbish several years ago. I already know it's an optically solid scope, so I'm ready to get it in my hands and start upgrading it. Think I'm going to flock the tube right out the gate and swap out the focuser for a better GSO Crayford I have on hand.
I was lucky enough to meet John Dobson in 1999. I was on a high school bus trip to San Diego (not even where he lived), and by chance ran into him at an In & Out Burger.
I was gobsmacked. I had my first job as a teenager to afford my first Dobsonian only a year before.
That is an amazing story about your chance encounter with John Dobson! I wish I would've met him. I built my first Dobsonian in the mid 1990's and I lived in California briefly, but never crossed paths with him. He did what I can only hope to do - he made the world a better place. By the way, don't worry about flocking. In the end, I found that it didn't make a huge difference. Probably only if you have a lot of streetlights that send strong light into the opening of the tube. Clear skies!
Great Video! Maybe the extra sheets of linoleum were placed inside as spare replacement pieces. They no longer make that linoleum so those are valuable pieces to have!
That very well could be. I looked at the other surfaces of the telescope and it wasn't used anywhere else. It was definitely not Teflon, so I'm stumped.
I wondered if someone moved them from the position where they should be. Perhaps they were intended to be on the side that would be down when the cope is horizontal?
Looks pretty neat... and pretty heavy.
It wasn't too bad once broken down into components.
A useful tool for removing large mirrors out of tight places, is the suction cup grip for installing glass or the suction cup for pulling out automotive dents. You can attach the suction cup to the center of the mirror and lift it straight out. Any rotating you need to do to get the mirror in can be done by turning your wrist. The suction cups are not expensive and do not damage the mirror coating.
That's a good idea and if this were my telescope, I definitely would try it. However, it didn't belong to me so I was super careful about everything. Thank you for the tip!
I love these low tech solutions, reminds me of when I ground and built a six inch reflector in the late sixties
I have a big pile of cleaned milk jug plastic flats - they come in really handy on so many telescope parts.
That broomstick secondary ‘screams’ John Dobson doesn’t it? I had to great pleasure of meeting him at a Winter Star party in the early 90’s. Let’s just say that he was definitely a hoot to chat with!
I've never seen a collimation system that used more than three screws - it was difficult to get zeroed in. I'm jealous that you got to meet Dobson!
Most of Dobsons secondary holders were simpler than that . Strips of shingles were used as spider vanes . You would just tilt the secondary vanes around in the cardboard tube until secondary was collimated and then put a fillet of glue around the vane where it connected to the inside of the tube .
Great video. I’ve been looking forward to seeing this scope worked on. I’ve not seen a secondary holder like that before! Not sure how good the secondary holds collimation. I wonder if using milk jug plastic around the broom handle would be beneficial? Looking forward to your next project 👍
That's a good idea putting a protective barrier around the dowel. It took me probably 2 or more hours to get that secondary collimated. It's usually a five minute task. The 8 screws added a crazy amount of complication.
Could you comment on the trunion configuration? Specifically, do you like the deep slot for altitude bearing and the configuration (ie angle between) the two teflon pads.
I've not had too much of a problem with the elevation teflon placements of various Dobsonians.
My theory: The vinyl tiles were mass-loaded vinyl to weight the bottom for better balance.
I like that idea - the confusing part is that the tiles are to the side and not on the bottom.
Just paint the wood flat black.
Curious. It seems to me that the hard, three point contact made by the dowels you removed would provide a more stable, longer lasting alignment. Won't the felt disks compress over time?
Then, for similar reasons, i would punch small holes in the faux leather membrane so the alignment screws made metal to metal contact and not be slowly working their way through the fabric.
And maybe a small dab of glue on the back of the metal, punch out disks to keep them seated in the holes.
Am I being too OCD? Are these possible, small movements really enough to effect collimation?
Good question! The detail that I left out was that this material is "hard" compressed felt, used for the feet of furniture (not the soft felt, but more plastic felt). I think it helps furniture slide over tiles without being too slidey. Having the metal screws directly on the washers might make for more of a shock if dropped? The mirrors have to be babied since they make up about 95% the cost of a telescope.
You are not being OCD at all. I had a list of improvements to do (cooling fans, painting interior black, etc.), but held off on this particular project due to its historical significance - John Dobson was the patron saint of home-built telescopes for about six decades. Note: I have another similar old wooden one that is next up for restoration. I bought it at an estate sale and it needs WAY more work, lol.
I think there's a problem with design of the primary mirror holding clips. Usually they are attached to a mirror support, but here they seem to be fixed to the bottom of the wooden box. When you collimate the primary mirror, you are tilting it that changes gaps between the mirror, and mirror clips, so the mirror can become too loose making that clunking sound.
Generally speaking, the job of the mirror clips is to prevent the mirror from tumbling forward and out of the telescope. As in all reflectors, they shouldn't actually touch the mirror. The hard work is being done by the triangular floats and the lower two "centering bolts". Depending on angle, there's a lot of force from the mirror weight on those two centering bolts. The addition of the milk-jug plastic greatly reduces the friction between those centering bolts and the mirror edge. At least, that's the goal. :)
Buen teléscopio
Gracias!
@@AstronomyGarage gracias amigo yo construí un dobsoniano de 16 pulgadas 406 mm 1800 de focal y 4.5 muy bueno tiene imágenes asombrosas
Ese es un telescopio gigante. Estoy celoso de las imágenes brillantes. ¡Disfrutar!
I really like John Dobson's pioneering work. I wish I could grind my own mirrors like Dobson did. I do not like his ideas about cosmology as he presented them in a TV series. Dobson's picture shown here is from that series.
I didn't know he had a TV series.
Well done! that was great especially seeing how careful you were with keeping the telescope in as original condition as possible. BTW does the telescope hold collimation well now? Did you find time to check?
Thanks for sharing your amazing work!!
Thankfully, it holds collimation very well now. The owner told me that it's producing the clearest images they've seen in 20 years. That made me very happy.
@@AstronomyGarage if I may make a suggestion, I saw in a veritasium video that a way to improve your video views is to change the title of your video a few days after uploading. Try with different keywords perhaps
I will try that. I'm not very good at promoting my channel, so it's worth a try.
@@AstronomyGarage all the best mate! You got to 9.5k subscribers on the basis of your content alone a little marketing will go a long way. The veritasium video i'm referring to is called "clickbait is unreasonably effective" have a look :)
Haha, my channel is the slowest growing channel on UA-cam. And... it's the most impossible to find because it thinks my channel name (Reflactor) is a typo.
The scope was built by Sky Designs , and could be circa 1990 if its been looked after . Painting the front of the aperture plate in the front of the mirror box black will also prevent diffuse light from being sent back up to the secondary , much in the same way the block the focusser was mounted on could throw light diffuse light at the secondary.
The mirror itself, according to the serial number, was made in 1992. It's very possible the telescope itself was built earlier. I'd thought about painting the inside of the box black, but I wanted to keep it all original (I saw a lot of guys on Cloudynights who also didn't paint their boxes).
i recognized the jet the second i heard it 😂
Truth be told, it was actually the Blue Angels doing a show about 8 miles from here! :)
Use wheelbarrow handles, wheels, and ramps to move and load the mirror box, cradle, and groundboard components.
The weight to lift at the handles is only 10#.
L
Excellent advice. Thank you.
Are the two lower centering bolts affecting the image? Would a sling or at least dispersing the high-pressure, produced by the point of the bolts, help? It would be interesting to do a Foucault knife edge test of the mirror in that mirror cell.
L
The two centering bolts might affect the mirror shape for sure. That explains why slings were common back then too.
Hi,
To make your own "Obsession Telescope" or to modify, or diagnose or improve ANY dob you have, get the Dobsonian reference book that has more information on these scopes than you will ever use.
"The Dobsonian Telescope: A Practical Manual for Building Large Aperture Telescopes" by Dave Kriege and Richard Berry
Thx
L
Thanks for the tip! Here is an Amazon affiliate link to that book: amzn.to/4dLM72z
Can i have it once your done fixing it. Ill pay for the shipping to the philippines, im pretty sure those dim globular clusters are gonna run for their lives once i start pointing this at them 😁😁
Haha. Unfortunately, I've already returned it to the original owner. :)
3:45 I mean I'm not sure how much that is doing considering there are no walls on the rest of the scope.
Presumably he has a light shroud
@@bowrudder899 maybe, I have seen many without one though.
Good question. The owner does have a black shroud.
A 2.6" 1/10 wavefront secondary would allow the highest magnification views. What is the diameter of that secondary 3.1 inch?
L
It was between 3 and 3.5 inches. I've given it back to the owner, so I don't have access anymore.
Wow
It was a fun project.
Get a drill press! With all the tools you have you should have one! Stop drilling holes like a caveman on floor!
No such thing as a Dobsonian telescope. What John Dobson made was a Newtonian telescope and put it on a mount of his own design.
I know I'm going to get a few comments about that, but let me ask this. If you were to build a Newtonian telescope, would it be a Smithian/Jonesian/ Brownian or whatever your surname isian? No, it will be a Newtonian, because it was invented by Isaac Newton.
I hear what you're saying, but allow me to share what I think has happened. The word Dobsonian refers to the mount style, and even with that, the Dobsonian is just a special case of the Alt-Azimuth type (as opposed to an equatorial type). However, Dobsonian mounts are so popular that the name has taken over the entire sub-type, similar to how "Kleenex" has become the generic name for all tissues.
@@AstronomyGarage Very true, most Dobsonian mounts are nothing like the one on the telescope in your vid, but are a variation on a fork mount. I've even made one for my Newt when I don't fancy using it on an equatorial mount. It has space for beer.
This whole Newtonian/Dobsonian telescope thing does cause confusion though. A few years ago someone arrived at one of our local astronomy clubs with his new (and very first) telescope on a table top mount. One of our members, a huge Newtonian devotee, then began regaling him on how all Newtonian telescopes need regular collimation and started to tell him the best way to do that and no doubt tried to sell the chap his booklet on colimation (yes, he was that much of a devotee). The new member then interrupted, saying that this isn't a Newtonian telescope, it's a Dobsonian. We then had to explain things to him, at which point he started to look somewhat disappointed at his new 'scope, as if he'd been conned into buying it.
Thankfully he kept coming to our meetings, and no doubt became even more disappointed in his own 'scope (somewhere around 3 inches/75mm diameter) when he saw the ones the rest of us had.