Sometimes something is started that ends up taking a long time to finish… And now that it is finished I need to thank a couple of kind folks!
Years ago I was gifted an 8” dobson telescope by the parents of a good friend of mine. It was decades old no doubt. The thing had been stored in a shed somewhere in France. Without the lid on. And swallows (of the European kind). I hardly ever used this one as I already had a LXD75 with 6″ newton at the time. So I also had it stored in the shed except for a trip to Kollase in Germany back in 2011.
Two years ago I decided on fixing the telescope and bringing it into the 21st century. I had quite a bit of money invested in my telescope but I hardly ever used the thing. Cycling I did do a lot so I sold the Sumerian Optics, bought another bike and started using the 8″ dobsonian. And thus started the upgrade project that would take a while to finish.
First a picture of what it looked like back in 2010. The telescope could either be a Piet Kuit telescope or a Darkstar telescope. If it is the latter the mirror could well be one made by David Hinds.
The mirror of the telescope was in a horrible state! But for now that was okay. I wanted to see if this telescope was salvageable or not. It was heavy, the finder was crap and the eyepiece tray was for .96 eyepieces. To name a couple of gripes.
The first step was actually made years earlier! To lighten the ridiculously heavy rockerbox me and my brother in law Martijn cut out quite a bit of wood from the rocker box. It was spring 2015. In all that shaved off a kilo or two. A good start! Thank you Martijn and Standcraft for letting us use the workshop.
Next up was the sale of the beautiful but not very usable Polarex finder scope to someone that was much happier with it than I ever was. I think Norbert S. bought it. Instead I opted for a Telrad finder. Never used one of those before but the degree circles of the finder to me seemed very convenient.
The OTA itself was a heavy PVC drain pipe. Some weight was to be gained here too! I put out a message that I was looking for a replacement OTA and not long after andre8x8 of Astroforum arranged for me a sturdy cardboard tube. With free delivery even! The replacement of the tube shaved off another kilo or … 3? It was August 2016.
Now I had to put the mirrors in the OTA and align all of it with the focuser. I am no expert in optics but luckily Astroforummer Bert Bogchelman is and he lives nearby. So on to Achterveld where we had a nice evening hacking away at the OTA. Also Bert explained how it all worked with the focal length, thickness of the tube, distance of focuser to the centre of the secondary mirror etc.The copper 1980’s spider vane was replaced by a simpler model that was easier to adjust. Someone sent me a free 50mm secondary mirror that was also installed. Thank you, Mr. John Doe! I forgot your name, sorry!
Without Bert B. I could not have done all of this so.. thanks, Bert! We have arrived in spring 2017 or thereabouts.
Funny thing: because of the changed weight of the OTA I had to add a kilo or so to the top of the tube. Paradoxically I had to mount a small steel plate on top but that also made it possible to add a knob for easier steering the telescope around. You loose some, you win some.
After a couple of observing sessions in 2017 where the Telrad fogged up I had to solve that problem really bad. I am no ATM expert but I do know some basic electronics and so I managed to add a 10 Ohm resistor to the Telrad glass. Running at 3V that just about works as a dew buster. Last week I did add a simple cover because when it’s really damp the resistor alone is not enough. The combination is golden though.
For the paint job I opted for what I call the Explore Amateuristic-look: grey, black and some yellow accents. I flocked the tube using black velours. The lightshield was made using hobby foam bought at our local hobby shop Pipoos in Amersfoort. A purple hair band to keep it all in place was stolen from my daughter.
In the summer of 2017 I made a solar filter using Baader Astrosolar foil I inherited from a old observatory club member, Joop. On Aliexpress a green filter was acquired to enhance the contrast a bit. All in all a pretty decent way to view sunspots. Unfortunately we are now in a solar minimum …
The dew protection for the eyepiece and fan were connected to my DIY 7Ah powertank somewhere in 2018. I made a larger 43Ah Powertank a year or two before together with observatory member Andries. That one is now used by a friend of mine and this smaller one suits the dobson better I think. The dew controller is a basic design by Astroforum member rwagter (I don’t think he’s active there any more though). This controller is basically just two LED dimmers bought on eBay crammed into a PVC shell. It works like a charm and cost me only 15 euros and functions like a 200 euro branded one.
By now I had also added dew protection on the secondary mirror using some copper wire and 2 penlite batteries. It runs for hours on 3V. Astroforum member Bart K. explained to me how it all worked with amount of Volts put in, the Ohms of the wire and how long the wire had to be for my secondary mirror.
Halfway in 2018 I finally thought it was time to re-coat the primary mirror. The public observatory in Almere is a 30km drive and they have one of few installations in The Netherlands that can coat mirrors up to 10″. Rob van Vrede was kind enough to tell me something about the process and a couple of weeks later I had a fantastic looking new coat on the mirror! Thanks, Rob! November 7th 2018 I had my mirror back.
Because the new OTA was a bit wider than the PVC one I had to rebuild the mirror cell too. It was a simple model with three messing arms and screws connected to a aluminium plate where the mirror was held in place by screws. Yeah… I know. I replaced the aluminium plate with a wooden one cut to size. The mirror was placed on three dots of glue the exact location of which was given by the application Plop. I read online you can get away with this way of mounting mirrors up to 10″ in size. Observatory member Dave den Hartog was kind enough to help me make the mirror cell to size. At home I added a small 12V fan to the cell where we left a hole in it so the air could easily reach the back of the mirror. Cooldown is now about 35 minutes instead of 2 hours.
The most recent upgrade was the addition of an eyepiece tray. I am now only planning on adding a filter slide and a 9×50 finder scope.
In the end only the primary mirror, the focuser and the rocker box have been reused. I have had a couple of pleasant observing sessions with the scope now. And it works fine. Is the mirror anything like a Nicols mirror? No. Is it okay though? Yep. Is it a Sumerian telescope? Hell no. Is it okay for a couple of observing nights a year? It certainly is! Is it perfect? Nope… she wobbles quite a bit after focusing and she’s a bit high on the legs. Nothing serious though. For now it is a fine telescope to own.
All things considered I have learned a lot changing this telescope to a 21st century model. Thanks to all I have learned I am now even considering building a new 12″ F4 truss dobsonian with Dave. We’ll see.