It was sunny when I arrived home with the groceries so I gathered up the solar observing kit and headed over to Bryant Park at about 1215 EST. In addition to a sunspot count and an attempt at Venus I wanted to zero in the solar finder I built.
seeing was very poor today. There was continuous boiling across the entire disk of he sun. I picked out two groups that I made to be close to the solar equator, a large one to the north and a smaller one to the south. It turns out they were both north. Phase rotation bit me. This close to noon I didn't think that would be an issue. The smaller spot kept disappearing in the boils and I wasn't able to get focus on he large spot so it isn't worth doing a full report on the observation.
After I finished up the solar observing I started to zero in the new Sun finder but found that it was dead on. Some of the screws are stiff enough in the nuts that I don't think it will ever come out of alignment in transport or handling.
This has been a longterm project. It started when I got my Celestron C70 Mini Mak Spotting Scope (Mini Mak for short).
I got the scope as a grab-'n'-go scope for solar observing but found that I also used it for nighttime observing when I didn't want to schlep the Dob (now called the mortar because of it's short tube). But the Mini Mak doesn't come with a finder and there are no provisions for attaching an accessory finder from Celestron or anyone else. I had an Orion EZfinder Deluxe that I got for the mortar. So I needed a shoe and a way to attach it to the Mini Mak without drilling holes. Double-sided tape wouldn't work since the legs of the shoe are too narrow and the bottom of the body too high off the round of he scope. Double-sided tape doesn't look strong enough to me to hold the finder which is very top heavy and I don't have confidence in it's longterm holding ability on the scope's rubber raincoat. Additionally the raincoat does not appear to be attached to the scope tube by more than a couple strips of double-sided tape so I was worried that the top-heavy finder might lean and not provide the repeatability I was looking for. I went down to Adorama to talk to Peter and Mike to see what suggestions they had. Peter was in favor of a 7-Eleven Slurpee straw rubber banded to the scope, an approach Peter Tagatac uses with his DIY scope.
I had been trying to figure some way to hose clamp the foot to the scope but wasn't making any progress. Just clamping the shoe to the scope wouldn't work because the foot is taller than the shoe. I bought the hose clamps anyway since I didn't see any other way to affix the shoe to the scope.
Then I remembered the laser at NYC Resistor. People are always making boxes out of light wood on it. So I decided to make a box out of plastic that would háve slits near the top edge for the hose clamps to pass through and holes in the bottom where the shoe would be bolted on. The box would be mounted open top down and have concave ends to accommodate the round of the scope. On my first attempt I didn't get the dimensions of my end pieces right and the plastic I used was too thin to take the stress of being clamped but it held the finder in place and I was able to use it to point the scope. Proof of concept.
For my second attempt I used thicker plastic and doubled it up in places to reinforce possible weak points. The reinforcement created another problem. Now the sides of the box were so thick that only the inside edges made contact with the tube and when I clamped it to the scope it cracked anyway. The crack was repairable with the plastic solvent and I used a Dremel to bevel the inside of the box for a better fit. That finished off that phase of development. I have used it a lot with success and having the box under the foot raises the sight to a more comfortable height above the scope tube.
Phase two was to come up with a foot to fit into the shoe and onto which the actual finder would be mounted.
I briefly considered using acrylic since I would be able to cut it on the laser with minimal assistance. But that would require bevel cuts which are not possible on the laser and I didn't think plastics would hold up to the repeated compression of the retaining screw.
Next I looked into Delrin and aluminum. Delrin looked promising because it appeared to be softer than aluminum, is dimensionally stable, and is machinable. But researching it I found that I would have to buy too much of it to be cost effective. So I switched over to aluminum and found the same cost issue there. Raphael at NYC resistor said he has some aluminum that we could use. He was also going to help me with the milling since I know nothing about CNC (computer numerical control) machines.
I started out designing the 3D foot in Google SketchUp. Then I found that we couldn't export the object in the digital format required by the milling machine. So I switched over to designing it in 2D in Inkscape. After getting it designed we had to get a plugin to export the proper file format. But we weren't able to turn it into 3D so I ended up copying and pasting one copy of the file for each pass of the router. After all that was don and Raphael and I coordinated time on the mill it took a couple of hours to get the piece cut. A few more hours were consumed in tapping the screw holes and figuring out what needed to be adjusted to get it to fit properly.
The final phase was to design and build the finder itself.
I had searched the Web for finders and found the "A Collection of Solar Finder Designs" out of Germany. I liked design #14 by Robert Pudlo but working in aluminum would require more milling and getting the end pieces bent in the right place so they are properly aligned would be difficult for me. But I could make something like it out of plastic.
To get around problems of not getting things perfectly aligned or not having the finder aligned with the scope I wanted to build in a collimation mechanism. I knew left right alignment could be easily taken care of. I was going to use two mounting screws aligned on the long axis of the finder. Making one elongated crosswise would allow that end of the finder to be swung a bit sideways. Up-down alignment was harder for me to figure out. I ended up designing a double base with a hinge at the front. The bottom base piece would be mounted to the foot with the front end lower than the back. A hinge would be mounted to the front of the bottom base and then the top base mounted to the other half of the hinge laying on top of the bottom base. Near the back end of the base a screw would pass through the top base, through the center of the spring, through the bottom base and into a captive nut. When the screw was tightened it would pull the top base down and the Sun spot would go up on the target. The reverse for loosening the screw. It wasn't going to be pretty but it seems like it should work. Then I decided to use a similar technique for left-right adjustment. It was getting very ugly now but should have worked.
I talked to one of the MakerBot Industries principles to get an evaluation of the design and he sent me back to see the guys in "Tool Town" who do a lot of design work. The guy who was there was the French guy. It took a long while to try to make him understand what I was trying to accomplish and his solution involved redesigning the back end to include electronics which I didn't want to do. The American showed up and after a lot of translation he started to draw something and said collimation and it instantly clicked. What I wanted to do was to build something analogous to a Newtonian mirror cell.
I designed the finder while I was working on the foot but it was still a couple of months before I had it to the point where I was satisfied enough with it to go to the laser.
I found some captive nuts that you press into your material while searching McMaster-Carr. They are working but it was a real pain getting them pressed into the plastic. I ended up using a huge C clamp. The major downside was that there wasn't enough plastic around the holes they were pressed into to absorb the stress and all three holes cracked in at least one place. I fused them with the liquid acrylic adhesive.
My screw holes for the mounting screws were not big enough so I had to file them out a bit. I guess I didn't get them filed evenly because the finder wasn't sitting square on the foot. I drifted one hole and things looked better. I mounted the mask and target to the back piece. For some reason which I can't explain that caused the bagk to bend in toward the front. I adjusted the screws to where things looked "right" and when I tried it out found that it was spot on. I have used it three times now and haven't had to make any adjustments.
I tried to find Venus without any success. Before heading out I checked her location relative to the Sun and swept the area as well as the area left, right, above and below where I thought she should be. Initially I had no idea what distance my binocular was focused on so I held the solar filter in front of one lens and focused on the Sun. I still wasn't able to locate the planet.
The NOAA forecast for tonight was for a cloudless sky so I sent email to Peter saying I would be heading for TotL after dinner. A couple of minutes later I got a similar email from him saying he was just arriving at Drip Rock and only intended staying for a couple of hours. I figured he might be leaving or gone by the time I passed there on my way to TotL but when I arrived two hours later he was still there.
We observed together for three hours concentrating on the area of the terminator around gassed. In his refractor we located Rima Snelius and Rima Gaseni and the mountains on the south rim of ___ looked very nice.
I started out using the zoom lens on my Mini Mak but when we got into comparing features between the two eyepieces I switched over to the fixed focal length eyepieces from the mortar hoping ghat I would be able to use higher magnification. I hound that 50x was OK but conditions did not support 83x on that scope. Peter was able to use a short eyepiece with a Barlow on his scope giving us some tight views.
late in the session Steve and Gracie Beltser arrived. We looked at the Great Orion Nebula in the Mini Mak at 50x with and without my UHC filter. Adding the filter extinguished the trapezium but greatly increased the nebulosity. Steve asked if we had ever seen the nebulosity in the Pleiades and we talked about our recent experience of observing with the filter at Custer Institute. I dropped my magnification to 18x and with the UHC installed he was able to see nebulosity around several of he stars.
For me this session lasted from 1930 EST until 2230 EST.
