A Special 6-Inch Triplet Refractor Encounters A Close Call With The Sun By Guest Host: Mario Motta
Two days ago, I decided to take solar images as it was clear and many sunspots were present.
With my solar scope I did take Ha images, both at prime focus and also with a Televue powermate, which came out well.
However, I also attempted to take white light images of the many sunspots with my Hershel wedge mounted on my 6-inch triplet refractor. I placed my scope pointing to where the sun was, took off the lens caps, and then opened my dome.
As the slit opening reached my scope I almost immediately saw smoke from the back end of the telescope. I had left the plastic dust cover on my focuser, and the concentrated light of the telescope vaporized it.
I covered up the scope and removed the lens cover with a large hole in it. (I have others, not in itself a problem). Can you imagine if anyone was looking out the back of the tube? So be very careful when pointing at the sun, or Venus nearby, etc. especially with uniformed visitors or children nearby. Instant blindness!
As I removed the burnt cover, lots of smoke came out of the tube. I left it for a while, but still the smoke continued. I used a small vacuum cleaner and tried vacuuming out the smoke, but it was still present.
So, at this point, I did an invasive “colonoscopy” on the telescope. I tried a “Flex tube” at first, but it kept getting caught by the baffles I built into the tube. I then resorted to a “rigid tube” and this finally got all the smoke out.
Yet when I viewed the sun, it was very blurry, I could not get good focus. I finally had to unmount the telescope, and take off the lens, which is a Zeiss style triplet, very heavy lens.
This was originally made by Roland Christian as an experimental lens which I obtained directly from him at a Stellafane meeting around 1990. It has a front element, air space to the second element, and a third element which is oil spaced.
Looking at the back of the lens, a film-like deposit which was from the smoke (?) and was able to clean it off. However, the oil space area didn’t look right, so I took the assembly apart, and with a rubber mallet separated the third element.
The oil had streaks and splotches. It’s hard to imagine that some smoke did this as I cleaned it, and noticed a blue tinge on the cleaning wipes.
I recall last fall cleaning the optics with my spray polymer from photonics Inc. This is a polymer gel spray, wait a half hour, peel off the polymer. Works very well on my 32-inch EQ mounted telescope. I tried it on my refractor, and it also looked good afterwards.
But…I suspect the spray somehow got into the oil space between the elements. So the oil was wiped off, then cleaned with acetone. When completely clean, a small amount of mineral oil is placed on the surface, then the third element is re-positioned onto the second element.
One must be very careful to match the alignment exactly as before, as you will notice in my photos that I have the elements marked on the edges to make sure of this.
I use a strip of old camera film, it’s just the right size applied as a girdle around the outer edge to keep the elements stable, tape that up, then carefully placed back into the cell.
Conclusion: I tested it last night, and happy to report that all is well, and now back to normal.
The advantage of building your own equipment is you know how to take it apart and repair if necessary. This job would have cost a fortune to “send back” to an optics or telescope company for repair.
So, the moral here: Be careful near the sun….Mario Motta
rogerivester.com 