Etalon reconnecting, Success !!!

Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...
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DavidG
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Etalon reconnecting, Success !!!

Post by DavidG » Sat Aug 22, 2015 4:07 pm

Last weekend I was in Vermont at the 80th Stellafane convention. Stellafane has a legendary Swap meet on Saturday morning and you'll never know what you'll find. In the piles of treasures was a PST that the owner stated gave a sharp image but the Etalon needed adjusting since his kids had dropped it. I looked it over and saw the the eyepiece tube holding the blocking filters was slightly out of straight and was hoping that might be the only problem. I found an eyepiece to try out the scope and held in against a tree to try to get a steady view of the Sun. As soon as I tried to focus the image I got multiple images of the Sun which indicated that the Etalon had decontacted. I told the owner that it was damaged more then what he thought and at the price he was asking plus sending it back to Meade for repair one could buy a new one. So I passed on the sale. After about an hour the owner and I passed each other and he thanked me for diagnosing the problem and asked what I would pay for it. I told him I would be taking a big chance in buying it, to see if I could fix so I gave him a number that I felt was fair and he agreed.
When I returned home I dug into the scope. The threads on the eyepiece tube had jumped a couple on one side so I carefully tapped the high side down and the tube then smoothly unscrewed. The ITF filter was cloudy so I repaired it with spare Maiers unit I had. I then disassembled the Etalon tuning mount and sure enough the Etalon was decontacted. Luckily all the spacers were intact. Three were on one plate and the forth on the other.
Being a research chemist, engineer, an ATM and Solar observing nut I have read a number of papers on optical contacting and how it works so I'll give it a try. I first carefully cleaned the surfaces of the spacers and Etalon with high quality Acetone placed on strips of lens tissue that were wiped only in one direction across the surfaces. The two halves of the Etalon were then placed in contact. Under each spacer I could see a few nice interference fringes. I have a CLF bulb in my desk lamp that allows them to be seen. You want to be sure that you see no tiny black dots in the fringes or that the fringes are distorted. If so there are dust partials and or other dirt on the surfaces. The surfaces must be perfectly clean. I then applied light pressure to the top Etalon plate and the fringes would spread out so only one was visible. When I released the pressure the fringes returned so the plates did not contact. So no luck in using the procedure that I have read about. I read a number papers were the bonding process is enhanced by activating the surface of the glass by placing hydroxyl groups (OH) on the surface of the glass. These attract each other, pulling the surfaces closer together which then allows the Si-Si bonds to form to make the optical contacting. So I decide to try an experiment. Water does a great job in put OH groups on Silica surfaces. I used ultra pure water that we have in the lab. I dipped a clean wooden stick into the water and touched it to the side of the Etalon plate right next to the each spacer. A tiny bit of water wicked under each spacer. I then placed about a 2 lb weight on the top of the Etalon and let it sit over night. The next morning the each spacer now looked perfectly clear and darker then the rest of the Etalon. The plates were also firmly stuck together. Just to be on the safe side I wrapped the Etalon with a single turn of Kapton tape since I did not want the two halves to rotates against each other if they came apart when I was trying to test the unit out. I reassembled the PST and took it out for a look at the Sun. The image came to sharp focus but no H-alpha detail. I slowly turned the tuning ring so I was tighten down on the Etalon causing it to tilt and all of sudden the image filled with H-alpha detail. There were a couple of huge proms visible and detail around the two Sun spots. The H-alpha uniformity is very good across the field. I'm real happy that I got this scope working again and I plan to mount it next to my other PST to make binocular set up.

- Dave
Engineering = Take what you have and making what you need

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marktownley
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Re: Etalon reconnecting, Success !!!

Post by marktownley » Sat Aug 22, 2015 9:42 pm

Good result there Dave!
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longtech
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Re: Etalon reconnecting, Success !!!

Post by longtech » Sun Aug 23, 2015 5:35 am

Gotta love it when a plan comes together :-)
Well done sir!

Solar B
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Re: Etalon reconnecting, Success !!!

Post by Solar B » Sun Aug 23, 2015 9:22 am

WoW superb result indeed .... very well done .... I've never heard of anyone
successfully repairing a de-contacted etalon before :bow

Brian
" Gentlemen only ever use Refractors "


Derek Klepp
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Re: Etalon reconnecting, Success !!!

Post by Derek Klepp » Sun Aug 23, 2015 10:34 am

Great reading. Its always good when things work out.

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