Do not turn the centre screw because it will effect the distance between the primary and secondary mirror. You don't need to move that screw to collimate the secondary. Only adjust the allen screws. release 1 slightly to tighten the ones opposite. this is very important.
Well, every time a newtonian is collimated that changes. And when the time comes to clean the secondary just count the number of turns and reinstall with the same number of turns. Just leave the 3 adjustment screws untouched and return the mirror to original position. It would just change the focal length slightly.
I have an RC for a few year and there’s a need to correct a few things in this video: - DO NOT tpuch the center bolt as that will change the distance between mirrors and give the scole astigmatism. - at minute 8:04: the laser returning to the hole has nothing to do with the primary mirror. It’s only bouncing on the secondary. - to align the secondary the ideal solution is to completely remove the focuser so eliminate focuser tilt from affecting collimation. Inset a plastic can with a small hole and calibrate the secondary to see the tiny hole back in the center of the secondary. (See kitchen counter collimation for more) - then adjust the primary by using the technique call „hall of mirrors“ (also on you tube) - only then correct the focuser tilt… (which can be a pain without a collimating ring). - be pacient and make tiny adjustments - always finalize with a star test. Good luck! -
Great video, thank you so much! I just bought an 8in RC and already had these collimators for my old Dob. The process was really easy, so really looking forward to seeing my first images with this scope :)
Great and very easy to follow video!! Thank you very much for taking the time and patience to speak slowly, which helps people to understand what is being said. Cheers
Just used your method on a Orion Classical Cassigrain 150 mm and your way was so quick and easy. Could not get it centered no matter how long I tried Just got the best colloimation ever. Thanks
wow These are great instructions and I learned a lot more than I planned on: tool list, terms, adjust procedure, telescope jargon. 😎 Thanks a lot for a great DIY starting point.
I have a Hotech flattener for my other scope, the compression/expanding rubber rings technic is 100% better than the copper ring thing. I wish telescope makers making astrophotography telescopes would give up already with the copper ring thing, they ruin the tilt, whatever telescope it is.
Secondary mirror separation is actually a thing, btw. It must be precise, and will be off if you mess with the center "SET" (NOT LOCK) screw. It can also be majorly adjusted with the collar on the secondary holder cup. RC6 and RC8, as well as CC6 and CC8 by GSO, and sold under many names. Orion for example will void your warranty if you mess with either, and they do not disclose the secondary mirror separation specification. If you get into this situation, email GSO and they will send you the complete optical drawing. For me it was the CC8 and the spec was 420mm. They also sent me the CC6 drawing and it is 322.4mm. Tell them you have their RC6 or RC8 and you need to know the "secondary mirror separation". Other people talk about using plate solving, but I would start with getting the physical specification back to factory default, which is the actual math for the design.
Just collimated my 2 mirrors on my RC6 with only cheap cheshire eyepiece. Was super easy. I finally used my laser only to put my focusser square who was really bad at first. Note: Don't ajust your laser with screw on your telescope cause focusser is attached with primary mirror. If not square, you will break your collimation. Only do it with cheshire. I used some tape behind my focusser to ajust laser in center cause hard to find tilting plate online. Worked perfectly and all centered.
Don't loosen up the center screw, the primary mirror could fall, download the owners manual for ioptron rc the correct procedure is explained in there.
Hello. No matter what I do, I cannot get this collimated with the stock focuser. I think part of the problem is the Crayford design makes the center of the focuser off axis, even if you have a collimation ring. The draw tube of the focuser isn’t aligned, and it gets worse by snugging the dial down. Did the TS focuser you bought make collimation easier? I’m about to abandon my sunken costs and move onto a different scope.
Hey Dave, I got the TS focuser because it could handle the camera weight and didn't shift when locking things down. The stock focusers on these RC's aren't the best, as you've discovered. But for some they're good enough. Have you tried collimation with the focuser removed somehow, working with just the visual back? You would probably need tot rig something up but it might be worth a shot. That might give you an indication if the problem is strictly with the focuser or within the OTA. Best of luck to you. Something we all need from time to time.
In the six inch rc the focuser is directly connected to the primary mirror. You will move the primary mirror with those screws.Those screws are only used to collimate the primary mirror. Unless you can independently adjust the focuser you are stuck with the alignment between the primary mirror and the focuser. The larger scopes have an independent adjustment. You can get an adapter flange from Teleskop Express. that allows you to independently adjust the primary mirror and the focuser. I made an adapter that directly mounts the focuser to the rear casting of the scope. The primary mirror is completely independent of the focuser like the larger versions. This way you can align the focuser with the optical axis of the scope and then you have to use the shape of out of focus stars to collimate the primary mirror.
Tue enough, but for us folks with limited funds this way is just fine. The star test was the best I have ever had, right in the center. This far better than the way in the instruction manual that comes with the Orion CC 6 inch. I am just a visual telescope user and this will work for the vast majority of users. Granted Jonathan yours is more precise but is good enough for me.
Hi: Kevin Zhou of IOptron recommended your TH-cam channel. I recently purchased the Scope and upgrading the Focuser as you suggested. Would like to image The Whirlpool and M27. Live in Concord, MA and have suburban light pollution. Can drive to New Hampshire and Vermont for better Dark Skies. Have an occasional Mountain Lion, but these animals are traveling large distances. Do have Black Bear, but usually young males. Is the Focuser attached to the Primary Mirror? Is this a real concern? Best regards, Carl Geyer. Love your channel.
Hi Kevin, the stock focuser is not attached to the primary mirror, unlike typical Schmidt Cassegrain Telescopes. Subsequently, there is no mirror flop when crossing the meridian. Just be sure the travel length of the new focuser doesn't exceed 55mm. Otherwise you run the risk of it bottoming out on the visual back in some situations. Other than that, it's a simple task. BTW: we have cats here in the Hills and occasional sightings of Black Bears. 💫
Really great video. Thanks for posting it. Question though. If I'm using the spacers for photography, wouldn't I want those in the image train? Then adjust to get everything as centered as possible with them in place? Otherwise, if I add them in later, it could possibly be off, in my mind. Thanks again.
Hey Jaymz, it makes sense what you're saying. The spacers do screw in which would limit the possibility of the imaging train being off after they were attached. I'd say try both ways and see. That would narrow it down. I like to know myself. Thanks for posting.
Excellent video. Question, what's the focuser that you got to replace the factory one? Is this a rack and pinion type? I'm looking to replace mine to avoid the constant slip and to be able to use my EAF as intended. Thanks in advance!
Here you go: www.teleskop-express.de/shop/product_info.php/language/en/info/p6970_TS-Optics-2-5--Rack-and-Pinion-Focuser---holds-Acc--up-to-6kg---travel-53mm.html Rock solid. You can also put a ZWO electronic focuser motor on it with a slight modification. Just remove the two screws from the bottom of the focuser that will allow the ZWO standard bracket to attach cleanly, no mods. Next, replace the screws that attach the ZWO motor to the bracket with longer ones that will allow you to build it out with a stack of washers or a couple of nuts used a spacers. Tighten it all down after making sure there's no binding on the flex coupler. Cheers
@@DakotaStarryNightsI have been looking for this focuser. The TS website says it is 90mm at the telescope side, but the RC6 is 96mm. Do I need an adapter?
@@davesmith9342 The one I got from TS fit the iOptron RC6 in the video above. www.teleskop-express.de/shop/product_info.php/info/p6970_TS-Optics-2-5--Rack-and-Pinion-Focuser-with-M90x1-Connection-and-360--Rotation.html The focuser has M90 x 1 female threads. If your RC6 actually has 96m male threads it would stand to reason you would need an adapter. TS does make custom adapters, so you could contact them. Or you could try it without one first and then order one if needed? Happy Holidays!
It comes with the scope. I got the Losmandy dovetail underneath for more stability and use the vixen for the guide scope. I must admit it is sharp looking. Cheers!
Strange, if I turn my center screw to losen the center mirror my f/8 is no longer f/8, e.g. plate solving on a loosened center screw results my RC8 to go from 1635mm to 1620mm, this cannot be correct.
The center screw should be re-tighten after the adjustment. Some have reported adjusting the secondary without loosening the center screw. If you chose that method then be careful. Loosen one side slightly followed by tightening the other side; or vise versa.
HI -- I have a 6" RC and the focuser is troublesome -- it's either too tight but holds the image train, or it's easy to focus but the image train slips. I considered a Moonlight focuser, but the one they recommend is expensive. Which TS focuser did you get for your telescope and how has it worked out for you? thanks for the excellent video
Hey Thomas, here you go: www.teleskop-express.de/shop/product_info.php/language/en/info/p6970_TS-Optics-2-5--Rack-and-Pinion-Focuser---holds-Acc--up-to-6kg---travel-53mm.html Rock solid. You can also put a ZWO electronic focuser motor on it with a slight modification. Just remove the two screws from the bottom of the focuser that will allow the ZWO standard bracket to attach cleanly, no mods. Next, replace the screws that attach the ZWO motor to the bracket with longer ones that will allow you to build it out with a stack of washers or a couple of nuts used a spacers. Tighten it all down after making sure there's no binding on the flex coupler. Cheers.
@@DakotaStarryNights Hey -- so I ordered the focuser linked above and it certainly looks like a quality piece of equipment. I am concerned, however, that it is so long that I will not be able to achieve backfocus with a focal reducer and a zwo 294mcpro camera. What is you imaging train and has this been an issue with you? I am about to return this focuser for a similar one that has 55 mm of drawtube travel but if yous works maybe I won't. Thanks in advance for your reply! cheers Thomas wicker
@@thomaswicker4368 It will not work with a focal reducer. I use a flatner that doesn't reduce the focal length to get the maximum power. So it works for me. So, yeah, I'd return it for the shorter one if you're wanting to reduce the focal length. www.teleskop-express.de/shop/product_info.php/language/en/info/p6970_TS-Optics-2-5--Rack-and-Pinion-Focuser---holds-Acc--up-to-6kg---travel-53mm.html (I've updated the link above just in case other guys want to use a focal reducer. :)
@@DakotaStarryNights Thanks for the quick reply. I meant to say flattener, not reducer. I actually tried it all out this afternoon, and it worked fine -- I achieved focus with all the parts included, with the drawtube in about the middle of its travel. Cheers, Thomas Wicker
Hello i just bought an omegon pro rc the 6" one and come from using a refractor so i don't know all these things practically, so i'll buy as soon as it will arrive a laser collimator but i even seen that a lot of people say i should buy a tilt adapter, what is it and why should i do it?
I haven't any experience with a tilt adapter so I can't comment on its effectiveness. Not all focusers will attach to the back of the scope in the exact same plane as the primary mirror. But a tilt adapter, as I understand it, tilts the focuser so that any deviation can be adjusted out. I would recommend to try to achieve collimation first with the laser collimator then star test it. If you find the results satisfactory, then good is good enough. Right?
Hello, I think it is underestimated to get the right distance between the main mirror and the second mirror. Unlike SC telescope, the RC telescope has hyperbolic mirrors built in and if there are problems with the images you should probably start there. I dismantled my scope and washed the mirrors. Afterwards, despite the good settings, nothing was right anymore, although I had made a video beforehand and Jupiter's satellites were round. th-cam.com/video/66NknidwvQQ/w-d-xo.html However, after cleaning, the satellites are more arrow-shaped. I also had the problem that the main mirror could be slid back and forth on the bearing tube by 0.8 mm. To fix this I had to apply 4 layers around the Tube of Kepton tape. Now I'm just waiting for a clear night to complete my adjustment. CS Werner
Do not turn the centre screw because it will effect the distance between the primary and secondary mirror. You don't need to move that screw to collimate the secondary. Only adjust the allen screws. release 1 slightly to tighten the ones opposite. this is very important.
Well, every time a newtonian is collimated that changes. And when the time comes to clean the secondary just count the number of turns and reinstall with the same number of turns. Just leave the 3 adjustment screws untouched and return the mirror to original position. It would just change the focal length slightly.
@@ohwell2790 The focal length is crucial for an RC telescope to produce a sharp image much more so than a Newtonian
@@Astronurd Do not use it anymore.
I have an RC for a few year and there’s a need to correct a few things in this video:
- DO NOT tpuch the center bolt as that will change the distance between mirrors and give the scole astigmatism.
- at minute 8:04: the laser returning to the hole has nothing to do with the primary mirror. It’s only bouncing on the secondary.
- to align the secondary the ideal solution is to completely remove the focuser so eliminate focuser tilt from affecting collimation. Inset a plastic can with a small hole and calibrate the secondary to see the tiny hole back in the center of the secondary. (See kitchen counter collimation for more)
- then adjust the primary by using the technique call „hall of mirrors“ (also on you tube)
- only then correct the focuser tilt… (which can be a pain without a collimating ring).
- be pacient and make tiny adjustments
- always finalize with a star test.
Good luck!
-
Great video! I ended up buying the same collimator for my 6" RC scope. I was able to get great results. Thanks!
Cool!
Great video, thank you so much! I just bought an 8in RC and already had these collimators for my old Dob. The process was really easy, so really looking forward to seeing my first images with this scope :)
Congrats on the RC-8! :)
Best how to on the topic
Thank you!
Great and very easy to follow video!!
Thank you very much for taking the time and patience to speak slowly, which helps people to understand what is being said.
Cheers
Happy to hear you found it useful. :)
Just used your method on a Orion Classical Cassigrain 150 mm and your way was so quick and easy. Could not get it centered no matter how long I tried Just got the best colloimation ever. Thanks
That's great man!
wow These are great instructions and I learned a lot more than I planned on: tool list, terms, adjust procedure, telescope jargon. 😎 Thanks a lot for a great DIY starting point.
Glad it was helpful!
Great review of the Hotech Laser Collimator. Compression is the way to go not the set screws.
It's pretty much the only way to get centered. Thanks for posting!
I have a Hotech flattener for my other scope, the compression/expanding rubber rings technic is 100% better than the copper ring thing. I wish telescope makers making astrophotography telescopes would give up already with the copper ring thing, they ruin the tilt, whatever telescope it is.
Secondary mirror separation is actually a thing, btw. It must be precise, and will be off if you mess with the center "SET" (NOT LOCK) screw. It can also be majorly adjusted with the collar on the secondary holder cup.
RC6 and RC8, as well as CC6 and CC8 by GSO, and sold under many names. Orion for example will void your warranty if you mess with either, and they do not disclose the secondary mirror separation specification.
If you get into this situation, email GSO and they will send you the complete optical drawing.
For me it was the CC8 and the spec was 420mm. They also sent me the CC6 drawing and it is 322.4mm.
Tell them you have their RC6 or RC8 and you need to know the "secondary mirror separation".
Other people talk about using plate solving, but I would start with getting the physical specification back to factory default, which is the actual math for the design.
Just collimated my 2 mirrors on my RC6 with only cheap cheshire eyepiece. Was super easy. I finally used my laser only to put my focusser square who was really bad at first. Note: Don't ajust your laser with screw on your telescope cause focusser is attached with primary mirror. If not square, you will break your collimation. Only do it with cheshire. I used some tape behind my focusser to ajust laser in center cause hard to find tilting plate online. Worked perfectly and all centered.
Don't loosen up the center screw, the primary mirror could fall, download the owners manual for ioptron rc the correct procedure is explained in there.
Thank you
if you loosen the center screw you are changing the distance at wich the secondary works!!!
Bravoooo!!!
👏👏👏👏
:)
9:05 my laser wasn’t true when i rolled it, laser twirled like a baton girl 👧 lucky i didn’t have to replace focuser. Great tips Dakota!
Hello. No matter what I do, I cannot get this collimated with the stock focuser. I think part of the problem is the Crayford design makes the center of the focuser off axis, even if you have a collimation ring. The draw tube of the focuser isn’t aligned, and it gets worse by snugging the dial down. Did the TS focuser you bought make collimation easier? I’m about to abandon my sunken costs and move onto a different scope.
Hey Dave, I got the TS focuser because it could handle the camera weight and didn't shift when locking things down. The stock focusers on these RC's aren't the best, as you've discovered. But for some they're good enough. Have you tried collimation with the focuser removed somehow, working with just the visual back? You would probably need tot rig something up but it might be worth a shot. That might give you an indication if the problem is strictly with the focuser or within the OTA. Best of luck to you. Something we all need from time to time.
In the six inch rc the focuser is directly connected to the primary mirror. You will move the primary mirror with those screws.Those screws are only used to collimate the primary mirror. Unless you can independently adjust the focuser you are stuck with the alignment between the primary mirror and the focuser.
The larger scopes have an independent adjustment. You can get an adapter flange from Teleskop Express. that allows you to independently adjust the primary mirror and the focuser.
I made an adapter that directly mounts the focuser to the rear casting of the scope. The primary mirror is completely independent of the focuser like the larger versions. This way you can align the focuser with the optical axis of the scope and then you have to use the shape of out of focus stars to collimate the primary mirror.
Tue enough, but for us folks with limited funds this way is just fine. The star test was the best I have ever had, right in the center. This far better than the way in the instruction manual that comes with the Orion CC 6 inch. I am just a visual telescope user and this will work for the vast majority of users. Granted Jonathan yours is more precise but is good enough for me.
Hi! I’m interested in that adapter to the focuser. It’s a great idea! Can you share a photo?
Thanks!
Hi: Kevin Zhou of IOptron recommended your TH-cam channel. I recently purchased the Scope and upgrading the Focuser as you suggested. Would like to image The Whirlpool and M27. Live in Concord, MA and have suburban light pollution. Can drive to New Hampshire and Vermont for better Dark Skies. Have an occasional Mountain Lion, but these animals are traveling large distances. Do have Black Bear, but usually young males.
Is the Focuser attached to the Primary Mirror? Is this a real concern?
Best regards,
Carl Geyer. Love your channel.
Hi Kevin, the stock focuser is not attached to the primary mirror, unlike typical Schmidt Cassegrain Telescopes. Subsequently, there is no mirror flop when crossing the meridian. Just be sure the travel length of the new focuser doesn't exceed 55mm. Otherwise you run the risk of it bottoming out on the visual back in some situations. Other than that, it's a simple task. BTW: we have cats here in the Hills and occasional sightings of Black Bears. 💫
Really great video. Thanks for posting it.
Question though. If I'm using the spacers for photography, wouldn't I want those in the image train? Then adjust to get everything as centered as possible with them in place? Otherwise, if I add them in later, it could possibly be off, in my mind.
Thanks again.
Hey Jaymz, it makes sense what you're saying. The spacers do screw in which would limit the possibility of the imaging train being off after they were attached. I'd say try both ways and see. That would narrow it down. I like to know myself. Thanks for posting.
Excellent video. Question, what's the focuser that you got to replace the factory one? Is this a rack and pinion type? I'm looking to replace mine to avoid the constant slip and to be able to use my EAF as intended. Thanks in advance!
Here you go: www.teleskop-express.de/shop/product_info.php/language/en/info/p6970_TS-Optics-2-5--Rack-and-Pinion-Focuser---holds-Acc--up-to-6kg---travel-53mm.html Rock solid.
You can also put a ZWO electronic focuser motor on it with a slight modification. Just remove the two screws from the bottom of the focuser that will allow the ZWO standard bracket to attach cleanly, no mods. Next, replace the screws that attach the ZWO motor to the bracket with longer ones that will allow you to build it out with a stack of washers or a couple of nuts used a spacers. Tighten it all down after making sure there's no binding on the flex coupler. Cheers
@@DakotaStarryNights You got an excellent video. Will this focuser be able to accomodate the infocus of my GSO 0.75x reducer. Pls assist.
@@abhijittamuli1609 If the original one did then this one should also. The draw tube travel is about the same.
@@DakotaStarryNightsI have been looking for this focuser. The TS website says it is 90mm at the telescope side, but the RC6 is 96mm. Do I need an adapter?
@@davesmith9342 The one I got from TS fit the iOptron RC6 in the video above. www.teleskop-express.de/shop/product_info.php/info/p6970_TS-Optics-2-5--Rack-and-Pinion-Focuser-with-M90x1-Connection-and-360--Rotation.html
The focuser has M90 x 1 female threads. If your RC6 actually has 96m male threads it would stand to reason you would need an adapter. TS does make custom adapters, so you could contact them. Or you could try it without one first and then order one if needed? Happy Holidays!
Doesn't adjusting the primary knock out the secondary mirror alignment you at the beginning??
Yes, it does. Step 3, the last step, readjusts the secondary after step 2. Cheers!
Where did you buy that nice top rail bar?
It comes with the scope. I got the Losmandy dovetail underneath for more stability and use the vixen for the guide scope. I must admit it is sharp looking. Cheers!
Could you share the Manufacturer/model of cheshire eyepiece please? Thank you.
Sure, it's an Agena 1.25" Cheshire. It's available at agenaastro.com. Cheers!
Strange, if I turn my center screw to losen the center mirror my f/8 is no longer f/8, e.g. plate solving on a loosened center screw results my RC8 to go from 1635mm to 1620mm, this cannot be correct.
The center screw should be re-tighten after the adjustment. Some have reported adjusting the secondary without loosening the center screw. If you chose that method then be careful. Loosen one side slightly followed by tightening the other side; or vise versa.
Yes it is and it is not good... You need to adjust your distance to be exactly at your native focal, or you will never be able to be 100% colimated.
HI --
I have a 6" RC and the focuser is troublesome -- it's either too tight but holds the image train, or it's easy to focus but the image train slips. I considered a Moonlight focuser, but the one they recommend is expensive. Which TS focuser did you get for your telescope and how has it worked out for you?
thanks for the excellent video
Hey Thomas, here you go: www.teleskop-express.de/shop/product_info.php/language/en/info/p6970_TS-Optics-2-5--Rack-and-Pinion-Focuser---holds-Acc--up-to-6kg---travel-53mm.html Rock solid.
You can also put a ZWO electronic focuser motor on it with a slight modification. Just remove the two screws from the bottom of the focuser that will allow the ZWO standard bracket to attach cleanly, no mods. Next, replace the screws that attach the ZWO motor to the bracket with longer ones that will allow you to build it out with a stack of washers or a couple of nuts used a spacers. Tighten it all down after making sure there's no binding on the flex coupler. Cheers.
@@DakotaStarryNights Hey -- so I ordered the focuser linked above and it certainly looks like a quality piece of equipment. I am concerned, however, that it is so long that I will not be able to achieve backfocus with a focal reducer and a zwo 294mcpro camera. What is you imaging train and has this been an issue with you? I am about to return this focuser for a similar one that has 55 mm of drawtube travel but if yous works maybe I won't. Thanks in advance for your reply! cheers Thomas wicker
@@thomaswicker4368 It will not work with a focal reducer. I use a flatner that doesn't reduce the focal length to get the maximum power. So it works for me. So, yeah, I'd return it for the shorter one if you're wanting to reduce the focal length. www.teleskop-express.de/shop/product_info.php/language/en/info/p6970_TS-Optics-2-5--Rack-and-Pinion-Focuser---holds-Acc--up-to-6kg---travel-53mm.html (I've updated the link above just in case other guys want to use a focal reducer. :)
@@DakotaStarryNights Thanks for the quick reply. I meant to say flattener, not reducer. I actually tried it all out this afternoon, and it worked fine -- I achieved focus with all the parts included, with the drawtube in about the middle of its travel. Cheers, Thomas Wicker
@@thomaswicker4368 Glad to hear it. Thanks for the update!
Hello i just bought an omegon pro rc the 6" one and come from using a refractor so i don't know all these things practically, so i'll buy as soon as it will arrive a laser collimator but i even seen that a lot of people say i should buy a tilt adapter, what is it and why should i do it?
I haven't any experience with a tilt adapter so I can't comment on its effectiveness. Not all focusers will attach to the back of the scope in the exact same plane as the primary mirror. But a tilt adapter, as I understand it, tilts the focuser so that any deviation can be adjusted out.
I would recommend to try to achieve collimation first with the laser collimator then star test it. If you find the results satisfactory, then good is good enough. Right?
@@DakotaStarryNights Sounds fair, thanks for the patience, keep going man🙌🙌
I wonder if all of this works on a D-K Cassegrain ie the Tak mewlon?
I can't say for sure. But give it a try and then star test it.
Can I get a link to the laser collimator? I couldn't find it on google
Here you go: agenaastro.com/hotech-2-1-25-sca-laser-collimator.html
Thx
Hello, could we repost your video on our social media in China?
Sure, no problem. You can repost it. Glad to help.
Hello,
I think it is underestimated to get the right distance between the main mirror and the second mirror. Unlike SC telescope, the RC telescope has hyperbolic mirrors built in and if there are problems with the images you should probably start there. I dismantled my scope and washed the mirrors. Afterwards, despite the good settings, nothing was right anymore, although I had made a video beforehand and Jupiter's satellites were round.
th-cam.com/video/66NknidwvQQ/w-d-xo.html
However, after cleaning, the satellites are more arrow-shaped. I also had the problem that the main mirror could be slid back and forth on the bearing tube by 0.8 mm. To fix this I had to apply 4 layers around the Tube of Kepton tape. Now I'm just waiting for a clear night to complete my adjustment.
CS
Werner