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Post by groverro on Mar 10, 2017 10:10:01 GMT -8
Hello All,
I wanted to ask if someone could assist with my collimation headache. I am using a glatter laser and tublug and when aligning the secondary under the focuser, I used a collimation cap such that the reflection of the primary mirror is fully centered in the secondary. However, I had gaps and tried to re-adjust that. Now what I'm facing is that when I insert the laser and have the beam hit the doughnut in the center, and use the tublug to align the center spot, the reflection is no longer smooth in the secondary mirror. Basically there is a larger gap. If I rotate the secondary to fix this, the laser no longer hits the secondary. I have attached pictures for reference and any advice will be greatly appreciated..
  
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Post by Deleted on Mar 10, 2017 11:07:06 GMT -8
Tough topic to do just verbally.
I can't get my perspective with your pics. Maybe one shot down the focuser would help.
One rule(?) Always ignore the primary until the very last. Get each previous step down first, starting with the focuser, then secondary position, then secondary collimation, then primary.
If that is already shot down the focuser..... then I'd start from the very beginning.
1) Squaring the focuser. Some scopes can come poorly squared. Measure the spider to be sure the secondary holding shaft is in the center of the telescope tube / spider. My book then says to measure the distance from the center of the focuser to the top of the telescope tube with a tape measure and then check that the focuser is pointing straight at the same distance down the secondary holder from the top of the tube. This is tuned by shimming the focuser. The book even suggests removing the secondary and replacing with a bolt down thru the spider to make sure the focuser is centered onto center of the bolt as well as the proper distance down the bolt -- shimming the focuser in both directions (by looking down a longer sighting tube mounted in the focuser).
2) Centering the Secondary under the focuser. Replace the secondary holder and center it under the focuser by possibly tweaking the spider vanes anchors if you have to. (ignore the primary's reflections) Watch the edges of the sighting tube that all is spaced evenly down to the secondary, rotating the secondary to appear perfectly circular.
3) Only after the secondary is directly positioned / centered under the focuser you can then collimate the secondary by adjusting the screws behind the secondary with the laser in the focuser. Tweak to get the laser to hit the primary's center dot. This is where you would start collimation in the field.
4) Tweak primary to return laser dot to center of laser. Then I fine tune with chessire replacing the laser. I shine a light into the side of the chessire and see the primary's center dot / donut in the center of the view in the chessire.
Hope this might help. Gotta go.
DSD.
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Post by groverro on Mar 10, 2017 11:31:48 GMT -8
Uhh okay. I last checked the distance for the spider bolt to the centre screw and I think they are all equal. I am not sure about shimming the focuser as I have never attempted that and figured it was correct from before. I have changed my focuser to a Moonlite though so not sure if that matters. Are you able to meet and you could perhaps show me what I am doing wrong? I live in New West and can come to you if that works with you? Thank you! Tough topic to do just verbally.
I can't get my perspective with your pics. Maybe one shot down the focuser would help.
One rule(?) Always ignore the primary until the very last. Get each previous step down first, starting with the focuser, then secondary position, then secondary collimation, then primary.
If that is already shot down the focuser..... then I'd start from the very beginning.
1) Squaring the focuser. Some scopes can come poorly squared. Measure the spider to be sure the secondary holding shaft is in the center of the telescope tube / spider. My book then says to measure the distance from the center of the focuser to the top of the telescope tube with a tape measure and then check that the focuser is pointing straight at the same distance down the secondary holder from the top of the tube. This is tuned by shimming the focuser. The book even suggests removing the secondary and replacing with a bolt down thru the spider to make sure the focuser is centered onto center of the bolt as well as the proper distance down the bolt -- shimming the focuser in both directions (by looking down a longer sighting tube mounted in the focuser).
2) Centering the Secondary under the focuser. Replace the secondary holder and center it under the focuser by possibly tweaking the spider vanes anchors if you have to. (ignore the primary's reflections) Watch the edges of the sighting tube that all is spaced evenly down to the secondary, rotating the secondary to appear perfectly circular.
3) Only after the secondary is directly positioned / centered under the focuser you can then collimate the secondary by adjusting the screws behind the secondary with the laser in the focuser. Tweak to get the laser to hit the primary's center dot. This is where you would start collimation in the field.
4) Tweak primary to return laser dot to center of laser. Then I fine tune with chessire replacing the laser. I shine a light into the side of the chessire and see the primary's center dot / donut in the center of the view in the chessire.
Hope this might help. Gotta go.
DSD.
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Post by groverro on Mar 10, 2017 12:19:52 GMT -8
Hmm looks like my reply didn't get posted. I am not sure about step 1 & 2 as I have never done it before and will probably make it worse than it is now. Would it be possible if you can show me what I am doing wrong? I live in New West and can come meet you if that works for you? Thank you!
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Deleted
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Post by Deleted on Mar 10, 2017 19:01:01 GMT -8
Looks like your focuser is not square in the optical path. Hard to tell with pictures. The gaps are supposed to be there.
They need to be more or less equal all around. And if by "smooth" you mean a sharp circle, well then no, it is
usually quite jagged and somewhat blurry, as in a not really defined edge. You are aiming for the middle dot after all.
Do this: center your secondary, with your laser, then tweak your primary. If it is still off then you need to square the focuser!
Bring it to our next meeting, we can look at it before dinner.
MMc
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Post by Deleted on Mar 10, 2017 20:22:11 GMT -8
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Post by groverro on Mar 10, 2017 21:29:58 GMT -8
Hi Vault 7
Uhh that was really creepy how you found my twitter lol. I only use it to complain to translink lol. Yes both my posts are the same and I'm DEFINITELY not Trolling. I'm just very Frustrated and wanted any help i could get so posted here, Stargazing lounge and Cloudy nights. Personally I'm more comfortable with someone showing me what I'm doing wrong and that's why i posted here, since I know amateur astronomers here are located in the Lower Mainland and can offer to help as we do not have a local store anymore.
Sorry if that doesn't make sense. I'll try to come to the meeting..thank you.
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Post by groverro on Mar 10, 2017 21:32:11 GMT -8
I forgot to ask when the meeting is..when is the meeting?
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Post by Deleted on Mar 11, 2017 8:59:28 GMT -8
Hi G,
I sent you a PM. Yes, things must be different now that there's no hands on store. Hope we can help.
The meeting is the second Wednesday of each month in Abbotsford (you just missed it). (see the calendar) (except for July and Aug or when the MSQ is on). At the last meeting we were discussing how we missed our workshop meetings we used to have -- so few builders like in the old days. You really had to know your instrument. Now it's just dinner meetings.
But I'm sure we can help before then.
DSD. |
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Post by craig on Mar 11, 2017 14:09:02 GMT -8
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Post by groverro on Mar 11, 2017 16:33:27 GMT -8
I tried again and this is what I got. I think for now I am okay with this. Once I get a star test I will find out. Thanks for your input everyone.  |
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Post by Deleted on Mar 11, 2017 20:55:45 GMT -8
That looks pretty good from here. Well done.
Hard to see the lower edge of the focuser bottom but the secondary might be a bit 'down' (in the pic's directions).
Should perform quite well.
That looks like a truss tube dob? Hope you have a shroud to keep out stray light from hitting the back of the eyepiece.
DSD. |
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Post by craig on Mar 11, 2017 22:16:04 GMT -8
looks like a collapsible sky watchers dob from the first pics what size i could only guess
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Post by Deleted on Mar 11, 2017 22:54:27 GMT -8
It's a 12 and so it's probably fast F / something so collimation is very important.
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Post by craig on Mar 12, 2017 9:17:09 GMT -8
that's for sure 12 is a nice size as well. hopefully the weather gets a bit nicer this winter has not been seeing friendly. the few nice days where dam cold. i bet shylock is still pretty snowy still.
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Post by groverro on Mar 12, 2017 9:58:36 GMT -8
Hello DSD and Craig.
Yes it's a sky watcher 12" Collapsible. I do have a shroud for it that I from All Star Telescopes. I felt the astrozap was a tad to expensive. It's a f-4.9. It's funny cause i loose collimation the moment i take it to my car. Usually do a final tweek before observing session. Hopefully we all get clear skies soon.
Thanks for all your input!
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