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Equipment Discussions >> Reflectors

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Javier1978
scholastic sledgehammer


Reged: 02/12/09

Re: Stucked with the collimation final steps... new [Re: Vic Menard]
      #5650487 - 01/29/13 02:54 PM

Quote:

That said, the registration problem (sloppy fit) you've described indicates a problem with the sight tube, 2- to 1.25-inch adapter, and/or the focuser drawtube.




My focuser and 1,25 adapter are rock solid, no slope at all. As said before, I tested it with the tublug reflection racking in and out and it has no slope at all. The problem is that this is a heavy and long device and even with tapes to prevent play, if put it and pusch up a little bit the reflection will move. But if you are pointing as a problem that the hole of the 1,25 adapter is oversized thatīs for sure.

Quote:

I also have a hard time when focusing the crosshair to perform the FAA and I donīt like the reflection that produces to perform the primary axial collimation, every thing is so tiny and confusing!



Some people find that if they pull their eye away from the sight tube pupil, the sight tube cross hairs become more distinct relative to the primary mirror center spot. With regards to "tiny and confusing"--everything's the same size as it is in your collimation cap, except the field of view is narrower. There's certainly more going on with the sight tube cross hairs overlapping the field of view, but the fact that you can "see" errors that aren't obvious in a collimation cap is the reason why sight tube collimation is important.




I did move out me eye to make focus, yet I didnīt find it accuarate because the image start to wander more if you take your eye from the peephole. As for the primary, the donut doesnīt seem to be a good figure to overlap. At some point it just hide a little bit and I donīt know any more whatīs going on, although Iīm quite sure I didnīt arrive to an accurate alignment. You are right about the size though. With my improved collimation cap I can see the hole into the donut, even I can see (its seen in the image) a tiny liquid paper point that shows the actual center of the mirror. And Iīm quite sure there is no possible slope with it.


Quote:

Anyway, while waiting it to arrive I made some last tweeks to the mechanicalls alignments and I improved my collimation cap with a shiny surface. Now is much easier to collimate the primary.

This is how my final collimation looks.



Why did you cover the primary in the second image?




I was trying to see the final shape of the secondary without any (to me at least) distracting reflection.

Thank you for the information, I will check your website later!!


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Stucked with the collimation final steps... new [Re: Javier1978]
      #5650938 - 01/29/13 06:54 PM

If you pull your eye back from the peephole to focus on the crosshairs, use your hand to place your thumb on your face and your little finger on the tool. Your head will not bob back and forth as much.

As for star images, once you have achieved collimation, you have only taken care of one of the three "C"s: collimation.
The other two are : Cooling and Conditions.

Cooling. Never examine the quality of star images if the mirror hasn't cooled down. If you don't use a fan, the mirror should have been outside at least 3 hours. If you do use a fan, one hour. Because heat in front of the mirror will warp the star images and keep them from beina as sharp as the optics may allow.

Conditions: Seeing varies from night to night and hour to hour. Most places, seeing conditions are better in the midnight-to-dawn hours because turbulence in the atmosphere has settled down.
If the jet stream is overhead, if the weather map shows the pressure isobars close together, if a front is coming through, or if you live on the lee side of a mountain, you will not see good seeing and your star images will be blobs. Also, never examine a star that is only a few degrees above a roof because the heat rising from the roof will create poor seeing.

When you see good seeing and star images are tiny little pinpoints, THEN you can evaluate the mirror and see the level of optical quality there.

P.S. A 2" combination tool has a much larger field of view and avoids the adapter fitment problem.


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Javier1978
scholastic sledgehammer


Reged: 02/12/09

Re: Stucked with the collimation final steps... new [Re: Starman1]
      #5651054 - 01/29/13 08:00 PM Attachment (14 downloads)

Thank you Don for the information about star testing and the hand tip.

Regarding the fit of the chesire eyepiece, maybe some images will clarify my thoughts. The 1,25 adpater is OK, I think the problem is that the portion of the chesire that goes into the eyepiece is too short compared to the other portion. This is, in my opinion, what cause a poor fitting.

Vic pointed the focal lenght of the eyepiece, but isnīt also important how much it goes into the eyepiece holder? I think if the proportion where the other way round (the mayor part of the chesire going into the eyepiece holder) I would be able to cover my secondary mirror.

Edited by Javier1978 (01/29/13 08:02 PM)


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Javier1978
scholastic sledgehammer


Reged: 02/12/09

Re: Stucked with the collimation final steps... new [Re: Javier1978]
      #5651055 - 01/29/13 08:00 PM Attachment (14 downloads)

And into the EP holder.

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Hothersale
sage


Reged: 10/13/09

Loc: Victoria, BC
Re: Stucked with the collimation final steps... new [Re: Javier1978]
      #5654471 - 01/31/13 02:56 PM

You are supposed to insert it farther than that. Insert it all the way up to the shoulder of the tube. Basically as far as it will go.

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Javier1978
scholastic sledgehammer


Reged: 02/12/09

Re: Stucked with the collimation final steps... new [Re: Hothersale]
      #5654603 - 01/31/13 04:05 PM

This is as far as it will go, I would be happy to insert it farhter.

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