Questions about Secondary Collimation

[Pogo007]

Hope someone with more experience than I, which basically means anyone that has successfully collimated a Newtonian, can answer a couple of compound questions I have based on my first and only attempt at secondary collimation of my SkyWatcher Flextube 250.

1) All three of my secondary collimation screws were extremely snug before I did anything and I was only able to comfortably turn them counter-clockwise.  Is this normal?  Do I need to loosen all three screws first before I can properly start collimation?  Should I be turning any screw beyond "snug"?

2) Before collimating, I placed a yellow sheet inside my OTA opposite my focuser tube and I placed a red sheet between my secondary and primary.  The view this gave through my focuser tube was of a red circle surrounded by a partial yellow ring (the secondary mirror stalk blocking a portion of this yellow annulus). While independently turning each of the secondary collimation screws counter-clockwise I looked down the focuser tube (both with and without a sight tube installed) expecting to see some change in the shape of the red area (more or less circular) and/or the yellow area (less or more even thickness).  I turned the screws no more that 2 complete revolutions.  I did not perceive any appreciable difference in what I saw and I turned each screw back (clockwise) to their original tightness before working with another of the screws.   Does it make sense that I didn't perceive any change?   Should I have turned the screws more revolutions?   Should I have loosened more than one at a time?

Very confused and looking for your help.  Thanks

[ronl]

http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/  if you follow this

you will get it spot on, this guide is superb. 

[sockatume]

I had exactly what you are describing, I think it’s normal for certain designs of secondary mirror holders. I don’t have the thread handy right now but perhaps you can see it through my profile. It made the process a bit less intuitive than with the primary but I haven’t touched it since.

I have a Skywatcher Heritage 130p and I imagine the mirror holder design is reasonably similar across their range.

 

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