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Classic Cassegrain Popularity?

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203 replies to this topic

#201 John59

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Posted 04 August 2019 - 08:49 PM

Hummm..I would would have thought that both the primary and secondary are adjustable on any classical cass except the peculiar system used for the Tak CN-212 which has a movable mirror. 

 

Ed

Ed, My mistake they are there just not where I thought they would be.  They are actually on the grip ring where the the focuser attaches.   I hope I never have to adjust these. 

When I first received it I did a collimating with a Cheshire and got excellent rings.

However when I finally got a clear night the star collimation was off more that I would have thought it would be.

It took a bit of tweaking on the secondary to get it right.



#202 Ed Wiley

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Posted 04 August 2019 - 09:10 PM

This is what I used back in the day. I found collimation very tricky.

http://bobmay.astronomy.net/CassNotes/

 

Ed


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#203 555aaa

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Posted 05 August 2019 - 01:57 PM

Tanks for the link, Ed.



#204 danielguo

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Posted 05 August 2019 - 07:25 PM

FYI, this is how I collimate my CFF CC250.

  1. (Once after delivery) Measure the distance between primary and secondary to make sure the distance is still correct after international shipping. Mine is still perfect.
  2. (Optional) Put a laser in the focuser and adjust the focuser tilt to let the laser hit the center marker of the secondary.
  3. Put a Takahashi Collimating Telescope in the focuser and adjust the secondary to align the dot to the secondary center marker.
  4. Center on a relatively bright star and adjust primary tilt to remove coma.

It sounds like a lot of work, but the scope holds collimation pretty well. The primary adjustment knobs are also clearly marked making it easier. Last week I was fine tuning primary collimation in a star party and it took me only half an hour to get it essentially perfect.


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