3 replies to this topic

[jgraham]

Just for yucks I thought that I'd share this since I happened to have the source images still sitting on my hard drive...

 

I have bought a CC8 and a pair of CC45s from Agena and they do a pretty good job of collimating them before shipping them out. However, the inevitably get banged around pretty good in shipping and need to be tweaked a bit when they arrive. I always start with the assumption that the primary is close enough 'cause that's the one I don't want to touch. If I'm happy with the image after aligning the secondary I let is go at that, and so far I'm 3 for 3 with that approach. I collimated my CC8 and my first CC45 visually, so I don't have a record of the progression, but I bought this second CC45 primarily for imaging, so I used it with a camera (Canon EOS Ra) to check the collimation and I kept the test images as a record of the process. These are all 5 second exposures of a centered star (Markab if I recall right) at ISO 200. I used a low gain and a long exposure to smooth out the seeing. After each tweak I re-centered the stars and checked the alignment. The top row shows the initial rough alignment inside the focus, the bottom row shows the second pass closer to focus for the fine alignment. What I am looking for is the bright spot to be centered and the diffraction rings to be concentric and even.

 

 

Not perfect, but not bad. I use this same procedure with my CC8, RC8, and my SCTs. The process worked fantastic with my relatively fast f/6.3 Meade wide field 8" and 10" SCTs. They really blossomed once I got the collimation zeroed in.

 

Works for me.

 

BTW, this particular CC45 was picked up on clearance and it was a return. It just needed the collimation to be tweaked (for me, close is not good enough with most Cats) and the focuser tension needed to be adjusted (the GSO focuser is a bit wonky until you figure out how to adjust it. (Hint; ignore the lock knob until the tension is snug/firm, then you can _lightly_ snug the lock, but it's not really needed.)

 

Anywhoo, food for thought.

 

Enjoy!

 

[quilty]

I always ignored the lock knob. Dont understand the problems with the focusser. It's not good one and I very much prefer the SC mirror focussers but its action is simple.
Lock knob only when it takes heavy load which which never happens in my case.
It's just no adjustment but a lock screw

[Sarkikos]

jgraham,

 

Do you collimate straight-through without a diagonal, or with the diagonal you will use in place?

 

Also, slop in the focuser can affect collimation.  Maybe best to use the lock-knob while collimating and then consistently, every time, after focusing.  

 

The collimation on my CC45 arrived obviously off.  It was so bad, at first I thought the scope was showing tube currents.  But once I took the time to collimate at the secondary, the images sharpened up.  I haven't made any adjustments to collimation at the primary.

 

I wonder if the collimation went bad during shipping.  I have my doubts, though, since the adjustment screws at the secondary were really tight when I received it.  How could it change?  I think maybe collimation was checked/adjusted while there was slop in the focuser.  Who knows?  But collimation was off.

 

Mike

Edited by Sarkikos, 05 November 2024 - 08:12 PM.

[jgraham]

I collimate with the scope configured as it will be used. Since this was for imaging it was configured straight-through...

 

 

My focuser has no significant shift now. I have basically quit using the lock at all as it can shift the draw tube. Instead, I'm just snugging the tension so that it is firmly holds the draw tube against all of the rollers. I was pondering borrowing the Moonlite off of my RC8, but this configuration is working so well I'm probably going to leave it as-is.

 

Simple is good.