Collimation techniques - Eyepiece or software assisted?

Hi Randall,

I have also the CDK14 and had some issues when collimating. I spent several nights with try and error.  Two things I found found out very quickly:

1. The light spandex shroud causes diffraction. Remove it - at least for collimating if you have one.
2. The CDK14 is sensitive to very tiny asymmetric collimation resulting in blurred or spiked stars. The de centering was not really visible in the de-focused star disk.

My attempts (also together with the help of PWI support):

First I had tried MetaGuide as assisted solution, but did not succeed to get any satisfying result. My seeing was to unstable to get a constant result. Still I had some asymmetric star discs and spikes.

I had the best result by the very old fashioned ways:

1. Made a 10 sec image of a star field
2. Imaged looping in 1s
3. adjusted the mirror in tiny moves in that direction the elongation/spikes were pointing to.
4. Loop through 1 to 3 until image is perfect.

I had to do the collimation because one of the spider vanes became lose, and the secondary moved out of center by 2 Millimeter.
Note: Watch out when cleaning the secondary! The center marker was cleaned away on the first wipe. Fortunately this is not so critical, since it is a spherical mirror.

CS
Rüdiger

Ruediger, Spider vanes loose! Uh oh...better check mine.

What does a 10s image followed by 1s looping mean? Are you adjusting while capturing 1s images? Why the 10s image first? To check the entire field and then adjust on a single star?

Are you adjusting to make any diffraction spikes the same length?


The truth is that while I understand that the optics need to be aligned, I have very little experience with collimation visually. And, it isn't trivial to take apart my CDK14 imaging train (including rotator, ONAG), get the right spacing for an eyepiece, and re-balance for the L350. An automated procedure using the imaging camera is so much easier. But, I want the best results.

Randall

Hi Randall,

watch out not to over tighten the vane holder screw. The support was warning me, since another customer overdid it an cracked it. Be gentle.

1s exposures to check permanently how far I have corrected the secondary and also of course the direction.
10s to reduce seeing fluctuation and have a clear direction to which to correct and not chase seeing.

No, I did not go for equal length of spikes. The big ones come from the vanes, but there were very tiny, fuzzy ones ones coming from not perfect collimation. I always call the "devil stars" since the have two horns.  See below

Though everyone claims the CDK is really easy to collimate and done in 15 minutes, it was a challenge for me to get it almost perfect, when you have bad seeing.
BTW: A good advise when working close to the zenith. Watch for the Allen key. If you drop it, it might hit directly on the main mirror . Therefore I secured it with a thin cord at my wrist.



Here another example.


Here an example of not properly aligned vanes. Look at the left spike. it is "V shaped"

Hi Randall,

here the Allen key:



Here a Lum Flat with the ASI6200:
Note: The flat is Histogram transformed to see any gradient. If only opening in Pi, you wont see any vignetting at all.

Hello,
I have no experience with CDK but I recently used theOcal electronique colimation with a newtonian and it was helpful in finding the concentrique alignment of the mirrors.