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Old 18-11-2018, 08:46 PM
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John K
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Join Date: Sep 2005
Location: Melbourne
Posts: 1,468
Collimation fine tuning advice

Hi guys,

I am "tinkering" with my 9.5" CDK type scope to try and get a better understanding on the long term collimation process for this type of scope. Having only owned a Newtonian, what a luxury!

I am only tweaking the secondary at this stage and have tried a version of CCD inspector but was unable to really get measurements from it to make worth while adjustments.

At this stage, I am using Firecapture and and putting an out of focus (inside focus) star to try and get the best looking image in the centre of the camera I have - 1600mm.

My idea as recommended by Stefan who completely rebuilt the scope and the way he likes to do it is to try and find the perfect centre of the imaging train and moving the star around the field until most of the image is totally concentric. This however I am finding hard to achieve and replicate! Another way I to shoot an open cluster like M41 with all of the images out of focus to see where the perfect centre is and then move the secondary accordingly.

I have read the DSI collimation process and the image I am attached I think shows a generally balanced image what slightly out of collimation is some of the corners.

Can someone make some suggestions on the best way to balance the attached image based on the standard 3 screw secondary (centre screw I am ignoring as it will alter the distance to the corrector). One question I have should 3 screws always be adjusted? e.g. if one is turned counter clockwise should the other two be turned the other way? Or can I balance the image by simply tweaking only 2 screws to adjust tilt in one direction?

The airy disk also does seem a bit unusual.

I am not using a Taka Collimator - checking the secondary mark that the scope with a Newtonian type laser is showing that the laser does not point directly at the centre of the secondary - does that make a difference in any way as many manufacturers say it does not??

Thanks in advance for any advice.

Clear skies.

John K.
Attached Thumbnails
Click for full-size image (Collimation Test Nov 18_2018.jpg)
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Click for full-size image (Collimation Centre Enlarged Nov 18_2018.jpg)
110.7 KB44 views
Click for full-size image (Collimation Test Nov 18_2018_Airy Disk Centre.jpg)
182.8 KB38 views

Last edited by John K; 19-11-2018 at 07:33 AM.
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