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RC6 Collimation - Continuing Saga
Sep 27, 2022 16:14:42   #
bwana Loc: Bergen, Alberta, Canada
 
This is a summation of my 3rd attempt to get my 3rd-hand 6" Ritchey-Chretien scope collimated.

After aligning both the primary and secondary mirrors in the scope I still had star stretch along one side and in two corners and, yes, I realize a RC doesn't project a flat image but if nothing else all the corners should look much the same...

Conclusion, the focuser is not aligned with the axis of the scope. Approach, shim the focuser to realign it.

Three hours later I've added two tin foil shims and shifted the axis of the focuser and totally redone the alignment twice. Last night was sky test time.

The result of this effort is shown in the attachment. Summary:
1) Not quite there yet but I've removed about a bit more than half the star stretch.
2) I suspect one more shim will resolve the problem to insignificant.
3) Shims were added opposite to the side with star stretch
4) Aligning a badly out-of-alignment RC is a pain in the a$$!!

I've also ordered a 1x Field Flattener for the scope which should eliminate any remaining corner and edge star stretch...

bwa

Centered on Altair
Centered on Altair...
(Download)

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Sep 28, 2022 22:02:50   #
Ballard Loc: Grass Valley, California
 
bwana wrote:
This is a summation of my 3rd attempt to get my 3rd-hand 6" Ritchey-Chretien scope collimated.

After aligning both the primary and secondary mirrors in the scope I still had star stretch along one side and in two corners and, yes, I realize a RC doesn't project a flat image but if nothing else all the corners should look much the same...

Conclusion, the focuser is not aligned with the axis of the scope. Approach, shim the focuser to realign it.

Three hours later I've added two tin foil shims and shifted the axis of the focuser and totally redone the alignment twice. Last night was sky test time.

The result of this effort is shown in the attachment. Summary:
1) Not quite there yet but I've removed about a bit more than half the star stretch.
2) I suspect one more shim will resolve the problem to insignificant.
3) Shims were added opposite to the side with star stretch
4) Aligning a badly out-of-alignment RC is a pain in the a$$!!

I've also ordered a 1x Field Flattener for the scope which should eliminate any remaining corner and edge star stretch...

bwa
This is a summation of my 3rd attempt to get my 3r... (show quote)


That is looking a lot better. I just got word that my heavy duty focus for my refractor finally has shipped (Ordered it last April). I'll probably need fabricate some adapters to attach my offaxis guider and camera, particularly when using the focal reducer/corrector since it requires the camera to be 55mm back from the end (probably need to put the offaxis guider in front of the reducer/corrector).

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Oct 4, 2022 07:51:44   #
Marc G Loc: East Grinstead, West Sussex, England
 
bwana wrote:
This is a summation of my 3rd attempt to get my 3rd-hand 6" Ritchey-Chretien scope collimated.

After aligning both the primary and secondary mirrors in the scope I still had star stretch along one side and in two corners and, yes, I realize a RC doesn't project a flat image but if nothing else all the corners should look much the same...

Conclusion, the focuser is not aligned with the axis of the scope. Approach, shim the focuser to realign it.

Three hours later I've added two tin foil shims and shifted the axis of the focuser and totally redone the alignment twice. Last night was sky test time.

The result of this effort is shown in the attachment. Summary:
1) Not quite there yet but I've removed about a bit more than half the star stretch.
2) I suspect one more shim will resolve the problem to insignificant.
3) Shims were added opposite to the side with star stretch
4) Aligning a badly out-of-alignment RC is a pain in the a$$!!

I've also ordered a 1x Field Flattener for the scope which should eliminate any remaining corner and edge star stretch...

bwa
This is a summation of my 3rd attempt to get my 3r... (show quote)


Looking much much better mate, further shimming will definitely help as well the flattener.

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Oct 4, 2022 07:59:44   #
Marc G Loc: East Grinstead, West Sussex, England
 
Ballard wrote:
That is looking a lot better. I just got word that my heavy duty focus for my refractor finally has shipped (Ordered it last April). I'll probably need fabricate some adapters to attach my offaxis guider and camera, particularly when using the focal reducer/corrector since it requires the camera to be 55mm back from the end (probably need to put the offaxis guider in front of the reducer/corrector).
That is looking a lot better. I just got word that... (show quote)


Hi mate. where to insert the OAG is normally determined by the type of imagining camera. If you are using a dslr the OAG will have to go between the flattener & scope, this shouldn't cause to many problems apart from the focal point on the draw tube will have shifted. The shift will be determined by the OAG thickness.
Should you be using a dedicated astro cam, the OAG can easily be fitted between the sensor & flattener by using the OAG as a spacer required to make up the 55mm back spacing.

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