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Collimation of 130pds


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Hello. I recently acquired an Ocal electronic collimator for my new 130 PDS and the image I see when I connect it is the one I attach. I can't adjust the green circle in the circle created by the end of the focuser. Not even helping me with the offset of the program, whose maximum is 20. I don't know if anyone has tried this collimator with its 130PDS. But it doesn't seem normal. Any ideas? Thank you.

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49 minutes ago, Catakraken said:

Hello. I recently acquired an Ocal electronic collimator for my new 130 PDS and the image I see when I connect it is the one I attach. I can't adjust the green circle in the circle created by the end of the focuser. Not even helping me with the offset of the program, whose maximum is 20. I don't know if anyone has tried this collimator with its 130PDS. But it doesn't seem normal. Any ideas? Thank you.

I would guess that the 2 screwed attachment on the end of the focuser is pushing the collimating camera out of line. Your first port of call will be to try and get that as straight as possible so the green aligns with the end of the focuser tube. When you find the position that camera needs to sit so it's straight, collimate. Then you have the issue of trying to get you imaging camera in exactly the same place. 

Sadly, the two screwed attachments on the SW's are notoriously annoying for pushing things off centre, introducing tilt. Some people tap a third screw and that can help a bit. Others change the attachment altogether to a compression ring, etc. 

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12 hours ago, Catakraken said:

I can't adjust the green circle

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Hi

I agree with @Jamgood. The two thumbscrews push the camera -or whatever is attached- off centre. The best way we've found to cure this is the third screw at 120º. Unfortunately the compression ring version still only has two screws and suffers the same mislignment, minus a bit for the thickness of the ring itself. So both require a third hole tapping.

Oh, also have you tried eyeballing using a collimation cap then using a simple Cheshire sight tube with cross hairs? You may find it easier.

Cheers and HTH

 

Edited by alacant
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That was the first thing I thought too, but the focuser screws are loose. When I squeeze them, it doesn't change the position appreciably. In the photos that I have put, the collimator is screwed to the baader coma corrector, and it is inserted into the focuser, without tightening the focuser screws. Therefore that possibility that you propose to me is discarded.

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15 hours ago, Catakraken said:

the image I see when I connect it is the one I attach. I can't adjust the green circle in the circle created by the end of the focuser.

As already said a possibility is camera tilt because of the attachment screws ; Another possibility is the focuser is tilted by itself ;
For the first case, try wrapping the camera barrel with a band of paper (maybe several turns) or duck tape so that you barely need the screws to sit it in the focuser, that should help get it straight and centered.

You could also accept the tilt as native and constant, and work around it with collimation. From your image I think you secondary might be rotated a bit around the primary optical axis, so as a first step you could try to rotate it (loosening appropriate secondary screws) so that the primary image goes upwards and gets into the red circle.

Edited by rotatux
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@Catakraken The first thing I would do is remove the Baader MPCC. There's no advantage collimating with that attached to the camera. 

Secondly, you would want to have the camera fixed firmly into the focuser for collimating. If you don't tighten the screws, even the slightest movement of the OTA will affect the view and having the OTA on a mattress/bed for the procedure won't help you at all.

When collimating, I have my scope on the mount. That way I can manoeuvre the OTA any which way I want and check collimation is good for all angles the scope may point. I don't use a camera to collimate but the same principles apply to whatever you use. You want you collimation tools locked in so that you have a constant and repeatable view. If you can lock in your tools the same every time, then you can lock in your imaging camera the same when ready to start shooting. As @rotatux said above, tilt is something that you will always have to work with as it's the nature of the beast. Sadly, no 2" fittings ever fit perfectly.

Edited by Jamgood
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1 hour ago, Catakraken said:

without tightening the focuser screws

Mmm. So it is displaced and tilted in the focuser barrel by the cable and it's own mass. Don't forget that with a Newtonian oriented horizontally, there is the tendency for the primary mirror to tilt forward toward the secondary; it is not held rigidly.

Perhaps best to fix the camera firmly and collimate at a series of angles at which the telescope could actually assume when in use imaging.

Cheers.

 

Edited by alacant
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Sorry, I don't think I explained it properly. The photos that I attach are those that I have put when I have given up on not finding the reason why the circle does not coincide with the end of the focuser. I have previously tested the collimation with the tube on the mount, in vertical and horizontal position, with the camera attached to the focuser with an adapter first and then with the coma corrector, and with the focuser fixing screws tightened. I have also tried rotating the camera 360 degrees and the position of the circle remains, it does not change at all. But the result is always the same, the mismatch seen in the photos.

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Hi

If you really do want to make the green circle coincide and it really isn't the thumb screws or tilt in the camera or the camera's sensor, try reseating the knurled collar, machining the top of the m54 thread square to the barrel...

Or (much easier!) collimate using a Cheshire sight tube. Don't forget to read both telia and seronik who tell it just as it is.

Cheers and HTH.

 

 

 

Edited by alacant
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