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Old 01-07-2013, 09:27 PM
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pvelez (Pete)
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Weird!!

Astute readers of this forum will have seen my multiple posts about collimation. Some of you have even proffered advice - many thanks to you all

I have been driving myself round the twist trying to get this right. So tonight I set myself the task of getting it as good as I could.

No luck - no real surprises there.

BUT...and this is the odd bit. Just for the hell of it, I rotated the camera and I found the aberration followed it. So if the stars were elongated north south (ie along the vertical axis) and I then rotated the camera 90 degrees, the elongation also became east west (ie along the horizontal axis).

So I concluded that my nosepiece or my camera itself has some sort of tilt in it.

Is that right? I expect that if the collimation were the main cause for the aberration, the dodgy stars would be consistently dodgy ie they would not be affected by rotation of the camera.

Any thought from the Brains Trust?

Pete
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Old 02-07-2013, 10:42 AM
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ZeroID (Brent)
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Eureka !.
Chip not mounted flat on the PCB ?
PCB tilted on it's mount points ?

Wouldn't take much I'd imagine. Could be just a wee piece of plastic flashing from moulding or something similar.
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Old 02-07-2013, 02:43 PM
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pvelez (Pete)
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Eureka !.
Not sure about that - I suspect its a combination of a whole host of issues that add up to a mess.

My main question is whether my diagnosis might be correct. I assume you agree that it might be.

Pete
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Old 02-07-2013, 04:10 PM
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tlgerdes (Trevor)
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If your aberration follows the camera rotation, then my diagnosis is that there is something wrong with the image train connection, not so much the collimation of your scope. Whether it is CCD chip tilt or camera to focuser connection is yet to be concluded.
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Old 02-07-2013, 04:34 PM
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g__day (Matthew)
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Maybe run an evaluation copy of CCDWare's CCD Inspector. Doing so revealed a tilt in one of my cameras - caused by one in six locking screws on an OAG being a bit loose!

Since then - no recurrence!
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Old 03-07-2013, 12:36 PM
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ZeroID (Brent)
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Originally Posted by pvelez View Post
Not sure about that - I suspect its a combination of a whole host of issues that add up to a mess.

My main question is whether my diagnosis might be correct. I assume you agree that it might be.

Pete
I think it points ot the issue being at the camera end. Other possibilities might be the nosepiece or case not being threaded perpendicular to the CCD plane. Crossthreaded maybe.

I had a pair of binocs where the front assembly of one objective was crossthreaded into the body. Usable but disconcerting due to parallax error until I pulled them apart and figured it out. Very fine thread made very small difference. But enough for sure.
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Old 03-07-2013, 12:43 PM
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Thanks guys - I have 2 different nosepieces to try - as well as a screw in variety to use with the rotator. Will test them all this evening

Pete
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Old 03-07-2013, 09:29 PM
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Nope - no luck

I tried a different camera - an ST10-XME this time. It has a different nosepiece yet suffered from the same aberration when rotated. So its not the camera or nosepiece

I'm at my wits end. All looks quite good in the Tak collimation scope but the stars are still distorted.

Perhaps its the spacing between primary and secondary - anyone know how to measure this on a RC8?

Pete
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Old 04-07-2013, 09:22 AM
cfranks (Charles)
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Pete,

The fact that the abberation is still there with a different camera suggests the problem is in the camera's connection to the scope OR the scope itself. If you can, make a note of the elongation and then rotate the OTA 90 degrees without disturbing the camera and see what, if anything, changes. I'm not familiar with your scope but my FLT132 has a similar problem which I'm almost certain is due to the focuser not being square to the optical path. The suggestion about CCD Inspector is good but you have to pick as even a star field as you can.

Charles
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Old 06-07-2013, 11:10 AM
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Joshua Bunn (Joshua)
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Hi Pete,

Here is a link to a site that you may like to look at to help get your scope aligned. HTH.
Also, if you have a good repeatable digital focuser, you can run 4 focus runs on each corner of the chip (on the same star by moving the scope) to see where best focus is. from the results, you can asses if one side of your chip is further back from best focus from the other side of your chip (assessing tilt).

CS
Josh
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