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Old 31-05-2020, 06:00 PM
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luka
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Checking tilt during daytime

Hi,

Is there a reliable way to check for tilt in the imaging train during daytime?

Thanks in advance,
Luka
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Old 01-06-2020, 02:04 PM
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Joshua Bunn (Joshua)
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Well, I guess you could see what happens if you shine a laser down your scope onto the chip. While at the same time rotsting the camerawith a rotator if you have one. If you shine down on axis, it should come straight back on itself I'm thinking. If tilt was present , it wound reflect back, but not on the same path.

I'm not sure if a laser would damage the CCDthough
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Old 01-06-2020, 06:25 PM
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I guess for daytime checking you would need some sort of target to aim at. Like a grid of some kind bolted to a fence that you can point the scope at.
The image taken of the grid would show tilt if the lines are not parallel.

Like this Sudoku grid but bigger.
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Last edited by billdan; 01-06-2020 at 11:42 PM. Reason: grammar
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Old 01-06-2020, 08:46 PM
Imme (Jon)
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Quote:
Originally Posted by billdan View Post
I guess for daytime checking you would need some sort of target to aim at. Like a grid of some kind bolted to a fence that you can point the scope at.
The image taken of the grid would show tilt, if the lines are not parallel.

Like this Sudoku grid but bigger.
Id say Bill has it here....great idea!

Maybe graph paper would do it???
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Old 02-06-2020, 09:13 AM
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Camelopardalis (Dunk)
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Maybe I’m being overly dense here, but how does one get the scope orthogonal to the grid?
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Old 02-06-2020, 10:31 AM
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billdan (Bill)
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Originally Posted by Camelopardalis View Post
Maybe I’m being overly dense here, but how does one get the scope orthogonal to the grid?
Those of us who have a Roll Off Roof, it will be difficult as you can't use the scope while its horizontal because the walls are too high.

If you did have line of site of a fence, you would use a spirit level to ensure the telescope is horizontal and measure from the ground the height of the optical axis.
Then place the grid onto the fence with its centre at the same height off the ground as the OTA optical axis.
Assuming level ground of course it gets more complicated with sloping ground.
I guess you could use a collimating laser to line up the OTA with the grid.

Instead of a grid you could use a Dart Board with concentric circles, those circles will become elliptical if there was tilt in the camera.
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Old 02-06-2020, 11:05 AM
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This is the procedure that Starlight Xpress uses. Similar to what Joshua mentioned in the 2nd post.

However this test is for the camera only, not the image train (filter wheel, OAG, focuser etc).

Our method involves reflecting laser light from the CCD surface and observing how the reflections rotate on a screen
when the camera is revolved. The CCD is properly aligned when the bright reflection from the CCD cover slip is
stationary on the screen, despite rotating the camera through 360 degrees.


https://www.sxccd.com/maintenance_info/Aligning_CCD.pdf

Last edited by billdan; 02-06-2020 at 11:33 AM.
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Old 02-06-2020, 11:40 AM
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Quote:
Originally Posted by Joshua Bunn View Post
Well, I guess you could see what happens if you shine a laser down your scope onto the chip. While at the same time rotsting the camerawith a rotator if you have one. If you shine down on axis, it should come straight back on itself I'm thinking. If tilt was present , it wound reflect back, but not on the same path.

I'm not sure if a laser would damage the CCDthough
Lasers can damage mirrorless camera sensor so perhaps they might. I have read about laser damage on a camera sensor on DP Review Of course there are different strengths of lasers but I would not shine a laser onto your sensor just in case.

Too much of a risk.

Also if it is only testing the sensor then that is unlikely to handle the problem. I don't know how often sensors are tilted but none of the cameras I have had showed that. It was in the whole system, adapters etc.

I don't see it as a problem needing to be solved. It does not take long once you are used to it to adjust for tilt at night.

Greg.
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