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Would you take longer exposures?

swag72

By swag72
in Imaging - Discussion

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Photosbykev

Photosbykev

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The right hand side vignetting appears darker and larger than the left hand side, so the centre of the optical path appears to be slightly off centre relative to the camera sensor.

Why it is I will leave to the real experts but probably some mechanical misalignment?

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swag72

swag72

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As I said Kev, I do have some issue with elongated stars, in this instance on the left hand side of the image as you look at it. That would tie in with the flat issue that you see.

I have made a couple of assumptions on another thread of mine and come to the conclusion that my focuser is causing sag - I hope that's the reason and it's nothing more difficult. Hubby absolutely refused to even think about looking at the lens alignment!!

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Photosbykev

Photosbykev

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it wouldn't take much mechanical movement or sag, probably a millimetre or less, to move the camera sensor off axis so that could be the problem.

cross posted with Peter: turning 180 would show it as well, even lightly pressing your finger to the side or base of the camera and shooting a flat would show up any movement.

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swag72

swag72

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If you think its sag and the scopes in rings... rotate the whole lot (camera as well as the scope) through 180 degrees and take another shot... and check to see what happens to the elongation...

I keep meaning to do this, I really do, but I am too worried that it will be something more difficult with the optics - Then that will be me well and truely stuck!!

If I just pressed on the side of the camera, I would want to press it towards the misalignment on the left hand side in this case?

To rotate the lot through 180 degrees as Billy says, just move it through the RA or DEC? He doesn't mean move the scope and camera within the scope rings does he?

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Photosbykev

Photosbykev

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I keep meaning to do this, I really do, but I am too worried that it will be something more difficult with the optics - Then that will be me well and truely stuck!!

it is much better to know you have a problem rather than think you have a problem which might not exist.

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Photosbykev

Photosbykev

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I keep meaning to do this, I really do, but I am too worried that it will be something more difficult with the optics - Then that will be me well and truely stuck!!

If I just pressed on the side of the camera, I would want to press it towards the misalignment on the left hand side in this case?

Try this, take 4 flats with light pressure applied to the top/bottom/left/right of the camera and then stretch and compare them.

I think Peter did mean rotate the setup inside the rings but using Ra and Dec does the same thing

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swag72

swag72

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And I would be hoping to see the vignette move around as I applied pressure in different places - Not technical speak, but I think you know what I mean!!!

If that works, it's the focuser?

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Photosbykev

Photosbykev

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And I would be hoping to see the vignette move around as I applied pressure in different places - Not technical speak, but I think you know what I mean!!!

If that works, it's the focuser?

the vignetting should move around and will point to some mechanical movement somewhere. I'm surprised you can't feel the movement, if it's there.

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swag72

swag72

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I'll try that tonight Kev - Thanks for the tip. If it's something more, such as optical then the vignette will not move I guess?

And, if it does move and it is therefore mechanical, then there's nothing else it can be other than the focuser, right?

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Photosbykev

Photosbykev

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I'll try that tonight Kev - Thanks for the tip. If it's something more, such as optical then the vignette will not move I guess?

And, if it does move and it is therefore mechanical, then there's nothing else it can be other than the focuser, right?

Focuser or camera mounting arrangement would be the mechanical areas to look at. Make sure the draw tube is locked off before shooting the flats

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