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Tim

urgent help required please!

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It's gearing up to be another clear night, but I have a problem.

I have egg shaped stars, and I dont know how to fix them :)

Here is an image from last night of NGC6992, the Western Veil Nebula.

The stars are pretty much the same shape across the image, although it does seem slightly more pronounced towards the centre.

I collimated the tube yesterday, and it is better than before, but still not right. Is it likely to be a collimation issue???

I had it 'right' with a chesire EP and also a laser collimator, but is there a way to collimate it with the camera in place? ? ?

Anybody got any ideas??? It is not a guiding or wind issue, every sub, even short ones are the same.

This is just a quick stack and levels process, I might spend a little time later in processing and 'fix' the stars, but i'd much rather get them right in the first place!

Cheers

TJ

post-14037-13387737177_thumb.jpg

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Here's a close up, RichieJarvis, don't you dare laugh :)

post-14037-13387737178_thumb.jpg

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Is there any slop in your draw tube, when inserting the camera, that might have affected the image ?

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Is there any slop in your draw tube, when inserting the camera, that might have affected the image ?

I'm going to check for that now, but I tried to ensure everything was in square and tight. There's no slop in the tube, I'm using a baader steeltrack.

If the camera WAS a bit twisted, would that do this to the stars? I have noticed that in the right hand corner the stars, while still elongated, are pointing in a different direction to the main, almost like a rotation/star trail effect, albeit small.

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I'm guessing if the camera isn't aligned properly, it might give an effect a bit like not being collimated properly.

An example would be a newtonian, if your camera isn't properly aligned, you're not pointing at the right place on the secondary, which in turn messes up what you see reflected from the primary.

Rich.

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I have added an extension tube which has firmed things up a little, meaning less travel on the focusser, perhaps there was a little play on the 2" tube that attached to my camera.

The only problem now.......CLOUDS :)

Thanks for the replies.

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I'm guessing if the camera isn't aligned properly, it might give an effect a bit like not being collimated properly.

Rich.

I can't see how. If the imaging plane is off, wouldn't you see a smooth variation across a row or column of pixels?

It's windy here tonight, maybe that's the problem.

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It looks like the guiding was fine for most of the exposure, but it does look like a small jump occurred for some reason, as they are not regularly trailed, it's more like there's a small bump in the 4 o'clock position.

This could be a bit of muck in the gears, or wind gusts.

How long are the subs?

Windy here tonight !

Cheers

Rob

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These were taken last night (i'd have to be somewhere in Russia I reckon to have this target this evening :) ), sub length 600secs.

But even subs of just a few seconds were the same, and every sub is identical.

The stars look a lot like Richies triangles

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Well, give your collimation a tweak, blind, and shoot another sub. You'd know for sure then, wouldn't you?

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It does look a little like pinched optics. The primary mirror clips should not actually 'grip' or 'clamp' the mirror in place, try leaving a small gap about the width of a business card. This will allow the mirror room to expand/contract. You might experience very slight mirror shift but not enough to worry about. Also, check the secondary, that can also be pinched. If it is the secondary then you might want to consider changing the fixing method to something more traditional, like silicone.

HTH

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I think Steve is on to something with his "pinched" idea.

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Tim, I am assuming it is the GSO f4? If it is the Mak-Newt then we had better have it back asap!

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Box it up please Tim and let us know when to collect.

There is no point persevering if it isn't 100%.

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Out of interest, Steve, how did James' ring neb from SGL4 come out? Stars look ok?

I think tonight the stars are better looking, the sky is fairly clear, its just the wind making things very hard!

PS. dont worry, i'm not about to start dismantling the mak newts secondary!! :)

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I think he had a variety of shapes but we put that down to the breeze catching what is quite a large tube. Things definitely improved at around 4am when their was less breeze but I don't think he was entirely pleased.

PS. dont worry, i'm not about to start dismantling the mak newts secondary!! :D

Good :)

My comments about the secondary were specific to the GSO, not the Mak-Newt.

We have yet to experience a faulty M190 but if you decide yours is the first then let us know straight away so we can arrange collection/replacement.

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I have just put my 400D on it, and the stars at first glance seem round and sweet all over. I need to get the pics into my PC to take a proper look.

I'll grab some M13 (lots of stars) and post the results.

Cheers

Tim

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