Colimation issues or not, this happens everytime.

[Catanonia]

One for the experts out there as this is doing my head in.

Everytime I do a colimation I get the exact same problem in the exact same place on the chip / image irrelevent of the orientation of the camera in the focusers.

I have done about 6 colimations now and the final one as close as I can with a Cats Eye system and still get the same results. Surely it can't be the colimation causing this.

I have check the focuser and as far as I can tell it is centered correctly. Everything is as tight as possible, no slop, nadda.

If it were the focuser not square, surely it would happen on more areas of the image and have other issues on the image, not just in this one place all the time.

Can anyone help as I am beginning to think there is something wrong with the scope optics.

Image attached of 5 x 30 seconds lum just stacked and stretched in PI after a Cats Eye colimation. I focused on a star about 2/3 of the way from the centre too.

http://dl.dropbox.com/u/10801850/Astro%20Pictures/Boren%20Scope/combined.jpg

edit : The image was guided OAG with no problems and I know the spiders are not perfectly straight as Vega vanes show. Also viewing wasn't great, misty skies but good enough to test with

[Catanonia]

I dropped the 5 images into CCD Inspector

I notice tilt here is high.. Is that the focuser tilt ?

Also I am surprised at the curvature tilt, that is high for what is supposed to be a flattened and reduced field with the ASA reducer.

Anyway the scope is back inside again and I am going to triple check the focuser alignment with the Cats Eye tools.

[Tim]

Those tails look like a feature of glass Steve.

Is the reducer sitting squarely in the scope? And is the CCD definitely square to the reducer?

On the Boren scopes you can use them without the reducer at F4. Be interesting to see the result.

Does the reducer rotate with the camera? or is it fixed into the tube?

[Catanonia]

Those tails look like a feature of glass Steve.

Is the reducer sitting squarely in the scope? And is the CCD definitely square to the reducer?

On the Boren scopes you can use them without the reducer at F4. Be interesting to see the result.

Does the reducer rotate with the camera? or is it fixed into the tube?

Just taken apart again and focuers is as square as I can measure it with the inside tube paper method and a cheshire sight tube.

The reducer screws onto the camera via a T2 thread so is static and rotates with the camera and so if it has optical problems, then this would always be in the same place.

6 colimations of varying degrees and the effect is always in the same place, not chance at all. The lastest colimation with Cats Eyes gave better results as you would expect, but the problem is still there.

About to put it all back together and -re cats eye, but not holding out much hope on this. It is suppose to be a flat field for 8300 chips sizes at 65mm from ccd and it doesn't appear to be the case in this scope setup.

As far as I can tell, the CCD is square with the focuser. But if it wasn't, I would expect problems across the whole image and not the same corner.

Also going to strip and clean the camera / ccd to ensure nothing on that, but doubt it.

[Tim]

Sounds like there is an issue between the CCD and the reducer then.

Have you a DSLR or something you can try it with?

[Jessun]

Hi Catanonia, looking at your dropboxed file it's fairly clear that you have elongated stars in the far right of the image - elongated 90° compared to the trouble corner and you reach a sweet spot along the optical axis.

I get similar problems but resulting in heart shaped stars in one corner and I am fairly convinced that it is all down to orthogonality. (I started a thread on this but nobody seemed to have any problems with it...)

I repositioned my 'train' which is only f5.4 reduced btw and it improved a great deal. Now I always kick off with an exposure that I stretch to the hilt to see how centered the light cone is on the image and that seems to help. My imaging train is not heavy, less than 2 ponds but it's all at the mercy of a five mm wide flimsy compression ring.

Good luck with it all!

[Catanonia]

Thanks Jesper, By repositioning your train I assume you mean repositioning the focuser ?

I have just double and triple checked the spider centre, the focus centre and it is bang on. I have just completed my best yet Cats Eye colimation and everything is locked down still bang on.

Too late now to get the scope out and cool down, clouds are out.

I am going to try a few things.

1. New exposure with existing CCD / OAG

2. New exposure without the OAG / Perhaps the diagonal prism is interacting ?

3. New exposure with a DSLR

Try and see if it removes any of these comet trails.

[Komet]

You've probably tried already but how about rotating the CCD only through 90 degrees and see, what if anything changes.

[Catanonia]

You've probably tried already but how about rotating the CCD only through 90 degrees and see, what if anything changes.

I can't actualy rotate the CCD as it is all held together by T2 threads.

[Tim]

if you use a milk bottle for a spacer ring you can! Or even just loosen the CD by 90 degrees and then secure it from spinning with electrical tape.

You'll get there in the end.

On the plus side, looks like you are getting the hang of the Catseye tools. Told you they were good

[Catanonia]

if you use a milk bottle for a spacer ring you can! Or even just loosen the CD by 90 degrees and then secure it from spinning with electrical tape.

You'll get there in the end.

On the plus side, looks like you are getting the hang of the Catseye tools. Told you they were good

Nice idea Tim with the space. Yes getting on with the CatsEye colimation set. Just posted a final review on it in the other thread.

[Tim]

When you see those reflections, you understand why it would be so hard to get the same collimation with any other method. But trying to explain that is hard without having the thing in front of you to demonstrate.

[Catanonia]

Also going to try and add in a 5mm T2 extender to see if that makes any difference.

Should notice a big difference in the curvature graphs on way or another.

[Moonshane]

I know nothing about this sort of thing but is the primary centred in the tube? if everything else checks out, you never know? being so critical perhaps everything needs to be right and whilst not something you'd check with a standard e.g. f5, maybe this is adjustable on yours?

[Komet]

I can't actualy rotate the CCD as it is all held together by T2 threads.

So you cannot actually frame anything to your choosing?

Really?

[Catanonia]

So you cannot actually frame anything to your choosing?

Really?

Yes I can, by rotating the whole setup in the focuser. The CCD / filterwheel / OA and Corrector are all locked together. The Corrector end just slots into the focuser.

[Komet]

Yes I can, by rotating the whole setup in the focuser. The CCD / filterwheel / OA and Corrector are all locked together. The Corrector end just slots into the focuser.

Thought it was a bit odd. Have you tried rotating that lot through 90 degrees? If so, then where were the artefacts then?

[kookoo_gr]

i would check the focusing of the camera with a bahtinov mask. take an exposure of about 5 secs with the mask on and see if the stars are focused. then image as you always do and after 15-20 mins check again the focus. form the main star i see the spikes are fat which might be bad focusing, could be slop of the focuser. at the following links you can see two of my last photos, at the first the focusing is perfect and it's about an hour's data, at the second link i forgot to check the focus, even though it was locked and it was off by 0.5mm, the stars are similar to yours.

http://www.astrovox.gr/forum/album_pic.php?pic_id=14025

http://www.astrovox.gr/forum/album_pic.php?pic_id=14022

when my focusing is going off i notice at each diffraction spike at the stars that there are two diffraction spikes (the star's spikes are getting fatter).

[Catanonia]

Thought it was a bit odd. Have you tried rotating that lot through 90 degrees? If so, then where were the artefacts then?

Same place on image no matter what orientation the setup is in the focuser.

[Catanonia]

i would check the focusing of the camera with a bahtinov mask. take an exposure of about 5 secs with the mask on and see if the stars are focused. then image as you always do and after 15-20 mins check again the focus. form the main star i see the spikes are fat which might be bad focusing, could be slop of the focuser. at the following links you can see two of my last photos, at the first the focusing is perfect and it's about an hour's data, at the second link i forgot to check the focus, even though it was locked and it was off by 0.5mm, the stars are similar to yours.

http://www.astrovox.gr/forum/album_pic.php?pic_id=14025

http://www.astrovox.gr/forum/album_pic.php?pic_id=14022

when my focusing is going off i notice at each diffraction spike at the stars that there are two diffraction spikes (the star's spikes are getting fatter).

Focusing is bang on with a Bahnitov mask and check regulary. The large star is because it is Vega on a 30 second exposure at F2.8

I focus on a star 2/3rds of the way off centre to ensure good focus too. Same happens no matter where I focus, always this section of the image has the problem.

[r3i]

It's a QHY9 you're using? If so it might be worth checking the orthogonality of the CCD within the camera itself.

I had a terrible tilt problem with my QHY8, one side was 0.5mm lower than the other - doesn't sound a lot but was very noticeable on my images. It was due to some plastic pins that QHY had used to push the chip against the cold finger using the front cover - presumably it was done to solve a problem but it created another as one side of the chip was being pushed down further than the other. After removing the pins the chip was level.

The easiest way to check is to use the depth gauge on a digital calliper and measure the depth of each corner of the CCD chip from front cover.

Edit: Found this blog posting (with pictures) from someone who had the same problem: http://b0rkb0rkb0rk.wordpress.com/2009/10/29/first-light-with-qhy8/

[Catanonia]

It's a QHY9 you're using? If so it might be worth checking the orthogonality of the CCD within the camera itself.

I had a terrible tilt problem with my QHY8, one side was 0.5mm lower than the other - doesn't sound a lot but was very noticeable on my images. It was due to some plastic pins that QHY had used to push the chip against the cold finger using the front cover - presumably it was done to solve a problem but it created another as one side of the chip was being pushed down further than the other. After removing the pins the chip was level.

The easiest way to check is to use the depth gauge on a digital calliper and measure the depth of each corner of the CCD chip from front cover.

Edit: Found this blog posting (with pictures) from someone who had the same problem: First light with QHY8 | b0rk b0rk b0rk

mmm thanks mate for the response and very interesting as this is the only thing I think it could possibly be. One end of the CCD qhip lower than the rest.

Thanks for the linky as well

I shall try to confirm this by imaging with a 1000D DSLR and seeing if there is a difference.

[themos]

I shall try to confirm this by imaging with a 1000D DSLR and seeing if there is a difference.

That's the best step. At such f ratios, the critical focus zone is very small and any deviations will show up.

[Catanonia]

It's a QHY9 you're using? If so it might be worth checking the orthogonality of the CCD within the camera itself.

I had a terrible tilt problem with my QHY8, one side was 0.5mm lower than the other - doesn't sound a lot but was very noticeable on my images. It was due to some plastic pins that QHY had used to push the chip against the cold finger using the front cover - presumably it was done to solve a problem but it created another as one side of the chip was being pushed down further than the other. After removing the pins the chip was level.

The easiest way to check is to use the depth gauge on a digital calliper and measure the depth of each corner of the CCD chip from front cover.

Edit: Found this blog posting (with pictures) from someone who had the same problem: First light with QHY8 | b0rk b0rk b0rk

Quite socking really and definately looks like a dud.

I have just cleaned my QHY9 mono and took the opportunity to check my depths using the same method.

It is all perfectly square at the same depth to the surface of the camera front. Used the vernier gauge method and bang on 16mm each corner.

[Catanonia]

OK everything checked and double checked.

Next tests are

1. Try it as it is now, freshly colimated with experience gained on the Cats Eye

2. Try it with an additional 5mm T2 spacer to give 70mm to ccd instead of 65 mm to see if it makes a difference. I cannot go the otherway with the OAG

3. Retest with the OAG removed with and without spacers to make the difference.

4. Retest with a DLSR set at 65mm with spacers.

Just need a few stars tonight, a bit of cloud / mist I can deal with, just about 1 hours of stars would be nice please.