Tear drops..

[Cosmic]

....and there almost coming from my eyes :P Below are some images of my dilemma, I have tried to figure this one out with no such luck yet.

Its not the following, im sure of it

-collimation is good, that's spot on
-added extra screws to the focuser body to try adjust tubes....no change
-coma because of the shape of the star.
-tracking/backlash

Here is two images of M8 as you can see the stars in both 1sec and 40 sec x 5 are consistent so its there from the word go. Its only really just above the center :shrug:

Big question will a coma corrector fix this kind of shape star?

Cheers,
Dan

[DavidU]

Dan, first off you should be very pleased with that image.Well done.
The focus is almost perfect. It looks like the camera is not square to the focal plane, although the camera is held tight it is flexing the focuser due to weight or the focuser needs to be squared up. Most Newt focusers are adjustable. The final problem is fixable by a comma corrector.
A little extra info about the type of equipment used would be great.
The subs are short so it is a little difficult to see tracking error.
Keep up the good work.

[Cosmic]

Thanks Dave for the kind comment, it really was a great night for imaging :) good skys here in the NT.

Equipment run down for you:

NEQ6 PRO
200mm 8 inch F/5 newton reflector
No guiding scope ..yet
No coma corrector ...yet either.

To give you a run down of the focuser setup. It goes canon <550d> <t-ring> <t-adapter 1.25"> <1.25" to 2" adapter> <2" Bintel Crayford Focuser 10:1 (2")....focus point 2.5 on side scale. The focuser/camera face downwards when facing polaris. Now how would I go about adjusting the focuser so that we could eliminate those tear drop stars.

Many thanks. :thumbsup:

[DavidU]

Have a read through this.
http://www.propermotion.com/jwreed/ATM/Collimate/Chesire.htm

[Cosmic]

Thanking you Dave, much appreciated. Ill report back with results next imaging night :thumbsup: I think this problem will be fixed.

[Visionoz]

Looking at you first image, it seems that the distortion irradiates from the center towards ALL the four corners; therefore it is most likely that you'll need a coma corrector to be able to "fix" this issue

Others more informed that I would probably jump in and let you know if my opinion is incorrect though

Good attempt and looks great - best to get auto-guiding going as it be giving you more imaging time per shot

HTH
Cheers
Bill

[Cosmic]

Thanks Bill, your right a auto-guide and coma corrector will be the shot! Now breaking to the wife, that's the hard part haha.


Dave I did a full realign and collimated the TS glass but unfortunately I had no luck...bugger. Hasn't phased me tho, im going to have my fingers crossed with the coma corrector. Because that's all it can be now, collimation is near on perfect and still the problem remains. Not to worry here's maybe a slight improvement with the shape of the stars and a big one with the processing.

Regards,

Dan

[mostschaedel]

Hi Dan!
You did an excellent picture of M8.
To get even more out of this image you haw to use "flatfieldimages".
Either real flatfields or artificial flatfield images.
I tried to make an artificial flat with your image and after flatfield division the whole image became more flat.
Have a look at M8_gw (http://www.werbeagentur.org/oldwexi/fotos/M8_gw.jpg)
(The flat field process should be better done on the raws!)

The coma corrector would improve the stars in the corners but thats
not so bad at all.

As the bright stars show an additional tiny spike upwards maybe
something is in the imagetrain? (Screw etc...)

Gerald

[Cosmic]

Hey thanks Gerald!

Trying to do the best with what equipment I have a the present. Looks good what you have done flatting M8, brought out and emphasized some sutel points in the image.

Without pushing the friendship whats the best way to go about doing a artificial flat to the image. Unfortunately my images are processed as Tiff a couple reasons, but that's anther story.

The search goes on for those little spikes in the stars, ill investigate the imagetrain for any little obstructions that could be possible.

Dan

[mostschaedel]

Hi Dan!
The artificial flat was made with the software
PixInsight (http://pixinsight.com/)
PixInsight has a process called DBE - DynamicBackgroundExtraction.
Thats a very simple to use but mighty process which creates an
artificial flat and divides it with your image. All
image formats are supported!
It was a 30 second job to make the image "flat".
If you are interested, PI can be downloaded and used 1 month
for free with ALL functions supported.

Good luck for finding the obstructions in the image train.

Gerald (PI-Fan)

[Cosmic]

Thanks a tonne Gerald!

I went to the trouble of requesting a license trail key and I tell you what....its a great piece of software I know why you use it. Although im a bit lost on how to navigate my way, the French video tutorials I came across are of what some help. :thumbsup: I may just end up have to buy this. I managed to do a DynamicBackgroundExtraction on the TIFF, came up a treat. If I get a bit stuck on my travels using it ill pm you.

Cheers Dan.

[Harryianpage]

Hi Dan

Don't you like mine :rofl:http://www.harrysastroshed.com

Harry

[Cosmic]

Hi Harry,

I must of missed when I went searching the entire web :P

Cheers for that, great tutorials!

[Cosmic]

Update, I dropped Bintel an email of a galaxy with the star shape as seen in M8 in this post, they call it a blip. They have informed me that its got to do with my RA, just want to know what the crowd thinks about this. I'm a little worried about binding my gears :question: do you think this is nessasary or can I adjust it with the backlash on the SynScan control.
Bintel quote from there email.

The 'blip' on the side of stars is aligned precisely with the movement
of the galaxy along the line of RA.
The most likely cause is a tiny amount of backlash or some form of
movement along the RA.

I'm grateful they where able to shine some new light on this problem thats haunted my imaging for months, next question should I perform this http://www.astro-baby.com/EQ6%20rebuild%20guide/EQ6%20worm%20alignment.htm

Kind regards,

Dan

[Visionoz]

Hi Dan

OK, you've actually got two "issues"; first one I already commented on earlier post - re: coma correction needed to handle the elongated stars irrradiating towards the corners and now that I've scrutinised the central lot of stars around the "lagoon", yes there are "blippy" stars which you were actually posting about and I missed that point because when I looked at your image first time I was impressed at the results of your attempt to image being a newbie and all

When I first started I also had a similar "issue" with those blip-like stars but mine was all over the image and unlike yours which only were in the central region - I finally resolved my issue by doing the EQ hypertuning so to speak and that fixed my problem for good - it was so good to be able to image for up to 4mins unguided and it was worth the effort to do the tuning anyway because I had a pre-loved one; see attached pix of my first image below - so it's really down to your decision really - YMMV!

HTH
Cheers
Bill

[higginsdj]

Coma or spherical aberation? I would say the latter due to large Camera chip size and fast optics.

The teardops are all over the field but are most obvious on the brighter stars. This looks to me like you have some movement in the mirror (or secondary) or in the DEC axis. Typically this happens when you 'goto' a target and then start imaging it. On occasion the backlash in the dec 'flops' out and your image moves.

One other posibility is if you are guiding in Dec and have some PE issues there.

Cheers