elongated stars - help

[itlee]

been slowly building up my collection of AP "tools" and last weekend I finally had the chance to put it all together and make my first attempts at this.

I chose M3 as I seem to be liking globular clusters at the moment and it was positioned well enough, so after a few test shots to ensure I was in the right place, fiddle with APT and alignment etc. I set up a plan in APT of 30x60s lights (I did do the bias, darks & flats after to, but that is irrelevant as u will see)

as the images were taken APT displays them, with this I could see that every 3rd image was of reasonable quality (well actually they are not on further reflection) but the other 2 inbetween were displaying elongated stars!

Any ideas why? is it the tracking or something else? I am not guiding, just letting synscan do its thing.

I have taken more images the other night and most have elongated features.

equipment used:

Canon 1100D

2xBarlow

Nilta (Skywatcher/Orion) 150P

EQ5 with synscan upgrade

APT

thanks in advance for advice

itlee.

edit: oops I put this in the wrong sub-forum, how do i move it?

[FraserClarke]

It's probably the periodic error of the telescope drive. That's pretty standard for most mounts. Guiding should sort this out.

If you take a series of shorter images (i.e. 5-10 seconds each), you should see the stars moving one way then the other. The period is typically a few minutes, depending on the mount. When the motion changes direction, you get a better long (60s) image. So one good image every few minutes is kind of what you expect.

[itlee]

Would PEC training be worth doing?

The synscan has this feature, and until I can get a guiding system sorted it may be my only choice for now.

Which leads to another question, would have to do the PEC training every time I set up or does synscan remember it?

Thanks,

itlee.

[FraserClarke]

Would PEC training be worth doing?

The synscan has this feature, and until I can get a guiding system sorted it may be my only choice for now.

Probably, but I don't have any knowledge of the synscan system, so someone else will have to answer the details I'm afraid..

[Tinker1947]

Getting back to Basics, is the Mount polar aligned, and balanced.......

[itlee]

Getting back to Basics, is the Mount polar aligned, and balanced.......

Yes and yes, to the best of my ability. I did use APT's DARV tool at some point (possibly after these photos) but still experience the elongated stars

I am going to try again with the various aspects of setting up the mount properly

Something else occurred to me, the target did move further across the images as time went on.

itlee.

[mallorcasaint]

Then your tracking is out. You should probably polar align accurately and then you can do the PEC.

[Digz]

The worm gears and drives in your mount will show errors (periodic errors) due to inaccuracies in their machining. Basically on the gears, there will be little lumps and bumps which will manifest themselves in certain subs as they rotate, that is to say they will be visible in some but not others. For example on my NEQ6 IIRC I could do two 3min subs (unguided) fine and every third 3min sub would show error as it hit the 'lumpy' part of the worm gears.

If you take enough subs then you can just ditch the ones showing the error and not worry about them. Alternatively you can try PEC (wouldnt know how to do this so google may be your friend here ) or guiding (which will add expense and complexity which you may not be up for at the moment.)

As with all facets of AP making sure you have a well balances system with good polar alignment can help minimise these effect.

[NickK]

You can undo elongated stars using a tool like PI's external PSF function.

By using a star as the PSF then PI will map back from the blurred star to a proper PSF (which is a round star) and it will then perform the same mapping on the entire image.

I've attempted to give you an idea of the outcome however the JPEG artefacts and noise cause the waviness:

[gcraib]

what on earth is PEC, PI and PSF?

[swag72]

PI is Pixinsight - A processing programme.

PSF - Point Spread function

PEC - Periodic error correction

I don't know what they all mean though!!!!

[Digz]

what on earth is PEC, PI and PSF?

Have a flick through this thread, a lot of common acronyms used are listed here....