I still have issues with my imaging train and/or my guiding - any thoughts

By awful do you mean square?

Hi Andy,
Looks like the stars are slightly stretched away from center toward the left and right - a possible misalignment or collimation issue? Any concerns with backlash, pinpoint guide stars, etc.? Did you check each of the subs individually for "one bad character"? Just a few suggestions.

– Steve

You have the usual triangular shape (that pimary cell stuck still there, isn't it?) plus miscollimation so that the "good" portion is the far upper right corner. Now you need to move the "good" portion toward the centre of the image in terms of collimation, something you can do with the imaging train in place.

Just checked my imaging train in daylight hours.  Two things I found:

* My coma corrector was slightly loose in the focusser; that would have introduced some tilt for a start.  (I have been trying not to overtighten the screws on the focusser, but I guess I was too gentle with them)
* My primary collimation had gone off in between me collimating inside and setting up the rig outside

From now on I guess I will check the collimation every time after having set up the rig as well as  making sure there is absolutely nothing loose.

On the plus side:  the secondary was still dead centre on the primary centre spot

I did the same re the comprssion fitting but it did not help collimation. I have a long coma corrector and it was a very sloppy fit at the scope end as there are 2 different diameters inside the focusser leading to slop at the far end. Mating up the coma corrector against the end of the focusser did not correct for tilt. I checked this out using feeler gauges between the corrector and the focusser wall when the focusser was off.  When I took the focusser off I could see, by laying a ruler right across the scope and adjusting the focusser position to be flat with the end that it was not aligned properly so I adjusted the 3 adjustment screws. I also packed the inside of the focusser with gorilla tape untill the coma corrector was a friction fit inside. I tapped a 3rd 120 degree screw thread (it only had 2) into the compression fitting I bought, to even up any remaining slack at the camera end. In practice there doesn't seem to be any.
I bought shims to correct for any errors in backfocus and have tried the out of focus star test for collimation though I have found my Cheshire eyepiece and Hotech laser collimator agree well and they collimate well. I may need to further refine backfocus. I also checked the laser collimator was itself collimated.
If you still want to remove the mirror I have done that by drifting it out gently at the mirror support edges, otherwise it was not possible. I uses a metal drift and hammer gently. It came out easily tapping around the diameter a little at a time. Getting it back requires easing over the metal tube join on the inside with a thin flat blade screwdriver. It is a sticking point.
After struggling for ages I now have very little tilt or none according the the ASTAP software. 
I have installed a mirror edge mask to remove sparkly light streaks radiating off the centre of bright stars. If you look at recent images of mine compared with older ones the improvement is obvious. I hope this helps.
My stars are not perfect but better than they were so that's progress.

Dan Watt:
This looks a lot like pinched optics to me. How tight are your mirror clips?

Long story which a lot of people on here are fed up of hearing about ..... try as I might I have been unable to remove my primary despite loads of suggestions from people on here .... totally stuck .... and yes, I have tried very hard more than 10 times now to remove it.

How about sending it in to the manufacturer - or maybe your vendor knows a good repair facility? Seems to me like you won't resolve your issues without addressing this topic.

Good luck and clear skies
Wolfgang

Thanks Wolgang and I do tend to agree with you.  Unfortunately the OTA only cost about £350 new in the first place, so the cost of having it fixed would probably outweigh that.  I should probably replace it with a higher quality OTA, however my wife gave it to me as a birthday present, so that is problematic.

I am going to persevere with fixing any tilt, collimation and backfocus issues as I am learning a lot by doing that.  If the mirror is actually pinched, then that will be the last thing I fix even if I have to take a hammer and chisel to it ;)

Andy Wray:

How about sending it in to the manufacturer - or maybe your vendor knows a good repair facility? Seems to me like you won't resolve your issues without addressing this topic.

Good luck and clear skies
Wolfgang

Thanks Wolgang and I do tend to agree with you.  Unfortunately the OTA only cost about £350 new in the first place, so the cost of having it fixed would probably outweigh that.  I should probably replace it with a higher quality OTA, however my wife gave it to me as a birthday present, so that is problematic.

I am going to persevere with fixing any tilt, collimation and backfocus issues as I am learning a lot by doing that.  If the mirror is actually pinched, then that will be the last thing I fix even if I have to take a hammer and chisel to it ;)

The price of the OTA and the value of the OTA are two different things. The fact that it's a present of your wife increases its value to an extent that sending it in for repair is worth the money in my humble opinion. Just my two cents.

Clear skies
Wolfgang

Andy Wray:

Dan Watt:
This looks a lot like pinched optics to me. How tight are your mirror clips?

Long story which a lot of people on here are fed up of hearing about ..... try as I might I have been unable to remove my primary despite loads of suggestions from people on here .... totally stuck .... and yes, I have tried very hard more than 10 times now to remove it.

Ah. Well if you want to fix it than it's time for try #11. A mallet and a drift (or at least flathead screwdriver wrapped in tape) can do wonders. A scratched up tube is better than sub-par stars.

OK, I've done the following:

* re-collimated the OTA including trying out an autocollimator for the first time briefly … boy is that sensitive!  I was a bit late in the day and the light wasn't that good, so not sure I made the most of it.
* re-calibrated PHD2 from start to end.
* tightened up stuff to try and make sure tilt was minimised.

So, I'm imaging at the moment and guiding RMS is varying between 0.47 and 0.52 arc secs.  That said:  RA is about 40% worse than DEC so I am expecting oval stars.

I will post my image below once I have about 20 Ha frames to see if there is any improvement.

I see this kind of statement time and time again. However, I don't believe you get tracking induced oval stars as long as you stay below your imaging scale with the RMS. Or is this a misconception of mine?

I guess if the tracking RMS was way below your image scale, then it would be difficult to see, but when the RMS values are close to your imaging scale like mine are then it will be noticeable.  Let's see what my stars look like.

Not sure it is going to get much better than this until you get the three-foil aberration tamed.