Surely it shouldn't be this difficult ......

[rubecula]

Not the best of days yesterday.  My artificial star finally arrived and the forecast was set fair for the night. I put the star in a bedroom window and hit the first problem - I couldn't get a clear view of it above the observatory sill.  I didn't want to take the OTA off the mount so with a bit of creativity with a clothes prop and some bungy cords I got it half way up the roof slope.  Still not high enough.  I could see three quarters of the de-focused image but not the full circle, so no idea which way to adjust.  What was clear with the still view that the artificial star gives you is that there is an issue. On one side of focus I could get some distinct rings, whereas on the other no matter how hard I tried I couldn't see any rings, just a blurry circle.  I suppose that means I'll have to take the OTA off and try again.  I only mention this in case it has a bearing on the issues below.

So come the evening I did 2 + 4 align and as I had not touched the alt-az screws or released the clutches I did a PHD2 calibration and took a preview image of M66.  The stars were hugely distorted.  Here is a crop of some of the stars from a 300 sec image. The stars were all egg shaped in the same direction,

 

I decided that the PA was off (not sure how) so I started a drift align in PHD2. The first run in azimuth was quite a shock - considering that last time I did a PA the results weren't bad:

 

I then did several drifts, gradually improving things.  As it was looking better in Azimuth I let the drift go on for a while and was surprised by this result:

 

As the drift proceeded the red DEC line was above the horizontal so I assumed that I need to correct it in that dorection but after a while it started to drop until it waa below the horizontal. So now which wat to adjust??  How can it change direction after such a long time?

I checked that everything was firmly tightened down and that no cables were catching.  All looked OK.

I gave up on Azimuth at that point and went to Altitude.  That was quite good so I thought I'd risk a short exposure to see what things looked like.  The result:

As you can see the result is awful, particularly the coma shaped stars towards the top left.

Does anyone know whats going on?

Where should I start?

Is this all down to a collimation issue?

I'm sorry that this is such a long post, but I'm getting desparate now. I love this hobby and don't want to give up but these issues are making me quite despondant.

 

[Nigel G]

This is way beyond me, but coma shapes in one corner suggest field rotation. 

Sorry I can't be much help but the image looks good to me ☺

Nige.

[alacant]

Hi. No expert here either but I had the distorted stars on one side of the image when my camera was not square to the focuser. Your shot looks good in the centre, worse as you go left and 'different worse' to the right. Camera squareness? But hey, that's quite an achievement on guiding what is (what I think is) a 1.5 metre focal length telecope. I'm still trying for my first PHD2 success at half that!

[rubecula]

Thanks Nigel and Alicante for your comments.  Seems nobody has an answer so I'll just have to persevere, starting with trying to get this collimation issue sorted out.

[richyrich_one]

You have some issues. One is focus. Get that right first. Identifying and then correcting the rest will then be much easier. 

[Scott]

As Rich has said, the focus is out and should be first thing sorted. get a bahtinov mask, it'll make focusing a breeze.

The next thing to look at is the stars. This could be part field rotation due to pa being out be also the optic train may not be right. you may need a coma corrector or field flattener depending on your scope.

Finally, yes....it is supposed to be difficult. wheres the fun in doing something that's easy?

hang in there,it'll all come together eventually

[alacant]

Hi, I think that's good advice. Maybe you are trying to do too much at once? After focus try say, 30s, mount only without PHD...

[rubecula]

Thanks Rich, Scott & Alacant, I appreciate your help.