First Light M81/M82 image advice needed

[RayD]

This is my first light image with my TS 80 triplet, and at the moment I'm not convinced I've nailed the FF spacing, nor looking at it the focus!! (although I have now found out how to use auto-focus so I am hoping that will resolve itself).

My main query is what to me look like elongated stars in the bottom left only.  CCD inspector shows a small amount of tilt (around 3% variable between images) and I wonder if that could be the culprit?  However, the high position of the target, coupled with the fact I hadn't at that point adjusted the backlash out on the AZ EQ6, meant I was getting a fair bit of oscillation in RA, although I was guiding and the graph was reasonably good. The puzzling thing for me is that is seems to my novice eyes to be in one corner only, which I can't get my mostly empty head around as I would have thought tilt or oscillation would be evident all over the image?

This is the first time I've used PI for stacking and calibration etc., and the image has had no "post processing" as such, just DBE and histogram stretch, so recommendations for the best route forward from here on the data collected very welcome, Although if I'm honest with myself I think the very soft focus means going and collecting again after using auto-focus.  I can see there is a fair bit of gradient still in the top left, which I think was from the lights being on in the house (this image was taken directly over the top of it), which is a lesson learnt.

Anyway, very dodgy focusing aside, comments and help welcomed as using PI was literally listening to tutorials (thanks Harry) on headphones via laptop whilst applying on Mac at the same time, so all very new for me, and I'd really like to understand why I'm getting eggy stars in one corner.

Image details:

L - 25 x 300s

R - 20 x 300s

G - 20 x 300s

B - 20 x 300s

All at -10.

Flats, Darks and Bias frames applied.

Atik 460EX, AZ EQ6, Baader LRGB filters, TS 3" FF

Very light crop to align subs after meridian flip.

[Nova2000]

Nice first try Ray. I think the focus has changed? 

[Tommohawk]

I honestly cant really advise because I'm not familiar with your kit or software; I agree with your critique - focus maybe a bit soft and slight eggy in corner, but for a first go with new kit and no post-processing thats a very good result to my eye at least.

[RayD]

12 minutes ago, Nova2000 said:

Nice first try Ray. I think the focus has changed? 

Thanks. Yes I think the focus is all over the place Rajesh.  I did use a Bahtinov mask, but I've tested the SGP auto-focus routine and am happy with how that works now so will apply that next time out.  Just seems odd to me that to my untrained eye the issues seem to be in one corner only (although I could be wrong).

[Shibby]

To my - also untrained - eye I can detect a drift from bottom-left to top-right over all of the image. The bottom left corner doesn't look so different to me, so I do think it'll be the tracking that's caused this. There's a few blue halos as perhaps expected when not refocusing the blue filter (?)

It's a really nice first light, though. Lovely star colour and nice, natural galaxy colour. There are clear hints of the outer halo on M81, too!

[RayD]

4 minutes ago, Shibby said:

To my - also untrained - eye I can detect a drift from bottom-left to top-right over all of the image. The bottom left corner doesn't look so different to me, so I do think it'll be the tracking that's caused this. There's a few blue halos as perhaps expected when not refocusing the blue filter (?)

It's a really nice first light, though. Lovely star colour and nice, natural galaxy colour. There are clear hints of the outer halo on M81, too!

Thanks Shibby.  

It would be a relief if it is corner to corner as I suspect the oscillation would explain that, and now having adjusted out the backlash I think that issue would be resolved.  Hopefully the auto-focus will resolve the focusing issues also as I will set that to re-focus on filter change, and every 1 degree temperature change.

[michael.h.f.wilkinson]

Very decent first shot indeed. Some of the faint satellite galaxies of M81 also came out

[vlaiv]

I've found in one imaging session that one side had problems with strange stars out of focus.

My gear was TS80, 2" field flattener.

I was shooting in very cold conditions with rapid temperature drop. Oddly focused star images were quite ok.

I thought at the time that two things might be causing this: FF distance. Other thing that I suspected was focuser. I noticed that if adjustment/locking screw on 2.5" R&P is a bit loose - there is a bit of a play when changing direction of focusing (in / out) when trying to reach perfect focus - star would hop a bit on screen by few pixels (this is rather small amount - since the camera I was using has 2.4um pixels). I noticed this because I was focusing in "video" mode using SharpCap - and FWHM tool.

Next time I had a chance to image I made sure that FF spacing is better and I also tightened the screw on focuser. I had no problems after that (at least I did not notice any, but to be honest I did not look for it - temperature was stable enough unlike the first time when after half an hour I started noticing defocus in subs and misshaped stars).

[RayD]

Thanks all, comments are really helpful and I have stuff to look at when I'm able to image with this OTA again.

I must say I'm quite liking PI, as whilst I've only dipped my toes and needed to follow the guides to this point, it does actually make sense, and I very much like some of the features.

[laudropb]

Very nice for a first go and lots of good advice to help you on your way.