NGC891 - second light with the Meade 14"

[gorann]

I managed to get 4.5 hours on this galaxy Monday night, which is the length of our astrodarkness up here now. It was supposed to get cloudy after midnight but for once the clouds never rolled in, at least not before I gave up at 3 am and the sky was slowly getting brighter. So, a clear sky but not very steady so guiding around 0.6-0.8 "/pixel. I recently had a 0.4"/pixel night so my EQ8 can run smoothly if it gets the chance, and I really need good guiding for such a big scope to perform.

Still I am relatively pleased with the result - it is at least a good RGB start that I can add lum to with my ASI1600MM later on, to get more details in the galaxy.

I think I solved most of the tilt problem I had before by removing a small screw on the Lepus reducer that probably made it sit slightly angled in the 2" eyepiece holder. Not sure what the screw did but nothing bad happened when I removed it and it looked like it had been put there by the previous owner.

Details: Meade 14" LX200R with Lepus 0.62 reducer (so f/6.2, FL= 2200mm) on my EQ8. ASI071 imaging camera (gain 200, offset 30, -15°C) and guiding with Lodestar X2 on a ZWO OAG. 27 x 10 min.

Edited September 4, 2019 by gorann

[wimvb]

That turned out very nice, Göran. Did you use deconvolution? Some of the stars and details in the galaxy indicate that you did. 

[geordie85]

A beautiful galaxy image. I notice some of your stars are blue on one side and red in the other. Do you know what causes this as I'm having the same thing happen with my star 71 and qhy183c. 

[gorann]

24 minutes ago, wimvb said:

That turned out very nice, Göran. Did you use deconvolution? Some of the stars and details in the galaxy indicate that you did. 

Thanks Wim! So it shows..... Yes I did a bit of deconvolution in PI but tried to add it carefully not to include too many of the obvious artefacts.

Edited September 4, 2019 by gorann

[gorann]

8 minutes ago, geordie85 said:

A beautiful galaxy image. I notice some of your stars are blue on one side and red in the other. Do you know what causes this as I'm having the same thing happen with my star 71 and qhy183c. 

Thanks! Yes, I wonder if a SCT (in this case an ACF) that is slightly out of collimation would show there red and blue edges on stars and if that could be the reason. It is quite irritating particularly when I do the processing and have to zoom in. If anyone has an idea of how I could get rid of it I would be grateful. I should maybe put more effort into the collimation - now I only do a quick check before the session and may not be critical enough. I am new to SCT imaging since I have previously been an almost strictly apo-refractor imager.

[Star101]

Very nice image Göran.

I was trying to image this 2 nights ago but my focus drifted and the stars became too bloated. Only noticed when processing and compared to last years image. Deconvolution would break under the strain on my new image.

Today I reinstalled my autofuser lol.

[gorann]

29 minutes ago, Star101 said:

Very nice image Göran.

I was trying to image this 2 nights ago but my focus drifted and the stars became too bloated. Only noticed when processing and compared to last years image. Deconvolution would break under the strain on my new image.

Today I reinstalled my autofuser lol.

Thanks! Yes, it is just all these small things that could wrong. I thought I grabbed some rather desent subs the other night and only realized when I looked at the stack that they were useless most likely due to a thin sheet of dew on the camera window - of course I had forgotten to tick the anti dew box in the ASICAP program controlling my ASI071. Make me wonder why the box is there since there is no reason not to tick it.

[peter shah]

another beautiful image Goran...super colour to it

[gorann]

19 minutes ago, peter shah said:

another beautiful image Goran...super colour to it

Thanks Peter, much appreciated!

[gorann]

Reprocessed a bit to take in the comments here. Thanks! So I backed off on deconvolution and instead did a bit of HiPass filtering. Then I reduced the star colour abberation. All in PS.

[geordie85]

3 hours ago, gorann said:

Thanks! Yes, I wonder if a SCT (in this case an ACF) that is slightly out of collimation would show there red and blue edges on stars and if that could be the reason. It is quite irritating particularly when I do the processing and have to zoom in. If anyone has an idea of how I could get rid of it I would be grateful. I should maybe put more effort into the collimation - now I only do a quick check before the session and may not be critical enough. I am new to SCT imaging since I have previously been an almost strictly apo-refractor imager.

I hope that's not the reason. I've not long had my star71 re-collimated (sent back to FLO, then done by Es Reid). But I'm not too sure what else could be the cause, maybe tilt? Would tilt show this sort of aberration? 

[Davey-T]

Nicely done Goran, BTW it's always worth checking against a stock image for Super Novas when imaging galaxies, you never know 

Dave

[gorann]

1 minute ago, Davey-T said:

Nicely done Goran, BTW it's always worth checking against a stock image for Super Novas when imaging galaxies, you never know 

Dave

Thanks Dave! Very good idea - will do. Should probably make it a rule.

[wimvb]

20 minutes ago, gorann said:

So I backed off on deconvolution

Whenever I see artefacts like those in your image, I slightly increase the bright deringing setting in deconvolution. This usually helps.

3 hours ago, gorann said:

So it shows.....

Only because I know what to look for. It wasn't anything obvious. 

[gorann]

8 minutes ago, geordie85 said:

I hope that's not the reason. I've not long had my star71 re-collimated (sent back to FLO, then done by Es Reid). But I'm not too sure what else could be the cause, maybe tilt? Would tilt show this sort of aberration? 

I had a similar problem with one of my ES refractors but not with the Esprits - so it could be misscollimation but at the time I suspected the reducer or flattener that I used. Have you tried with and without reducer/flattener?

[gorann]

2 minutes ago, wimvb said:

Whenever I see artefacts like those in your image, I slightly increase the bright deringing setting in deconvolution. This usually helps.

Only because I know what to look for. It wasn't anything obvious. 

I will play a bit more with the settings - but there are always just soooo many of them in PI🙄

[wimvb]

4 minutes ago, Davey-T said:

Nicely done Goran, BTW it's always worth checking against a stock image for Super Novas when imaging galaxies, you never know 

Dave

The photometric colour calibration tool in PI reports stars that are not in their correct position. I wonder if this feature could be put to good use? Not just fir supernovas, but also for detecting minor planets/planetoids

[wimvb]

1 minute ago, gorann said:

I will play a bit more with the settings - but there are always just soooo many of them in PI🙄

[gorann]

2 minutes ago, wimvb said:

The photometric colour calibration tool in PI reports stars that are not in their correct position. I wonder if this feature could be put to good use? Not just fir supernovas, but also for detecting minor planets/planetoids

How many star does it have in the data bank? I expect it would be a small minority of the stars in an image and then it would miss any supernova.

[wimvb]

It uses online star catalogs; Vizier, etc. Then it reports stars that are "in the wrong position". It would be interesting to know what the cause of the error is. It may just be wrong entries in the catalogs. 

[gorann]

34 minutes ago, Davey-T said:

Nicely done Goran, BTW it's always worth checking against a stock image for Super Novas when imaging galaxies, you never know 

Dave

OK, I just compared it "manually" with a nice 2016 image I found on Astrobin, and no, no supernova this time😐

[kirkster501]

That is superb Gorann!!!  Well done man!

[geoflewis]

An excellent image Göran with lots of colour, well done.

Geof

[geordie85]

2 hours ago, gorann said:

I had a similar problem with one of my ES refractors but not with the Esprits - so it could be misscollimation but at the time I suspected the reducer or flattener that I used. Have you tried with and without reducer/flattener?

I cannot try without a Flattener because it is built Into the focuser

[gorann]

11 minutes ago, geordie85 said:

I cannot try without a Flattener because it is built Into the focuser

Oh, I see, one of those quadrouplet / Petzval things. Then you probably need to ask FLO why your stars are so colourful - seems like a collimation problem. If your stars are nicely shaped across your chip it could at least not be tilt and even tilt should not cause chromatic abberation in a good apochromat since they are supposed to keep the colours in order even when out of focus.