First attempt at Centaurus A

[guggle]

Hi everyone,

This is my first attempt at Centaurus A. I found this one difficult to processes and had several attempts at it before I was happy - even then, after comparing it to others in this forum, I can see it could be better. Is this a typically hard object to photograph?

40 x 60 sec subs, darks, bias frames
ISO 800
Stacked in DSS, processed in StarTools and tweaked in Photoshop.

[LightningNZ]

Hi Michael,

Looks pretty good to me. What was the scope/lens you were using?

Have you cropped the image a fair bit?

Cheers,
Cam

[BeanerSA]

According to his sig

[guggle]

I didn't crop the image much, mainly just to get rid of the stacking artifacts.

[raymo]

I don't know what is going on with your image Michael. It is
incredibly noisy for ISO 800. Was the ambient temp high at
the time of acquisition? When enlarged, the stars can be seen
to be strangely coloured, aquamarine and bright pink. If the
individual frames are all good there shouldn't be any stacking
artefacts to remove. It is not a difficult object to photograph,
except that it is a bit small. I suggest that you forget Startools
and PS for now, and do all the basic processing in DSS, it has a
fairly comprehensive user guide in the help tab.
raymo

[cometcatcher]

The image is quite good. Though the background looks a bit mottled. That may be coming from strong noise reduction as the colour saturation overall is pretty high. Selective saturation increase might be better. That way the background would be quieter.

If I want colour in stars I select the bright stars with the colour range tool, expand by 4, feather by 2 and wind the saturation up. That way the background doesn't get colour noise.

[guggle]

@Ray: temperature was probably around 15-18deg. I think the coloured stars was due to over saturation.

@Kevin: thanks for your thoughts. What software do you use for processing

[raymo]

Being a Canon man I have no idea how noisy your Nikon is, but it does
seem noisy to me for 800 and 15-18 degrees. My image that
immediately precedes yours was taken at 1600 and similar ambient, and processed in DSS. No attempt was made to address noise, except to
stack more subs than you did with your image. It'll be interesting to see
how much noise your next image displays. Are you going to reprocess this one with less saturation?
raymo

[cometcatcher]

Just Photoshop.

[jenchris]

I find your pic a little fuzzy.
I'm surprised that 40 mins of f4 didn't produce more light on the target.

[doppler]

Do you check each sub berfore you stack? A couple of bad ones can mess an image up. I have had a few images go a bit fuzzy when my secondary was starting to dew up.

[guggle]

@ raymo: yeah, I will have another crack at it and take into account the feedback I'm getting.

@ Kevin: do you use any add ins to PS? e.g Noel Carboni's Astronomy Tools Actions? Does anyone?

@ Rick: no, I generally don't check each sub. What I sometimes do, but didn"t this time is tell DSS to only use the best 90% of photos. When I re-do this, I will reduce that to maybe 80%.

Thanks again everyone for your comments!

Best regards, Michael.

[guggle]

I've had another crack at this - I still used StarTools and for those interested, I've included my work flow:

1. Crop
2. AutoDev using ROI
3. Bin
4. Wipe with defaults
5. AutoDev, Redo Global stretch, with small ROI
6. Wipe using Vignetting defaults
7. Develop - Digital Deve = 70.38%
8. HDR using Optimize preset
9. Sharpen; Amount = 249%, Small detail Bias = 89%
10. Deconvolution; Manually created inverse star mask, defaults
11. Life, same mask as above, used Isolate presets
12. Colour, full mask, red bias = 1.72, green bias = 1.19, blue bias = 1.24, saturation amount 226%
13. Stop Tracking - Final noise reduction, all scales = 90%

I also tweeked a little in PS, mainly local contrast enhancement around the central structure.

Cheers, Michael.

[cometcatcher]

That's very noisy and no colour. Sorry I can't help with StarTools.

The only addons I actively use with Photoshop are RC- Astro's gradient Xterminator and StarShrink. Otherwise I do all processing in Photoshop.

[guggle]

hmm, I think I might file this one away and forget about it..

[cometcatcher]

Do you have anywhere you can make available the stacked raw file before adjustments for download? It would be interesting to have a go at it.

[guggle]

Raymo asked the same question so I have uploaded 7 lights and 7 darks (.NEF files) to my Dropbox account: https://www.dropbox.com/sh/xoqlgp8jgzrr6oq/AAAHpn0R6x9IYMFobvjgPVbFa?dl=0

Thanks for looking!

[cometcatcher]

Okay thanks for that. I was kinda hoping for a single file full stack, but 7 frames will do!

I think I have found your problem. According to your date stamp on the EXIF data, this was taken on April 29 at 20:24pm. You are competing with a Moon that's 80% illuminated just 56 degrees away! First rule of deep sky imaging. Don't do it with a big bright Moon in the sky! You have overstretched the image to try and compensate for this unsuccessfully.

I have processed your 7 frames and stretched it about as far as I would go with 7 frames. Your image looks normal, even quite good for this amount of time given the big bad Moon.

[guggle]

Hi Kevin,

I never even stopped to think about the moon that night - all I saw was very clear skies and I immediately started setting up my gear..

I didn't post the fully stacked file because I usually use FTS files in Startools (this one was 163 Mb) and forgot I had a TIFF (about 19 Mb). Never mind, I am very grateful to you for your efforts :thanx:!!

I would be interested to know what workflow you used on the files I sent you..

Thanks again!

Warm regards,
Michael.

[cometcatcher]

I didn't do much to it. Just a linear stretch and tweaked each channel to align the RGB levels, slight noise removal and run gradient exterminator to even the field.

[jenchris]

I took this one during dark of the moon with my dslr.
I perhaps should have removed the reducer, but I think it works ok.
The overall exposure was about 48 or 51 mins.
I think one frame was rejected by DSS.
No bias or flats just two darks.