M45 - Grey original, artifacts and over-processing?

[AndyUK]

Hi there - I thought I'd try my arm at M45 (now that it's risen above next door's garage before 11pm) - I used a Canon 40D, 180mm/f3.5 800ISO, 120s (40 subs, 20 darks, no bias, no flats or flat darks) attached straight to a plate on a CG5+synscan.

As I'm new to imaging (but am sadly badly hooked! ), I may be trying to do too much at once (or maybe not understanding the true importance of some of the technicalities), but I've come up with the attached (using DSS, CS5 (inc Astronomy tools & gradient xterminator).

Although I'm sort of half-pleased with it, I have a feeling that I may have tried to force this perhaps a little too much as, close up, it shows quite a few what I assume are processing artifacts (but that's something I can obviously go back on). However, I'm a little confused that although the raw images contained colour, after stacking, the output was grey - DSS noted that all the subs were gray 16 bit(?) and the only way I could get any nebulosity colour back was by using the magic wand tool (surely that's not right?), in addition to which all the star colour had completely disappeared and I also seem to have somehow picked up some concentric "noise" rings along the way - Has any one any ideas where these may have come from, or how I could get rid of them? (I haven't seen them before... )

I've attached my attempt and also the original DSS (grey) output file (adjustments applied - RGB alignment)

[Cloudwatcher]

I have no idea what caused the concentric rings but there is nothing wrong with using the magic wand to isolate and reduce them. Strange that the star colour vanishes though.

I prefer the original myself............ once the grey is eliminated.

[AndyUK]

Hi CW - Thanks very much (once again) for your input...

... But once again I have to ask "how did you do that?!" - You've somehow reworked this and managed to get the colour back into the stars...

[Cloudwatcher]

Hi Andy,

Couldn't do anything about the lost colour in the image with the 'rings' but it's all there in the 'grey image' and is easy to bring out.......... nice capture actually although I think I might be inclined to crop it a little.

Anyhow,image with history column attached......... and as usual, how you use your tools is up to you.

[AndyUK]

Cheers CW - I think that (perhaps) part of my problem is that I'm being lazy and depending too much on the "auto" tools such as Astronomy tools and gradient xterminator (although I must admit, that does seem pretty good as I haven't got to grips at all with removing gradients "manually"...!)

Thanks very much for the history - I'll try and follow these (and steer away from the macro's / plug-ins). I do agree with you about it needing a crop though - I was going to do that right at the end... if it was worth it!

[AndyUK]

Here's a re-work and crop...

Okay, I couldn't follow all the history as I obviously had no idea what was being selected to use the tool on(!), but this version involved a LOT less processing than the original, and being somewhat aggressive with the saturation tool got the nebula and star colour back very quickly without having to resort to the magic wand tool . To my eye, it looks a lot more natural now - Thanks CW .

I can't wait to get some more subs to add to this now to see how much more I might be able to squeeze out of it... Although probably not effecting this target, unfortunately my guidecam funds have been raided once more by "my manager" - She wants us to take a short break in late October .

[SlipperySquid]

Hiya mate I had the same sort of effects it's to do with the processing but can't for the life of remember what it was so this post does not help in anyway

I seem to remeber using a gradient removing tool that made that sort of circle effect?

Matt.

[AndyUK]

Hi Slipperysquid - I also suspected it might be too much aggressive use of the gradient remover, so I went back to the tutorial and followed it to the letter. It didn't show anything immediately afterwards, but when I then used one of the astro tools on top (Enhance DSO and dimmer stars) it then came in with avengeance...

I steered clear of ALL tools / filters for the rework and as also confirmed from CW's rework from the original stack, it doesn't appear to be in "manually" processed versions, so I'm now guessing this must be coming in with use of an auto tool or gradient filter as well, but it's still weird - I haven't seen this appear on any of my other attempts . Ho hum...

[MarkF]

I had a quick look at it and there was definitely a lighter area in the centre of the picture, moonlight maybe?

[AndyUK]

Yes, I noticed that - The center IS lighter than the edges, but this wasn't due to any moonlight, and although obviously there's light pollution about, I wouldn't have thought it would have that pattern... This seems to be evident in all long exposure photo's I take with the 40D, which I why I've been trialling gradient xterminator. Is this something I might be able to remove with flats perhaps?

I've only tried taking flats once, but the result with them (and flat darks) was worse than just using the subs and darks. I don't supposed anyone has an example of what a single flat frame might look like? The ones I took were simply grey frames and didn't appear to have any variation across the image at all...

[martin_h]

Here is a single flat frame from my setup - everyones will vary depending on setup.

[AndyUK]

Thanks very much Martin - I think that this may be at the root of my gradient issue, as I can see in your frame a shade of darkness in the corners, which is what I'm also getting in my longer subs...

I think I'll concentrate on finding out how to take correct exposure flats (and flat darks) for the next time - The ones I took before were just... well, totally flat!

[martin_h]

Stick the camera on auto (AV mode) and let it sort it out itself.

[AndyUK]

Cheers again Martin - I'll have another go next time. I'd read somewhere that it mentioned something about using the Histogram to set the right level, which confused me somewhat...

I assume I use the same aperture as that used for the subs, take a note of the shutter speed, flip to Manual again and set the same shutter speed for the flat darks?

I'm currently using 20 darks (10 before/10 after) and 20 bias frames so I'm guessing that 20 flats and 20 flat darks should completed the set? (Sorry to ask such basic questions...)

[melsky]

AndyUK

I've only just picked up this thread but I thought it would be a challenge to have a go at the original DSS (grey) file in PhotoShop to see if I could get rid of the concentric rings (see attached file)

Mel

(I love playing with PhotoShop)

[AndyUK]

(I love playing with PhotoShop)

2 or 3 weeks ago I'd have thought this was really sad (), but now I think I'm beginning to sort of understand... even if the more I try and play with photoshop, the bigger the application seems to get! I could probably tinker with an image in photoshop almost forever... but trying to remove those bl**dy rings has got me stumped.

However, it certainly looks as though you've managed to get rid of them, but that's one helluva history trail to try and follow (). I've been trying on and off all afternoon to see how I might be able to get shot of them, but to no avail (well, without resorting to the clumsy black eye-dropper that is!)...

But if you found them even in the straight DSS output file, I reckon these must either have crept in from the original frames (subs / darks) or maybe they're an artifact from the DSS process(?).

Hopefully taking flats and flat darks next time (and subtracting bias frames) will sort it out, but if they're STILL there... well, I guess they might either be coming from the camera sensor or the lens, although this is the first time I've seen them, and I've used this combination before...

(I'll see if I can get outside tonight and rattle off a few frames... oh look... clouds... how unexpected )

[SlipperySquid]

You could always make a false flat which is possible with about three tweaks.

Make a copy of the image as a new layer.

Go to filter ..then noise....then dust and scratches....set it so the image blurs so all you see is light and dark areas.

then use the clone stamp and select the clone to a dark area of the picture then clone over the top of anything you want to keep...that is the main stars etc and the neblosity.(Neater the better)

Then Gaussian blur the image so it all looks smooth.....set the parameter for that layer as "difference" and adjust the opacity to suit.

Should improve the image....good for getting rid of amp glow etc! Have a bash

[AndyUK]

Slipperysquid - That's amazing... Instructions that even I can understand - Thank you SO much !

I've had a very quick play on one of the versions I was playing with (trying to get Pleiades to stand out better from the crowd) and I can see how that will work (when I have more time). I guess it's no real subsitute for good flats/flat darks but assuming I can't work out where this is coming from, this technique will come in VERY handy, and not just for removing these rings... Thanks again!