The Admiral

Well, bitten by the newly found workflow, I thought I'd have a bit of fun with my Pacman snap. What I really like is the ability to control how obvious the background star field appears in the image, because up 'til now they've been blasting the ol' rods and cones something chronic. And of course, being able to treat the target nebulosity without a thought about the stars getting too wayward. Hats off again to Steve fro spotting that one . The stars in this one seem larger than in my original one though, and some of the nebulosity is not coming through as well. I'm still trying to work out how you can work on the stars as well. It seems that the stars don't respond once they've been extracted - may be that has something to do with tracking being turned off. This is where ST loses me! Ian

Oh Nige, sorry to hear that. Hope it's something simple like a wire having got detached, or at least, something that is visible to the eye and readily put right. I think you'd be wise to put it away and start again tomorrow, when you're fresh. Ian

That's a super image of M45 Ken, I love the nebulosity, which looks even better on my main PC. I think you are being too hard on yourself. I feel sure that there's a lot of detail in that image itching to be released. Are you able to do the equivalent of what we are doing in ST, with PI? Ian

Thank you all for your kind comments, and it was a rush job an' all. Mind you, I probably couldn't reproduce it! After a while I find it quite hard to be objective about one's images. I too was impressed at the extra detail visible in the nebula. That sequence of operations certainly gives a lot of power to one's elbow. Ian

I couldn't resist using the processing strategy in Steve's link, on my Heart Nebula image. I've got some way to go, but it seems to show a lot of promise. For a start, I can reduce the visual impact of the star field. Here's a comparison, first using the standard, less aggressive processing in Lightroom (which I haven't previously posted in this thread, though I did in my Gallery), and second, with the refined technique. As I say, early days. There's a bit of a stacking issue in the bottom LH corner that I should have cropped out in the second version, and sorry about the different sizes. Anyway, enough to get a preliminary handle on the way it works. Ian

I've just had a quick look at this and I must say there is a dramatic improvement to the nebula in his example. Well spotted Steve! I'll need to have a go some time. It does seem that ST can offer an awful lot, if only you know how to use all of its features! Ian

That's a really worthwhile improvement. Ian

A good start Ken! Nebulosity coming through on a single sub, should be good when it's all put together. I'm presuming this is M45 rather than IC1848? As to your alignment woes, is it possible to use a much shorter capture time in order to get more of a Live View experience? Or is this a case for a Star Sense Ian

Nige, I've just had an Archimedes moment regarding your fuzzy stars! Have you heard of something called "zoom creep"? It's when a zoom lens slowly extends under its own weight whilst it's being carried around on the camera. I was wondering if that could have happened in reverse, so that whilst it was pointed up at the sky it was slowly collapsing and the focal length changing? The zoom barrel would need to be fixed in position some how. Ian

Those nights always turn up from time to time! Good luck and looking forward to seeing your results. Ian

Well I took the view that any lens distortion would be axially symmetric, so it wouldn't depend on rotation. That said, I suppose everything is possible and without testing I suppose one couldn't rule out non-symmetric distortion. At the back of my mind I think I've read of a stacker that can account for different scaling (or zoom settings). PI doesn't cope with that does it? As to which button in ST to use, I just take it literally. I choose the "Linear, was not Bayered or is whitebalanced", simply because my Fuji doesn't have a Bayer array. If it did, I would choose "Linear, is Bayered, is not whitebalanced", on the basis that it is a Bayer sensor, I'm using RAW, and I'm assuming that provided you switch off all the colour correction options in DSS and use the autosave FITS, then it would be the best match. Could easily be wrong of course . In fact, I think this demonstrates one of the deficiencies in the ST documentation, in that all of the modules have sub-settings with parameter names that don't really mean much to me, and their individual functions are not explained. True, you can try each to see what it does (often nothing that I can see!), but it often feels like wading through treacle. Ian

I think you captured that well Nige, and it's good to note that all the extra work doing flats and darks has paid off. As Ken says, though, there is something odd going on in the top left, as though the scaling of the image has changed slightly during the session so that the stars can't be made to line up throughout the whole image. I presume it is taken with a zoom lens, so is it possible that you might have nudged the zoom ring a tad part way through your session? Another thought, does your lens have image stabilisation, and if so, was it turned off? Not sure how that would affect the stacking process mind. It needs to be off anyway because it can 'jitter' when the camera is rock solid. Also, as it is cropped, is it symmetrical? In other words, do you have the same issue on the other side of the frame that has now been lost? I like your globular. They are relatively easy to process as one doesn't need to tease out the minutest detail, which can come as a welcome relief! I too am drawn to them. Ian PS Just to add, I can't see that lens distortion would cause this, as all the frames would be distorted equally.

Looks good to me. Ian

Nige, if you are stacking RAW frames then auto white-balance shouldn't affect the colour balance, as the colour balance is only applied to the creation of the JPEG. RAW is RAW data, though the file header will have information about the colour balance setting of the camera so that RAW developers can apply an appropriate setting from the off. In the case of DSS I shouldn't think it uses the header information, as the file interrogator used, DCRaw, should just read the channel information directly. That's my take on it anyway. Ian

Yes, that's a much more emphatic nebula now Steve, though I suspect this has rather more to do with general processing than with switching off colour calibration. Ian

Steve, in the past did you use "Linear, was not Bayered or is whitebalanced" or "Linear, is Bayered, is not whitebalanced"? Presumably, if "Per channel background calibration" was set to "on" then the first option would be expected by ST, if "off", then, with your Bayer sensor, the second? If I understand things correctly (and that's a big if!) Ian

I think it's mentioned on p18 of the StarTools Manual Steve. Ian

I look forward to seeing what a proper astro camera can produce Ken. I'm not sure I'd like to dispense with an all-in-one unit though, and the thought of doing LRGB doesn't excite me! Good luck with your new venture. There have been some interesting reports of micro-PCs being strapped to the OTA to avoid issues with laptops being used out of doors and to minimize a trailing cable jungle. Ian

In addition to close cropping, I tried upping the wipe aggressiveness a lot to get rid of apparent gradients, but who knows whether that got rid of nebula as well. I also tend to use a dark anomoly filter setting of 10 or 15, don't know if that helps. Cheers, Ian Ian

Ah, my mistake! Ian

But this isn't with the 'scope, is it? I though it was a csmera lens. Ian

Nige, I can't resist a challenge, stop, stop it! Well, this is what I managed to get out of it. Completely different in appearance, a very fussy background of, what I take to be, stars. I used the colour module with this, it didn't seem to 'go ballistic' as it sometimes does. Finished with a bit of fettling in Lightroom. I must say that that you have a hell of a lot of gradient in there, (or is it uneven noise), so I really think flats and darks would ease the processing demands. No masking used. Ian PS I still prefer yours though, the starfield doesn't impact on the image as much, and the stars seem much smaller. Anothef one of those 'start again' moments perhaps

Nige, another thing is that the night-time temperatures have been quite high of late, and I wonder if that is resulting in more noise? Ian

I always find star colours to be a pain in ST; more often than not the colour module makes them green or purple! And the sensitivity of those colour bias sliders...! To be honest, I'm always starting afresh. When you stack in DSS, do you use kappa-sigma clipping? If not, it might be worth a try at default settings, particularly if you don't use darks. Something I read somewhere . And speaking of darks, I really do think that you need more. Of course, I've no experience of using long exposures and the darks appropriate for that, and you might indeed be able to get away with fewer. But for 30-40s exposures? Hmm, not so sure. I also wonder if doing flats would be worth a try? It wouldn't be difficult to do them now as you are talking about a camera/lens combination. You wouldn't have to set up your 'scope to do it. Ian

Hey, we just gone over the 1000th post on this thread! Ian