First LRGB image - strange RGB glows around edges

[BrendanC]

Hi Mike,

Right, well, this is brilliant. I am so grateful. I was freaking out initially, not really knowing where to start.

The ASTAP recommendation is a good one, and I'm going to learn more about that. I do need some quick way of analysing lots of subs, and that could be the one.

There's field rotation, and this is a known problem when I do a flip - I think I have cone error, which I've lived with for a while, and just need to fix, but it keeps getting pushed down my 'to do' list. However, if they're within filter sessions then I don't understand that at all. My polar alignment is pretty good. Do you happen to know what could be causing that?

Other thoughts are:
* I should return to unity gain which also means offset 21 according to ZWO recommendations.
* My RGB exposures are too short. This is because I didn't notice that the table I was using was based on luminance.
* My L full integration time should be around the same as RGB combined.
* The object was shot low in the sky.
* There's another bright DSO just off the FOV which doesn't help.
* I need to learn about ADUs more thoroughly, and how to analyse images.
* The object was also captured as it should have skimmed a tree, but I'm now wondering whether I misjudged that, and the tree has in fact screwed up a decent proportion of the subs.

So, all in all, I made a bit of a mess of this! Plus, I probably chose a tough first DSO. I'm going to try Bode's Galaxy, hopefully tonight, which is nice and high, circumpolar, and I've done it before so I get a decent comparison. I might even be able to have a stab at LHaRGB if I can get the LRGB bit to work out.

In the meantime I might just try and stack the top 50% of the subs, just to see what else this brings out. If nothing, then I'll probably scrap the lot and put it down to experience. Won't be the first time, definitely not the last!

Again, thank you, really.

Cheers, Brendan

[BrendanC]

OK, it's happened again. I'm nearly at my wits' end here.

This is what I get for the Bode's and Cigar galaxies - stacked in APP...

Honeyview_app.jpg (148.24 KiB) Viewed 3894 times

... and stacked in DSS.

Honeyview_dss.jpg (121.99 KiB) Viewed 3894 times

(Yes, I know there are sat trails in the DSS version, and possibly walking noise in both, these don't bother me because I know the fix - dither more frequently, use a different algo in DSS)

Both processed in StarTools, using pretty much the default settings, no noise reduction applied. I haven't tried getting 'the best' result, because I can clearly see these images are not right. I can process pretty much any other set of data I took with my DSLR using the same default settings and they're OK.

This is a high, easy target which I've shot before with my old DSLR, no problem. No bright lights nearby, Bortle 4 sky, no wind, no clouds, no Moon.

I've checked that the right filters are in the right slots, the right way around (they're mounted, so it's impossible to get them the wrong way round because they screw in), and that the right filters are selected in APT, by literally watching the correct filter appear when I select it manually.

I'm going to try and provide as much detail as I can here, in case anyone can help. I've tried to (re-do) everything by the numbers here. I really do not know what I'm doing wrong.

* All lights and calibration frames are shot unbinned, at gain 139, offset 50, temp -15C (some of the Luminance flats were between -11C and -15C)
* Taken over two nights, but with everything absolutely untouched between each shoot and virtually identical sky conditions
* Luminance is 60s per sub, RGB is 180s
* Total integration time is L 5880s, R 2520s, G 1980s, B 2340s
* Flats were taken on the first night, in astro darkness, using an LED screen, with a perspex sheet and some sheets of paper, after using the APT flats tool to calculate exposure times
* Dark flats were taken last night, again in astro darkness, using the exact same plan as for flats so that all details matched up, with the scope on the mount, cover on, a hat over that, another hat over the primary mirror end of the OTA, and two thick towels over everything
* Darks were then taken in the exact same conditions last night, for 60s and 180s exposures
* 25 flats per channel, 25 dark flats, 50 darks per sub length
* Kit list is 130PDS, NEQ6, ASI1600MM-Cool, ZWO EFW with 1.25 inch mounted ZWO LRGB and Baader HSO filters, Sky-Watcher 0.9x coma corrector, Sky-Watcher auto focuser with HitecAstro DC Focus V2, APT, PHD2, APP and DSS to compare stacks, StarTools

Questions are:

* When I was checking my filters, I noticed that my ZWO L filter is actually called UV/IR cut. I think this is the same, but could someone confirm?
* I have the 8-wheel EFW and just 7 filters, so position 8 is empty. Could this be causing any problems?
* Am I definitely right about the filter wheel being such that the EFW lettering is on the camera side, and the screws on the coma corrector side?
* I've read that the older ZWO LRGB 1.25 inch filters may suffer vignetting, especially with faster scopes. With my 0.9x coma corrector, I'm at around F4.5. Could this be an issue?
* I did get a calibration warning in APP while stacking, but when I retried the exact same files - as in, literally just pressed the integrate button again with the same file list in place - it worked. I've posted about that here: https://www.astropixelprocessor.com/com ... bration-2/ Could this be a pointer to what's going wrong? DSS didn't spot any issues.
* I know that the LED screen approach to flats isn't the best, but I know other people have said they use it successfully. However, again, could the flats be at issue? They worked fine for narrowband, and with my DSLR. How would I check? Should I try something like sky flats or the t-shirt method and see if that yields better results?
* When I'm processing in StarTools it seems fairly obvious to me quite quickly that there's heavy vignetting going on. Could that be the flats? Or, could it be the filters?
* Given that some of my Luminance flats were between -11C and -15C, surely that wouldn't have such a dramatic effect, would it?
* Finally... deep breath... given that I'm losing what little hair I have left here, would any kind soul (@Mike in Rancho?) be willing to take a look at the entire set of data? If so, it's here - subs, flats, dark flats and darks, total 13.4GB unzipped: https://1drv.ms/u/s!AqovBuVZMwj3ku8zByE ... Q?e=NaPSm2

... or 5.7GB zipped in separate folders (I couldn't get the whole thing to upload in one big zip file): https://1drv.ms/u/s!AqovBuVZMwj3kvMCfUj ... Q?e=5QLric

Actually, finally finally, what do I do if the camera is borked? It's second hand so I don't have much recourse if so, and I certainly wouldn't be able to sell it on. And if I did get, say, an OSC instead, and there's something wrong with my technique, then I'm back to square one.

My workflow was totally sorted with the DSLR, so I thought it would be a fairly smooth transition to LRGB. I got the hang of narrowband with this camera pretty quickly, so perhaps it's not the camera, it's me (photo below very compressed so that I could upload it):

Honeyview_trunk.jpg (92.25 KiB) Viewed 3894 times

If you've managed to read this far, then thanks!

TL:DR
I'm going insane trying to get my new camera to work and if you could help, I'd really appreciate it.

Thanks, Brendan

[BrendanC]

Also, Ivo (who is I believe @admin) - it would be wonderful if you could take a look at the data too? I know it's cheeky to ask but I need all the help I can get!

[Mike in Rancho]

Hi Brendan! Wow, very colorful.

Sorry I didn't respond earlier to your post the other day. Trying to catch up on things. Last night I finally got out for the first time since February really. Managed about 45m on M44 through some terrible transparency, but mostly I was just testing out my new 178MC in a guiding configuration along with some other ways of setting up my computers and cables. Today was yardwork. But I'll look things over (I hope it's not OneDrive!) and try to start responding to various things.

Prior to that though, did you say you used this setup before but the camera is the only change? I do see that it's a Newt, and Newts leak light all over the place. Have you tested yours out (just take some "darks" in a bright room or using a flashlight, or even watch live view through ASICAP or something, dust cap on and the front covered with a dark blanket), or taken any remedial steps?

My Orion leaks from the backside of the scope as well as up at least one edge of the focuser drawtube. So I have to put a bucket of sorts over the rear when imaging, and wrap the focuser in something opaque. It may not seem like much, but any stray light can and will get in and make its way to the sensor. And of course with the scope tracking, those leaks will smear themselves out. It all leads to crazy gradients. Same goes for flats. I have to cover things up, do it in a dark room, with my tracing pad a few feet away, the front opening covered in diffusion sheets, oh and I have to block off the floor too. Else the light from the pad will reflect off the floor and ruin the flats. Once light gets into these Newts, it can bounce all over the place.

Before I go re-read, let me try to remember ----- yes UV-IR cut and L can be considered the same thing.

Your subs still seem long. Maybe not though. I'll try to check the files. But if I'm not using NB or duoband and have my UV-IR cut on instead, I'll blow out stars in no time. Last night I was saturating (just the very cores though) the mag 6 stars of M44 in 10 seconds at ISO200. Now it's a 150mm scope and F/4, but still.

Anywho, I'm clouded in tonight so should be able to look at things, if I can get them to download. Might also have to take a nap though.

[Mike in Rancho]

Alright Brendan, I had a gander at your data tonight. And OneDrive was actually working fast tonight, so not a big deal there. Thought it's still 12 or 13 GB, as you noted.

I didn't see anything that bad, really. Everything seems well organized, uniform, and properly matching. A few subs are flipped over, and I thought I would go back and cull them out if they were causing problems, but I never did.

Flats may have been a wee bit on the bright side, but that's all and I don't believe they were clipped. And again, your choice as to just how many star cores you want to burn out, especially as the targets here are galaxies.

Seems you were trying to stretch things out more than I did, perhaps? Really not a huge amount of integration here, so it can only take so much IMHO.

I stacked each filter set in DSS, mostly just because it's quite fast. Then I opened each set individually in ST to give them AutoDevs and see what's going on. The L actually looked pretty good. As did the G. Your R set does seem to have a vignetting overcorrection from the flats going on, for whatever reason. The B filter also seemed to have either some flats overcorrection, or extra LP gradient, or both.

So, I thought this might be a candidate for just running a separate Wipe on each filter and then compositing those, if things turned out too messy for ST to handle. I've done that successfully at times when I've ended up with some wacky light leak problems from the Newt. But, ST and Wipe actually handled your data just fine, after cranking up some settings.

What I did then was take the four (renamed) DSS autosaves (normal ST recommended settings, except Standard instead of intersection) into ASTAP, where I put in the RA and DEC for easy solving and then ran analyze followed by calibration and alignment only. Of course they are already calibrated so nothing happens in that regard. What it will do though is register them, and spit out new files with "aligned" added to the name.

(another option would have been to take either the output, of say L, or the known DSS reference frame, and use that as the (unchecked) reference for stacking the ensuing filter sets).

I then composited in ST and even used L+Synth L with the known exposure times. After crop and bin, Wipe with pretty heavily increased aggressiveness and a DAF of about 2 gave an even enough field to accept and go forward. Not too unusual for broadband especially with LP, gradients, and some vignetting issues.

Followed that with A/D, put a ROI around M81. The background is a bit noisy, so I squeezed the shadow dynamic range in the Contrast module.

Anyway, not quite sure what you were aiming for. I wouldn't say my result is great by any means, but seemed reasonable for the data and fairly short integration. There's some nice little fuzzies strewn about, and a bit of blue patch from Holmberg IX.

I don't know if your stacking results ended up similar? Feel free to link if you want. Or I can link the aligned ones I created tonight. I don't know APP but I can help with DSS or ASTAP if needed. Finally you can let us know what your ST log was too if you want that reviewed.

Brendan M81-M82 LRGB ST8 1A.jpg (480.46 KiB) Viewed 3876 times

[BrendanC]

OK, so once again, I am so grateful Mike. You rock my world.

So, it seems that there is a half-decent image there, it just needs to be coaxed out. This is good to know, but it still strikes me that generally, when I'm fighting in StarTools, it's because the data isn't good. The only reason for this data not being good, if everything else in the optical chain is doing its thing, is the acquisition time. However, I doubt that getting more time will remove the RGB blooming around the edges, because they're so very similar to the previous image I shared, which was 9 hours' worth.

So when you say that you stretched each filter separately first, is that a normal thing to do in StarTools? I thought it was a case of loading them up into the Compose module, and ST would sort them out.

Also, the ASTAP stage is beyond me. Actually, I find ASTAP a strange beast: brilliant at plate solving, some useful features such as the image inspector, but the interface is appalling and I've never been able to work out stacking with it. But let's assume the ASTAP stage could have been done in DSS, as you say: you're then using an aggressive Wipe, which echoes my feeling about there being a TON of vignetting in the channels, which I would have thought the flats should have corrected.

Finally, did you use AutoDev, or FilmDev? Because for me, that's the clincher. AutoDev works really well with good data. FilmDev is the backup solution when the data can't stand up to AutoDev. In my image, I just ran pretty much the defaults, to get an indication of what I had, and that included AutoDev.

You've already been so helpful, but you did indicate that you'd be happy to look at the ST log, in which case it's here: https://1drv.ms/u/s!AqovBuVZMwj3kvMt1Yv ... A?e=eYb7Vo - the last session is the one I ran just now, which replicates my images exactly.

And if you could share yours with me, that would also be really useful. I could try and fire up STReplay again (although I find that a bit hit and miss) and see what you did. It would also be super useful to be able to see the registered LRGB files you used in StarTools.

That's the processing, but you also mention light leaks. I just did some sample subs in broad daylight, with the front and back of the scope covered, but the camera/filter wheel/adaptors/focus tube uncovered, and from what I could tell, there were no leaks. I have a waterproof hat over the primary mirror end of the scope after I thought I was getting some leaks a while back, and that's always in place. So I'm not sure this is an issue, but I'll do some more testing on that. To be honest, the 130PDS is a bit of a pain: the focuser tube intrudes on the light path and causes little bitemarks out of stars, but I'm not prepared to upgrade my scope (yet) having just spent so much on the camera.

Finally, again, thank you for helping me out here. I'm hoping perhaps you learned something along the way too? I do actually wish I could send some sort of payment or token of my appreciation your way, but I know that's a bit creepy...

Cheers, Brendan

[BrendanC]

Hmmmm, so I restacked everything in DSS, then in ST pushed the Wipe to about 95% and then I get this.

Honeyview_dss1.jpg (56.88 KiB) Viewed 3868 times

This is definitely an improvement.

However, I'm still concerned that I have to use such an aggressive Wipe. Is this... normal?

Also, I just realised, I kept the very first shot I took with the camera, which was also Bodes, but without any calibration at all, just processed fairly quickly in ST and then removed the vignetting in Affinity. To my eye, this is better! I cannot remember anything about the sub length or total exposure. Doesn't this imply there's still something wrong with my calibration?

NewComposite-DeNoiseAI-low-light affinity.jpg (82.83 KiB) Viewed 3868 times

[BrendanC]

... and the latest from my APP stack, which takes about 100x longer than DSS and is generally a pain, but I do believe produces cleaner stacks that are easier to work with. Again, I'm wiping very aggressively, at 94%, and while that seems to fix things, it doesn't really seem right somehow. I'm getting help on the Stargazers Lounge forum too, and there's a suggestion that there could be some light leak from a constant source, because it seems to move across the image as the scope slews throughout the night. I'm in far from ideal conditions, it's true, in a back garden in a semi-rural environment, so there are houses around, but I'm still surprised at how aggressive the Wipe needs to be.

So, I'm not 'there' yet, but I'm certainly in a better position than when I started. Thanks again Mike.

Honeyview_app (3).jpg (287.33 KiB) Viewed 3866 times

[Mike in Rancho]

Hi Brendan, and thanks. Doing all this investigative work on various conundrums actually is pretty good learning for me, both with ST and various analytic and stacking software. Bound to come in useful for me along the line!

You seem to be progressing pretty good here. Though your newer and DSS versions are way better than that beet-red Affinity modified one, IMHO.

I only stretched each file individually as part of the "research" and testing, just to compare the filter stacks and see if the problems were limited, or across the board. I never saved anything from doing that, though I could have to put together a comparative collage I suppose.

As for separate Wipes, eh, it just sort of depends. Ivo would have to provide the technical details as to whether Wipe looks for it's uneven field and undulations in each channel separately. However, I have had some cases where I wanted to use different Wipe settings on each filter stack, some more aggressive. That helped me out in February with my SHO Rosette using DSS stacks. Though I think later using ASTAP stacks I just threw everything together and Wipe handled it fine all together. Go figure. But with the DSS stacks I would end up with some edge gradient (I believe in the OIII), and if I pushed Wipe harder to remove and flatten that out, I would also start losing some Ha data in the middle of the target, and I didn't want that.

I will check out your files and workflow for sure later, after a little more yardwork today.

Here's a link to the four files I created from your data. Stacked in DSS individually, and then I just used ASTAP to align those already-created stacks. Also an ST log file. I believe I posed the 1A version, not the subsequent tweak to the gamma and skyglow which was 1B.

https://drive.google.com/drive/folders/ ... sp=sharing

As for why, and also why on your 9 hour previous data? Dunno. The red file and maybe the blue did seem to show signs of possible flats overcorrection, or at least some kind of excess gradient in there. As to the overall data clarity, that's a bit beyond me also. I know the 1600 is an older camera, 12-bit, and may not have the lower noise characteristics of modern sensors. I really don't know the best gain for it or what your exposures should be, and if it requires more integration time compared to say, a 2600. For your rig though, I might drop the exposures some, especially for the L, in order to saturate fewer star cores. ? The PDS may also have a smallish secondary for an astrograph? That 4/3 sensor is probably about max for it. I'm uncertain as to the 1.25 filters, but some of the flat subs did look like they might have some corners cut off, or starting to get cut off?

You might do some tests to make sure your EFW is stopping in the right spots for each filter, though I can't say if that's why your red file seems to have a calibration problem.

Good that you've already got the back side of the Newt covered up. The other common leak spot is the focuser/drawtube. Currently I'm using a piece of rubber and a couple long velcro straps, but it's not very good. Last night on CN somebody mentioned neoprene as being good for this, so I might look for some kind of sleeve of that to make work.

As for Wipe being "too strong," well, you have to dance with the data that brung ya. If needed, you can also use a mask in Wipe to uncover the target (use invert tricks in Mask if you want), so you can go even more aggressive on the background without hurting your galaxies.

Oh and one other technique - if you find your color filter data is not up to the quality you'd like, you can always compose as straight L, RGB with no Synth L. That way all your detail comes from the L, no detail comes from the color filters, and the RGB just colors the L when you get to Color module. I'll test that out on your data, but that could help particularly with your R and B files maybe having some excessive flaws, gradients, and noisiness.

[BrendanC]

Hi again Mike,

Very interesting to know how you approach these things, and I've learned a lot over the past few days. I'll be trying masked Wipe and the other L with RGB approach too.

Thanks for the links to your files too, I'll check them out later.

Regarding the vignetting, well, some say they have no problems with it, others do. It was a known potential issue when contemplating buying the kit, apparently the older 1.25 inch mounted filters had this with faster scopes. I'm pretty certain the EFW is working correctly - as in, I physically took it apart, made sure all the filters were in the right slots, put it back together, actually watched each filter appear when I selected it in APT. So, perhaps it's just something I live with until I find a fix.

The light leak issue has come up a lot in the equivalent thread on the Stargazers Lounge, so this is definitely something I'll be looking into.

Thanks again for all your help.

Cheers, Brendan