Short integration of NGC 4725 & friends incl LoTr 5

[Mike in Rancho]

This has been a rough month, even beyond the despised (to me) May Gray.

Despite taking the Newt apart a couple times and flocking or blacking out everything I could think of, so far anyway, I am still plagued with vignetting miscorrection using the 2600, and weird curving color anomalies in my OSC. I presume the latter from a light leak or stray light reflection? Baffling and irritating.

So that forces me to use Wipe pretty much maxed out. At least in galaxy season there doesn't seem to be too much of a loss there, though I wonder if I should try again but with a protective Wipe mask.

Between moon and clouds, all I could manage on this project-of-the-month was 5.5 hours total, all thrown into the blender together, possibly utilizing dubious techniques...

Four nights, four datasets, three cameras. The first was 2 hours of lum with the 2600, fighting passing high clouds the whole way. Next up was a bit more than an hour and 10 minutes with my stock D5300, used as a test in case my other D5300 + UV-IR cut filter could be causing my gradient issues. They weren't. Next I took 1 hour with the full spectrum D5300 through an L-eNhance, polished off with 1 hour and 16.5 minutes of the 2600 and the L-eNhance.

All stacking in ASTAP to create the four sets. Resampling the mono files and splitting the OSC files was done in Siril. ASTAP was then used to register all 8 files, as it can handle the scale difference.

Compositing was done as L, RGB for both the broadband and duoband data. The color was fairly weak and flawed, so I pulled back on saturation. On the bicolor, Ha was throttled back, but I'm not sure there's a lot here anyway.

The finished files were then blended in Layer using lighten mode, and sort of an inverse star+galaxy mask. Or maybe better described as an "anti luminance" mask, since that's how I created it? The end result is RGB stars and target with OIII/Hb background. The noise of both short integration and the blue-green side of the duoband then left me trying to use SS and whatnot to tame the background other than LoTr 5, which was the reason for this whole complicated mess in the first place.

The tidal streams of NGC 4747, and the faint PN LoTr 5, are only barely visible. A dark border might help, and luckily the ST forums have that. This could be worthy of putting some real time into one day. Next year I'd say, probably early Spring, as it is already setting a bit too early to easily rack up data.

NGC 4725 2600-D5300 L-RGB blend LE-OIII ST8 1C.jpg (441.38 KiB) Viewed 1433 times

[Stefan B]

Hi Mike,

I didn't know that one! Despite the problems you encountered you got the faint outskirts of NGC 4725 and quite some details in it. So I guess a nice job overall!

May I ask how bright your imaging spot/backyard is? I think mine is dark enough to not have problems with light leaks even if the image trains wasn't 100% light proof anyway. All the LED lights are taped in my setup. Do you maybe have the opportunity to somehow shield your setup from surrounding lights or are there street lights everywhere?

Regards
Stefan

[decay]

Hi Mike,

the despised (to me) May Gray

There's really a lot to learn here on the ST forum, even beyond astronomy. I didn't know that term, and so I read the article June Gloom on Wikipedia. Very interesting weather pattern. Greetings to San Francisco Bay!

Regarding your image - once again, you left me speechless I guess, I only understand half of all the things you wrote. But anyway, I like your image and this may be an interesting new target for future shots for me.

Best regards, Dietmar.

[Mike in Rancho]

Thanks Dietmar and Stefan,

Particularly as to LoTr 5, and that I used L, RGB composition, it probably really only counts as a bit over an hour of integration. The DSLR just adds a little bit of coloring. So, kind of surprising I got anything. But the vague shape and features of LoTr 5 that shows is fairly comparable to real images of it on the internet. At least enough to know I'm on the right track and wasn't turning noise into incorrect structure.

4725 itself is also decent considering the short time, but the outer reaches (the swirls of which are really quite cool) were a headache. Possibly due to my oddball scheme of combining 2600 with D5300 data. Maybe things will be better when I have real LRGB filters someday. That said, if I didn't lower the overall saturation the spirals would be too purple, and there really wasn't any good rebalancing that would fix it. But desaturating did the trick, and actually the inner galaxy remained reasonably colored. The star field, however, became too dull, but...oh well. SS Saturate only helped so much. I could probably preserve more star color with masking, but this is kind of a blended Frankenstein already, and I don't want to make it too much of a patchwork.

Dietmar, San Fran is way way far away! They of course get their famous marine fog, but by and large that's different from the So Cal spring gloom, even if they occasionally get similar effects.

I'm in what would be called the Inland Empire, albeit the western part of it. Say 40 miles east of Los Angeles, and 50-ish miles from the nearest point of the Pacific, which is probably Huntington Beach. But the marine layer was so deep yesterday that there was no sun the entire day, and it was all of 62 degrees. Brrrr. Today isn't much better. This weekend is supposed to be the unofficial kick-off to Summer, but on average Summer really doesn't get started here until July. Some years are different.

[Mike in Rancho]

ST forums are pretty good about having some Newt imaging experience, that's for sure.

Stefan, I do have a couple streetlights nearby. One I always block with the canopy of a yard swing, bolstered with a towel hanging from the bar. For the other I built a tarp stretched between two poles. I hammered some PVC pipe into the ground over there, and so I just slide the poles in. I suppose that tarp may not be opaque enough, and some light gets through? I can try to remedy that.

However, I suppose that doesn't stop the streetlights from causing scatter bouncing off the walls of my house and whatnot?

That said, the back-end of the Newt is blocked off with a darkened bucket I made, that's decently deep. It's lined with tin foil and then covered in black duct tape and then a matte black construction paper, to stop possible reflections bouncing down in through even the small gaps where it fits around the scope. I put this on after the mirror has cooled down. For the focuser, I have a cut neoprene sock with velcro straps that fits over the drawtube to focuser body connection, and goes up to near the compression ring connection. I've tested it out with a bright flashlight and found no leaks, but...maybe I need to test more.

I could cover over any LED lights, as there are several, but...they are all below the scope so I don't know where any such light could be getting in. It's worth a try though.

For stray light into the aperture of the scope, I bought some flocking paper from Scopestuff and flocked...almost everything I could think of. The entire inner OTA. The extra Orion backing plate. The exposed primary cell surrounding the mirror. The inside of the focuser body. And the inside of the drawtube itself, up to the point where the Sharpstar MPCC (with a 2" filter on the end) inserts down to. I also used ultra matte paint as well a a Sharpie to black out the edges of the secondary.

There are only a couple things left, I think. The spider vane adjustment and tightening knobs are shiny, so I could put strips of flocking around those. Also, I guess I could add some flocking to the surface of the primary mirror clips. I need to readjust those again anyway, to make sure I am not too tight.

Beyond that I just don't know. My collimation might be poor, but I don't think that poor. Still, I am wondering what kind of decent, 2-inch, collimation tools I might look into.

Other possibilities include the inside surface of the ZWO adapters/extenders, maybe even the T-ring with DSLR? But the light would still need to get in from somewhere, if not through the actual aperture.

Sigh...more testing.

Anyway, at least for the most recent sets of data, with the 2600 I was getting what looks to be flat miscorrecton. At least as to the vignetting profile. The dust spots it is working fine for.

WIPE 75 - 2600MM scaled.jpg (93.42 KiB) Viewed 1401 times

And with OSC - which I have tested using the f/s D5300 with UV-IR cut filter, and a stock D5300 with no filter needed - I am getting really strange, curved color anomalies of green and red.

WIPE75 - STOCK D5300 - ASTAP NORM FLATS scaled.jpg (177.27 KiB) Viewed 1401 times

Weird, huh? I actually think it is the green channel causing it rather than red, and the red is just showing through areas where the green is lacking. The curvatures make me lean toward some kind of inner reflections...but off of what? And why so many differently vectored such anomalies?

I really want to fix this of course. Squashing it down in ST takes a lot of Wipe - often 98 or even 99% aggressive, sometimes with a protective mask if I remember to. Of course, that is not an optimal way to get started.

Oh and I have no idea what that big glow is on the left side of the OSC there...that doesn't usually happen. And hopefully won't again.

[Stefan B]

Hi Mike,

I see, you took a lot of measures to prevent light leaking in...no idea what you can do on top... Hope you can fix it. I probably would have already given up.

Regards
Stefan

[decay]

Dietmar, San Fran is way way far away!

Oops! I must have confused Alta Loma and Palo Alto. Sorry! No idea, what happened.

They of course get their famous marine fog, but by and large that's different from the So Cal spring gloom

OK, I understand. Thank you for clarifying!

Regarding your stray light / curving anomalies: I would have expected that this behaves likewise with both cameras. Hm ... strange. Would it perhaps make sense to do a test (at night) with a light source (torch) and very short exposure times? So you could check out the parts under suspicion? Just a thought ...

Best regards, Dietmar.

[Mike in Rancho]

Thanks again Stefan and Dietmar.

Of course I was hoping that somebody has had the same thing and could say "oh yeah, I know exactly what that is."

I had the scope apart again last night. I added some flocking to the tops of the mirror clips, and likewise wrapped the ends of the spider vane knobs that stick inside the tube. And cleaned the mirror, though I don't know how well I did on that. Finally I tried to get the installation just right. I added a little tape to the inside of each holding prong in the cell, to prevent mirror shift, and then made sure the rubber for the clips were just right. Not too tight or too loose, just to the point of touching the edge.

But today I think I will set up in a bright room, seal the dust cap, and maybe take 15 minutes or so of shots as if they were lights. Then I will stack them and stretch it. I believe that should let me know if some sort of faint light leak is getting in. If not, then my problem (if not fixed by the new flocking) would likely seem to be resulting from light entering the aperture, as it should, but going wrong from there.

Anyway, though Ivo recommends against endless tweaks and repetitive re-tweaking, I had to tweak my 4725. Too much desat of the stars was just bugging me too much. So I did an auto star mask, cleaned up a couple spots like galaxy parts that were accidentally captured, and added back in some color. Of course this starts revealing some of my color flaws again, at least on pixel peeping, but I think I am happier with some color flaws (mostly in the diffraction halos) than a bleached star field.

This was our May beginner DSO challenge target on CN, so this may be my final version. No more tweaking!

NGC 4725 2600-D5300 L-RGB blend LE-OIII ST8 1D rot.jpg (477.79 KiB) Viewed 1370 times

EDIT: I decided to replace the earlier-posted image with one that I rotated 180°. Yep, more tweaking. While I think having LoTr 5 in the upper right emphasizes it a bit better, the flipped about orientation seems to have a better balancing of the stars. Or I'm just crazy.