Wipe needs Dark Anomaly bump; why?

[TelescopeGreg]

Hi Mike,

The AVX does need to get upgraded, but it's working well enough and to replace it will trigger a nearly-complete rebuild of the imaging rig from the ground (er, trolley) on up through the software. So there it remains. My plan was to next get a reducer / flattener for the OTA, but recently realized that adding its 3 lbs to the tail of the scope would very likely push the AVX over the edge. So, I probably should do the mount first, and that's a big step. {sigh}

Last night, no, I opted to keep the imaging train the same as it was before, with no filter. I figured the Moon will become more of a factor over the next few days, so saved the one last night with it more or less out of the way to duplicate what I had before, but under better observing conditions. That will answer my thought about the really poor transparency as perhaps a factor. Got another 14 subs at 5 minutes (just over an hour). (Dang, it got cold out there all of a sudden!)

---------

Ok, got the calibration frames, and did a quick processing pass... Interesting. 2nd night by its self looks a lot better in terms of image noise, even though it was the same exposure and total duration. Transparency, for sure. But I see the same behavior in terms of DA. Adding in the first night made for a bit better image (expected), but essentially NO change in the need for DA filtering. As expected, there was a significant offset between the two nights, so there is little chance that FPN is the root issue.

Plan for what to do next? I'll probably throw on the UHC filter and try for another couple of hours of imaging, just focusing on the nebula and not the DA issue. Any thoughts about what to do to understand why I need the DA filter in the first place?

For the curious, here's the current Pacman Nebula image. DSS stacking of the 2 nights, StarTools processing using AutoDev, Crop, Wipe, AutoDev again, Color (using star field sample), DeNoise, and Contrast. Love the colorful star field.

[Mike in Rancho]

Yes, nicely colored stars. And good little nebula also for just 2 hours, I must say.

Well, what I would do is start comparing the stack, where at least some of the issues are known and visible, to one of the light subs that went into said stack. Might as well just stay all on one night, in case you had any field shift between the two. In doing so, I would zoom to the pixel level, stretched if need be (Gimp could be good for this), and try to line things up spatially.

My guess is you might find some hot pixels? As for cold pixels, might be tougher lol.

Add it to the link and I'll poke around too if you want. First night sub would be good, since I think that's the stack linked earlier in the thread?

EDIT: Another test you might run is to do a restack but turn on the cosmetic hot/cold pixel repair in DSS, second to last tab. This is an ST no-no, and it'll mess up the star cores such that color balance sampling can go bad...but maybe to see if it lets you get through Wipe without a big DAF (not that I think 3 is very big), that would point to the issue (and also therefore the solution being dither+kappa sigma rejection, and turn cosmetic back off).

[TelescopeGreg]

EDIT: Another test you might run is to do a restack but turn on the cosmetic hot/cold pixel repair in DSS, second to last tab. This is an ST no-no, and it'll mess up the star cores such that color balance sampling can go bad...but maybe to see if it lets you get through Wipe without a big DAF (not that I think 3 is very big), that would point to the issue (and also therefore the solution being dither+kappa sigma rejection, and turn cosmetic back off).

Ding! Ding! Ding! Ding! Ding! Ding! We have a winner.

Turned on the cold pixel repair (2 pixels, 50%), and left the hot alone (off). All other settings unchanged. That made a huge difference in the need for raising the DAF level. No brilliant colors. I almost could have left it at 1 pixel; bumping it to 2 looked pretty even. The final star coloring wasn't much different (certainly didn't make a mess of them), so I may just continue to do this in the future.

So, is the bottom line that it IS my camera's fault after all? The "cold" pixels aren't really all that cold (minimum value for a Dark was ~460, with a mean of 501), but I guess they're dark enough that they are outliers when stretched. If so, why are the DA zones not aligned between this image and last month's?

[Mike in Rancho]

Well that's cool! And no holes to deal with, even if you had masked them out in Wipe.

I don't know much about cold pixels or their values. Possibly also affected by any gain and offset you had going?

I wonder if ST might be more benign about cold pixel repair too, as those will be different than messing up saturated star cores that DSS interprets as hot pixels. Need Ivo's input there...

[admin]

Cold pixels are indeed typically rather well ignored/repaired by modules, as long as they are single pixel in size and do not "bleed" into neighbouring pixels (making them clumps/blobs, streaks, etc. which starts becoming artificial detail).