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Disaster on PacMan (NGC281)

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#1 limeyx

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Posted 22 September 2020 - 12:26 PM

So I had really high hopes for this one. It was the first clear day after the weeks of fires here. I had a 4 hour window before an entire week of cloud. Of course we had (in our COVID bubble) guests suddenly arrive so all my prep time got eaten up.

 

It was actually crystal clear even before Clear Outside said it ought to be so I got setup and a really good polar alignment pretty rapidly (at least as good as you can get on a skyguider pro without a guide cam)

 

Used plate-solving to get onto the target, this worked REALLY well (once I remembered to update my focal length from 200mm to 300mm in APT since I changed lenses)

I was stunned when after three solves, Stellarium confirmed I had Pac-man in frame (took a few more shots to get it centered). Did have a few issues with the camera hitting the mount so I had to go back to the non-optimal ballhead instead of mounting direct on the declination arm with the Skyguider

 

Took some ISO3200 / 30 sec exposures and stretched in APT and saw a faint fuzz of PacMan

 

Focus was ... once again one of the hard parts. I have Bahtinov mask (finally) but ... wow, adding that to the lens really cut the exposure down. I used APT's Bahtinov helper, but wow, just a sub-mm turn of the focus ring make a huge difference (really glad I got the internal focus version of the lens so touching the lens wont move the focus). I was getting pretty low FWHM values but could not get a Bahtinov score of better than -5 or something

Eventually I had to go with the best focus I had since I was running out of imaging time (for reference, Pixinsight during stacking had FWHM of >15 for my subs :( )

 

I figured that since at f5.6, ISO 3200, 30 seconds I could see the target (stretched), then 120 seconds, ISO 1600, f5.6 would work (f4.5 is wide open for this lens)

 

Started a sequence in APT-- couldn't see the target even stretched but my friend who was imaging the same target sent me a screen grab (he has a GOTO) and my star pattern matched exactly

 

Had to go inside for a bit to referee a fight between the kids "But no matter, APT is just taking shots ..."

Got back out (40 mins later) and I had stupidly set the sequence to ISO 159 instead of 1600 and 5 shots not 30. Ugh (I REALLY hate the APT input boxes -- I make so many mistakes)

 

Restarted and things looked good. My final 8 or so subs were ruined by dew (need a heater) but I had (what I thought was 70 good subs. Unfortunately this included the 10 or so ISO150 ones)

 

Spent the whole day stacking and stretching yesterday in various apps and conclusions

 

1. Focus is NOT good enough

2. As far as I can tell my stars are "round enough" at 120 seconds

3. Thank goodness the neighbors garage gas external 110V power as my laptop was about to die

4. Need a power adapter for the Nikon D5300 as I had to change battery and that jiggled the mount

5. I still suck at flats. Tried the T-shirt method. T-shirt was covered in dew. It was 2am so I gave up and took them the next day with an iPad through T-shirt. They look "OK" and seem to help but I dont know how to evaluate them

6. Aperture ring appeared to be between f5.6 and f8 on the lens :( I must have nudged it

 

Sadly I don't think my exposure was enough to get a signal against the background (my friend was guiding and dod 180 seconds at ISO800 on a 71mm William optics, and actually got a decent image)

 

Looks like this data is useless (except the lessons learned). If i stretch it to insanity, I can JUST pull out a vague pac-man like shape but nothing close to workable

Now it's cloudy for an entire week so I can't even go out and practice ...

 

On the other hand, things are getting easier all the time but definitely a LOT here still to learn

 



#2 Boeglewatcher

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Posted 22 September 2020 - 12:43 PM

Reading your hard work tells me that you surely will hang on and get the shortcomings solved one by one. You learned a lot during this night and you will remember (most of) it next time you’re taking pics. I find such nights stressful but afterwards they are very rewarding because you know what does not work and what works. Actually, when you shoot RAW, the ISO can be lower, your Nikon has a sweet spot around 400 or 800 ISO (I think) which you can check here: https://www.photonstophotos.net 


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#3 limeyx

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Posted 22 September 2020 - 01:00 PM

Reading your hard work tells me that you surely will hang on and get the shortcomings solved one by one. You learned a lot during this night and you will remember (most of) it next time you’re taking pics. I find such nights stressful but afterwards they are very rewarding because you know what does not work and what works. Actually, when you shoot RAW, the ISO can be lower, your Nikon has a sweet spot around 400 or 800 ISO (I think) which you can check here: https://www.photonstophotos.net 

Thank you. I appreciate the kind words. I shot ISO 200 on M31 but it's much brighter. I know the D5300 is supposed to be close to ISO-less and 200 is the optimum but I was "scared" to try that on something so dark

 

I think my next session needs to be a deliberate throwaway so I don't get my hopes up and just play with focus, ISO, duration and  not expect any data

 

There are definitely days I think I should have dipped further into savings and got a 70MM refractor, EQ6R-PRO mount and a guide-scope and saved all of this hassle



#4 Boeglewatcher

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Posted 22 September 2020 - 01:05 PM

The Pleiades are out now. Can shoot them as well. Should look great w your setup.
(belief me, other equipment brings other challenges :-) )



#5 limeyx

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Posted 22 September 2020 - 01:12 PM

The Pleiades are out now. Can shoot them as well. Should look great w your setup.
(belief me, other equipment brings other challenges :-) )

Yeah haha. I think they are currently behind a huge tree that I cannot cut down (at least during reasonable imaging times). Will have to wait a little but it's 100% on my list



#6 F.Meiresonne

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Posted 22 September 2020 - 01:27 PM

It is not an easy target....

 

I tried it too, got something, not a big deal but was glad i could see it in 2 colors....with a stock DSLR and no filters at all...

 

My goto was a bit off...probably my own fault in not tightening the bolt hard enough, it may have shifted a bit.

 

I did not know that you can stretch in APT,how do you do that...??

 

I was figuring out star patterns to convince me i had it in the frame, but i could not see it....it is like flying blind...makes me nervous and unsure...

 

Took me about half an hour to convince myself i saw the right star patterns comparing to CDC



#7 Boeglewatcher

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Posted 22 September 2020 - 01:35 PM

FDB3F5E5-B5F4-4424-823F-EC6861DE217A.jpeg

this is what i got with my modified Canon 2000D, 1hr exposure. Need more exposure time for sure...


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#8 Boeglewatcher

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Posted 22 September 2020 - 01:40 PM

Tools - Histogram - Auto Stretch will stretch your picture. Clear will clear it.

 

 

„I did not know that you can stretch in APT,how do you do that...??“


Edited by Boeglewatcher, 22 September 2020 - 01:40 PM.


#9 limeyx

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Posted 22 September 2020 - 01:45 PM

It is not an easy target....

 

I tried it too, got something, not a big deal but was glad i could see it in 2 colors....with a stock DSLR and no filters at all...

 

My goto was a bit off...probably my own fault in not tightening the bolt hard enough, it may have shifted a bit.

 

I did not know that you can stretch in APT,how do you do that...??

 

I was figuring out star patterns to convince me i had it in the frame, but i could not see it....it is like flying blind...makes me nervous and unsure...

 

Took me about half an hour to convince myself i saw the right star patterns comparing to CDC

APT stretch

 

Click the "Auto Str" button (it's a bad stretch but enough). To unstretch you have to unselect that then press the "C" button -- Man I love APT but the UX is ... not intuitive

 

I am going to try ISO200 against my instincts, as well as replace the ballhead with pano head. Baby steps (and a lot of unused gear haha)

Anyone want a pile of ballheads, bahtinov masks and tele-converters ?

 

It will stretch all future subs until stretch disabled. Super noisy but helpful

 

Getting blind plate-solving with a local Stellarium server was a game changer for me for locating targets (my biggest concern with the SkyGuider)

APT-Stretch.png


Edited by limeyx, 22 September 2020 - 01:48 PM.

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#10 RJF-Astro

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Posted 22 September 2020 - 03:17 PM

Yes, you need these nights to learn. I think we all had our share, and somethimes forget how important this has been in getting better at AP.

Also there is a delicate balance between getting better gear to improve and getting to know your current gear. Yours looks ok, although 300mm is pushing it on a tracker. I would only be comfortable with this combination when guiding, be it RA only. So in this case it might be holding back on your development. A better mount would definitely improve that, or a step back in focal length and an easier target like M31.
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#11 limeyx

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Posted 22 September 2020 - 03:22 PM

Yes, you need these nights to learn. I think we all had our share, and somethimes forget how important this has been in getting better at AP.

Also there is a delicate balance between getting better gear to improve and getting to know your current gear. Yours looks ok, although 300mm is pushing it on a tracker. I would only be comfortable with this combination when guiding, be it RA only. So in this case it might be holding back on your development. A better mount would definitely improve that, or a step back in focal length and an easier target like M31.

 

This is my M31 with the (lighter) 70-300MM zoom set to 200MM. I Definitely want to tackle it again as this is only an hour of integration (and dubious flats) but I also wanted to tackle a different target since I got a bit sick of M31 and Pac-Man is really nicely placed in the sky for me and still a somewhat reasonable size

 

Focus & Flats are my real frustrations right now that I need to work on but no clear nights until next monday

 

https://www.astrobin.../full/94054v/B/


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#12 F.Meiresonne

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Posted 22 September 2020 - 04:58 PM

Yeah haha. I think they are currently behind a huge tree that I cannot cut down (at least during reasonable imaging times). Will have to wait a little but it's 100% on my list

On my latitude i have to wait a little longer....guess october , november will be much better


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#13 limeyx

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Posted 22 September 2020 - 10:05 PM

And if anyone wants to take a stab at it, this is the best stack of the data I could get. If you can pull a Pac-man out of that I will be impressed

 

I'll have to pull it down at some point as its a bit file

 

https://drive.google...iew?usp=sharing



#14 Boeglewatcher

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Posted 23 September 2020 - 09:34 AM

And if anyone wants to take a stab at it, this is the best stack of the data I could get. If you can pull a Pac-man out of that I will be impressed

 

I'll have to pull it down at some point as its a bit file

 

https://drive.google...iew?usp=sharing

a quick evaluation (the pic has some vignetting, color gradient, dust particles) shows no clear trace of the nebular. my post processing skills are not the greatest, but I think the vignetting and the gradient is too strong.

I added the frame of my pic above to the pic.

pacman disaster.jpg


Edited by Boeglewatcher, 23 September 2020 - 09:41 AM.


#15 NightBear

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Posted 23 September 2020 - 10:16 AM

And if anyone wants to take a stab at it, this is the best stack of the data I could get. If you can pull a Pac-man out of that I will be impressed

 

I'll have to pull it down at some point as its a bit file

 

https://drive.google...iew?usp=sharing

I tried processing your image in PixInsight. Your image has a ton of vignetting, did you use calibration frames? I was able to smooth it out the gradients but the main issue is all the stars are blurry with red centers. I'm guessing either you were significantly out of focus, or your scope was covered in dew, or both. I wasn't able to bring out any nebulosity in the image, there is too much noise, or due to the focus/dew/lack of total integration time there's just nothing to bring out.

 

Big version: https://i.imgur.com/QvYJbfg.jpg

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  • 2020-09-20-NGC281-Stacked-LN-nightbear-small.jpg


#16 limeyx

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Posted 23 September 2020 - 11:06 AM

Thank you both and agree on your feedback. It is super frustrating -- so much to learn.

This is a stack of about 57 images of 120 seconds. 100 Bias frames, 15 darks and 35 flats (taken the day after, not moving focus, 1 second exposure of a white panel through a T-shirt)

 

If I stack without the flats and then do an extreme stretch in Pixinsight, this is the result I get, so the flats are helping but wow this looks horrific. Problem is that I have no scientific way to evaluate the flats so I am unsure if I am taking good ones or terrible ones

 

 

Focus is really really hard with this lens and I definitely need to work on it. I ended up the best I could (-4.5 on the Bahtinov tool in APT) because this  is the only 4 hour window of imaging time I will have in about 6 weeks. I may need a mechanical way to turn the lens a fraction

 

It was definitely dewy (lost at least 8 other subs to this, which I excluded) -- I ordered a dew heater

 

I feel the stars look a lot less worse in the subs than the stack (maybe that is normal)

 

https://drive.google...iew?usp=sharing

 

Definitely not perfect but they look like stars ...

 

Of course my friend imaging the same target takes no calibration frames whatever (although he has a proper GEM mount, guiding and a 71mm refractor), no bias, darks or lights and gets the darned Nebula (admittedly he got 60 subs at 180 seconds)

 

For now, flats and focus are my two biggest issues. This is bad in a way as I dont know how to improve them (yet) but good because on my last session, just getting the target in frame was tough

 

I have some better equipment (pano head and AC power for the camera & dew heater) to try to resolve some of these issues.

 

 

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  • NoFlats.jpg


#17 limeyx

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Posted 23 September 2020 - 11:09 AM

Dew was definitely an issue toward the end of the night (I used to think Dew heaters were for once you got everything else figured out but learned that lesson)

 

I *think* I got all the dew subs out but of course some may have been impacted gradually (there was definitely a big onset of dew around midnight that was super obvious but it may have crept up on me)

 

 

Attached Thumbnails

  • Dew.jpg


#18 limeyx

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Posted 23 September 2020 - 11:14 AM

Looking at my flats, its frustrating. When I took them in APT they seemed OK but now that I bring in each one to Pixinsight they seem to be horrifically underexposed ... unfortunately focus has been since changed.

 

I think while the next week or so of rain hits us, I need to figure out a way to take and evaluate flats. 

 

So much to learn here ... I see other beginners saying "Oh, I gave my camera to my wife and she took this ..." or "Oh, here is my first image ..." and they look super awesome

And it feels like I am down in the mud right now but I suppose it's got to get better as I improve



#19 Boeglewatcher

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Posted 23 September 2020 - 11:33 AM

keep your head up :-) !

you can take flats in the AV setting (thats the Canon setting for automatic exposure. there is an equivalent Nikon setting for sure).

focus is the though part... need heater bands, take flats at the same setting right after the exposures.

you'll get there, for sure!


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#20 limeyx

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Posted 23 September 2020 - 11:38 AM

keep your head up :-) !

you can take flats in the AV setting (thats the Canon setting for automatic exposure. there is an equivalent Nikon setting for sure).

focus is the though part... need heater bands, take flats at the same setting right after the exposures.

you'll get there, for sure!

Thanks. Unfortunately the D5300 doesn't have the lens connections to power the aperture on this lens so I have to set it manually. I attempted to take them at the same time but ...I need a dew heater for the "white T-shirt" as it was soaking. It was also 2am and I had to work so yeah ... definitely not perfect

 

Next time we get a clear night, I am going to work on nailing focus with the Bahtinov mask. Not sure yet exactly how. I may need to fashion up an ad-hoc focus ring expander so I can get finer control. From one side of -5 to +20 on the APT tool was barely a mm of travel on the lens (at least it felt that way)

 

I am getting less worse every time but clear nights are hard to find right now.

 

Will actually be in the Los Angeles area for 6-8 weeks at the end of the year which will at least give me more clear nights (although more light pollution)

 

I really appreciate your help. I could have sworn the APT histogram on flats was about 1/3 of the way but bringing it into PI, its way off to the left for flats



#21 limeyx

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Posted 23 September 2020 - 05:21 PM

One thing that I have wondered regarding flats. I have been assuming they are bad (which they likely are) but I do also wonder if I am getting more than expected vignetting on the subs or maybe even bias/darks somehow

 

If anyone knows of tools that help analyze these frames I would be eternally grateful

 

Each individual sub doesn't seem horrid, its only when stacked that I start to see major issues and there are so many components that go into that it't hard to know where the issues come from



#22 Boeglewatcher

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Posted 24 September 2020 - 12:33 AM

When you take flats you make sure that the light source (or tshirt) is directly on top of the front lens. No big distance in between, e.g. no extended dew shield. 


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#23 limeyx

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Posted 24 September 2020 - 01:17 PM

When you take flats you make sure that the light source (or tshirt) is directly on top of the front lens. No big distance in between, e.g. no extended dew shield. 

Yup. I am going to look into a light box I think. Or at least the photographers translucent cloths. I need to make flats scientifically correct and repeatable or I am going to shoot myself



#24 F.Meiresonne

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Posted 24 September 2020 - 01:57 PM

keep your head up :-) !

you can take flats in the AV setting (thats the Canon setting for automatic exposure. there is an equivalent Nikon setting for sure).

focus is the though part... need heater bands, take flats at the same setting right after the exposures.

you'll get there, for sure!

On my canon i had to overexpose to get descent flats, 2 stops

 

ADU of canon800d sensor is max 16384 if am i not mistaken , you need flats about 7500 to 9000 ADU, roughly 40 better just below 50%

 

So you need to know what is the ADU for your camera .

 

That is what i learned sofar.

 

i made them using a computer screen, started up paint wich present a white background....put the scope as close as  i could..

 

Gave up the white T-short method...


Edited by F.Meiresonne, 24 September 2020 - 02:00 PM.


#25 Boeglewatcher

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Posted 24 September 2020 - 02:12 PM

Yup. I am going to look into a light box I think. Or at least the photographers translucent cloths. I need to make flats scientifically correct and repeatable or I am going to shoot myself

actually, I gave up the t-shirt method and bought a second hand light box which works just fine




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