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Newbie here - first attempt at M51. Is this poor focus or just noise?

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#1 stream41

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Posted 26 March 2020 - 05:08 PM

Hauled out the EQ6-R and the EdgeHD 8" last night! The EdgeHD has a 0.7 reducer on it now, putting it at ~1422mm and f/7. It got a little hazy about halfway through the session, and PHD2 lost its guide star a few times. That may be part of the problem?

 

This is about 70 minutes of light on M51 with an ASI183MC Pro. 70 lights, 30 flats, and 20 darks - all at 100 gain and 18F, calibrated/registered/integrated in PI. Had really bad amp glow and finally tried unchecking the "optimize dark frames" option in PI in the batch preprocessor, which did the trick - boom, no more amp glow.

 

Followed a pretty basic workflow in PI that I saw on Youtube - ABE, Color Calibration, then some adjustments using a basic mask.

 

Took me forever to get the focus right with live view in APT, and I'm still not sure if I missed, or if the blurriness is just noise from not having enough subs. What do you guys think?

 

Here's the full-resolution TIFF:

 

https://www.dropbox.... final.tif?dl=0

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  • M51 final.jpg

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#2 zakry3323

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Posted 26 March 2020 - 05:19 PM

The haze surely didn't help. To me, focus looks a little soft. What method are you using for focus? I don't use APT, does it use FWHM or Half Flux Radius to determine good focus? 



#3 stream41

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Posted 26 March 2020 - 05:31 PM

The haze surely didn't help. To me, focus looks a little soft. What method are you using for focus? I don't use APT, does it use FWHM or Half Flux Radius to determine good focus? 

The haze wasn't too bad - I'd say it was still mostly clear. Yeah, I'm using the "focus tool" in APT, which uses FWHM. The live view was running on an 8s loop, which of course makes it super hard to make adjustments. I think the lowest FWHM I got was like 2 or 2.6. I have a Bahtinov mask for the Esprit but not for the EdgeHD yet - guess I need to buy one!


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#4 zakry3323

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Posted 26 March 2020 - 05:43 PM

It's still a great shot, well framed, good color, especially for only 70 minutes at F/7. Have you tried a re-stack with only the sharpest subs to see how much of a difference the atmosphere made? 



#5 stream41

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Posted 26 March 2020 - 06:11 PM

It's still a great shot, well framed, good color, especially for only 70 minutes at F/7. Have you tried a re-stack with only the sharpest subs to see how much of a difference the atmosphere made? 

That's a good idea! Will try that soon. I also remembered that the scope had some dew on the front too by the session's end - that couldn't have helped! Lots of things working against me last night, now that I think about it.



#6 zakry3323

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Posted 26 March 2020 - 06:29 PM

Post results please! I haven't had the opportunity to image with my Edge8 yet (I also don't have a baht mask for mine) and look forward to seeing your results!

#7 jerahian

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Posted 26 March 2020 - 06:30 PM

For whatever problems you faced, you still got a great image. I agree in the only issue I see, as you surmised, is your focus was a little off.

#8 scadvice

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Posted 26 March 2020 - 06:33 PM

Also when you redo Sub Frame Selector look at the FWHM on the the plot. I did M51 Last week and had the worst FWHM I've ever seen at up to and over 10. Most of mine where I live run 1.4 to 4.5  and I normally throw out any over 3.0 to 3.5. This last image was also quite grainy and fuzzy. Focus was dead nuts with the Bahtinov mask.

 

Earlier that night I did just over 2 hours of Seagull Nebula and it's FWHM were only slightly better at 3.3 to 6.5. I'm running it through BBP right now so hopefully it is better than my M51.

 

I'm guessing it was just a bad image conditions night... though it did not look like one.  shrug.gif


Edited by scadvice, 26 March 2020 - 06:39 PM.


#9 TOMDEY

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Posted 26 March 2020 - 08:16 PM

Cursory examination... Actually a pretty nice shot! It "feels" like soft focus, but M51 is a pretty small target, albeit relatively bright, compared with other galaxies. And those miniscule 2.4 um pixels can lull one into thinking the image should look as ~sharp~ as that, which is impossible at F/7. At best, an unsaturated star core would span several pix across. Your cores are maybe around five across, which could be a combination of mediocre seeing and a tad of defocus. Note that your pix are 0.35 arc-sec across. So, you are resolving something in the neighborhood of 2 arc-sec. I'd say that is in the ballpark of what to expect on deep sky targets. On a superb night, with everything going great --- you might occasionally achieve twice as good, but that would be pretty rare. PS: I'm pleased that you did not oversharpen your image. That's one of the most common... enhancements that people use to ~touch up~ their images.

 

Here's an ancient film pic I took in the 1980s 1900mm F/6. Also somewhat soft, but comparable.  Tom

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  • 07.3 Tom's M51 onto film circa 1980 1900mm F6.jpg

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#10 calypsob

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Posted 27 March 2020 - 09:52 AM

Its soft because you are heavily oversampling. Your seeing snd pixel size are the challenge here. I think the 183 oversamples around 700mm in average seeing
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#11 stream41

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Posted 27 March 2020 - 10:20 AM

Its soft because you are heavily oversampling. Your seeing snd pixel size are the challenge here. I think the 183 oversamples around 700mm in average seeing

 

Yeah I was playing with the CCD suitability calculator and noticed I'd be way oversampled. Thought I could overcome it with careful guiding. So what cooled OSC cam can I use with that EdgeHD at 1422mm? I'm at .35"/pixel with the 0.7 reducer and ASI183. The ASI294 would put me at .67"/pixel - it has the largest pixel size I can find on a cooled camera. But on my Esprit 80ED (400mm) the ASI294 takes me to under sampling at 2.39"/pixel. Dad gummit! I really don't want to own two $1000 cameras just to avoid sampling issues.


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#12 TOMDEY

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Posted 27 March 2020 - 10:41 AM

Yeah I was playing with the CCD suitability calculator and noticed I'd be way oversampled. Thought I could overcome it with careful guiding. So what cooled OSC cam can I use with that EdgeHD at 1422mm? I'm at .35"/pixel with the 0.7 reducer and ASI183. The ASI294 would put me at .67"/pixel - it has the largest pixel size I can find on a cooled camera. But on my Esprit 80ED (400mm) the ASI294 takes me to under sampling at 2.39"/pixel. Dad gummit! I really don't want to own two $1000 cameras just to avoid sampling issues.

If you bin 2x2 that would do it. That would capture most of the intent, using your existing camera.    Tom



#13 Bill001

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Posted 27 March 2020 - 11:00 AM

Hauled out the EQ6-R and the EdgeHD 8" last night! The EdgeHD has a 0.7 reducer on it now, putting it at ~1422mm and f/7. It got a little hazy about halfway through the session, and PHD2 lost its guide star a few times. That may be part of the problem?

 

This is about 70 minutes of light on M51 with an ASI183MC Pro. 70 lights, 30 flats, and 20 darks - all at 100 gain and 18F, calibrated/registered/integrated in PI. Had really bad amp glow and finally tried unchecking the "optimize dark frames" option in PI in the batch preprocessor, which did the trick - boom, no more amp glow.

 

Followed a pretty basic workflow in PI that I saw on Youtube - ABE, Color Calibration, then some adjustments using a basic mask.

 

Took me forever to get the focus right with live view in APT, and I'm still not sure if I missed, or if the blurriness is just noise from not having enough subs. What do you guys think?

 

Here's the full-resolution TIFF:

 

https://www.dropbox.... final.tif?dl=0

You can use PI’s Subframe selector to examine the quality of your subs one by one. That will give you an objective way to access the sharpness of your lights. With practice one can tweak out significant improvements . I shot M51 last year and it looked like crap as that was my first try with PI. Then reprocessing a few times I got the same data to look great. Get a diffraction mask for establishing  focus.  I don’t know what your sky quality is but I use gain 0 with good dark skies.


Edited by Bill001, 27 March 2020 - 11:01 AM.

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#14 stream41

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Posted 27 March 2020 - 11:16 AM

If you bin 2x2 that would do it. That would capture most of the intent, using your existing camera.    Tom

Holy cow that's right! So my ASI183 is right in the middle of ideal resolution with the Esprit 80ED, and if I bin at 2x2 on the EdgeHD with the 0.7 reducer, it puts me back in the green zone. Good idea!! Any unintended consequences with binning 2x2 on the 183?



#15 Bill001

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Posted 27 March 2020 - 11:29 AM

I forgot to mention i did the same thing you’re doing; I turn to others for advice. Given what you state as your setup I think the pix is nice, perhaps a bit out of focus. I think M51 in general has a softer appearance then some other galaxies. Maybe somebody w a 20” Dob who’s actually looked at M51 could give their opinion on the overall appearance,

 

Here’s my first try, setup similar to yours (ie a C8 w reducer), w/o a diffraction mask to establish focus. I used 6 minute subs (too long for tracking)  on a Canon at 800ISO when I made this one. 96 minute total light.  I manually polar aligned. The whole setup was a hip-shot.

 

I should add I shot this in late March so possibly looking thru less atmosphere then you (I don;t stay up late) It was shot at about 4,500’ altitude.

 

 

14CD86B6-AA12-499D-97B5-11E6D6611931.jpeg


Edited by Bill001, 27 March 2020 - 11:40 AM.

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#16 calypsob

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Posted 27 March 2020 - 07:35 PM

Yeah I was playing with the CCD suitability calculator and noticed I'd be way oversampled. Thought I could overcome it with careful guiding. So what cooled OSC cam can I use with that EdgeHD at 1422mm? I'm at .35"/pixel with the 0.7 reducer and ASI183. The ASI294 would put me at .67"/pixel - it has the largest pixel size I can find on a cooled camera. But on my Esprit 80ED (400mm) the ASI294 takes me to under sampling at 2.39"/pixel. Dad gummit! I really don't want to own two $1000 cameras just to avoid sampling issues.

when they come out with the night owl edge reducer you can get pretty close, no need for a new camera https://www.cloudyni...e-initial-test/

Maybe pickup a hyperstar 4 adapter and this and you have an all in one. 


Edited by calypsob, 27 March 2020 - 07:38 PM.


#17 stream41

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Posted 27 March 2020 - 07:43 PM

when they come out with the night owl edge reducer you can get pretty close, no need for a new camera https://www.cloudyni...e-initial-test/

Maybe pickup a hyperstar 4 adapter and this and you have an all in one. 

That's definitely interesting, but at ~870mm I worry I wouldn't have enough reach for some objects - 1400 with the 0.7 reducer seems to be the sweet spot without being slow. With the above suggestion to bin at 2x2 taking care of the pixel resolution issue, I think I'm set!



#18 stream41

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Posted 31 March 2020 - 02:38 PM

Also, could this have been bad collimation? A few months ago I got my collimation to "close enough" for visual use, but I probably didn't get it to AP standards. Picking up some hex bolts to replace the factory collimation screws, and gonna give MetaGuide a chance!




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