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any help appreciated! bad bode

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#1 jdono



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Posted 08 April 2021 - 07:47 AM

bodsmall.jpg Hi, I've given bodes and the cigar nebula another shot and I definitely need some help, I have no idea what went wrong but I'm going to look into it more.


I used the same settings as I did a few days ago (gain 360, 14 second exposures, 80 offset) but this time it came out quite differently.

For some reason the color info was lost, and there is this weird spiral pattern on the photo. Also Bodes didn't come out well at all. I processed the photo to emphasize the problem not to make it look good.


My original thought for the spiral was field rotation but again I've taken many photos before which didn't have spirals under the same settings (and the exposure time is quite small). I am using an alt-az (nexstar evo 9.25 with the reducer) with an zwo 294mc pro.


I can't guarantee that sharpcap used exactly the same settings but I did load it from the same preset that I used before with much better results  (though I think the color profile was on auto and I did notice that it was 35% red and 35% blue). Same gain , offset, and  exposure time for sure and I think I had decent focus.


any ideas what I did wrong? I can also process it differently and have the weird spiral pattern come out in different colors so I'm wondering if the colors and the spiral are related.


I appreciate any help that you can give, I'm obviously quite new at this

Edited by jdono, 08 April 2021 - 09:13 AM.

#2 RedLionNJ



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Posted 08 April 2021 - 07:57 AM

Can we see the result, please?  No image was attached.

#3 jdono



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Posted 08 April 2021 - 08:00 AM

sorry there you go! 

#4 c2m2t


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Posted 08 April 2021 - 08:54 AM

Hi Jdono!

I don't believe it is field rotation...your stars don't really exhibit any rotational elongation, mind you, your exposures are short. I assume that this is a full frame image ie, not cropped. What is troubling is that the circular ghosting that we see is not centered in the image. This would suggest that it is not related to telescope optics. Have you checked your filters to see if there are any anomalies on their surfaces? Do you have an empty filter holder in the filter wheel. If so, shoot a series of images without a filter. I guess you could remove a filter and image through the blank. If the anomaly remains, it could be camera related. You might go back to the very first images that you made with the camera and see if you can tinker with the exposure to bring out this same anomaly. Other than that, I am stumped!!


Best regards, Chris. 

#5 randcpoll



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Posted 08 April 2021 - 09:01 AM

Is your 294mc cooled? I'm not sure what you are using for stacking, but from your description it sounds (and looks) like the stacker is de-rotating your subs, but in doing so is giving you smeared hot pixels in the shape of arcs. If your camera is not cooled that may be what you are seeing.


Also for some stackers you need to tell it that it is an RGB image before stacking to get color output.


If the above turns out to be true you need to take some darks at the same settings and temps and process them before stacking.

Edited by randcpoll, 08 April 2021 - 09:04 AM.

#6 jdono



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Posted 08 April 2021 - 09:09 AM

It is cooled, I cooled it to -15c (just edited the orig post to add pro). I do have darks and flats for this one. I took several sets of flats and have tried the whole lot of them.


I am using deep sky stacker


I don't have a filter holder but I am using a lumicon deep sky filter. Its just screwed in between a few of the adapters that came with the camera. I can try removing it and trying again tonight.

Aren't flats supposed to take that sort of thing out of the final image though? there could be dust on the reducer too for all I know I can check.


I didn't crop it. I'm not sure if DSS cropped it in order to meet the stacking parameters. the tracking wasn't exact and I assume there was some drift over time and some of the image had to be eliminated or something (thats a guess, but I know there was drift)


also when I look at the bayer pattern in the fits header it says 

BAYERPAT= 'GBRG    '           / NOTE: Use RGGB on some software (eg PixInsight)


is that right? 


for some reason in the luminance graph on DSS the red and blue are exactly aligned with the green off to the right


actually I just tried 'clean remaining hot pixels' and that seemed to take care of the spiral pattern, so maybe thats it. I can get another set of darks I guess, just cool it to the right temp and retake. is it possible that new hot pixels formed after the last set of darks just a week or two ago?

Edited by jdono, 08 April 2021 - 09:25 AM.

#7 gcardona


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Posted 08 April 2021 - 09:26 AM

The spirals are a stacking artifact due to rotation between subs, possibly noise or hot pixels. Even though each sub was no (or very small) field rotation, the rotation adds up over time due to your alt-az mount. As to your loss of color, we need to know how you are processing.

#8 jdono



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Posted 08 April 2021 - 09:35 AM

I saved it in sharpcap to fits files, and I'm using DSS to stack them. for flats I'm using median and darks average. Using kappa sigma clipping for the lights. The setting for loading the fits is standard RGGB (which is what I've always used before). 


it looks like the R and B graphs in the adjustment graph (RGB/K) at the bottom are just a sharp spike (with a tight normal distribution around it) while the green graph has actual data


the fits header is 


SIMPLE  =                    T / C# FITS: 04/07/2021 22:16:35
    BITPIX  =                   16
    NAXIS   =                    2 / Dimensionality
    NAXIS1  =                 4144
    NAXIS2  =                 2822
    GAIN    =                  360 /
    DATE-OBS= '2021-04-08T02:16:21.5514004' / System Clock:Est. Frame Start
    SWCREATE= 'SharpCap'           / v3.2.6480.0, 32 bit
    BAYOFFY =                    1 /
    BAYOFFX =                    0 /
    BAYERPAT= 'GBRG    '           / NOTE: Use RGGB on some software (eg PixInsight)
    COLORTYP= 'GBRG    '           / NOTE: Use RGGB on some software (eg PixInsight)
    CCD-TEMP=                -14.8 /
    XBINNING=                    1 /
    BLKLEVEL=                   80 /
    YPIXSZ  =     4.63000011444092 /
    XPIXSZ  =     4.63000011444092 /
    EXPTIME =                   14 /
    BSCALE  =                    1 /
    BZERO   =                32768 /
    EXTEND  =                    T / Extensions are permitted
    YBINNING=                    1 /
    INSTRUME= 'ZWO ASI294MC Pro'   /

Edited by jdono, 08 April 2021 - 09:46 AM.

#9 jonnybravo0311



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Posted 08 April 2021 - 09:46 AM

Why such high gain/offset settings? Also, something definitely doesn't look right in the screenshot. Besides the cores being completely blown out, it's almost like the image is 8 bit. The smeared arcs have already been explained. I also find it strange that SharpCap would state the Bayer pattern of the 294MC is GBRG.


I'd definitely take a look at your settings in DSS.

#10 unimatrix0


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Posted 08 April 2021 - 09:48 AM

Just my 2 cents, SharpCap is not super good for DSOs,  I always get artifacts, it's just something to do with the calibration files aren't correct. Making darks and flats with it is more planetary oriented than DSOs.
It's a cool thing to live-stack semi-bright to bright objects (like Orion or star clusters etc)  and planetary photography it's excellent, but not something I want to use for faint deep sky objects.
  SharpCap 4.0 is coming soon, it's in beta, which will have sequencing and more deep sky photo oriented settings. 
I'd say you should try N.I.N.A, just do the same thing, copy your settings /gain/offset/exposure etc. and use that also for calibration subframes as well. 
Just an idea. 

Edited by unimatrix0, 08 April 2021 - 09:49 AM.

#11 jdono



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Posted 08 April 2021 - 10:12 AM

thx! I'm definitely going to lower the gain and offset next time. its just odd though because I've used these settings before for bodes and the output was definitely better. I guess the big advantage is that I can see whats going on before stacking with the higher gain and offset with a lower exposure time. again it worked once (I tested it with less total exposure time) and i assumed it would work again, my mistake. 

Ideally for me I would use some sort of livestacking which also saves the subframes so that I could see its going to according to plan and then process it better after the fact.


Which DSS settings would you like to know? Currently I'm using RGGB there but I've tried GBRG  and it doesn't work either. Creating colorless superpixels winds up with just a bizzarro result thats no good ( a green screen with white squiggly lines). The other settings are what I mentioned above but are pretty standard.


It does look off despite of that though. and yes I agree its very strange, I don't see a setting in sharpcap for me to change the bayer pattern of the camera either, I was looking for it. I definitely set it to RAW16 too


I'm definitely open for nina or other programs thx. I'm just getting started with this. 


it would be very tempting for me to use a very easy to use but less powerful one to start and then move up from there. 

Edited by jdono, 08 April 2021 - 10:49 AM.

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