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Hi All, I am having a lot of fun as a novice astro imager and am striving to learn more and improve all the time. After what felt like a ridiculously long period of cloudy nights, I finally got out last week and photographed M42. It is a beautiful, big and bright target. While it might be one of the easier deep sky objects to photograph, I am learning that it can be quite challenging to process really well. In an attempt to capture greater detail in the nebulosity, I seemed to have sacrificed detail in the core (which unfortunately appears quite blown out). Given my current skill level, I am very please with the result but know that it could be much better. Please see attached image. Does anyone have any suggestions for next time? I was wondering if in addition to the light frames I captured, if I should have targeted a second set of lights at a faster speed and/or lower ISO. In theory by selectively blending both stacked sets I could end up with the best of both integrated exposures. Does this make sense? Any and all guidance and feedback would be very much appreciated. Here is a list of the equipment and settings I used:
Thanks   |
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Hi, Not bad for a novice You pointed it right by saying "second set of lights at a faster speed and/or lower ISO", then integrate both sets separatly, and finally merge them together in PixInsight, using the HDRComposition process. It's what I did some time ago. The ZS61II is a marvelous little refreactor. With a proper polar alignement you could also consider acquiring a third set of data, with a greater acquisition time. Vincent |
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Vincent Bchm: Thanks Vincent. I am looking forward to getting back out there on the next clear night to try it again. |
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I don't know what processing software you are using, but I use Pixnsight now. Very diverse but it has a steep learning curve.....at least for me. It was suggest to me to take a seperate set of subs, say 30 to 60 minutes of 5 to 10 seconds each. Integrate them and then use to HDR composition tool in Pixnsight to combine these to your final image. Give it a go. Pat |
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Yeah, as mentioned above, separate session for Trapezium area is the best way to capture all detail. Since it's super bright it does not have to be long one. It can be blended together even with masks in Photoshop |
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Patrick Graham: Thanks Patrick. I am using AstroPixelProcessor for calibration, stacking and some stretching and then Photoshop for some final fine tuning. I will definitely try integrating some shorter subs next time. |
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Dominik Sito: Thanks for the feedback. I am looking forward to trying this next time. |
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Hi Bluespeck! Everybody here so far, has given you great advise. I'd like to add that if you are not quite up to speed in Pixinsight you can still manage well in APP and PS with a shorter exposure time and more subs, exposing for the core and stretching carefully or masking for the shadows and darks. I have an image, in fact my first one, like yours, taken with a DSLR and a StarAdventurer stacked in Deep Sky Stacker and processed entirely in Photoshop, but you will eventually find PI to be an incredibly useful if not essential tool. You are well on your way, like the rest of us you just need more clear skies! scott |
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Hi. yes, to corroborate what everyone else has said, I was actually just out taking some short exposures to resolve the individual Trapezium stars for an eventual Orion Nebula with a new camera. I took a set of 4sec frames and a set of 30second frames (then clouds arrived). Next clear night, I’ll take some longer duration frames and blend the three sets together. PI does have that HDR stacking feature, but I also use mostly APP and GIMP. If it isn’t obvious, you just want to stack all the frames in the different sets simultaneously in APP, but use the”Multi-session” option to assign each set to a different session number. Then in integration, there is an option to save separate integrations for each individual session. This way all the master integrations are Registered identically. Then like you, I do background calibrations, rough stretching, etc. Finally, in GIMP, I use a layer mask and the radial gradient tool to blend the layers together as smoothly as I can by hand. The core of the Andromeda galaxy has the same dynamic range issue and is a good one to try this fall. Your Orion image is terrific already! Far better than my first attempt (admittedly done with a 12 year of dslr). |
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Patrick Graham: You can probably restore some detail in the core by raising the HL slider in APP. Also, 3200 is too high for the D750. Above ISO400 or so, you don't gain anything in terms of read noise reduction while you lose dynamic range ie make it more difficult to capture faint stuff without burning the bright stuff. Cheers, Dimitris |
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| An HDR comp would certainly help. Echoing Dimitris, I’d recommend a much lower ISO too. I’ve been shooting my D7100 mostly in the 200/400 range — unless I’m going for a very dim target. (http://dslr-astrophotography.com/iso-values-nikon-cameras/) looks to be the same for the 750. Lower ISO will get you more dynamic range (fact) and less noise amplification (imho). |
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Hi Bluespeck! Everybody here so far, has given you great advise. I'd like to add that if you are not quite up to speed in Pixinsight you can still manage well in APP and PS with a shorter exposure time and more subs, exposing for the core and stretching carefully or masking for the shadows and darks. I have an image, in fact my first one, like yours, taken with a DSLR and a StarAdventurer stacked in Deep Sky Stacker and processed entirely in Photoshop, but you will eventually find PI to be an incredibly useful if not essential tool. You are well on your way, like the rest of us you just need more clear skies! Thank you for the guidance and words of encouragement. |
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Patrick Graham: Thanks Dimitris. Great advice. I will try dialing down the ISO a bit next time. |
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As you use Photoshop I can recommend to use the RegiStar program to align, scale, rotate the two 'final' M42 images, meaning the image you have taken/shown here & then do a second session for the trapezium area as it's very bright. For the 2. image, just lower subs exposure time/ ISO setting => check the histogram for optimal camera settings, not to blow out the trapezium area. The two aligned images can be blended, merged together with masks in Photoshop. Here is one example of that 'process', that I did lately on M42, https://astrob.in/q3rxds/0/ The RegiStar program can be found here, https://aurigaimaging.com/ Good luck :-) |
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@bluespeck before buying any new software  you may try Siril or DeepSkyStacker.Siril is open source and it is actively developed. DeepSkyStacker is now open source. Don't be intimidated by the above github link, you may visit http://deepskystacker.free.fr/english/index.html for a great introduction to image stacking. I am not a Siril user but I still encourage you to start with it. @Cyril Richard, one of its developers is also an Astrobin member too! Clear Skies! |
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Die Launische Diva: Thanks |
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Niels V. Christensen: Thanks for the suggestions. Love your M42 image... thanks for the link |
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Your mileage may vary here (and very dependent on gear/skies etc) but as a reference, I went waaaay overboard and took subs at 5s, 10s, 15s, 30s, 90s, 180s. See below for examples of a sub from each length (5 sec top left, 180s bottom right), just auto-stretched in Pixinsight Next time I would go as low as 1 sec (I think this was ISO400 on a D5300) and maybe 60-90 and then 180 or 240 (180 is my current max). Definitely not more than 2-3 different exposures Hopefully this might save you some time (please ignore my terrible focus - this is 6H of basically useless data even though I processed it anyway)  |
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| @Nick Ambrose you should examine your series of subs unstretched (auto-stretch will blow everything up) in order to see if and where they are saturated. If the Trapezium area is unsaturated, then you are good to go. In my case, 5s, even 15s (both at f/2 and ISO 800) are usable. |
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Die Launische Diva: Definitely will!, thanks. |
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A big thank you to everyone for the great suggestions and feedback. Unfortunately M42 is now out of the field of view from my backyard but I until it returns next winter I will practices some of these techniques with other deep sky objects that have similar high dynamic range. Again... thanks |
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Looks like I got in late to the conversation.... I'm very much a novice to astrophotography and have had the same problem. This Youtube video was very helpful and attached is my attempt to reduce the center brightness. I didn't take shorter photos or photos with a reduced ISO. For the center I used the same stacked photo but didn't stretch the colors as much. With that said, I should have taken longer subs to get more detail in the outer cloud and then the center would have been so blown out that I couldn't have been able to use the technique that I used. But I'm with you, I'm going to have to have to wait until winter before I'll be able to try again. I'm in Bortle's level 8-9 and the location of Orion now is in a very light polluted part of the sky for me. https://www.youtube.com/watch?v=uLVZanCDgDA&t=2008s  |
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Just to add a different perspective. And not to invite any flak from what I am about to say, such HDR methods can be very powerful, and like all the other tools at hand with any given software such as color saturation, hue, denoise, stretching, blackpoint clipping, whatever..., it can be overused or abused. With the "terrestrial" applications of HDR, which are generally limited by the automatic software settings, it is easier to understand visually because of reduced degree of the algorithms is usually adjusted to fall within a perception of reality and experience within a human's expectations. In other words, many people have actually seen snowcapped mountains and deep blues skies above, but our photos rarely show that. Well the HDR setting on a newer camera gets that..., and the image makes sense to a human brain. In astrophotos, if overapplied, to me it makes some of these HDR processed images look crushed in dynamic range. Understand that even our 16 bit, >100,000 e well depths cannot necessarily capture the full range that M42 presents. And there is a reason for that. Although, please see my recent attempt with my new camera at zero gain  Orion Nebula - First Light with new QHY268c, Celestron Motor Focus, N.I.N.A., multistar guiding with PHD2 as I was trying to figure out the best settings and exposures. In those conditions I still blew out some of the brighter stars (see the widefield "revision" ), yet was able to see a lot of detail in the trapezium "nursery" area. Yet I would struggle to get good presentation of the wonderful dark nebulosity that should be in the wider field that can be desirable for some (and me!). (The flairs in some of the brighter stars in the widefield image is from diffraction from tree branches!) In many bright nebulae, the source (or more importantly the direction) of illumination is clearly definable (M42, Iris, Cygnus Wall, etc.). Our brains naturally understand that illumination falls off as a function of distance. Its no different between a bright cluster buried in clouds and a lamp situated in a dark living room. That gradient defines a lot about the structure of the object. To remove that, by the over-application of HDR methods, thereby flattens the image. But I do concede that it can be done very well. So HDR is very much like some of those others things like color, etc. Yes you can do just about anything, but in the end it is your judgement, since this is art. I personally love the cloud structures and colors that naturally drop in illumination a they extend some distance from the trapezium. Whether I can count and separate the stars of the trapezium, well, there are stars enough in the image... But overuse of HDR often makes the clouds of M42 look more like a USGS contour map of some mountain range rather than a deep sky image. If you have a deep 16 bit image and deep well sensor (lower your gain/iso as stated above), you can do an awful lot with gradually masked stretching to get you more deeply into that bright region. And all with a single stacked image and a few rather simple steps. But that will likely not get you the trapezium if that is a must. Bottom line, this is art, so to each his own! |
