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I'm hoping that this thread will encourage people to break out of their comfort zone when it comes to light pollution whether that be from the moon or a man-made source. Today's modern CMOS cameras are truly remarkable tools and we can capture amazing details with very short exposures. It doesnt take much to get above the noise floor, and if you couple that with modern techniques for gradient removal, it's quite amazing what can be accomplished under less than ideal conditions. I see over and over and over where people say that they can't achieve a certain type of image due to their skies or that they are unwilling to image when there is any kind of moon out. Very recently someone was talking about how it's not even worth imaging with narrowband filters when the moon was over 50%! To me that is just nonsense. I live in the northeast USA and my weather is just terrible for astronomy. If I only imaged when conditions were ideal... I'd NEVER image. Because my weather is not very condusive to astronomy, I image when I get the opportunity. So I've made a bunch of images at and around the full moon, and while the moon certainly makes it more challenging, it's not impossible! Decent results are quite achievable! My light pollution is not that bad, I live on the edge of B3/B4. Vermont's largest city, Burlington is only a few miles to my East and within a 30 minute drive we have a population of about 250,000 people. So it's not like some of you city dwellers, but it's also not like I live at a dark site. I can't see the milky way from my yard during the new moon... well, maybe there is a little bit of a smudge, but it's not spectacular like the night skies I've seen up in the Maine North Woods. What inspired me to write this, is that I recently made an image of the Iris Nebula and surrounding field. I collected about 3 hours of color data and about 3 hours of luminance. Data was collected just after the new moon, and was very nice. I didnt quite get the colors I wanted so I waited for another clear night. That was two nights ago during an 82.5% moon. The moon rose before sunset and set at around 1:30 AM. I was able to capture 43 subs of 180 seconds each of Red, Green and Blue. My target went behind some trees at 4:00 AM, so most of this data was from when the moon was bright in the sky. Total integration time was 6.45 hours. I did not capture any Luminance Data. The sky looked like milk, or soup, or your favorite opaque liquid. Scope was the Epsilon 160ED. So yes, a fast scope, but remember that despite being f3.3, this scope has a central obstruction and has about 45% light fall off across my sensor. So it's fast, but not revolutionary. So mabye a couple of nights of data with an average telescope could achieve a similar result. So, here it is. 82.5% moon with broadband data. No other data, just what was captured under that big bright moon. Don't be afraid of the moon! With a modern camera and decent processing, it's amazing what is possible! I'll also add that I just did a quick and dirty processing on this. I could have hit it with more attention to the little details and gotten an even better result. High Resolution: https://astrob.in/ni3zof/0/ Low Res:  |
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I'm hoping that this thread will encourage people to break out of their comfort zone when it comes to light pollution whether that be from the moon or a man-made source. Hi Chris, I am not scared at all with the full moon and Narrowband data is easily collected and as long as I have clear skies I get out and image. Like you I don’t have great sky conditions, I’m bortle 4 and my seeing isn’t very good around here. I struggle to get 3” resolution so I rely heavily on image processing. Which I’m still trying to learn that btw! This said I do get choosy however for objects around the FM specifically faint galaxies and galaxy clusters. In fact I’m waiting now for the moon to subside here for my next project. I’ve found that nebula with NB filters work very well during the FM or there about. Planetaries work well as well. Here is a couple examples of mine at nearly 95% & 67% full. https://www.astrobin.com/k0zbvd/D/ https://www.astrobin.com/bkyont/F/ There is always something that can be shot and I just adjust myself for whatever the situation calls for. Dale |
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Dale Penkala: Exactly Dale! There is ALWAYS something that can be shot. Ordinarily under an 80% moon I'd be shooting narrowband and not dark nebula.... but I just really wanted to finish off a half-done target so I went for it. |
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I agree 100%. Full moon, clouds, wind, cold, in between rain storms, duo band, no filter, I will image anytime, any condition. as far as full moon... how about * 99.51% * https://www.astrobin.com/bxg6q1/?nc=&nce= OSC, no filter 63.8% https://www.astrobin.com/6tacko/ |
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Like you I have to use any clear night I can get hold of. You're blessed with your B3/B4 sky and a fast scope. My sky is B5/B6 and full moon pushes it into B7 based on my sky quality meter readings. Last full moon night in September I tried to image the bubble nebula in combination with the lobster claw which is a quite faint target - at least for my standards. The OIII data of the lobster claw suffered a lot from the full moon and in general I had to fight with a complex gradient in my images. In the end result the lobster claw turned out kind of ok for my beginner standards but far from great (Lobster Claw, Bubble and Messier 52 under a full moon ( kuechlew ) - AstroBin). So there is a price to pay. But yes, it's better than staying at home and getting no data at all. Be prepared to work harder to get something reasonable out of your data. Clear skies Wolfgang |
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Chris, thanks for the optimistic point of view. However, if I had Bortle 3-4 skies, I would think I do live in at a dark site. And, I certainly would do LRGB/RGB. However, my skies or Bortle 7 and approaching Bortle 8. I am one of those naysayers you speak of, in professing that one cannot do RGB well from light polluted skies. But when I say "Light Polluted", I am not referring to Bortle3-4 skies. My dark sky site, Cherry Springs State Park is Bortle 2, and on a clear night, which is few, the skies or excellent. I am aware of dark skies growing up in Texas and visiting New Mexico, Arizona, Hawaii and visiting Wyome/ Montana last summer. I too, live in the N.E. in eastern Pennsylvania with over 85% clouds any given nightly week. And poor seeing also. Confession: I'm an older imager teethed on CCD starting with the old Sony HX916 to the H9 (ICX285AL) and eventually the excellent Sony ICX694AL, ICX814AL & O.K. Kodak KAF12600. I have had the QHY268M (Sony IMX571) for less than a year. The QE is excellent and low noise. I have only done narrow band with it and very pleased. But, I have been entertaining the idea of doing short sub RGB and possibly light pollution filtered luminance. Your Iris image is very encouraging, and I have achieved less dark nebula results from a dark site. As you mentioned, I see a number of excellent image results from short subs. However, with an enormously large amount of sub files from the point of view of an old CCD imager. Also, as you mentioned, software development has increased the opportunities. I will give it a try on the Andromeda Galaxy. Thanks for sharing your Iris, Lynn K. |
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| So, it is 95.3% illumination now out there, just finished raining and I'm imaging IC63, the Ghost of Cassiopea. OSC, not narrowband. |
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| Chris, you gotta remember, that even with a full moon, your Bortle 3-4 skies only go up to Bortle 5 unless you have haze. And Bortle 3 really is as dark as it gets in Western Europe. I start out at Bortle 6, and the moonlight adds to the LP. While the noise only adds in quadrature, the moon makes the gradients much more complex, so getting rid of them becomes challenging. The problem is worse in widefield shots, the RC at 1600mm really doesn't suffer too badly. The SNR only goes down on a few days around the full moon or if there is reduced transparency. I regularly shoot broadband at 70% illumination and try to stay 90° away from the moon. |
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| Well, there's haze here so I'm up to > Bortle 8 now due to the moonlight. I can make out Jupiter, the moon, and what I believe are Vega and Deneb. Not a night for taking images. |
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Torben van Hees: I disagree. I have imaged from B1 skies and at FM is a total washout. Might as well do it from my own backyard, B6-B7, for the difference it makes. |
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Lynn K: Well, I'm certainly not saying it's easy, nor am I recommending that one shoot Broadband over Narrowband when the moon is big. I'm just hoping to show people that it's not a lost night just because the moon is out, or if there is other LP. A decent image can be had even under poor conditions and I think people often talk themselves out of even trying. We all know what we get when we don't give it a shot! |
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Torben van Hees: I'm not sure what the conversion is for the moon to Bortle, I'll have to take a look at that. The image I linked in the OP is a huge FOV, IMX455 at 530mm FL. I think best practices are in order. Shoot away from the moon, use NB filters if possible..... I just see a lot of people posting that it's not worth imaging something due to their skies or the moon or whatever... With my KAF8300, I couldnt do what I did above. I think that the new Sony BSI chips really give us a leg up when it comes to imaging under mediocre skies. |
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andrea tasselli:Torben van Hees: I think you misunderstood me somewhat, and believe we’re basically in agreement. I wasn‘t suggesting it is worth to travel to a dark site during full moon. But if you are there anyway, because you live there, your data might still be better than someone else‘s in LP only. Especially gradients will be far less complex. |
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| Chris, I never used a KAF-chip so can‘t comment. But it‘s interesting that you got acceptable RGB data because that‘s what‘s suffering most for me when the moon is bright. L is usually quite alright. |
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Chris, I think it makes a huge difference that you are using a 160 mm f/3.3 and your background LP level is B3/B4. I live in B6. With my 80mm f/6, it is very hard to get good results with broadband even when there is no Moon, but with my 200 mm f/4, very much easier. You just build SNR so much more quickly with a fast scope that it is a lot easier to overcome LP or moonlight. Narrowband is very different. |
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Torben van Hees: I think it's all about gradient removal. It does take more effort to coax a nice image out of lower quality data. I compared the RGB data from the big moon to the new moon and it wasnt even comparable. It did however still contain useful signal and when I combined the "moon" rgb with the "new moon" rgb it gave me a lot more to work with. Here is the image using all the data:  |
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Arun H: Well, keep in mind that the e160 is not imaging at f3.3 to the corners, Thats just on axis. With 45% light fall-off its more like f6 at the corners of IMX455. The aperture helps no doubt about it. So you might need two nights with your scope to achieve a similar result. As long as you get out there an image when its clear whether thats broadband or narrowband it doesnt really matter. Again, I'm just advocating that people dont just give up because they have it in their heads that you cant image with the moon or because someone told them it wasnt worth it. |
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A few things: I know you focus mostly on moonlight but you did mention light pollution and I will say that in the city it makes things very difficult for broadband targets. You are super blessed to live on the border of B4 because for a lot of us B4 is a dark site. I agree that the affect of the moon can be overblown out there but not LP. I don't even find it worth doing broadband anymore unless I find myself at B4 minimum. There is no joy in processing a soupy, noisy broadband mess from the inner city. Here is what I think about the moon: For us city slickers:
Low bortle skies:
Lastly, fast focal ratios really help with the SNR. When you do the math and compare, it is a huge difference in terms of hours needed. For example I just spent 6 hours on the Veil at F/2 and that would of taken me 36 hours if I still had the Redcat51 at F/4.9. That's without accounting for the 135mm's increase in aperture at F/2 over the Redccat51. People should not fear the moon but they should respect it and the effects it can have. Altitude and position count for something. It's one thing to image the Iris Nebula which is opposite of the moon, than say trying to image something closer in the sky to it. Also if the moon is at a lower altitude it opens up more possibilities because it is not beating down on the entire night sky. |
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If someone wants to share a reasonable integration of broadband data from heavy light pollution I'd love to take a shot at the data. Say something in the 6 to 12 hour range. Don't care about the scope.. just the unprocessed integrations. Please PM me if you want to share. |
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Ideally you do the Oiii during a new moon or below 40% because Oiii really hates anything that impedes sky conditions. Sii is not as bad but because the signal usually sucks you want to make the most out of when you use that filter. This is one of the reasons I made this post. I image Oiii during full moon all the time. I have a half dozen narrowband images here on Abin with Oiii captured at the full moon or within a day or two. Here are some. https://astrob.in/heinco/0/ https://www.astrobin.com/ve3lv4/ https://www.astrobin.com/422376/B/ https://www.astrobin.com/q3fsh4/ https://www.astrobin.com/v7htuo/C/ |
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A few things: Couldn't say better, great explanation. |
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Great picture Chris btw, You are surely correct about the moon and narrowband. O3 seems the main problem and even with only a 6nm rather than a 3 nm filter it is not that problematic if the object of interest is well away from the moon since DBE in PixInsight can usually sort out the gradients. However for broad band galaxy images my usual Bortle ~ 6.5 cannot compete with what I get from (what is for me) a relatively dark B4 site. Working the total exposure numbers it doesn't seem practical to expose for long enough at B6.5 to get the SNR down to a level that shows up outer galaxy details visible at B4. The tactic that I have adopted is to use my B6.5 -sometimes very short - exposures at low F to concentrate more on getting good galaxy detail at the galaxy core and then go for a high dynamic range composition to incorporate more of the outer detail using the B4 exposures from occasional visits to a dark site. It is all relative of course - but I have sort of adapted the hobby to local conditions and made it more about resolving detail in bright areas than about detecting overall shape and extent. If of any interest to anyone this attached is an example of mixing up B4 and B6.5 into a single composition...rather wish that I could have found a B2 site though to extend it further.. https://www.astrobin.com/mjngy3/C/ Tim |
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| The trick with high Bortle skies (>= 6) and broadband imaging is to stack zillions of exposures. For a relatively bright galaxy I wouldn't countenance much less than 10 hrs and for dimmer ones way above that, think tens and tens of hours. |
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Lastly, fast focal ratios really help with the SNR. When you do the math and compare, it is a huge difference in terms of hours needed. For example I just spent 6 hours on the Veil at F/2 and that would of taken me 36 hours if I still had the Redcat51 at F/4.9. That's without accounting for the 135mm's increase in aperture at F/2 over the Redccat51. Hi SemiPro, One thing to bear in mind is that aperture is used to calculate F-ratio and therefore your calculation on relative advantage of an F/2 system over F/4.9 already accounts for the difference in aperture. Essentially faster system means that for the same focal length there is more aperture and therefore more light hits any given pixel (the relationship is quadratic, while the relationship between SNR and F-ratio is linear assuming the same exposure time) I agree with your point, one can get a better SNR with a fast system much quicker. However, that is relative to a slower system. Relative to a a darker sky location, the disadvantage remains. A faster system gathers signal quicker but it also gathers unwanted light pollution signal quicker as well. As such, compared to a dark sky location, both fast and slow systems' SNR suffer to the same extent. Even if gradients can be removed reasonably well, the light pollution noise remains. So to get the same SNR as can be achieved from a dark sky location integration time should be increased by the same multiple. Often the integration time required to get good SNR is too long for light polluted locations especially in case of broadband, therefore the viable solution is to use a faster system. Light pollution will still be detrimental but it will allow for a faster build-up of SNR. To put those thoughts into perspective let's assume that one shoots 10h of data from a dark sky location with a F/5 system and gets SNR of 4. With an F/2 system the SNR with the same exposure time would be 4*5/2 = 10. Let's assume that light pollution results in a reduction of SNR from 4 to 2 for an F/5 system used from a light polluted location. Then to get the same SNR of 4 one option is to increase integration time to 40h. Or one can use a fast F/2 system which will result in a SNR of 10/2 = 5 for a 10h exposure (or SNR of 4 for 6.4h exposure time). The original post was about the effect of the Moon, but the calculations apply. One needs to shoot more data to overcome light pollution/Moon effects. Sometimes, too much data is necessary to get good SNR and using a fast system is a good option to overcome the problem. In addition the calculations assume, that it's possible to fully remove gradients which is not 100% possible in practice especially in case of strong/complex gradients. Evgenii |
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Ideally you do the Oiii during a new moon or below 40% because Oiii really hates anything that impedes sky conditions. Sii is not as bad but because the signal usually sucks you want to make the most out of when you use that filter. I'm not saying don't image Oiii but what I am saying is if the weather allows for it try and plan to do it when the sky conditions are not as damaging as a matter of good practice.  Full Moon Crescent - Redux Like the Oiii here was during a full moon (although it didn't really get high up there in July) but I would of greatly preferred to have taken the Oiii under better conditions. My main point is to take what your sky gives you but that doesn't mean to throw all caution to the wind. Lastly, fast focal ratios really help with the SNR. When you do the math and compare, it is a huge difference in terms of hours needed. For example I just spent 6 hours on the Veil at F/2 and that would of taken me 36 hours if I still had the Redcat51 at F/4.9. That's without accounting for the 135mm's increase in aperture at F/2 over the Redccat51. Yeah that is true, I was keeping my comparison simplistic. A fast focal ratio is not a replacement for dark skies like you say (but dang if it ain't nice to have!). |
