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Lee Mize:Gary JONES: Hi Lee, Many thanks for your kind compliment - I do hope that info was helpful  Gary (South) |
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Hi Alan, Many thanks for your reply - and of course you are right, stretching for faint detail does not always saturate stars, but often does, particularly for brighter stars, and its the brighter stars that APs usually struggle with. It all depends on the subject - as anyone who has photographed the Flame Nebula would know. I guess my main point was that it's helpful to understand what causes stars to appear fuzzy or bloated, so that one can manage their appearance during capture, rather than depending on post-processing. In terms of smaller stars, yes, I agree that sometimes it's better to let them go. In fact, zillions of small stars can be just as distracting as a few dominant bright stars. But IMHO small stars add to the depth and beauty of the image, and give context to the main subject. In some of my early images, I over-processed the stars to the extent that faint stars disappeared completely, but in revisiting the same data years later, found that 'bringing back' the small stars yielded an image with much more depth and beauty. It all gets back to your subject and artistic intent - it's the balance that counts. Gary (South) |
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Completely agree on all points including my reprossessing ventures lately. With the exception of my Flying Dragon, where I wouldn't have gotten image at all. But I intend to revisit that to bring back some of the stars. BXT. Sharpening should actually assist in that. No doubt, those bright stars are difficult for us all. But in his video for his star reduction method, I found it interesting that his goal was to not address those big stars. But the middling ones. Granted he really only showed very subtle reductions, no doubt to not squash star dynamic range over the whole frame. My personal take on all this (which I don't think I actually stated in my posts). Is that for me it depends on the images. My mosaic of the elephant trunk  IC... (IC 1396, Full Emission Nebula and Surroundings in OSC. Mouseover of unidentified nebular features. 6 Panel Composition) I actually posted several renditions, one with all stars as possible left in, with a simple stretch. Most feedback preferred the more highly stretched and star reduced image. So much for the AstroBin audience being the judge. But heck, I can't decide. So with new tools, I revised to bring back more stars (but sharper ones) and stronger stretch! But for me, my goal overall with that image was to highlight the nebulosity around the brighter, typically shown in almost every image. So stars never were The goal with the image. The new tools can deliver both now! |
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Alan Brunelle: Hi Alan, That is a very interesting series of images ! With 12 revisions, this illustrates perfectly the challenge of getting the right balance between too many stars, and too few - particularly for a difficult target such as IC 1396 Most importantly, your images attracted a lot of comments, which is one of the best confirmations that an image is interesting Gary (South) |
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Carastro: I think to reduce the stars can actually make the image a little more realistic (hear me out lol). When you take long exposures, especially with broadband, the stars can bloat rather significantly, or at least thats common in my imaging from home. Poor seeing doesnt help either... There is definitely a limit as to how much star reduc is "realistic". Too much generalized reduction to the entire image can degrade the star shapes or even make the smaller stars nearly disappear. Adam Block has a good video on selective star reduction to "de-emphasize" the stars carefully. But sometimes you have to bring the star bloating under control or else you can barely see the nebulosity Its part of the artistic side of astrophotography, some like it a lot or get rid of the stars completely, while others think any reduction is destroying the image. I think most photographers are in the middle of this spectrum. Also, where do you draw the line as to what is an "astronomy image". Seems subjective. Then again so is what makes a good astronomy image I understand your point Carastro, but done worry, the stars arent being deleted from my images #starlivesmatter |
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23:59 complains about small stars 00:00 gallery full of images with tiny stars It is interesting the fact that you "attack" other people's images then if anybody gives you your own poison this is being agressive. How so? In general one should be happy with his/her own images and that is it. My images are very "raw" and almost crappy but I'm happy with them. It is similar to what I see when the subs keep coming during my image session. I don't do it to make other people happy. Astrobin gives me space to host my images in an organized template with the data and I like to take a look at them every once in a while and follow my progress long term. Perhaps you should stop thinking about an arbitrary "limit" to star size. If anybody posts starless images let them be happy with their images. Are you not happy with yours? They seem very nice and I like the small stars. Using 3nm NB filters? Excelent! I'm not bothered by the fact that you reduce them considerably. |
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Oh wow, so many replies to this topic - yes, it is a very good an valid question and therefore here my point of view: Starreduction is useful and necessary if the stars are bloated for whatever reason and your equipment does not allow you - or your current skills - to get to smaller stars during taking subs. Star size depends not only on the resolving power of your complete optics, but also on the gain, on offset, on the pixel size of your camera, on the wavelengths used for imaging, on the exposure times, on the seeing quality... I think that are most of the common influencers regarding star size. I think that in an astrophotography image, the stars should be present but not dominating - with other words, I would like to see the stars be present but not the primary factor in the image (Star clusters of course are different matter). I do reduce the star size most of the times if I apply a rather long focal length which results in a higher aperture number like 11 or 16 (in terms of photography). But if your reduce them too much, you get artefacts surrounding the reduced stars and they do not look good at all. So, to summarize - no stars is a no-go with some exceptions, too small stars is not my way either - stars well balanced with the main theme of the image, that would be my goal CS, Georg |
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Rafael Amarins: I totally missed the part where the OP was attacking other people's images. All I read was the OP voicing their opinion on a style and asking for feedbacks in a civil way. You seem to take a view that everybody should be able to enjoy their experience on Astrobin -- perhaps you may start with not calling other people's opinion "poison". Just my two cents. |
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Alan Brunelle:James Peirce: I’ve steered clear of this thread as far as it relates to the subjective quality of how an image “should” look with respect to the size of the stars. However, I’d like to provide a more technical view about the optical issues and the historical goals of image processing in general. Alan’s explanation above is quite good but I want add a few additional comments. A ground-based imaging system includes three major components. The first is the telescope, which Alan explained quite well. The second component is the sensor and the third component is the atmosphere. The atmosphere adds wavefront errors to the optical system that varies with time. When we take “long” exposure images, the sensor integrates instantaneous images of the aberrated stars. During the late 60’s, astrophysicist Anthony Moffat developed a modification to the Lorentzian function that provided a very good fit to the shape of the integrated stellar profiles in film images. Even though film isn’t a very linear sensor (only over a fairly narrow range of exposure), the Moffat function still provides a very accurate fit for stellar profiles with modern digital sensors. Of course the Moffat function only fits well for stars that are not over-exposed. The Moffat function has different orders, which must be well selected to get a good fit, but no matter what order you use, the wings of the Moffat function are much brighter and more broad that what you might expect from a lightly time-dithered Airy function. Intuitively, that makes sense since atmospheric wavefront distortion tends to redistribute energy out of the central lobe into the outer regions of the Airy pattern. So, right from the start, it’s important to realize that it’s the Moffat function and not the Airy function that determines what stars will look like in any image with an exposure of more than a few seconds (~2s-10s). When we stretch an image, the goal is to boost the really low-level signals that we are interested in, but the undesirable side effect is that the stretch also emphasizes the wings of the Moffat function. Unless the telescope optics have problems, stretching the wings of the Moffat function is generally what causes “star-bloat” in stars that are not over exposed. Over exposed stars have even larger wings but they will also show a distinct circular white core that cannot be color corrected. (A few years ago I worked out a way to fit the wings on over-exposed stars to repair over-exposed stars but it would require a special tool in PI that I don’t have the skills to implement.) Physical optics is the field that covers the physics of how an image is formed using the wave properties of light. In an incoherent optical system (which we deal with), the irradiance distribution in the image is given by the convolution of the point spread function with the intensity distribution of object. This relationship is what limits the response of the optical system and the goal of image processing has historically been to overcome this limitation. The ideal deconvolution algorithm goal was to be able to perfectly reconstruct the form of the object from the measured image. NASA, during early moon shots, and the military funded a lot of the early efforts to computationally solve this problem. The “perfect” deconvolution algorithm would produce pinpoint star images with signal strength being being the only measure of star brightness. Of course the perfect algorithm doesn’t exist; however in my opinion, BXT is a huge advance for astronomical imaging. In my view, there isn’t a limit on how small the stars “should” be in an image. It’s ultimately a question of limiting artifacts and a judgement call in how to best represent the presentation of “scientific data”—and that boils down to what amounts to an “artistic” choice. In my opinion, that means that there isn’t a right or a wrong answer about how to best present stars in an image. John |
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Rafael Amarins: Rafael, Like Yuxuan, I have read this thread and tried to contribute to it in a positive way. I'm not sure who you are directing your post to, but the community here on Astrobin thrives on mutual respect and support, so comments attacking other people's views in a negative way are not helpful. I'm glad that you're happy with your own images - and the freedom to express your views here in this forum. You seem to agree that everybody should be able to enjoy their own images and present them in their own way, whether they are beginners or experts, or whether the images are good or bad. So perhaps you can respect the different views expressed here when it comes to stars, and avoid using disrespectful terms such as "poison". |
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And by the way Raphael, I think you do yourself a dis-service describing your images the way you do - I particularly like your images of the Carina Nebula and the Dolphin Nebula - stars included |
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There have been some very good responses on this thread, and I have learned one or two things, but I find it very disturbing that I can ask a civilised question inviting feedback and find myself being attacked in a most uncivilised way - twice now!!! No I am not a fan of vastly reduced stars to the point of having to even search for the stars, or starless images and I was just wondering what other people felt about it. I do mainly do narrowband because I live in Bortle 8. I did say I would ask to shut this thread down if there was any more of this behaviour but I think many of you may be disappointed with this action. I am therefore going to withdraw from this thread. I would like to thank those who have contributed their vast knowledge and understanding, and also slapped down those who want to turn this into something nasty. Quite frankly I am shocked that such people take part in this hobby, I have always found Astrophotographers to be the most generous and helpful individuals. Carole |
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Carastro: I am seeing this happen increasingly on Astrobin. On three occasions in the last week. The relative anonymity of an online forum brings out the worst in people and you say things to others you’d never say to their face. Why should astrophotographers be exempt from a broad human condition? It used to be a close knit community where people knew each other even if they didn’t comment or like others images. But it is a much larger community now and with that, all the associated problems. CN forums have been moderated for a while with topic restrictions. I suppose it is a matter of time before that happens here as well. |
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Arun H:=14px CN forums have been moderated for a while with topic restrictions. I suppose it is a matter of time before that happens here as well. Not to get too deep in the weeds on a tangent, but I stopped visiting CN altogether over a year ago because of pervasive not-it-all-ism and frequently unnecessary aggressive tone. There is a much more helpful and community oriented vibe here. At least that's my experience. Other's results may vary. |
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Carastro: Hi Carole, I'm very sad that you've decided to leave this thread - your question has been the motivation for a very valuable discussion, and I thank you again for asking it. I suggest that the best way to feed bad behaviour is to give in to it. Leaving the discussion is no guarantee that bad behaviour won't resurface, and if it doesn't resurface here, it is very likely to pop up somewhere else. Salvatore (the founder of Astrobin) is very approachable - reporting bad behaviour might be a better way to prevent it from resurfacing at all, and to help maintain the friendly and cooperative discussions for which Astrobin has become so well known. So, I invite you please - 'come back' |
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This is an very interesting topic and there are two points of view ... from a "scientific" perspective anytime that you "alter" an image you lose any scientific purpose of that image. However, from an "artistic" perspective ..."beauty is in the eye of the beholder" and the majority of the people posting "post-processed" images are nothing more than just that..."pretty pictures". Therefore, my take on this...it's a shame that this thread has ended in this manner. |
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| James Webb as well as the previous Hubble images are highly processed, sometimes almost starless, they spike stars, I guess I don't really know who the experts are in Astrophotography but whoever at NASA processes these, they don't follow a lot of rules..... |
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Gary JONES:Carastro: Gary, there are a few topics that grow quite long, and while not the longest, this one has had a pretty good run. No Need to fret! After a certain length, it becomes burdensome to read long threads and to understand everything from the start. Repetition, understandably creeps into the mix because of the aforementioned issues. So it can become tiring for the creator and for early responders to continue following. I usually check unfollow when it's served any purpose for me. No one should feel obliged to stay with a topic, even the originator. And to the point that a few bad apples get into the mix, becomes essentially an example of a statistical analysis and not surprising at all! However, even if the originator of the thread and early responders leave, the topic can still have value with new blood arriving. But I expect that the combination of a relatively small pool of APers, coupled with this topic, which many likely want to avoid, means this one may be coming to a close. In fact, more information to the original question might have been achieved had there been a poll associated with this. |
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Dan Kearl: Hi Dan, Actually, HST and JWST images appear almost starless because :- 1. they have large apertures, so the Airy Disk of the stars is really small. They are not starless, it's just that the stars are well represented as point sources. 2. there is no atmospheric seeing to fuzz the stars and make them appear larger. Hence the super-crisp, tiny stars. In terms of spikes, that is an unfortunate side-effect of using support vanes for the secondary mirror. You cannot escape the physics unfortunately - it's caused by diffraction around the support vanes and the edges of the mirrors. Interestingly, you'll notice that the Hubble Space Telescope has 4 spikes - like this. In contrast, the JWST has eight - like this. Six small spikes (the horizontal two + 4 at 150°) are produced by the 3 support vanes, and 6 large spikes at 60° are caused by the edges of the hexagonal mirrors. 4 of those 6 line up with 4 of the first 6, giving the appearance of 6 large spikes and 2 small ones. I'm confident that NASA had a building full of people designing these telescopes, and that all the rules (of physics anyway) were well followed |
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Having been reprocessing a lot of images i feel that a subtle approach to stars but i feel that it does vary on all images , always needs stars though. Rog. |
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| Without an atmosphere, real stars would be very, very small. Reducing stars is not contrary to science. But I think that the real reason that in recent years/months the photographs we see show few stars, is that we have better reduction tools. Excessive enthusiasm in its use is inevitable. It's not the norm, it's the fascination and the fashion. I think that with time the reduction tools will be better used. With the improvements of the software we have more and more freedom and efficiency in the processing, and this makes necessary a greater rigor and respect for the original shots. |
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Without an atmosphere, real stars would be very, very small. Photographically perhaps, but not visually, since the diffraction limit of our eye is about 20 arc seconds or more. |
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I like to keep a fully starry image as an alternative to the final product. But I think they detract a bit from the nebula. What I like is the sheer number of faint stars that I see. It blows me away . I can’t believe the night sky is dark when I look at my photos! There’s just billions of faint stars out there. Very few of them show up on any star app either. So what’s their limiting magnitude? Am I picking up mag 30 stars? After only a 3 minute sub? 2 hours total? Can’t be that faint. Here’s a zoom in of my osette, before any star reduction. E57DD1D2-81C9-48B2-8763-9A4366171E5E.jpeg |
