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Hello all, I wanted to address the issue of ARTIFACTS of imaging here, because I think it is important to consider this in Astrophotography. The description below, was derived from one of my posts, in which, by processing an image from the Hubble Archives, I found a really weird object. After researching this, I could not find any info, so I posted the image in case somebody had seen it. I also wrote to a collaborator of the principal investigator of the project that produced this image at John Hopkins, who graciously replied pointing me to an article describing this "object", a typical artifact found in one of the detectors of the Hubble Telescope camera WFC3 (link  https://www.stsci.edu/~INS/2010CalWorkshop/dulude.pdf). THE MYSTERY: I was looking at Hubble archive data to process, while I wait the collection of sufficient telescope imaging of my own to process. My interest here is primarily artistic, but I also have scientific curiosity. I was looking at data in the Eta Carina area, and I found a very interesting object imaged with a blue narrow band filter (f502n). My first idea is that this was just an imaging artifact, but note that this was not found in any of the control images, only in the blue filter and the aggregate image of all filters. It looks like an "infinity symbol" composed of concentric structures (see inset). I searched the internet and literature, and I found that Eta Carina and its accompanying nebula (see little summary below) does have "sort of" a 3D structure resembling an infinity symbol, but nothing like what I see in the image. Also, I don't know the exact identity of the stars in my image, as the PixInsight plate solving protocol in AstroBin does not seem to be able to solve any of my Hubble images (any help out there?). In any case, being a scientist I am still skeptical about whether this represents a real physical phenomenon or not, but I am trying to contact the investigators in this project to see if they have anything to say. Any comment or clue is welcome. MYSTERY RESOLVED! Thank you for those that responded. Like you and me, the suspicions that this is an artifact are correct! I wrote to a collaborator of the principal investigator of this project, and he introduced me to typical artifacts produced by the UVIS IR detector of camera WFC3 (see attached pdf of the article). In this case, this is what is called "ghost window". It is produced when a bright object reflects in the layer of filters. Interestingly, this varies with the filter, as different filters are produced with different methods by manufacturers. This totally explain the fact that I only saw this with one of the filters. LESSONS LEARNED: 1. It is OK to be curious if you find something unusual in an image; just don't accept it as fact. 2. Lack of evidence for something is "not evidence" or anything. I mean, that somebody else has not seen it before, does not mean that it is not "something". There is an explanation by our physical laws. 3. Research the source. In this case I feel grateful that an investigator at NASA took me seriously and helped me find the source of my observation. I hope the article is helpful Clear Skies, Vivian |
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Thank you for recounting your research on this topic. I applaud your diligence. I found it very useful. CS, Gary |
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That's what I call "the scientists mind set". Never let go before you understand what's going on. Thank you for your contribution Wolfgang |
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Gary Lopez: Thank you Gary, this is one of the things that I have had trouble once in a while to understand. I thought perhaps it would be a good idea to have a place, perhaps this forum, in which to develop a collection of artifacts with unclear explanation. I have found quite interesting ones myself, but it took a long time until I found somebody else that had seen the same as I and had some kind of explanation... what do you think? |
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I found the same artefact when I processed the Pillars of Creation from the Hubble archive (top left corner). M16 processing from Hubble Space Telescope Legacy Archive Since no one ever reported a weird infinity-shaped object I assumed it had to be an artefact. Obviously your approach is the correct one, don't assume and investigate :-)...thanks for sharing your story! |
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Another interesting artifact of imaging with my ASI 2600 camera and SKyWatcher 100mm refractor, using ZWO LRGB filters. As you can see, each filter has its own mostly non-overlapping pattern. It appeared when a bright objects was close to the target object (but I am not sure if this is the cause). This appeared specific to the ZWO filters, as no such artifact was observed either with Astrodon narrow-band filters or with Chroma LRGB or narrow band filters. I am not sure of why this happens, but I assume it is a prism-like effect, perhaps due to the edge of the filter (??). Very annoying. best, Vivian  |
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Michele Vonci: Exactly! If one assumes that it is an artifact because nobody has seen it before, then there would not be any discoveries and science would not progress. It is because scientists pay attention to something that has never been seen before, that great discoveries are made everyday. Of course, maybe 95% of the times that new thing will be an artifact, but for the 5% that is real, it is all worth it. Thank you for your comment. CS, Vivian |
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Thank you for this topic. Very interesting. All the explanations are very clear. And I love the conclusion. Nowadays we are facing a New trend. People creating artefacts using AI. Making some small gear images better than Hubble images. You take 4 hours data. Need a few (not that much) skills to pre process and tune curves. Then use (clic) Artificial intelligence. And get an APOD. I personnaly prefer Natural intelligence. And scientific aproach 😁 JF |
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I generally agree.... Nevertheless, perhaps some people here are not necessary looking at scientific aspects, but more at using the images as a form of art...I think both approaches are OK, as long as the people using these tools (Ai, etc) disclose their use. Then, one can decide to take the image more or less seriously. I too like the scientific approach, but I appreciate artistic aspects as well. However, I do not see both approaches with the same lens. One is trying to describe a reality, the other an idea about the reality. As long as we do not confuse one for the other, I think it is OK. At least that is my view. I respect other views as well. Thank you very much, Jeff, for your comment. It is important to talk about these issues. all the best and clear skies, Vivian |
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Vivian Budnik: I think discussing artifacts is an important part of photography, especially astrophotography. All of us posting here at AstroBin are dealing with artifacts with every image. We have hardware artifacts (e.g., image artifacts from secondary mirror vane, camera sensor, filter reflections, etc.), software artifacts (e.g., image artifacts from poor calibration, aggressive noise reduction processing, etc.), data collection (e.g., artifacts from dust in the optics, poor tracking, airplanes and satellites), environmentally-created (e.g., wind, rain, clouds, unstable atmosphere, the dog bumps the tripod, etc.), and more. In other words, artifacts are part of every astroimage we make. To your point, every once in a while, something unusual in an image is not an artifact, but a feature. |
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Vivian Budnik: You are right I think. This is the very important point. Happy Christmas and clear skies for 2022 JF 🦖 |
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| Thank you for your scientific approach. Persistence is the thing that makes us move forward |
