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I took this March 9, 2021 with my 12 inch SCT on a Paramount MyT using my ASI2600mc. Interesting comparison between this image and my last attempt (only a 10 minute exposure) with my 10 inch (right above) rotated and cropped/scaled to the same field of view. Looking at the FOVs shows you what a difference the placement of a focal reducer makes... Meade series 4000 f/6.3 on a 12 inch (left) and OPTEC Lepus 0.62X on a 10 inch(right). You would think the field of view on the 12 inch would be at best the same or smaller, but clearly I'm actually getting a larger field of view on the 12 inch! Aside from that, I learned a new trick in PI...to get rid of magenta stars, invert the image and use SCNR...works like a charm! |
I didn't realize the Owl Nebula could look so beautiful in narrow band (in this primarily Halpha and OIII). I'd been trying for years to get a decent picture of M97, but it always seemed so amorphous and lackluster in my limited attempts. Granted, my previous attempts were all limited in exposure time using my 10 inch and without a filter, but I had still held out more hope for it. Well, my effort finally paid off with this image, a 5 hour exposure with my 12 inch using my ASI2600mc and Optolong L-eNhance filter. It was done under a quarter moon in a Bortle 5+ sky but I'm thinking now it's definitely worth trying in a darker sky. I was even able to get a hint of M97's outer nebulosity - subtle - but definitely providing just enough signal to pull out its asymmetric shape. You'll have to turn up the brightness on your monitor to catch a glimpse of it though - it was extremely hard to do the enhancement to enable it to show up in the final image. What a beautiful planetary! I also like the colors the L-eNhance seems to pull out of my ASI2600mc. I don't get the blue I'd prefer from the OIII, but the green seems to come out more readily in place of it along with the occasional yellow, which is really great. My color calibration might be off a little, but I like it, so who's to tell me it's "wrong"? ***. |
This is one of a handful of known planetary nebulae to have a central Wolf-Rayet star, an extremely hot, Sun-like star that has had its hydrogen atmosphere completely shed to reveal only a bare carbon-oxygen core. The central star's surface temperature is a blistering 240,000 degrees Fahrenheit and it lies at distance of about 4,300 light-years in the constellation Gemini. Apparently, this type of star in a planetary nebula is quite rare, which suggests that we don't really yet understand how such stars evolve. I struggled with what to do about the color for this nebula. In broadband, the nebula comes out bluish, so I was tempted to shift the hue a little to get a blue tinge for the outer parts of the nebula. However the Ha and the OIII emphasis of the L-ENhance filter seems to want an reddish/orange and green tinge to it, so I left it at that, merely enhancing it somewhat. I was surprised at the nice detail I was able to pull out of it, especially comparing it to others' attempts out there with much larger scopes and longer exposures. The images on the right show a comparison of raw images for the nebula using various combinations of data from two different nights, one completely moonless, the other with a gibbous (93% full) moon in Leo about 10deg away. The bottom row compares the same length of exposure (37 @3min per sub ~ just under two hours) with the Moon (bottom right) and without the Moon (bottom left). Comparing stars, the focus is practically identical. I would have to say I must reserve judgement on whether the difference in detail is due to atmospheric conditions or Moonlight, or a bit of both. Comparing the bottom left with the top left, both taken without the Moon, is much more straightforward. There is a clear reduction in noise going from 111min (bottom left) to 171min (top left) and the detail improves noticeably. Comparing the top left (171min) with the top right (288min) which combines data from the two nights, the result is less clear. Is it the worse data from the moonlit night that limits the quality improvement? Or is it the diminishing returns going from 3h to 5h? It's likely a little of both, but I'm tending towards the latter. Although you get detail and noise improvement going from 2 to 3 hours, I've seen much longer exposures from people with results that are the same or worse. All this says though, is that there is likely a sweet spot in terms of exposure time for all objects, but going beyond that doesn't necessarily pay. |
All this rambling about how narrowband filters allow you to image in moonlight is a little bit of a red herring. The bottom line is that a narrowband filter will simply rebalance the wavelengths of light that land on your sensor. You basically *see* different things because Ha, Hbeta and OIII areas of the spectrum are enhanced at the cost of other parts of the spectrum, which happen to lie in the parts where moonlight and light pollution are most prevalent. Clearly, contrast in the image is enhanced when that light is omitted, but *THAT IS TRUE WHETHER YOU HAVE A FILTER OR NOT*. And, no matter what filter you use, you are omitting wavelengths of light that might or might not be "important" to visualize your object of interest. So ultimately, it's your object that matters and what you want to emphasize with respect to wavelength, not sky conditions! However, that said, if your sky is worthless because of light pollution or excessive moonlight (or both), you might as well get rid of as much of it as possible, and concentrate on the wavelengths that are interesting to see in your object - but make no mistake - the object will naturally look different, but it will NOT be a cleaner version of the unfiltered one. If you're (extremely) lucky, a broadband light pollution filter will eliminate light pollution and moonlight but leave in, say, galaxy light that still makes the galaxy look similar to its unfiltered appearance - if so, great, but it needn't always be the case. In all likelihood, the broadband filter will remove the same light that makes your galaxy look like the galaxy you expect to see! So remember: Filtered image = different image, NOT Filtered image = same-but-better-unfiltered image. Anyway, this may seem obvious to most of you out there, but my desire to do an apples to apples comparison (with filter/without) really opened my eyes to what this is all about. Imaging details are here for the unfiltered moonless-sky version of M1 and here for the L-eNhance version of M1 in a moonlit sky, both imaged in my Bortle 5+ sky. |
I also used StarNet for the first time to try processing a starless version of this nebula, then adding the stars back in. The result wasn't bad for a my first time...you can see my final image above on the bottom left, along with the starless foreground on the right, which I enhanced to showcase the nebulosity. This is actually a set of three dark nebula: B26, B27 and B28, from Edward E. Barnard's 1919 catalog of dark nebulae. The dark nebulae are all due to the extensive interstellar dust clouds in this region of the sky, which stand out nicely against the background star field. The beautiful blue and yellow reflection nebula is vdB 31, the 31st object in Sidney van den Bergh's 1966 catalog, surrounding the stars AB and SU Aurigae. The hot blue star AB Aurigae is around 470 light years away, which Hubble has shown to be surrounded by a disk of material in the middle of planet formation! |
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The sensitivity of the ASI2600mc camera is notable in this 5 hour exposure, revealing nice structure in the larger pair of galaxies but also bringing out multiple edge on galaxies in the field as well, in addition to several "fuzzies" around NGC672 itself. There's no way I could have gotten this much detail using my DSLR! I took this image Dec. 10, 2020 with my 12inch classic Meade SCT on an MyT Paramount. I acquired images using a cooled ASI2600mc stacking just over 100 3 min exposures. You can see I'm slowly improving my processing with Pixinsight! You can see another processing attempt here. |
For those of you interested in Pixinsight workflows...screen transfer function stretch, dynamic crop, DBE with carefully selected points, histogram transformation, color calibration, deconvolution, multiscale linear transform for noise reduction, local histogram equalization (250 pixel window size), curves transformation, and finally, a masked curves transformation to eliminate vignetted corners. |
NGC891 is a beautiful example of an edge-on galaxy, about 30 million light years away. Its many filaments and tendrils extending out of its plane are thought to be the result of the ejection of material due to supernovae and intense stellar formation activity. In the upper left part of the image, right under NGC891, you can also see a tiny image of a distant spiral galaxy in the background. For more imaging details, look here : |
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