The Pleiades (M45) is a cluster of hot, young stars 444 light-years from Earth. The stars are passing through a cloud of gas and dust, lighting it up from the inside and making it glow blue.
The Pleiades has been on my hit-list for a while, and so with the arrival of winter I decided its time had come. Being a broadband target, I didn’t use my faithful Optolong L-eXtreme filter. In fact, this image was taken with no filter at all. See my article on light pollution filters for more on why I don’t use one. Instead, I rely on long integration times to brute force my way through light pollution and obtain a good signal-to-noise ratio.
I tried a different method of stretching the data in PixInsight for this image. Normally I’ll use EZ Soft Stretch or simply apply the STF function to HistogramTransformation, but I’d come across a Stargazers Lounge post about how some keen astroimagers have made a new process, called Generalised Hyperbolic Stretch (GHS). It’s quite complex to use, but there’s an instructional video on YouTube that helps.
Here’s my data stretched using three different methods:
The first two methods produced a fine result, but GHS did a better job of keeping the stars nice and tight, while bringing out more nebulosity. So, I kept the GHS version and went on to fully edit it. GHS has got a lot of potential, and I plan to use it for future images too; and maybe even re-edit some old data using it as well.
The rest of the processing was fairly straightforward. I did a little bit of DarkStructureEnhance and a few other tweaks in PixInsight. I tried to use StarNet to remove the stars, with a mind to process them separately to the nebulosity, but too many artifacts remained. Happily, the GHS stretch controlled the stars so effectively that I could actually use Topaz DeNoise AI on the whole image, including stars, and it worked nicely. (Normally Topaz DeNoise AI doesn’t handle stars well, so I just use it on starless versions, then add the stars back in later).
Then it was into Lightroom for some tweaks, and that was pretty much it.
* Dec 2021 – Jan 2022
* Bristol, UK (Bortle 8)
* Telescope: Askar FRA400 f/5.6 Quintuplet APO Astrograph
* Camera: ZWO ASI 2600MC-PRO
* Filter: none
* Mount: Orion Sirius EQ-G
* Guide: William Optics 32mm; ZWO ASI 120MM Mini
* Control: ASIAIR Plus, ZWO EAF
* Software: PixInsight, Lightroom, Topaz DeNoise AI
* 660 x 120 seconds
Total integration time: 22 hours
By Lee Pullen
Example source data
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A wall canvas worthy picture. One of my favorite targets and I absolutely love the color that you brought out on this target. One that I am anxiously excited for when my new rig comes in.
I’m curious of the cropping you used. Did you use dynamic crop, Pixinsight? Beautiful target and beautiful photo.
Thanks, I do actually have this one printed and framed on a wall! I always use DynamicCrop as the first stage of processing, but only to take a few pixels off each edge, in case there are any stacking artefacts. The next time I do any cropping is as the final stage of processing, before exporting the image.
Thanks for the insight on how to get the nebulosity from a polluted site, I did attempt this last winter from London but to no avail in capturing any nebulosity. But that was before I understood the frequencies of reflection nebulae are usually filtered out when using multiband or general pollution filters. I will attempt again this winter without any filters and as much exposure time as possible. I assume I should avoid this target on moonlit nights as well.
I am enjoying your site, some very helpful information here. Thank you for this and some great images.
Thanks Kurt! I actually image regardless of what the Moon’s doing. New Moon, Full Moon, it makes no difference to me. If the skies are clear, I’ll be collecting data. Good processing skills using software like PixInsight make all the difference! And for reference, most of the data used in this Pleiades photo was obtained with a bright Moon very nearby in the sky.
Just found your website Lee, great info here! I too image here from Bristol, near Henleaze so I guess Bortle 6.5 ish. I’m planning to image Pleiades next clear nights with my latest setup (125mm APO f5.9). Last time I used my skytech l-pro max lp filter, but dealing with the halos was a pita on this target, so will try without! I agree with integration time, I always try to get close to 10hrs min on targets. Cheers.
Oh wow, you’re only a 20-minute drive from me – we’re practically neighbours! Good luck with your image, I’d be interested to see the end result. I’m tempted to give it another go with my new telescope too…
On your ASI2600mc camera, did you use 0 gain or 100 gain as you didn’t use filters.
Some Cloudynights posts say to use 0 gain for broadband objects from a light polluted area, while others use 100 gain for every object.
FYI, I just received my ASI2600mc a few days ago and it’s been cloudy since. I’m probably going to try 0 gain on some galaxies and globular clusters from my Bortle 8 location just to see. Would you recommend 120 exposures as a start for Bortle 8 skies or would this oversaturate the stars?
I use gain 100 and 120-second exposures for everything. It’s worked well so far! I guess I may need to reduce the subframe length if imaging something with lots of very bright stars, like The Pleiades, using my Askar 130PHQ, because it just collects to much light.