Overview
The Rotten Fish Nebula is a type of object known as a dark nebula. The blackest areas, seemingly empty of stars, are dense clouds of gas and dust that are blocking the light from background stars. We can see some areas of wispy nebulosity that are reflecting the light from nearby stars. The Rotten Fish Nebula is also known as the Angler Fish Nebula, or by its official designation LDN 1251.
Background
This is an incredibly challenging target to tackle from city skies! It’s very faint, and is actually close to the Shark Nebula. Like the Shark, the Rotten Fish is a broadband target and so doesn’t benefit from narrowband filters like the Optolong L-Ultimate. So, very long integration times are needed to achieve a respectable signal-to-noise ratio — although this image is a bit of an experiment…
Optolong Optics have kindly sent me one of their brand new filters, the L-Quad Enhance. This is a broadband light pollution filter, so in theory ideal for targets like the Rotten Fish. Click here to read my review. For this target, I captured 10 hours of data with no filter; and 14 hours with the L-Quad Enhance. I’ll show a fair comparison in the eventual review, but for now this image is the result of integrating all 24 hours. To be honest it could do with longer, as it’s still fairly noisy, but hopefully that’s not too noticeable so long as you’re not pixel-peeping. I was also plagued by tech issues — specifically, my camera disconnecting — that knocked a few clear skies on the head.
Imaging details
| Date | 22 September to 15 October 2023 |
| Location | Bristol, UK (Bortle 8) |
| Telescope | Askar 130PHQ Flatfield Astrograph |
| Camera | ZWO ASI 2600MC-PRO |
| Mount | Sky-Watcher EQ6-R PRO |
| Guide | William Optics 50mm Guidescope with 1.25″ RotoLock; ZWO ASI 120MM Mini |
| Control | ASIAIR Plus |
| Software | PixInsight, Lightroom |
| Filters | – No filter 300 x 120 seconds (10 hours) – Optolong L-Quad Enhance 420 x 120 seconds (14 hours) |
| Total exposure time | 24 hours |
| Image credit | Lee Pullen |
Processing
I used GraXpert for the first time when processing this image. It’s a free piece of software that removes gradients from an image (like ABE or DBE in PixInsight). It’s not a PixInsight plugin, so needs to be run separately. I tried the beta, which features an AI algorithm that I found to be effective. If you want more info, I recommend this video by YouTuber Cuiv.
The weather forecast is awful coming up, but when there’s a gap in the clouds I’m going to image the galaxy M33. This is a new target for me, and another one that the L-Quad should be good for. Once that project is complete, I’ll write a review of the filter.
Source data
Seestar S50
Seestar S50 image to be added later…
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