
THE ROTTEN FISH NEBULA
LDN 1251 • Dark nebula • Cepheus • 1000 light-years from Earth
🔭
Askar 130PHQ
📷
ZWO 2600MC Pro
🌃
Bortle 8
⏱️
24 hours
🗓️
Sep & Oct 2023
Overview
The Rotten Fish Nebula is a dark nebula, a type of object defined by what it obscures rather than what it emits. The darkest regions in this image are dense clouds of gas and dust that block the light from background stars, creating areas that appear almost starless. Interwoven with these shadows are faint wisps of nebulosity that reflect light from nearby stars. The object is also known as the Angler Fish Nebula, and is catalogued as 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.

Close-ups
Kit list
This is the equipment I used to capture the image.
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Telescope: Askar 130PHQ
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Camera: ZWO ASI 2600MC Pro
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Mount: Sky-Watcher EQ6-R Pro
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Guidescope: William Optics 50mm with ROTO Lock
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Guidecam: ZWO ASI 120MM Mini
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Control: ASIAIR Plus
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Filter: Optolong L-Quad Enhance
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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.
Example source data
Here are example single subframes and freshly integrated stacks, just with simple stretches applied.


Seestar S50 image
Here’s an image of the Rotten Fish Nebula taken using a Seestar S50 telescope. It’s just about possible to make out the head of the fish. The easiest point of reference is the brightest star, easily visible in this Seestar photo, and the main image.

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