NGC 7023 - The Iris Nebula | Astrophotography Tips & Pictures
Updated: May 17, 2023
If there were a place to call heaven in space, this would be it. This magnificent, blue reflection nebula has a bright young star in its center and gradually becomes darker as it is surrounded by clouds of interstellar dust.
NGC 7023 itself is bright, but it is surrounded by very faint dust. It is a gorgeous object located in the northern constellation of Cepheus. The Iris Nebula is a difficult target for beginner astrophotographers, and will test your processing skills to the max!
Object Designation: NGC 7023, Caldwell 4
Also known as: The Iris Nebula
Constellation: Cepheus
Object Type: Nebula
Distance: 1,300 light-years away
Magnitude: 6.8
Discovery: October 18, 1794 by William Herschel
We have imaged the Iris Nebula several times and will show you our attempts below. The three main tips we can give you if you plan on photographing the Iris Nebula are to escape light pollution as much as possible, take very long exposures, and practice processing faint interstellar dust.
Iris Nebula Wide-Field Astrophotography with the QHY600C Camera
August 2022, Bortle 2
In late August 2022, I decided to spend two full nights on the Iris Nebula from a dark site.
My main goal was to get as much IFN (Integrated Flux Nebula, or space dust) in the area around the Iris Nebula. I decided to shoot it using a small refractor telescope and a full-frame camera.
The combination of the two gave me a wide field of view and allowed me to include a lot of things around the object itself.
You can see the setup used on the left. The mount was obviously overkill for this lightweight rig, but this was a few days before finally receiving the ZWO AM5!
I made a video about capturing the Iris Nebula from a dark site. It was a great night but full of bugs attempting to kill me. It was also my first time using NINA for astrophotography!
I am overall pleased with the image. Bringing out so much of the IFN meant sacrificing some of the quality and multiplying the noise, but I really wanted to see as much dust as possible.
Our image of the Iris Nebula showing the amount of dust all around. Click for High-resolution.
GEAR USED:
Camera: QHY600C
Telescope: Radian 75
Mount: GM1000HPS
Guiding: ZWO ASI 290MM Mini
Accessories: Pegasus Astro Pocket Powerbox
Power: Jackery Lithium Battery
Processing: Pixinsight, with RC-Astro plugins
ACQUISITION DETAILS:
Total Exposure Time: 15 hours
Exposure Time per frame: 10 minutes
Filters: N/A
Gain: 26
Iris Nebula Astrophotography with a Reflector Telescope and Full-Frame Camera
April 2020, Bortle 2
First light with our first full-frame camera!
The Iris Nebula has always been one of our favorite deep sky objects, but we never were able to get a good-enough image of it to be proud.
The Iris Nebula region is pretty faint and cannot be imaged in narrowband, so you will need to escape light pollution in order to photograph it. On top of that, interstellar dust is very difficult to work with and requires special editing techniques. As you can see below, the image is full of such dust.
The fact that the central star is so bright and that the nebula itself has an enormous amount of details does not help either. If you feel like you have the dark skies and the processing skills needed for this wonderful nebula, go ahead and capture it, but be ready to spend several hours processing it.
Here is our image of the Iris Nebula, 4.5 hours in total taken from a Bortle 2 zone.
NGC 7023 using the QHY128C
GEAR USED:
Camera: QHY128C
Telescope: 8" Astrograph
Mount: Orion Atlas EQ-G
Guiding: ZWO ASI 290MM Mini
Processing: Pixinsight
ACQUISITION DETAILS:
Total Exposure Time: 4.5 hours
Exposure Time per frame: 5 minutes
Filters: None
Gain: 3200
How to find the Iris Nebula in the Sky?
The Iris nebula can be found 1,300 light-years away in the constellation Cepheus.
The best time to image the Iris Nebula is in the Summer, but it stays available in the sky all year long for many regions in the northern hemisphere. You will need to travel far from the city and evade light pollution if you wish to get the best possible view of NGC 7023.
If you are having trouble finding the constellation Cepheus, first locate the North star, Polaris. The constellation we need is the one just to the south of Polaris, not far from Cassiopeia.
To locate the nebula itself, look for the bright star Alderamin, and simply go north until reaching another bright star (Alfirk). NGC 7023 will be a little bit to the southeast.
The Iris Nebula is not visible to the naked eye, even from a dark site. Spotting the object with binoculars is a nearly impossible task. A 10”+ telescope will reveal some faint nebulosity, as well as its bright central star.
Iris Nebula Information
The Iris Nebula has the designation NGC 7023, but is also known as Caldwell 4. NGC 7023 technically refers to the cluster of stars visible inside the nebulous gases of the Iris. The designation for the full-size nebula is LBN 487.
Being a reflection nebula means that the gases are illuminated by the stars within. In this case, most of the light comes from the bright central star, SAO 19158 which has a magnitude of 7.4.
The Iris Nebula is made up of "petals", making the object look like a blue flower in space. It spans 6 light-years across, and is surrounded by dark interstellar dust also known as IFN (Integrated Flux Nebula).
The image above was taken by NASA using the Hubble Space Telescope. It shows a very small portion of the Iris Nebula (3.3 arcminutes) where you can see some beautiful gases interacting. The picture appears reddish because it is a composite of four exposures using blue, green, near-infrared and H-alpha filters.
This specific part of the nebula is lit up by a bright star just above the frame, HD 200775. This star is about ten times the mass of our Sun.
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Recommended Equipment for Astrophotography of the Iris Nebula
The Iris Nebula can be captured with and without a telescope. Although the object itself is very small, there is plenty of interesting features all around it, making this target great for both close-up and wide-field views.
If you are a beginner astrophotographer or on a budget and do not yet own a telescope, you can try capturing the Iris Nebula with just a camera, a lens, and a star tracker. Preferably. we would start with a fast 85mm or 135mm lens like the excellent Samyang 135mm f/2, and do 3 to 6 minutes exposures tracking the sky with an affordable star tracker. Capturing NGC 7023 untracked with just a tripod and a camera will force you to take very short exposures in order to avoid star trails, and that is simply not enough for this target.
Another key point if you plan on imaging this target, with or without a telescope, is to do so from a dark site. We suggest several nights under a Bortle 4 sky or better if you hope to also get faint dust around the object.
The equipment we used for our last attempt at this target can be seen above. We used a small-ish refractor telescope at f/5.4 with a full-frame cooled astronomy color camera. The accessories used were a guide scope and guide cam, an auto-focuser, a Pegasus Astro Pocket Powerbox and a USB hub for cable management. All this was mounted on top of a German equatorial mount.
Do I Need Filters to Photograph the Iris Nebula?
The Iris Nebula is a reflection nebula. Unlike emission nebulae, reflection nebulae simply reflect light from nearby bright stars. These are best shot in broadband, meaning in "RGB" light. So the best way to capture the Iris Nebula is simply either with a One-Shot-Color Camera (like a DSLR or a cooled OSC) or with a monochrome camera using LRGB filters.
You also do not need an astro-modified camera for the Iris Nebula. Astro-converted DSLR and Mirrorless cameras excel at capturing faint hydrogen alpha gas, which is non-existent in and around the Iris Nebula.
Processing the Iris Nebula
The Iris Nebula is, in our opinion, one of the most difficult "popular" targets to process.
As we mentioned earlier, there are tons and tons of interstellar dust clouds all around the nebula, and a very bright star in its center. One crucial step to pay attention to is the background extraction process. If using PixInsight, you will need to use Dynamic Background Extraction and go through each generated point to make sure none of them are on top of interstellar dust.
Because all this dust might not be very apparent in your Master Light file, here is a tip we would like to give you: Look for other great images of the Iris Nebula on Astrobin or other websites, and place it on a side window so that you can see where dust is supposed to be. This will help you ensure that none of the Dynamic Background Extraction points are affecting invisible dusty areas of the image.
Overall, I mostly followed our usual PixInsight workflow for this target. If you are interested in learning how I process all our images, you can access our "follow along" processing guide that contains walkthrough tutorial videos, written lessons, our custom pre-sets for your dashboard and even raw data HERE. It also includes a section on how to download and process data from the James Webb Space Telescope.
I did come across one tricky artifact while processing the Iris Nebula. Because I was using a One-Shot-Color camera, an artifact called a Microlens Diffraction artifact occurred on the very bright star visible near the object. I was able to remove it using an easy technique in PixInsight, and decided to make a video about it in case you encountered the same problem. You can watch the video below.
Iris Nebula FAQ
In which constellation is the Iris Nebula located?
You can find the Iris Nebula in the constellation Cepheus.
How big is the Iris Nebula?
NGC 7023's "blue petals" spans 6 light-years across.
How far is the Iris Nebula?
The Iris Nebula is located 1,300 light-years away from Earth.
How long should my exposure time be when photographing the Iris Nebula?
300 seconds (5 minutes) is a good starting point for telescopes with a focal ratio of f/5 and most cameras. If your guiding is excellent, we recommend doing 10-minute exposures (600 seconds).
Should I use a filter to image the Iris Nebula?
NGC 7023 is a broadband target, so you do not need any filter. It is best imaged with a color camera or a monochrome camera using LRGB filters.
What equipment do I need to photograph the Iris Nebula?
A tracker or equatorial mount is crucial. You can then use either a fast telescope or a fast camera lens to image NGC 7023.
What type of nebula is the Iris Nebula?
The Iris Nebula is a reflection nebula. It is visible by reflecting light from close-by bright stars.
Final Thoughts
The Iris Nebula is definitely a tricky target, and is not easy for beginner astrophotographers. The trickiest part is that you will need a dark site for the best possible results.
The processing is difficult and will test your patience and skills.
The object itself is bright, but bringing out the faint nebulosity all around is hard and can ruin your image if you aren't careful about the noise. Still, it doesn't matter what skill level you have, go ahead and capture the nebula! Over the years, you'll be able to look back and compare your results which always feels nice. You can see our attempts below.
All our attempts at photographing the Iris Nebula
Overall, we are pleased with our latest result and it is definitely an upgrade from our previous attempts!
Clear Skies,
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