What is IFN and How to Photograph it in Astrophotography?
Updated: Feb 15
IFN stands for Integrated Flux Nebula, and is mostly made up of space dust illuminated by all the stars in our galaxy. IFN is a term used in both scientific astronomy and astrophotography, but because it is so faint, it is mostly visible through astrophotography. IFN is often misunderstood and confused with ISM.
In this guide, we'll tell you what IFN is exactly, how to capture it in your images, and give you tips on where and how to photograph IFN.
Get our guide on processing space dust which includes full-resolution raw data.
What is IFN - Understanding Integrated Flux Nebula
Despite the inclusion of "nebula" in its name, IFN is not considered a nebulous object as there is no star formation activity going on, but rather just interstellar dust. IFN is also known as High Galactic Cirrus and is mostly composed of dust particles, carbon monoxide, hydrogen, and very minor traces of other elements.
Unlike the nebulae we all know and love (emission, reflection, etc), IFN is not illuminated by the stars near it but rather by the integrated flux of every star in our galaxy. This means that IFN clouds are very faint without any brighter regions, making them very difficult to photograph and almost impossible from a light-polluted location.
When photographed, IFN looks like faint, barely visible grayish clouds in the background. Special processing techniques can be used to enhance the brightness and details of the IFN, which we'll discuss later.
To better understand the mouthful name of Integrated Flux Nebula, here is a breakdown of each term:
Integrated: The combined amount of light coming from the stars in the Milky Way that altogether illuminates the dust
Flux: The total amount of light, known as Flux
Nebula: The nature of the diffuse structure itself.
The two images above show an interesting view of the Galactic Cirrus. The left image was produced using the space telescopes IRAS and COBE, and shows the shape of the dust seen from our point of view. The image on the right is a composite done by BQ Octantis using NASA and ESO images. It shows the dust and the Milky Way panorama once again from the point of view of our solar system.
The Difference Between IFN vs ISM
IFN and ISM look very similar so the two are often confused. IFN is usually what is labeled by amateur astrophotographers for most pictures containing space dust.
Let's make sure we all understand the difference between the two so that we do not share false information when uploading our images on social media. This is important in order to avoid a snowball effect of misinformation.
ISM is Interstellar Medium. It is space dust that is located within our Milky Way galaxy. ISM is illuminated by nearby stars.
A great example of ISM is the Taurus Molecular Cloud Complex. Although it looks like IFN, the dust is much closer and gets its light from specific stars.
Differences between IFN and ISM at a glance:
| IFN | ISM |
Nature | Space Dust | Space Dust |
Location | High Galactic Latitudes | Within the Milky Way |
Illuminated by | Glow of the Milky Way | Individual Stars in Milky Way |
Composition | Dust Particles, Carbon Monoxide, Hydrogen | Hydrogen, Helium, Carbon, Oxygen, Nitrogen |
Where can you find IFN in the Sky?
IFN can be found in several regions of our night sky, with the majority of it being located at high galactic latitudes, both to the north and the south celestial poles.
IFN has been found near several popular deep-sky objects, here are a few:
The Iris Nebula (might be ISM)
Polaris (The North Star)
Messier 74 (the Phantom Galaxy)
IFN is found only at high galactic latitudes, so only targets located far from the Milky Way plane will have IFN. The only exception would be if your object is in a very clear part of the Milky Way but IFN is present far away in the background.
As you can see on this screenshot taken from SkySafari, M15 (right) is located much farther and much more south of our Milky Way galaxy plane than the Hyades (left), yet both have a lot of dust! This is because the dust by the Hyades is... not true IFN!
The Hyades is the closest open cluster to Earth and lies in a busy region of the Milky Way, where there is no IFN. The dust visible is from the Taurus Molecular Cloud complex which is considered ISM. Messier 15 on the other hand, can be found very far south of the Milky Way plane, at a perfect place where true IFN can form. This tells us that the space dust in the M15 image is very likely to be real IFN.
Can you see IFN visually?
IFN is one of the faintest matter out there, and is often believed to only be visible with astrophotography.
Mel Bartels, who enjoys visual astronomy, built several small and fast telescopes in order to look for IFN from his dark sky location. Some of his favorite instruments include a 6-inch f/2.8 Richest Field Telescope and a 10.5-inch f/2.7 telescope.
He started a journey of finding as many IFN regions as possible visually in 2006, using M81 and M82 as the first place to look! Mel explains that even though he assumed that this challenge was going to be impossible, he was very surprised when he realized that he was indeed able to visually observe some of the IFN clouds around M81/M82.
Since then, Mel devoted himself to researching IFN all over the sky. He explains that the key to being able to visually see IFN is to use a very fast wide-field telescope with enhanced coatings capable of low power wide angle views at maximum exit pupil, very dark skies, and to emphasize large-scale low contrast objects during the observing process.
Mel also explains that his lower power eyepiece has a 100-degree apparent field of view, and that he uses averted vision as well as tapping the telescope in the hopes of finding the IFN more easily.
He almost never uses filters, and his main eyepiece is 6-7mm.
On the right, you can see Mel's sketch for the IFN clouds near M81 and M82. This is a very busy region that can be captured with astrophotography and look just insane!
This specific IFN section was observed with Mel's 10.5 inch telescope on May 9, 2017. It is called the "Volcano Integrated Flux Nebula".
Since he started, Mel Bartels has sketched 140+ IFN regions from his observations, including this incredible all-sky map of IFN clouds for the Spring!
How to Capture IFN
There are three major requirements to be able to capture IFN, ranked in my opinion from most to least important:
Integration Time
Location
Equipment
Integration Time:
If you want to photograph IFN, you'll need some patience. Integrated Flux Nebula is extremely faint, and you will need to spend many hours capturing data if you hope to reveal any trace of IFN. The best exposure time to use depends on the camera you own, but most cooled astronomy cameras these days have an optimal exposure time of 10 or 30 minutes.
The total integration time you should aim for is simple: as long as you possibly can. We suggest aiming for at least 20 hours of exposure time for most cases. This number can vary depending on the quality of your sky, which we cover next.
What Filters to Use for IFN?
IFN is extremely faint, and is made up of just two separate colors, Red and Blue. Steve Mandel spent time trying to capture IFN using different filters from a dark site, and the signal was only great through the red and blue filters.
Red: The red color coming from IFN is believed to be extended red emission
Blue: The blue color is believed to be blue luminance
Both colors come from different atoms and are the fluorescence of the dust.
Location:
Because of how faint IFN is, you will need to get away from the city and image far from light pollution. Bortle 1 and Bortle 2 skies are the best for this, with Bortle 3 and 4 skies being okay. Getting great IFN in your shot will be very difficult if you image from Bortle 5 or worse, and/or will require much more integration time than if you were to travel a bit farther to darker skies.
In the video below, I drive about an hour and a half away from Las Vegas to image the Iris Nebula, including the IFN around it. I purposefully drove North of the city so that the light pollution dome was to the south, as this target is located in the north sky.
Note: It is difficult to tell if the dust around the Iris Nebula is IFN, ISM, or both. Mel Bartels annotated his sketch of the Iris Nebula dust as IFN/ISM. This region of the sky contains both, but the boundaries for each are difficult to outline.
If you are planning on imaging a specific target soon from a dark location, make sure to know if it is south or north from your home. If your target is, let's say, to the south, you'll want to drive south so that the city lights are behind you to the north. It is very important that you point your telescope at the darkest part of the sky and not towards the city.
Equipment:
You can photograph IFN using almost any equipment, even with a stock DSLR camera and no telescope! The most important piece will be your lens/telescope as it requires to be fast.
If using a telescope, we suggest a reflector telescope (f/4), a RASA (f/2), or a fast refractor telescope (under f/5). For most of our IFN shots, we used our RASA 8 or our f/5 refractor. A fast telescope is crucial if you want to be able to see the IFN without spending weeks and weeks on the same target.
If you do not own a telescope, you can use a DSLR lens instead! We recommend a high-quality lens that is also fast. The very best lens for this task (and any other deep sky imaging work) in our opinion is the Rokinon 135mm f/2 lens. It is fast and has a great focal length for many deep-sky objects.
Check out our guide to the 25 best astrophotography targets with a 135mm lens.
Read our full review of the Rokinon 135mm lens.
Would you like to learn Milky Way photography with our premium online course?
Join our Milky Way astrophotography course!
It is divided into two sections, beginner, where you'll learn how to take your very first picture of the Milky Way, and advanced, where we teach you how to take Milky Way Arch panoramas, tracked Milky Way shots, stacking, and more.
How to Process IFN
Processing IFN is hard. Very hard. The key is to reveal as much IFN as possible without completely ruining the target you were originally shooting. This can happen because of the difference in brightness between deep sky objects and the IFN. Bringing up the details and brightness in the IFN without protecting your galaxy, cluster, or nebula will result in a completely overblown result.
The key to processing IFN in a clean manner is to:
Use masks to protect your main object(s)
Only work on the IFN details and brightness in the starless version of your data
Use the detail-enhancement and noise-reduction tools very conservatively
Always check how your main object looks like whenever applying a process to the IFN, just in case it got affected
What coloration should IFN be?
This is a tough question, as you may not know how much to push the red, green and blue colors for the IFN clouds during processing and end up with an unrealistic result.
IFN is believed to be either gray-blue if it is mostly illuminated by hot young stars, or gray-red if the integrated flux light coming from the Milky Way originates from cooler older stars.
To be sure to stay accurate, first raise the overall saturation slider and see if your IFN dust becomes more red or more blue, then work from there!
Want to learn how to process images with IFN or ISM? Download our premium raw data pack below which includes a full-resolution master file and a 4K walkthrough video on how to process it from start to finish! You will learn how to reveal as much ISM/IFN as possible within the image and end up with a clean, noise-free result.
Check out our PixInsight Tutorials page for more tips on Astro-photo processing.
Final Thoughts about IFN
IFN, or Integrated Flux Nebula, is interstellar space dust illuminated by all the stars from our Milky Way. It is usually found at high galactic latitudes far from the galaxy's core. IFN is much easier to see with astrophotography than it is visually, but capturing it is a challenging task that requires a dark location far from light pollution, long hours of integration time, and the right equipment. IFN is also very difficult to process and so is not a good target for beginners.
After many years of doing astrophotography, I now love to capture IFN and it always feels rewarding to be able to reveal as much as possible.
Please try not to confuse IFN and ISM when sharing your images online. Although the difference between the two is visually very minor, it is always better to keep things as scientifically accurate as possible!
Need help processing your data? Check out our processing services or download our processing workflow guide!
Be sure to check out our other PixInsight tutorials, and don't hesitate to let us know if you have questions below!
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