Stretching and HDR Processing

Although my previous post using M42, the Orion Nebula, was to demonstrate image stacking in astrophotography, the image based on the 80x8sec stack is quite good and so I decided to redo some of the post processing and make a few additional improvements.

First, the nebula suffers from the large dynamic range in brightness between the inner core and the subtle outer regions, i.e., the core tends to get 'blown out'. This is true of a number of objects that have bright interior regions, such as galaxy cores, and in this case, bright nebulae. M42 has the famous Trapezium Cluster, a young open star cluster with four equally bright stars in a tight orientation, located in the center of the nebula. But because the nebula itself is so bright the cluster is hard to make out.

Second, I did not properly account for the background when applying the Multiscale Adaptive Stretch (MAS) and so some of the fainter outer regions of the gases did not appear as I would like. 

But before showing the result of these improvements I need to explain the concept of stretching.

Stretching  

Both stacking and stretching are always necessary in astrophotography post processing. Whereas stacking helps increase the SNR of the image and gain the benefit of a long integration time without having to take extremely long exposures, stretching is necessary to make the image visible.

In astrophotography, stretching an image means remapping the brightness values in the photo so that very faint details become visible, without blowing out the bright parts. It’s a core processing step for deep‑sky images.

When you capture the night sky (especially galaxies, nebulae, or dust clouds), the camera records light in a linear way. If you have twice the light hitting the sensor, the pixel value where the light is recorded is twice as high. However, most of the signal from faint objects is packed very close to black. Only stars and bright cores of nebulae and galaxies stand out in the image. In fact, if you looked at the raw or stacked image, it usually appears almost totally black, maybe with a few bright stars. But there is a lot of data there; it just isn't spread across the range the human eye can perceive.

Stretching applies a non‑linear transformation that expands the dark tones, where most of the image data resides and compresses the bright tones. In other words, it separates faint structures from the background.

MAS is a form of stretching that has recently been introduced in PixInsight, my processing software of choice. Similar to the other tools in PixInsight I have used in the past, it stretches the image so that the faint data can be brought to light. However, MAS also provides some additional options to make the stretch even better and offers the user a lot of flexibility when it comes to contrast preservation, enhancement of faint details and removal of the background sky glow.

HDR Multiscale Transformation

Handling the large dynamic range in brightness of an object is accomplished with an application of a High Dynamic Range transformation process. Usually this is done by stacking subs with small exposures (to capture the bright areas) and large exposures (for the dimmer regions). The stacking process will then provide a more pleasing result preserving detail across extreme brightness differences. The HDR Multiscale transformation process allows one to do this without the need of exposing subs with different exposure times. You can apply it to the single final stacked image.

Applying the Processes

Here is the original image of M42 right out of the camera with minimal initial post processing. As expected, it is almost totally black. The bright inner core is visible as is the Trapezium cluster.

Applying the MAS stretch reveals the data lurking down in the image. This is the same image as the 80x8sec image in my previous post. The nebula now stands out (note the Trapezium is swamped by the bright emission gases in the core). 

However, the default settings on MAS use the complete image to determine the mean background intensity and so it was not handling the removal of the background as best as it could. By selecting an area of the image devoid of any real signal (I used a section in the lower left) and providing that as the background reference for MAS, the result is much better - the outer extent of the nebula can now be seen.

However, the core of the nebula is now even brighter, and the details of the gas structures is almost non-existent. This is the problem with M42 - the range of brightness between the lightest regions and darkest regions is very large. And this is where HDR comes in. Applying HDRMT with just the right settings (a trial and error manual process by the way) we get the following image.

A run through with Paint Shop Pro yields the final result, ready for printing and hanging on my office wall!. All the wonderful elements of this famous nebula are now clearly visible, from the inner core detail to the outer edges and even the Trapezium.

 

The Science of Image Stacking - Experimenting with Sub Exposure Times

Stacking multiple astrophotography images—often called image stacking or integration—is one of the most important techniques in modern astronomy imaging. It allows photographers to reveal faint celestial details that would be lost in a single exposure.

Instead of taking one very long exposure (which can be ruined by a plane crossing the field or wind moving the equipment), astrophotographers take many shorter exposures of the same object (a galaxy, nebula, star field, or planet). Each image records the signal (real light from stars and deep-sky objects) as well as noise (random fluctuations from the sensor, heat, electronics, and sky background).

Because astronomical objects are effectively static over short time spans, these multiple images contain the same signal but different random noise patterns. Since the signal is consistent across images it adds together as the individual subs are built up, but the noise is random and averages out toward zero. As a result, the signal-to-noise ratio (SNR) improves by the square root of the number of images stacked (√N).

Indeed, the sky background, due to excessive light pollution, limits exposures of under 3-5 minutes in order to prevent the object from being swamped out. In very dark skies this is not generally a problem; but near cities where streetlights and buildings are dense, it is.

Noise is the biggest enemy in low-light imaging. Stacking reduces random noise far more effectively than any single long exposure, producing smoother backgrounds and cleaner detail. In addition, stacking allows bright stars and faint structures to coexist in the same image without clipping highlights or crushing shadows, revealing more tonal information across the scene.

In summary, image stacking works because math beats physics: Physics limits how much light a single exposure can collect without noise while statistics allow many imperfect images to combine into one high-quality result allowing modern amateur astrophotographers to produce images that rival professional observatory photographs from decades ago.

Of course, you need to determine an appropriate exposure time to capture the needed photons (if no photons are picked up by the sensor it doesn't matter how many subs you stack in the end). But you can limit the exposure time by quite a bit depending on the object of interest.

As an example of just how well this works, I imaged the famous Orion Nebula, M42, with my EdgeHD telescope in Hyperstar mode (an f/2 optic train). This nebula is the brightest nebula in the night sky. A single 60 second exposure can give you a nice result (albeit a bit noisy). A ten-minute exposure would really bring out the detail. But 10 minutes is way too long of an exposure in the light polluted sky of my backyard. The science of stacking, however, claims that a stack of ten, 1-minute exposures would provide the same image as a single ten-minute exposure with the added benefit of reduced noise, hence better SNR.

Here are three final photos of the Orion Nebula taken with differing sub-exposures and stacked to provide the total integration time of ten minutes.

 

10x60sec

40x15sec

80x8sec

Can you see any differences? In fact, looking at the original images (these are reduced size JPGs for posting here) the 80x8sec stacked version is noticeably better in terms of SNR, although the post processing software I use has some terrific noise reduction tools that were used in the creation of these images.

The drawbacks of this are few, but worth mentioning. It takes 8 times the storage to hold the 80 8-sec subs vs the 10 60-sec subs and the post processing time (and required storage on the computer) also goes up. But this is a small price to pay for such wonderful results.

Next time I'll target a fairly faint nebula to demonstrate how this really shines!

Total Lunar Eclipse this Tuesday Morning

Although the weather doesn't look like it will cooperate for the Maryland region, you never really know what might be in store, and this is the last total eclipse of the moon for the next 3 years.

The eclipse favors the western half of the country, as well as Australia and the Pacific, where the entire eclipse can be seen. Here on the east coast the total phase begins as the moon is getting ready to set in the western horizon.

The moon will enter the earth's shadow early on Tuesday morning, March 3, at 4:50 EST. Totality starts at 6:04 when the moon will be a scant 6 degrees above the horizon. By mid-eclipse the moon has already set.

So, if the sky is clear, get to a location where you have an unobstructed view of the western horizon. The next total lunar eclipse won't be until Dec 31, 2028, and that one only from the west coast of US.

A very small nebula indeed!

Minkowski 1‑8 is a tiny planetary nebula located about 13,000 light‑years away in the constellation Monoceros. Spanning only about 20 arc‑seconds—which corresponds to roughly half the apparent size of Jupiter—it presents a really compact but visually striking structure. Its outer rim glows more brightly in H‑alpha, while the inner regions are dominated by OIII emission, revealing a multipolar, bow‑tie–like form viewed side‑on. There is a bright central torus that stretches across its core, but no obvious progenitor star is visible in this image. Despite its small size and subtle features, its shape and coloration evoke the well‑known Little Dumbbell Nebula (M76).

Minkowski 1-8 - February 12&13, 2026
EdgeHD11/ASI2600mm
HOORGB - 5hr 12m integration time

So, why did I decide on capturing this elusive PN? Well, it was after I completed the installation of a new auto focuser on my Edge (in the cold I might add) that I noticed a faint patch in the star field while reviewing the test subs. Curious, I loaded the image into PixInsight for annotation, which revealed a small planetary nebula. Over the following two nights, I collected enough data to process a reasonable photo of it. 

Soldiers Delight Star Party - February 21, 2026

 

Soldiers Delight Star Party - February 21, 2026

Don't miss the next SD Star Party:

"Astronomical Phenomena: Eclipses, meteor showers, and other spectacular events in the night sky"

Astronomical phenomena such as eclipses, meteor showers, and other spectacular events in the night sky captivate our imagination and offer a glimpse into the vastness of the universe. Eclipses, whether solar or lunar, occur when the Earth, moon, and sun align, casting shadows and creating breathtaking visual displays. Meteor showers, like the Perseids or Geminids, result from Earth passing through the debris left by comets, producing streaks of light as meteoroids burn up in the atmosphere. Other phenomena, such as auroras, are caused by solar particles interacting with Earth's magnetic field, painting the sky with vibrant colors. These events not only provide stunning visuals but also deepen our understanding of celestial mechanics and the dynamic nature of our cosmos.

All ages welcome.

All programs rain or shine. Time machines will be provided by the Westminster Astronomy Club.

Activity: Dark Sky Wheel

You can find out about special local events by contacting us at https://www.westminsterastro.org/

Date: Saturday, February 21, 2026

Time: 6:30 p.m. - 8:30 p.m. Eastern Standard Time

Location: Soldiers Delight Environmental Area - Visitor Center

5100 Deer Park Rd.

Owings Mills, MD 21117

New Discovery in the famous Ring Nebula

A recent study has identified a previously undetected iron bar within the well-known Ring Nebula, an astronomical object extensively examined by both professional and amateur astronomers for centuries.

Image via Royal Astronomical Society/ University College London.

The Ring Nebula is composed of gas and dust expelled by a progenitor star as it exhausted its nuclear fuel, resulting in the formation of a central white dwarf.

Here is my photo of the Ring taken back in 2024:

And here is the Ring by the Hubble telescope:

Image via The Hubble Heritage Team (AURA/STScI/NASA)

At the core of this nebula, the research has uncovered a bar-shaped cloud of iron. This structure measures approximately 500 times the length of Pluto's orbit around the Sun and possesses a mass comparable to that of Mars. The origin of this feature remains uncertain within the astronomical community.

Latest Photos from Mikey's Place

Spider Nebula

IC 417, known as the Spider Nebula, is an emission nebula located in the constellation Auriga, roughly 7,100–10,000 light-years from Earth. Spanning about 13 by 10 arcminutes, it is part of the Aur OB2 association on the near side of the Perseus Arm of our galaxy. This active star-forming region contains the young open cluster Stock 8, whose massive stars ionize surrounding hydrogen gas, creating the nebula’s vivid glow. Its intricate, web-like filaments of gas and dust make IC 417 a striking example of stellar birth and evolution in the Milky Way (Wiki +).

IC 417 - Jan 21, 2026
GT102/ASI533mc/TriBand filter
54x300 sec subs

This image was an effort on my part to test the new Antlia Triband RGB Ultra filter for use on my EdgeHD11 in Hyperstar configuration. But alas, I ordered the wrong bracket for my ZWO EAF and so I decided to try it out on my GT102 instead. The filter is basically a light pollution filter, with transmission bands that are much wider than typical NB filters and centered on the Ha, O3, S2 and N2 lines with a band also in the deep blue spectrum. It supposedly can produce some reasonable SHO images with the proper processing techniques. And, according to Starzona (where I purchased the filter) it can handle the f/2 fast optics of the Hyperstar.

Medusa Nebula

The Medusa Nebula (Sh2-274), also known as Abell 21, is a striking planetary nebula located about 1,500 light-years away in the constellation Gemini. Spanning roughly 4 light-years across, its delicate, serpentine filaments of glowing gas inspired its name, recalling the snake-haired Gorgon from Greek mythology. Formed when a dying red giant shed its outer layers, the nebula’s intricate structure is illuminated by the ultraviolet radiation of its hot central star, now transitioning toward a white dwarf. This ethereal remnant offers a glimpse into the final stages of stellar evolution and the beauty of cosmic transformation.

Sh2-274 - Jan 21, 2026
GT102/ASI533mc/TriBand filter
46x300 sec subs

This is my second DSO imaged with my new Altlia Triband RGB Ultra filter. Some of the takeaways on this as well as on IC 417 - the Spider Nebula is the need for more integration time and probably longer exposures (600sec vs 300sec). The dynamic range just isn’t quite there! And, of course, the details are minimal in the interior of the nebula unlike the much better resolution achieved with my EdgeHD11 (Abell 21, Sh2-274: The Medusa Nebula. A Michael/Uwe teamwork - AstroBin ). Lots more experimenting to do.

Blue Snowball

NGC 7662, known as the Blue Snowball Nebula, is a striking planetary nebula about 2,000 light-years away in the constellation Andromeda. Its vivid blue hue comes from ionized oxygen gas illuminated by the intense ultraviolet radiation of its central white dwarf star. Measuring roughly 0.5 arcminutes across and shining at an apparent magnitude of about 8.6, this nebula represents the final evolutionary stage of a Sun-like star, showcasing intricate shells of gas expanding into space.

NGC 7662 - Sept and Nov 2025
EdgeHD-11/ASI2600mm
LRGBHaO3 - 5 hrs integration time

This was a real challenge to process and keep the core from being blown out. While processing this DSO I uncovered some flaws in some of my existing processing steps which I’ve corrected - and added the newer tools such as MAS to my new processes.

Hopes are High for a new Sun grazing Comet

C/2026 A1 (MAPS)

A new sun grazing comet could become quite bright! Sky watchers are excited about this newcomer heading toward the inner solar system, as it's already appeared large and visible at 18th magnitude even while still twice as far from the sun as Earth is. Although magnitude 18 is much too dim for unaided eyes, that level of brightness is impressive for a comet at such a distance.

This could be the most distant observation ever made of a comet like this—a suspected Kreutz sungrazer, belonging to a group of comets known for passing very close to the sun. The comet—now officially named C/2026 A1 (MAPS)—is traveling toward its closest approach to the sun, or perihelion, which will occur on April 4-5, 2026. Detecting it early indicates it’s probably fairly large, so there’s a chance it will get quite bright—even potentially easy to spot in our skies.

Early measurements estimate that the comet’s nucleus could be as much as 1.5 miles (2.4 km) wide.

Can this sun grazing comet survive?

Comet C/2026 A1 MAPS will pass just 487,088 miles (783,892 km) from the sun, with the sun’s diameter at 865,370 miles (1,392,678 km).

At such close range, comets often disintegrate due to intense heat and the sun’s gravity, but if this one survives, it could shine brightly in our skies at dusk after its closest approach in early April.

There’s reason for optimism—comets like C/1965 S1 (Ikeya–Seki) and C/2011 W3 (Lovejoy) survived even closer solar encounters and became extremely bright, with Ikeya–Seki reaching magnitude -10 and Lovejoy matching Venus at magnitude -3 or -4.

 

No, it won't look like that!

Has anyone seen the latest (although this Facebook post has been around for a number of years) Facebook post showing the Jan 23, 2026 conjunction of the Moon, Saturn and Neptune? Here are text and image from the post:

Tomorrow — January 23 | Moon Meets Saturn & Neptune
Look up tomorrow evening for a beautiful triple conjunction in the sky! The Moon, Saturn, and distant Neptune will appear close together, creating a peaceful and eye-catching celestial scene.
What to look for: • The Moon and Saturn will be easy to spot with the naked eye
• Neptune will be very faint — binoculars or a telescope needed
• Best viewed just after sunset, low in the western sky
This rare alignment is perfect for sky watchers, photographers, and anyone who loves the night sky. Don’t miss this cosmic smile in the heavens!

Ok. Now that would be cool to see, if only it were true! In reality, there are the obvious reasons this is nonsense.

First and foremost, the actual placement of the objects is just unequivocally incorrect, especially the location of the planets IN FRONT OF THE MOON. 

Here is an illustration of where the objects really are in the sky (with the red reticle marking the location of Neptune). Note the size of the moon!

Second, although the text in the post did say Neptune would be dim and a telescope or binoculars would be needed, it is really dim - at 8th magnitude you'd better have a good set of binoculars and a dark sky. And based on the actual positions of the objects in the sky you can't get the Moon, Saturn and Neptune in the same field of view in binoculars (in fact, no two of these objects can). 

These posts, seemingly from 'notable' sites (note the "Science and Astronomy Lovers" tag line) are getting more and more frequent and most of them are misleading and downright untrue. I've even seen posts claiming to be from NASA or NASA related sites - ridiculous. 

So, beware what you read. 

Sorry, but I just had to post this.

NightSky Observatory is happening soon

It’s been a long time coming—and no shortage of tough deliberation—before finally deciding to invest in a permanent observatory on the Mangieri estate. But the wheels of progress are officially in motion.

My original plan was to build a roll‑off roof (ROR) observatory from SkyShed: essentially a wooden structure whose roof slides away to give the telescope(s) an unobstructed view of the sky. It’s a relatively cost‑effective approach, though not without its challenges, particularly the need for a robust foundation and a long north–south footprint.

Recently, however, SkyShed introduced their new POD‑S series: a fully automated, classic domed observatory.

It’s a more expensive option than the ROR, but it offers significantly greater capability and a slightly smaller overall footprint. After weighing the pros and cons, I opted for the 5‑bay POD‑S. The order went in back in December, with delivery expected sometime between March and April. Once assembled (yes, it’s a DIY build), it will become a state‑of‑the‑art permanent home for my EdgeHD11 and GT102 telescopes. The new observatory will be named NightSky (yes I know, not very original, but it is the name of my videography side-line business).

More updates to come as this project takes shape.

Experimenting with the new PixInsight Tool - VeraLux HMS

Like in any tech field, advancements in technology, tools, and processes keep pushing the boundaries of what’s possible, and astrophotography is no exception. Just last week, a new tool called VeraLux HyperMetric Stretch, originally created for Siril/Python by Riccardo Paterniti, was released as a script for PixInsight, my preferred processing software. Touted as the “next best thing since sliced bread” and a “game changer” for astrophotographers, I couldn’t resist giving it a try to see what all the buzz was about.

Although I first tried it on my latest photo of the M35 star cluster (shown below), I was eager to really put it to the test on a narrowband image.

I chose IC1848, the Soul Nebula, for its expansive nebulosity and rich stellar gas. I first photographed it in November 2022 and added more data in December 2023. The original 2022 image was over-processed, with excessive vibrancy. After adding the new subs in 2023, I re-processed the image using some new software tools that weren’t available back in 2022—Russell Croman’s BlurXterminator and NoiseXterminator - and with new wisdom of how to properly handle image stretching and color enhancement.

November 2022

December 2023

The difference is clear. The 2022 image was a bit over-the-top, with overly saturated colors and contrast so strong it hid some details in the heart of the nebula. The 2023 image, on the other hand, offers a more subdued and realistic look, revealing intricate details throughout the inner nebula. While the additional data from 2023 played a big role in enhancing the detail, the processing was also done with a softer, more refined touch.

December 2025 - enter VeraLux HyperMetric Stretch. VeraLux operates on a fundamental axiom: standard histogram transformations often destroy the photometric relationships between color channels (hue shifts). And although one can (and I have) spend hours using the existing stretching tools to accomplish the same task Veralux does it with a single push of a button (well, maybe two). Here is the result of taking the original calibrated subs from the 2023 version of the nebula and using Veralux as the only stretching process.

The results are impressive. With minimal effort, I matched the outcome without the tedious manual stretching required by HistogramTransformation (HT) or GeneralizedHyperbolicStretch (GHS). The stars look less bloated and more vibrant, and the subdued star field really makes the nebula stand out as the focal point of the image. I do wonder about the authenticity of some of the star colors, but overall, the result is solid.

VeraLux is still in its beta stage, and I expect it to keep improving, but it has already secured a spot in my toolbox as my go-to stretching software.