Astrophotography Archives - Infrared Conversions, IR Modifications & Photography Tutorials

Simple Ways to Improve Your Astrophotography

For eons, mankind has looked up into the night sky in wonderment. All the stars and celestial bodies which hover over our heads have always held a nearly indescribable allure. Since the advent of photography we have looked for ways to photograph all the beautiful happenings of our galactic home.

You might think that making photographs of stars or even our own galaxy requires special equipment or extensive knowledge of mind numbing photography concepts. Nothing could be further from the truth. In reality, it all comes down to a few simple techniques and basic camera gear. In this article we are going to look at a few key points that can help you start making great photographs of the night sky right now!

Use a Tripod

Having a stable shooting platform is always a good idea for any type of photograph. The introduction of sharpness-robbing camera shake is one of the largest hurdles to overcome for any photo maker and it is especially true in astrophotography.

Always use a tripod(like the one from this LifePixel article) so that you can eliminate as much motion as possible in your images of the night sky. Speaking of motion….

Make Use of the 600 Rule

We often forget that even though our cameras seem to be perfectly still they, and ourselves, are moving along through space at around 67,000 miles per hour(30 km per second!). That’s not exactly slow. What this means for our astrophotography is that we are constantly working in a moving environment. Depending on the type of night photograph we want to end up with there is a very simple way to make sure all those stars stay in place. It’s called the “600 Rule”.

This was shot at a 7 min 30 second exposure using a 14mm lens. Note the the visible star trails….

Well, it’s more of a guideline for exposure rather than a rule. Since, the earth is moving so fast, longer exposure times results in “star trails” which is the streaking of starlight due to motion. This can be a good or a bad thing. Luckily, we can estimate the longest shutter time we can use based on our lens so that we don’t see star trails. Conversely, we then know what the approximate minimum exposure time needed so that we do see them. And it really is a easy…I promise. The 600 Rule states that the focal length of your lens, be it 14mm, 50mm, 85mm, ect., should be divided into 600. Here’s the equation:

600/focal length of lens = Maximum Shutter Time in Seconds

See! That wasn’t so bad. There are a few versions of this rule which use different numbers such as 400 or 500. They all yield similar results so use whichever one works best for you. I use 600 but this is simply a preference.

Include Interesting Elements

Make your astrophotography more than just pictures of stars by including elements into your foregrounds. People, buildings, trees, even light pollution(unwanted artificial light) can add wonderfully interesting elements to your astro photos.

The fence and building light in the background works to lead the viewer up towards the beautiful Milky Way.

Make use of your entire environment to bring a unique perspective. Sometimes it helps to see just how small we really are in a wide universe.

Use a Remote Shutter Release or Timer

We’ve already learned that camera motion is our enemy when shooting long exposures. Even a small amount of camera shake can ruin a perfectly composed nightscape. You might not realize it, but the impact vibration of pressing the shutter button can cause enough motion to appear in your photo. To combat this, consider using a remote shutter release. Most cameras today have wireless remote capabilities(even budget cameras) and the remotes like these are cheap.

This wireless remote cost me about $11

No remote? Try putting setting your camera to a 2 second or even 10 second timer. This will make sure your camera is as still as possible.

Closing thoughts….

Astrophotography is an almost magical goal for some photographers. When I first began making photographs one of my personal goals was to make a photo of the full moon. It doesn’t take much to be able to make wonderful images of the night sky. Follow the simple tips in this article and you will see…dare I say…ASTROnomical improvement in your photographs! Photography jokes are fun….

Focusing a Full Spectrum Camera

If you’ve read any of my other blogs, you might know that I started IR photography as a spinoff of my astrophotography. Both of these types of photography have some similarities. First, most cameras need to be modified to shoot IR photos. For the exact same reason, you’ll need to modify your camera to shoot nebula-type astrophotography. This is needed because the internal UV/IR cut filter blocks the both the IR light for IR photography and the H-alpha light for shooting nebula (See my astrophotography series for more details).

When I first got started with astrophotography, I modified a canon 300D (Digital Rebel) with a full spectrum modification. I figured it would be the most flexible. Six years later, I still feel that way. I like the full spectrum modification as I can shoot astro, or any flavor of IR. by adding an original white balance filter allows me to use the camera for regular color photography.

The biggest drawback of a full spectrum modified camera is the need for external filters. These block the light that would normally pass through the viewfinder. Lifepixel calibrates their IR modified cameras for autofocus. But when shooting IR with a full spectrum mod, you loose the use of the viewfinder.

When shooting the 300D, I would compose, focus and prepare the shot with the filter removed. I’d then screw on the filter and set the lens to the higher f/numbers and shoot. It was sort a crap shoot whether or not I’d get what I wanted. It did work and I shot many photos like this. One of my all-time favorites was shot with the 300D, using this technique.

I was enjoying shooting IR and wanted a better way to compose and focus my images. So my second modified camera was a Canon 40D, also modified for full spectrum. It was one of the first DSLR’s that had a live-view option. I found that this was the key to effectively using a full spectrum camera. Since the camera is modified, it sees right through the externally mounted IR filter. So live-view works quite normally. I used this camera for several years before upgrading to a slightly higher resolution Canon 50D. This camera also had a better live-view LCD, which made focusing much easier. Then I finally bought and modified a full frame Canon 5D Mk II. All my cameras were modified with a full spectrum modification.

When you shoot IR with live-view, you can see the scene just as the camera sees it. After all, it’s the main sensor shooting this live-view image. I found that shooting with a green white balance gives the images in the live-view window a more appealing color. It is much easier to compose and focus. Having a custom white balance also makes the post-processing easier.

This is typical of what you’ll see on the camera’s LCD if you shoot without a CWB.

This is the same shot with a Green CWB frame and the camera set to use this frame for CWB.

The biggest problem for me was being able to see the LCD screen, while shooting in the bright daylight hours. I tried shading the camera with a black cloth draped over the camera. But this was pretty tedious and uncomfortable. So I bought a Hoodman loupe and never looked back. This allows you to see the LCD very clearly. On many cameras you can also zoom live view, which will further improve your focusing with the loupe.

Keep in mind that using the LCD for composing and focusing will consume more power than viewfinder methods. So be sure to carry an extra battery or two. Alternatively, if you use a battery grip you’ll have longer sessions before a battery change is needed. This comes at the expense of portability.

The camera & loupe can be a handful to manage if you’re doing hand-held shots. So I resolved myself long ago to shooting with a tripod. I made a custom tripod which is a little more compact and works perfectly for my IR set-up. But nearly any tripod will work, as long as it is stable.

Focusing an IR modified camera can be a challenge. So I thought it might be worth reviewing this topic again. With a little kit and a little practice, focusing becomes an after thought allowing you to concentrate on the other aspects of getting a great image. You don’t have to have a full spectrum modified camera to use this technique. But you should use this technique if you have a full spectrum modified camera. Practice, have fun and happy shooting.

If Your Eyes Could See… Part 2

In Part 1 of this series I presented a few color astro photos that represent what you’d see, if your eyes were super sensitive. In part 2, I’m presenting similar images, only these will be presented in one color, the color of H-alpha. Hydrogen alpha is likely the most important emission, for imaging the night sky. In my astrophotography blog series, I discuss the importance of H-alpha and how to image these nebula with a modified DSLR.

The Veil Nebula Complex

The Great Orion Nebula

The images in part 2 were all photographed in the H-alpha wavelength (656.28 nm). The exposures are long. The equipment is expensive. The tracking is critical. But the results are some of the most stunning images that I’ve ever photographed, all of which are invisible to the naked eye.

The California Nebula

All of these H-alpha images required a series of 30 minute long exposures. These are then stacked and processed to achieve the final result (again, see my astrophotgraphy series). Like their color counterparts, the subjects of these images are so dim that they are invisible to the naked eye. This makes locating the subjects somewhat tricky. The use of a computerized mount reduces the time needed to get the telescope pointed at the target. Then it’s just a matter of fine tuning and framing. The focus is set, , the guide camera is calibrated, the filter wheel rotated to the proper filter and the exposures begin. Thirty minutes later, I check the resulting image to see if I hit the target as intended. If so, the imaging continues until the object is too low in the sky to continue.

The Heart Nebula

The Jellyfish Nebula

Sometimes, I’ll look up an uncommon object and point the telescope in the general area and shoot a test exposure. Many times, this technique isn’t too fruitful, but once in a while, a gem is recorded. This is the case of the image below. I scoured the web looking for similar images, to no avail. So this particular area, rarely photographed, is one of my favorite subjects.

B30 and Friends

Probably one of my all-time favorites is my mosaic of the Orion area. This is an 8 frame 60 megapixel mosaic that required many nights to shoot and many more nights to assemble and process. Anyone that has processed very large images in Photoshop will sympathize on the amount of work required of the computer and it’s operator. Each frame was individually processed. When they were all complete, each one was registered in a special piece of software called Registar. Then all 8 were imported into Photoshop, assembled, blended and processed. more than 40 hour of post-processing was performed on this image alone.

The Orion Complex Mosaic

Imaging deep sky targets is not for everyone. It can get complicated quickly, with steep learning curves on both the imaging and post-processing sides. Imaging with a DSLR can be a superb entry into this field. If your interests lie in photographing H-alpha, like the images here, the DSLR will need to be modified, and an H-alpha filter purchased. An astro-modification or a full spectrum modification can be performed to allow the proper H-alpha wavelengths to pass. My preference is the latter for the maximum throughput and flexibility. It allows my DSLR to be used for astrophotography, IR photography or any other application I can dream up.

The Horsehead Nebula

I hope you’ve enjoyed this short series highlighting some of my favorite images. A modified DSLR is a great way to get started doing astrophotography. If you’re interested in giving this a try, take a look at an H-alpha modified DSLR or a full spectrum version.

If Your Eyes Could See… – Part 1

For those of us that shoot IR photos, we already have a glimpse into what the world looks like illuminated in the invisible light of infrared. It has fascinated me that photos photographed in this light can have such interest and depth. Similarly, I have seen things in the heavens that only those with the appropriate telescope and imaging equipment have seen. I say “seen”, but it in reality, our eyes are not sensitive enough to actually see these magnificent & hidden astroscapes.

In this series, I’ll be showing a few of my deep sky astrophotos. These were all shot with my widefield imaging equipment. First covered will be the nebula shot in “color”. The camera (a cooled, full frame CCD) is monochrome. So the color is assembled by shooting through a series of filters and assembling the color images in Photoshop. There are a couple RGB images that contain only red green and blue light and others shot through narrowband filters. You can also review my Astrophotography series, for more detail on some of this, including shooting with a DSLR.

M45 – The Pleiades

M45 is a beautiful open cluster that’s a little difficult to photograph. It’s a reflection nebula, which means the dust that is visible is being reflected from the nearby starlight. It needs to be imaged with RGB filters, instead of narrow band filters. So it is much more affected by light pollution. Even so, this image was shot from my backyard in a fairly heavily light polluted area. There is much more dust and nebulosity to be seen here when imaged from darker skies.

Tulip Nebula

If your eyes were much more sensitive, the night sky would look very different. Most of these images represent a field of view of about 4 x 8 full Moons. So the features are large and would be prominent in the night sky. Imagine looking out your window and seeing the Tulip Nebula rising from the East.

A telescope’s main function is to gather light. This is one of the purposes for larger and larger telescopes. Resolution is also improved, but let’s just look at the light gathering ability. Compare the diameter of a telescope’s aperture with the pupil in your eye. This large aperture gathers many times more photons than your eye alone. The larger the diameter, the better the light gathering and the easier it is to see faint objects.

M42 _The Great Orion Nebula

With the exception of the Orion nebula (shown above), most of the objects in photos shown here are not visible to the naked eye. The additional light gathering ability of the telescope helps to increase the visibility. Long exposures improve the image depth and visibility even more. This basically stacks more and more photons on the film or CCD until the image is visible. All of the images shown here contain at least several hours of integration time. As an example, the California Nebula was photographed with 6 filters, RGB and 3 narrow band filters over a period of 7 nights. This resulted in a total integration time of 18 hours. This may seem excessive, but image stacking helps significantly reduce the image noise. Even images from a modified DSLR produce fantastic results.

RGB Barnard 30 & Sh2-264

The image above was shot only with RGB filters and exposures of 5 and 10 minutes. The total integration time was 2.5 hours. I wanted to point out the difference of this image and the one directly below, which also includes data from 3 additional filters, Hydrogen Alpha (H-Alpha), Oxygen III and Sulphur II (narrowband filters). Each narrow band exposures were 30 minutes in length. Many were recorded over several nights bringing the total exposure integration time to nearly 20 hours. As you can see with longer the exposures, much more detail is visible.

HaRGB Barnard 30 + Sh226

Each of these images also requires a significant amount of processing time. The individual monochrome image stacks needed to be processed. Then the data from each filter color needed to be color mapped, aligned and overlayed. Some final processing is done and the image is complete. At least, that’s the way it’s supposed to work. I always found that I never seemed to actually finish any image. I’d continually tweak and adjust until I was happy, each time thinking it was done.

IC2177 – The Seagull Nebula

My imaging telescope is considered widefield (530mm f/5). It provides lower magnification, in favor of wider views of the night sky. Although slightly magnified, the images would still appear fairly large if you could see with super sensitivity.

SH2-129 – The Flying Bat Nebula

In the next part of this short series, we’re going to take a look at similar celestial views. However, these images were recorded using only a single filter. I’ll share some of my all-time favorites in my favorite formats. Stay tuned.

Aside: Did you know that Life Pixel does camera modifications for astrophotography? As I described in an earlier astrophotography blog , most stock cameras need to be modified to be able to see the all-important hydrogen-alpha emission. This emission is deep red and is blocked by most stock camera UV/IR cut filters. Replacing this filter with a modified version that passes the H-alpha emission is very important for the highest sensitivity and best results. Alternatively, the camera can be modified for full spectrum use and external filters added for astrophotography use. You can find details in the links below:

Full Spectrum Modifications

Hydrogen-Alpha Modification

What’s In My Camera Bag?

The question that I get asked the most is what camera equipment I carry with me when I go on an assignment. My first bit of advice to anyone is to only carry what you need. After all, who wants to walk around all day with an extra 10kg on their back? But at the same time, you don’t want to be caught short, so as always, planning carefully and creating a shot list before you travel can be invaluable. The second bit of advice is not to get too concerned about your actual equipment. A great photo will look great whether it’s taken with a smart phone or the latest DSLR. Composition, lighting and creativity are far more important than how much your camera cost.

When starting out you should try and get together a basic set of equipment that will cover you for most situations. You can then add more specialized equipment depending on the nature of your shoots and your experience.

Camera

I have always used Canon cameras and my camera of choice at the moment is a Canon 5D MK III. It is an exceptional camera that won’t let you down and stands up very well at high ISO settings. Whenever possible I try to carry an extra body with me that I leave in my hotel room just in case anything happens to my main camera. This is especially valuable in remote places where you won’t be able to find a spare. The last thing you need when you have limited time at a place is to have to run around to try and find another camera or even worst be without one, so a spare can be indispensable.

Lenses

Canon 24-70mm f/2.8 II USM zoom lens

This lens is my workhorse and what I use the majority of the time. I love this lens because the focal range means it is perfect for landscapes as well as a wonderful lens to take portraits with. The great thing about this lens is that you have to get close to your subject. It is also fast enough to use in low light conditions, so ideal for places such as markets.

Canon EF 70-200mm f/2.8L IS II USM lens

This Canon telephoto lens, which comes with a hefty price tag, is an outstanding lens and definitely worth the cost. Great for portraits and close-ups, but also fantastic for landscapes if you want to isolate a small section of the scene.

Canon EF 50mm f/1.2L USM lens

If I could carry one lens with me, it would be this lens. My head would say my 24-70mm Canon lens but my heart would go for this. The great thing about prime lenses such as this are that as a photographer, you have to move and get up close to what you are photographing. This becomes especially powerful when photographing people as it helps build a connection with your subject. Photographer Robert Capa once said “If your pictures aren’t good enough, you’re not close enough”. This is where prime lenses can really help you. This lens is also fast enough to mean that you can photograph in low light conditions without having to bump up your ISO too high.

Canon EF 100mm f/2.8L Macro IS USM

For anyone interested in travel photography, one of the most important parts of a destination is the local food. Although not essential, macro lenses are great for photographing food as they allow you to get really close and pick up the beautiful details of what is on the dish.

Flash

One of the common misconceptions of flashes is that they should only be used in low light settings, but this is probably the worst time to use a flash as it can wash out the subject if not used correctly. Flashes are extremely useful when you need some fill flash (for example, if you are taking a portrait of someone in intense light which is causing harsh shadows on their face, a flash can help eliminate the shadows). For this reason, I always carry my Canon Speedlite 580EX II flash with me.

Tripod

Most photographers will probably tell you that their tripod is the one essential accessory that they can’t live without. A tripod is essential if you are planning any shots which require long shutter speeds as you simply will not be able to keep the camera steady enough by hand.

But a tripod is also what’s going to support all your expensive camera equipment so you should choose it wisely. The Manfrotto 055CXPRO3 is a sturdy carbon fibre tripod which is lightweight to carry. I also use a Manfrotto 327RC2 light duty grip ball head to connect my camera to the tripod.

Filters

All of my lenses are fitted with a Hoya Pro 1 Digital UV filter. This helps protect the lens glass, especially in very harsh conditions such as the desert. I also carry a range of Cokin Neutral Density filters and Graduated Neutral Density filters which are extremely beneficial for landscape photography. The only other filter I carry is a Cokin polarizing filter which is very useful for eliminate reflections and boost blues and greens.

Other bits

Memory cards, hard drives and laptop – I take enough memory cards with me so that I can cover each day I’m away on a separate card. I also take a few additional ones in case I need more than one in a day. However, at the end of each day, I still back up my card on two separate 250GB hard drives so that all my photos from that day are saved in 3 different places.

Lens and camera cleaning kit, spare batteries and chargers – You should get into the habit of giving your camera and lenses a wipe at the end of each day and charging your batteries so that everything is ready for the next day. I have seen so many newbie photographers turn up somewhere only for their battery to run out with no spare, so make sure you are prepared.

This is a basic set of equipment that I carry with me wherever I travel to and I add to these as I see fit. For example, architectural photographers might want to take a tilt and shift lens or wildlife photography a 400mm lens. But remember try to only take what you are going to need.

Astrophotography Image Processing

Here we are with the final installment of our astrophotography series. We’ve looked at doing astrophotography in the daytime, shooting simple objects at night, and some more advanced equipment and stacking techniques. If you missed any of these, you can catch them here.

In this series finale, we’re going to take a look at some of the processing techniques to get the most out of your astro images. Most of the work is done in Photoshop. But there are also some extra tools that I cover. These will further enhance the results of the images that you process in Photoshop. They are not necessary, but will make your processing go much smoother.

Let’s jump right in with a before and after example. First is an example of an image shot with a simple set-up, using my old first generation, astro modified Canon 300D Digital Rebel. It was shot through an EF 70-200 f/2.8 lens fixed at 200mm mounted on a small equatorial mount. This image is of the Heart & Soul Nebula, along with the double cluster (IC1805, IC1871, NGC 869 and NGC 884). This is basically how an image might look, right out of the camera.

This image is what we’re striving to achieve, after some stacking and processing.

There are probably a thousand ways to process these images. Sometimes it’s better to do a certain step before another step. It requires a lot of experimentation to get a good recipe. I’ve outlined what seems to work for me, in most of my images. There are always outliers that require something different, or some other tools. But generally, these basic techniques will help you get from a rough stack to a decent final image.

Again, here’s something similar to what you’ll have coming out of your camera. If you’re shooting from dark skies, your starting image may be much better. It’s always easier to process images shot from dark skies as much of the work in post-processing is removing the artifacts added by light pollution.

After stacking, it will have a little more detail and less noise depending on your particular subject.

Next, adjust the levels to reduce the black point. Just be aware that if you move the black pointer past the start of the histogram, you’ll be clipping valuable data. It’s also usually better to leave a little space between the black pointer and the start of the left hand side of the histogram.

This is the result after a levels adjustment.

Some astro images will develop a green hue to them. Many times this has to do with light pollution, other times it will arise from processing. But there is a free tool called HLVG that will attempt to remove the green hue. You can experiment with the level of strength required for your particular image. It’s free and well worth installing and using.

Here’s the appearance after running HVLG on the strong setting.

Several of the next processes use a set of Photoshop actions from Noel Carboni. These actions were developed specifically for astrophotography and are available at very small cost. They are one of my go to tools for post processing my images. The tool used on this operation is Enhance DSO and Reduce Stars. This action generally helps pull out some of the faint detail and reduces some of the star intensity. Be aware that this action takes quite some time, so be patient and let it run. Here’s what you get when it’s done.

Similar to the green color filtered above, sometimes astro images will have a stronger gradient across the image. This is especially true if you’re shooting from an area that’s light polluted. The gradient is difficult to see in the small blog images. It is also less severe than what I typically have. These gradients are typically very difficult to remove manually, but luckily there is another tool that helps to remove them. It’s called GradientXterminator (GXT). This tool loads as a filter in Photoshop. This filter is also available at a small cost. But if you’re planning to get serious with astrophotography, it is almost a must-have addition to your processing toolbox.

Here’s the result after GXT has been run on the coarse detail, medium aggressiveness setting. It was followed-up with a levels adjustment, exactly as performed before.

Then finally, depending on the image, I usually follow up the processing with another action from the Noel Carboni set called Increase Star Color. The change is subtle but many times the entire star field will all appear monochromatic. Usually the stars are much brighter than the object being photographed. So the stars can get saturated. This action will help add the proper color to the stars, which adds more dimension to the image.

There are loads of other tweaks and adjustments that can be done to the images. Here are a couple things to keep in mind when making the final adjustments. First, calibrate your monitor. This is important, but more so with astro images. Second, the sky background shouldn’t be jet black. A pure black background tends to make the images look synthetic and over processed. I generally try to keep my black point (as reported by the Photoshop info/cursor over the darkest areas) at about 20,20,20 (RGB), but certainly no blacker than 10,10,10. Third, I found that less is usually more when doing this kind of processing. Use a light hand and the image will look realistic. Heavy handed processing has an appearance that looks edgy and has many artifacts. Finally, have fun. This is a hobby and should be enjoyed as such.

I hope you’ve enjoyed this astrophotography series as much as I’ve enjoyed sharing it. Doing this kind of imaging has been a dream of mine since seeing my first astronomy magazine more than 40 years ago. Sharing what I’ve learned will hopefully help you shorten your learning curve that was nearly vertical for me. Good luck and dark skies.

Astrophotography Image Stacking – Astro Stacking

Hopefully you’ve been out shooting and applying what you’ve learned about astrophotography. For most there’s a fairly big learning curve with astrophotography. I was always pretty good with the computer, electronics, and the mechanical hardware, but learning to process the images was a huge challenge. Hopefully I can share what I’ve learned to help speed up your learning process.

There’s a lot to learn when it comes to taking the images from the camera to making a final image for display. You’ll find that 99% of the deep sky images that you shoot will require some form of post-processing. But before we even discuss doing any processing, let’s discuss how to best shoot the scene.

In the previous blogs, I’ve hinted about a technique that will let you get the most out of your astro images. Shooting very faint moving targets can be pretty challenging. It takes fairly decent equipment to get the really faint stuff, but beyond this, it’s important to properly photograph the subjects. There is one valuable technique that will help tremendously with processing and make the most of your data. This technique is stacking.

Let’s take a look at stacking in very basic terms. Shooting faint targets makes for generally noisy images. This is true for astrophotography as well as regular photography. This means that the photos look grainy and lack the silky smooth transition. In astrophotos, noise will disturb the transition from the target object to the dark regions. But if you shoot many photos of the same subject and stack them together, the result is far better than that of a single frame. The noise and graininess is filled in and the image will appear much smoother and complete. When I was going for the best quality images, I would generally shoot for between 10 and 20 hours of open shutter time. But again, these were for my very best deep sky images on professional level equipment. For me, that meant shooting over many nights and stacking all the data in the final image. I was shooting exposures that were ½ hour long,o I needed fewer frames. But the end result was a lot of data, that when assembled, resulted in very good data sets.

If you’re just starting out it’s not necessary for you to shoot this much. But generally the more you shoot the better. There’s a big difference that can be seen immediately in the final image. There is a point of diminishing returns, but most astrophotographers will never come close to this limit. So if you can start with shooting a couple hours you’ll end up with fairly decent data. But even shooting and stacking 10 images will be better than one single frame. The better the data, the easier it is to process into the final image.

How do we begin…? Once you have your mount aligned (see my previous blogs) the target framed and the lens or telescope focused, you can start shooting your images. Shoot the same subject, over and over. I generally use a computer or an intervalometer to take the work out of this. This allows me the ability to walk away and let the camera shoot until it’s done. Just be aware that you may need several batteries or an AC adapter for your camera. This is especially true in the cold. For your first outing, try to shoot for at least an hour of open shutter time. That means if you’re shooting 5 minute shots you’re going to want 12 of these to make an hour. It’s generally best to shoot with an exposure as long as possible, but not so long that the image becomes saturated with light fog or you begin to get star trails. I generally tried to shoot until I reached about 25-75% on the camera’s histogram. But this depends on the target and from where I’m shooting (and how much light pollution is present). Just keep in mind that 1 hour is not a magical number. Shoot more, if you have time and patience. This will make the post-processing after the stack easier and the final image even smoother.

Once you have the stack, what’s next? You need to process all these images into a single image. This is possible in Photoshop and there are some really great videos and information on the topic. So I’ll leave this learning process to those interested in doing the stacking in this manner.

The real benefit is doing the stacking in a program that is meant for processing astrophotos. There are many programs that are available to do this, some are even available for free. I used a program called MaximDL which is a high-end piece of professional astrophotography processing software. In addition to doing some processing, it also handles camera control, filter wheel control, focusing, guiding and many other aspects of shooting deep sky images. In a complex setup, it’s very beneficial to have control of everything in a single piece of software. However for those just starting out, look at getting Deep Sky Stacker (DSS). It is an excellent stacking program and is available at no cost. This allows you to practice shooting and processing images without investing a lot of additional money in software.

Be sure to take a look at the excellent instructions on the DSS website and online. It is fairly powerful and capable producing nice images. It will also allow the addition of calibration frames (discussed below), which is another very powerful feature for noise control. I generally found that I liked doing the stacking in DSS and then doing the remainder of the processing in Photoshop or similar image processing program. But that’s totally my preference. Each photographer should investigate the best workflow and combination of programs to use to produce the final image.

One really great feature of DSS is the comet stacking routine. Processing comets is even more complicated as the comet is typically in a different location in each frame. Some move slow enough not to have to worry about it. But others can move significant amounts in each frame. This typically takes some crafty processing to get a decent image. DSS takes a lot of the work out of it. This image was processed in DSS and Photoshop.

Coat hanger Asterism (CR399) and Comet Garradd

When beginning the stacking process, the images need to be quality sorted first and then aligned (or registered) first. The quality sorting can be done automatically in DSS, but I generally liked poking through the images and picking out the ones that were blurred from movement, or had clouds or planes. The registration or alignment will adjust the images up and down and also in rotation in order to bring all the frames in perfect alignment and then stack them together in one of several stacking methods. I generally prefer one of the median stacking methods.

Many of my astrophotos, including the comet photo above, were shot with professional level equipment. This equipment cost about half what my first house cost. To be fair I wanted to show what can be done with a DSR and Lens (or small telescope), so I re-processed some of my earliest images in DSS, knowing what I know now. These were shot with an Astro-modified, 6.3MP Canon 300D (Digital Rebel). This is one of the earliest DSLR’s. It was noisy and did not generally produce very clean astro images. But even with this old camera, the data was very usable and produced some fairly decent images. We’ll take a look at a few of these below:

My first modified DSLR for Astrophotography

Stacking Examples

Here are some examples of images right out of the camera and also some processed images. The first is a single frame that shows the Heart & Soul nebula (IC1805, IC1871, NGC 869 and NGC 884) as well as the double cluster. The top is out of the camera the next is after stacking and processing.

Unprocessed, right out of the camera

Stacked and post processed

The difference in these is drastic. In fairness, the single frame image was fogged by heavy light pollution. But this is a problem that will plague the majority of astrophotographers. The only way to combat this is to shoot from dark sites away from the city lights.

This next example is not as drastic. The top is out of the camera, the bottom is stacked and processed. Also included are crops of a single frame and stacked and processed images.

Single Frame and crop of the Rosette Nebula (NGC 2237)

Notice the missing details in the crop of this image.

Stack/post processed image and crop of the Rosette Nebula

The stacked image makes is much cleaner and much of the missing data has been filled in. Also note the better detail that is visible in the crop of the Rosette. This is the real benefit of the stacking method. One thing that you need to keep in mind with processing astrophotos is that it’s an incremental process. No single step is going to make a magical image from junk. Each step will add a tiny improvement, and with enough tiny steps you’ll end up with a very pleasing image. If you’re stacking many photos, most pieces of stacking software will take quite a while if you’re computer isn’t up to the task (like mine). So be patient and just let it run until it’s completed the registration and stacking processes.

Here’s another example of a single frame vs a stack. This one is of the Horsehead Nebula (B33) in Orion.

Single Frame and crop

Stack/post processed image and crop

It’s fairly easy to see the benefit of stacking when shooting astrophotos. One more advanced technique that will help reduce the noise in your stacks is called dithering. Basically this is moving the camera a couple pixels in a random direction after every frame. When using a median stacking method, objects in a different location on each frame will be eliminated. So using the stars as the alignment reference, the galaxies, nebulae or other subjects will remain in the same place. But hot pixels, satellites, planes, noise and other random effects will be in a different location, with respect to the stars, so these are eliminated when stacked. There are many guiding or tracking programs that will do dithering automatically. But even with a manual shutter release, it can help tremendously if you manually move the mount between exposures. It seems like a hassle, but dithering will add a fairly significant level of improvement. None of the images above (except the comet image) used dithering.

Another helpful addition is to add calibration frames. These will serve to help remove additional noise and other artifacts from the images. Dark frames will help remove hot pixels, Bias frames reduce read noise and flat frames will help clear up any dust spots or other specs that are caused by looking through the lens or telescope. There is a superb description of this in the FAQ section here. The newer more modern cameras tend to provide better noise and hot pixel control, so calibration might not be needed. But at the very least, flat frames should be used to ensure the removal of artifacts caused by a dirty lens or sensor. It will also help reduce any vignetting that occurs in the images. Remember: incremental improvements.

In the final installment of this Astrophotography series, we’ll discuss some of the details of going from a rough stacked image to the final image. This is where a lot of the magic happens so I hope you’ll stay tuned. In the meantime get out and shoot. See you soon.