Introduction to Astrophotography - Part V

My AstroTech 12" Richey-Chretien telescope with 

If you've made it this far, you've survived Parts I through IV of my series on astrophotography. There are so many more topics to cover but I hope that with what I've covered you've been able to get a handle on what's involved when you start down the path of shooting celestial objects.

We're about to get serious. So far I've tried to keep the equipment involved to what most would consider reasonable, especially if astrophotography is not going to be something you do regularly. But for those of you who may want to take it to the next level, this is where we will now be going. In this segment, we'll take a look at telescopes and mounts.

Learning To Run

My friend's Takahashi TOA 130 APO Refractor on an AstroPhysics mount inside his roll-off roof observatory. The TOA 130 is considered one of the finest imaging scopes available and provides a 1000mm focal length at f7.7. AstroPhysics is considered the Mercedes Benz of astronomical equipment and its mounts are highly regarded.

My Takahashi TSA 102 4-inch refractor on a Celestron CGEM mount

Adding more sophisticated equipment such as a bigger telescope and mount will yield larger and/or  more detailed images of your targets. For comparison, here are images of the nebulae in Orion taken through a 4” Takahashi refractor with its 800mm+ focal length at f8 (slightly shorter and faster with the flattener) on a Celestron CGEM mount. The equipment investment is now in the $5,000 range (new), $3,500 used, not counting the camera and accessories. Compare these  to images of the same target that I posted in Part III and you can see how much tighter the images are with much more detail.

Orion's nebulae with shorter focal lengths

Horsehead and Flame Nebulae in Orion with Takahashi TSA 102

Running Man and Great Orion Nebulae with Takahashi TSA 102

Sprinting

Now let's really push the envelope. For comparison, below are examples of the the nebulae posted above but through my 12” AstroTech Ritchey-Chretien truss tube telescope, a Takahashi EM-400 mount, and a QSI 683 mono CCD camera with a full compliment of filters.

Horsehead and Flame Nebulae

Great Orion Nebula

Flame Nebula in Orion with Narrowband filters

The telescope has a 2,432mm focal length at f8, a bit shorter and faster with the flattener, and 12-inch light gathering capability. The monochromatic CCD camera has a full frame 8.3MP sensor and a built in cooling mechanism that will cool the sensor down to -40 degrees Celsius to minimize noise. An integrated 8-position filter wheel allows me to decide whether to shoot with standard color filters (L, R, G, & B) or add narrowband filters (H-Alpha, Sulfur II, and Oxygen III) to bring out colors in a very narrow band of light that can be used to create what is commonly referred to as a Hubble palette.   

Takahashi EM-400 mount

Finally, while AstroPhysics may be the Mercedes Benz of astronomy gear, Takahashi equipment is its Japanese counterpart much like what Lexus is to Mercedes. The Takahashi EM-400 mount is a favorite of many astro imagers, tracking and slewing like a well oiled machine. All in all, I've been very pleased with the combination of the AstroTech Ritchey and the Tak EM-400 mount. Here are more examples of what the rig can do.

Cone, Christmas Tree, and Fox Fur Nebulae 

Eagle Nebula (with narrowband filters) 

Sombrero Galaxy, an example of an edge on galaxy orientation

Western Veil Nebula, aka the Witch's Broom 

Pinwheel Galaxy, an example of a full front galaxy orientation

Part VI - Cameras

Next up is a discussion on astrophotography cameras where I'll walk you through the world of CCD cameras, including CCD one shot color models, monochromatic versions, and filters. 

Introduction to Astrophotography - Part IV

Final image, Great Orion Nebula (R) with Running Man Nebula (L)

If you've been following the previous three posts in this series on astrophotography (Part I, Part II, and Part III), you're appetite for astrophotography has been whetted and you're itching to get out there and start creating some images of your own. In the first three parts of this series, I've touched on some astrophotography basics but haven't talked much about things you can do to help your images look their very best while you're shooting. Before continuing with actual image acquisition beyond what I've covered so far in Parts I, II, and III, this is a good time to digress for a moment and discuss some things that will minimize noise, increase contrast, eliminate vignetting, and otherwise make it possible for you to create the best possible final image.

Anything you can do with your camera before importing an image into Photoshop serves as the foundation for any image. But it's especially critical in astrophotography because with astrophotography you will be dealing with very dimly lit subjects that will push your imaging equipment to its limits (and beyond). That is why you must do anything and everything you can to maximize the signal to noise ratio in your images.

Signal to noise ratio is not a concern for me when I'm shooting portraits, daytime landscapes, or even sporting events under the lights/indoors. Today's professional digital cameras and the technology they incorporate can adequately deal with varied lighting conditions and minimize noise to an acceptable level. For the most part, signal overpowers noise making the images look "grainless" or at least not so grainy that the grain is objectionable. Even when I'm shooting an indoor basketball game at ISO 6400, as long as I make sure to use a correct exposure setting, the image will be relatively clean from a noise perspective.

Unfortunately, astrophotographic images are almost always underexposed. Underexposed images are a nightmare to correct in post processing as any efforts made to correct exposure will reveal a lot of undesirable, objectionable noise. The solution? When you're shooting a celestial target, take as many images as you reasonably can and also include a set of flats, darks, and bias frames. Import all of these images into "stacking" software, generate a "stacked" image, and then complete the image processing in Photoshop.

Before getting into the nitty gritty, I will assume that you will be shooting your images in RAW as opposed to a JPEG format. Never, ever shoot in JPEG. Doing so will drastically limit your ability to post process images. Now, let's start with a discussion on shooting flats, darks, bias frames, and why they're important.

DEFINING OUR TERMS - FLATS. DARKS AND BIAS FRAMES

A "flat" frame

Flats
“Flats” are images taken to eliminate as much dirt, dust, reflections, and other undesirable things in astro images. "Flats" are also used by the stacking software to correct any difference in brightness in the main image. They are created by covering the end of the lens with a white T-shirt and shining a flashlight on it, or taking an image of an evenly lit flat surface such as a computer monitor, a light box, or the sky at twilight."Flats" must be taken with the same ISO, f stop, and shutter speed as the astro image you intend to shoot. Ten to twelve "flats" usually suffice.

Darks
“Darks” are images taken after covering the end of the lens or telescope with the lens cap. Darks correct the dark signal flaws in image sensors, which is essentially a form of noise reduction. Ten to twelve "darks' will do with half taken at the beginning of the image session and the other half at the end with the same f stop, ISO, and shutter speed as the main image.

As an aside, you may not know it but DSLR's can internally create "darks" when you use the camera's high-ISO or Long Exposure noise reduction features.  These settings do essentially what you are doing when shooting "darks" manually - the camera takes a "dark" frame immediately after taking the main image and subtracts it (the noise generated) from the main image for you. If you are shooting with a DSLR, you have the option of using the camera's long exposure noise reduction or high ISO noise reduction features if you would rather let your camera take the place of shooting darks. When I'm shooting with my CCD cameras (a whole different animal than a DSLR, to be discussed in a later post), I don't have the option of in camera noise reduction features so shooting darks are a part of my imaging process.

But even when I use a DSLR, I've always resisted the temptation to use in camera noise reduction as I believe that manually taking my "darks" will always give me more flexibility and generate better results than any image processing performed internally in my DSLR's. As an analogy, I don't program my camera bodies to sharpen my images in camera as I can do a much better job of sharpening post-process. I would rather create the image and have the flexibility to decide how much or how little I want to sharpen the image, but that's impossible if I set the camera to sharpen the image for me. The same goes for noise reduction,

Bias
“Bias” frames are images taken with the fastest possible shutter speed the camera can shoot and the lens cap on. They contain only the noise generated by the camera’s electronics on the sensor which is subtracted from the data in the darks to identify the true sensor noise. Ten or so bias frames will suffice. 

These extra images are time consuming but they will allow you to create the best possible final image. All of these images are used in the pre-Photoshop processing of images in software commonly known as "stacking". "Stacking" images in software specifically created for this purpose is an essential step in the image creation process.  Images are "stacked" in the software, generating an image that will then be opened in Photoshop as the final step in the image creation process.

WHAT IS "STACKING?"?

One image of the Great Orion Nebula without any stacking.

When you shoot multiple images of the same scene, a camera basically takes a number of samples of the scene. The more samples you record of the scene, the more uniform it can ultimately become when software uses the best portion(s) of each image to create an image that uses the best of the best from each image - exposure, noise, detail, contrast, etc.

Several images stacked of the Great Orion Nebula. Detail, exposure and color saturation are improving.

This is similar to the concept of HDR images where you shoot various frames of the same scene with a range of exposure differences.  HDR software then takes the best exposure for any given part of the scene from each image and merges all of this information into one image that improves on the overall exposure by having both shadows and highlights exposed correctly.

All images of the target are now stacked. Detail, saturation and exposure are much better with room for improvement. Noise will be eliminated once darks, flats and bias frames are introduced into the mix and the overall exposure will be improved as well. Afterwards, the image will be ready for importing into Photoshop.

Like HDR software, stacking software takes information from all the images, averages the brightness, darkness, noise, etc. and from every image it grabs detail and contrast from all this additional information and adds it to the final product. But that's not all. Stacking software allows you to remove any images that you may not want to include, such as images where an aircraft travels across the night sky, or images that include cloud cover that passed through the area you were imaging. It then performs another critical step, aligning all the images so they are superimposed precisely one on top of the other.

Darks, flats, bias frames have been stacked with the other images. Image was then finalized in Photoshop.

After image alignment, stacking software uses the flats, darks, and bias frames that were taken. It uses the flats to eliminate any brightness variances and uses the darks and bias frames to subtract noise.

STACKING SOFTWARE

Deep Sky Stacker and RegiStax are two free stacking programs you can download and use. Deep Sky Stacker would be my pick from the two but experiment with each and make your own decision. If you don't mind the $99 cost, Nebulosity (v. 4) is a great choice and is the stacking software I prefer to use.

That wraps up the discussion on pre-Photoshop image enhancement techniques. In Part V we'll get into more sophisticated imaging with telescopes and CCD cameras.

Introduction to Astrophotography - Part III

My astrophotography home in Chiefland, Florida, a 10 foot dome (center) that houses my equipment. Left is a roll off roof observatory belonging to a friend, right is a pod dome belonging to another friend.

This is Part III of a multi-part series of posts on astrophotography. In Part I, I discussed astro images that can be taken with basic photography gear. In Part II, I took it up a notch and delved into imaging solar system targets like the moon and planets. In Part III, I'm going to take you into the world of imaging through telescopes without breaking the bank.

 DEEP SPACE – THE FINAL FRONTIER

Two types of mounts - (L) Altitude-Azimuth mount; ® German Equatorial Mount.

Celestron Advanced VX mount - $799 new, less if you buy used.

For deep sky targets such as nebulae and galaxies a motorized mount is a must. There are two types, Altitude-Azimuth mounts (Alt-Az) and German Equatorial mounts (GEM). GEMs are the best choice for astrophotography. Once the mount is polar aligned, lengthy exposures can be taken without any target movement. Expect to pay $500 to $1500 for a quality GEM that can handle a DSLR with long lenses and/or many telescopes. To ensure smooth operation while imaging, when selecting a mount, make sure that you review the mount's specifications. The mount’s rated weight capacity must be twice the weight of the equipment you intend to use so purchase wisely.

 All of the mounts in the $500-$1500 price range are motorized and come with a "Go To" feature. "Go To" mounts allow you to select a target from a menu on the hand controller, push enter, and the mount will automatically slew the telescope to the selected target.

Screenshot of Stellarium software after a search for "Great Nebula in Orion"

Alternatively, the mounts can be hard wired to a computer and controlled the same way through planetarium or imaging software. You simply open the software, type in the name of a target (e.g., Great Nebula in Orion) and the software finds the target in the night sky. If it's visible on that particular evening, it appears on the computer screen.

Stellarium screen shot showing what you get when using the "ocular view" feature for a target. In this case, the target is the Great Nebula in Orion.

There are several planetarium programs on the market, some free and some that you must buy. My favorite among the free programs is Stellarium which has a lot of features that make it a program I keep open on my desktop even though I don't use it to control my telescope mounts. One of the features I really like is the ability to see what a target will look like in an image depending on the telescope being used. Stellarium has a built-in cache of images depicting most celestial targets and by accessing them through the "ocular view" feature you can get a preview of whatever target you have chosen. If you like what you see, you can then proceed to the imaging phase of your evening. If not, you simply move on to another target. This makes finding image targets a relatively simple process even if your astronomical knowledge is limited.

If Stellarium isn't your cup of tea, Cartes du Ciel is another free planetarium program you can try. You can also go to http://freeware.intrastar.net/planetarium.htm for a list of many other free astronomy programs available for download.

Learning To Walk

Sky-Watcher Pro ED80, a good, starter 80mm refractor suitable for astrophotography. 600mm focal length @ f7.5. Expect to pay approximately $600 new, less for a used one.

Deciding how to shoot deep sky targets will determine equipment selection that will in turn dictate the size, quality and detail of the targets being imaged. Wide field images can be captured with a DSLR, a modestly priced 80mm (3-inch) refractor telescope, and a Celestron Advanced VX GEM mount (30 pound load capacity). Not counting the camera, your investment would run approximately $1,500 to $2,500 by the time you add desirable accessories such as flattener, a dew heater, a T-mount, and an auto guider.

Wide field image of the nebulae in the constellation Orion. Orion’s Belt is the diagonal line formed by the three blue stars on the left, ending with the blue star in the center nebula.

Above is an example of what is possible with a similar setup, including the accessories. I shot a total of 160 images at various shutter speeds ranging from 10 sec to 45 sec at ISO 1600, and 10 images with 1-3 minute exposures to layer in a sky saturated with stars at the end of the Photoshop process. Before wrapping up, I shot ten “flats” at each shutter speed, twelve “darks” (half before starting the imaging process of Orion's nebulae and the other half at the end of the imaging session) at each shutter speed, and ten “bias” frames for the pre-Photoshop processing in software that “stacks” the images together.

Say What???? Flats, Darks, Bias Frames and Stacking???

“Flats” are images taken to minimize or eliminate dirt, dust, reflections, and other undesirable things in astro images. They can be created by covering the end of the lens with a white T-shirt and shining a flashlight on it or taking an image of an evenly lit surface such as a white computer monitor, any other flat screen light source, or the sky at twilight. They’re used by the "stacking" software to correct any difference in brightness in the main images. 

“Darks” are images taken by covering the end of the lens with the lens cap. Half of the darks are taken at the beginning and the other half at the end. Darks correct the dark signal flaws in image sensors. 

“Bias” frames are images taken with the fastest possible shutter speed the camera can shoot and the lens cap on. They contain only the noise generated by the camera’s electronics on the sensor and is subtracted from the data in the darks to identify the true sensor noise. These extra images are time consuming but they will allow you to create the best possible final image.

All of these images are used in the pre-Photoshop processing of images in software that is commonly known as "stacking" software. Darks, flats, and bias frames will be covered in the next post (Part IV) of this series; stacking will be the topic in Part V.

Introduction To Astrophotography - Part II

The Moon - Nikon D300, Nikon 400mm f2.8 lens w/1.4X TC, ISO 200 @ f16, 1/125^th sec.  

Background – Nikon D3S, Nikon 17-35mm f2.8 lens, ISO 3200 @ f2.8, 25 sec.

This is Part II in my series of posts on Astrophotography. In Part I, I discussed astrophotography that you can do with a DSLR and various photography lenses. In Part II, we'll take it up a notch and get into some basic imaging using a long telephoto/zoom lens or a telescope. If you missed Part I, you can get to it here.

TAKING IT TO THE NEXT LEVEL

Solar System Imaging – The Moon

Imaging the solar system is a natural progression from wide-angle sky images and an easy way to delve deeper into astrophotography. Because targets are bright relatively speaking, exposure times are usually short enough to minimize blurry star images. 

The moon is an ideal first target and presents a variety of opportunities to create interesting images. The moon has many phases, ranging from a sliver crescent to a complete circular ball of light. Each phase alters the way the topography appears due to the shadow created by the earth. That in turn allows you to experiment with images that have a completely different look when compared to each other.

A tripod as a base will suffice and a full frame DSLR will yield better images than cropped sensor bodies.  Added cost will come into play if you lack a long focal length lens. If you're a fan of composite images, using moon shots as background images lend themselves to some interesting creations like these images of airliners I silhouetted in a couple of my moon shots.

As far as the actual process of shooting the moon, after set up, find the moon in your viewfinder. Experiment with shutter speeds, but as a general rule of thumb at ISO 400 and f16, I find that they will typically be 1/250th second for a full moon, 1/60th second for a quarter moon, and 1/15th second for a slivered crescent moon at ISO 400 andf16. Once you have the moon composed in the viewfinder, shoot quickly because the moon will not stay in your frame for long.

Solar System Imaging – Planets

Mars

Going from moon to planetary photography requires a step up in equipment. To avoid blurry, faint images of planets, a telescope that has a focal length of 2000mm or more is needed to achieve the necessary magnification for these targets.

Jupiter - Nikon D3S, Celestron Nexstar 8 telescope & Televue 4X Powermate. 

Ninety images @ ISO 800, f10, 1/10^th sec to 1/30^th sec.

Saturn – Nikon D3S, Celestron Nexstar 8 telescope, Televue 5X Powermate. Ninety images, 

ISO 800, f10, 1/2.5 to 1/6^th sec. Star field – 17-35mm lens, f2.8, ISO 3200, f2.8, 25 sec.

An investment of $500 or so in a used 8-inch Schmidt Cassegrain telescope (SCT) will give you the necessary focal length. Celestron and Meade have been making SCT telescopes for years and are plentiful on the used market. You can go bigger than an 8" SCT but I have found that anything larger is too heavy and cumbersome to be portable.  

You will also need a T-mount attachment for your camera to connect a DSLR camera body to the back of the telescope. Finally, a Barlow lens is a must. Barlow lenses increase magnification without affecting f-stop value. They come in various magnification factors from 2X to 5X, and while you can scrimp on these lenses, the only ones I would recommend are Televue Powermates. These are optimized for photography and are well worth the price tag of approximately $200 for a new one, less for used ones.

The imaging process is the same as the one described for shooting the moon with one exception – because of the slower shutter speeds, use a remote shutter release or the camera’s self timer feature to trigger the shutter. You should also lock your mirror in the up position. This will minimize camera vibration that produces blurry images.

Next Up - Part III

In the next post, I'll step it up even more as the discussion will move on to wide field imaging of deep sky targets with telescopes, DSLR's and CCD cameras.

Introduction to Astrophotography - Part I

Inside my dome observatory during an imaging run

Astrophotography is my photographic escape. As a professional sports photographer, I am paid to run around freezing athletes in split second moments in time. For the past three years, my relaxation has been astrophotography, the yang to my yin as I spend hours in my observatory during new moon weekends imaging celestial targets.

Since it is impossible to cover all aspects of astrophotography in one blog post , this will be a multi-part post. This is Part I, intended as a walk through of astrophotography that can be done cheaply and simply with basic photography gear. Subsequent posts will migrate to more equipment intensive imaging and some of the more detailed aspects of the process. How far you choose to take it is entirely up to you.

GETTING STARTED IN ASTROPHOTOGRAPHY

     

My first astro image, a shot of a full moon through a telescope with a 35mm film camera in 1980

A full lunar eclipse shot through a 400mm lens and a teleconverter with a DSLR in 2010.

The images above are examples of what can be easily accomplished with basic equipment, be it a telescope or long lens and an SLR camera, one film and one digital. Astrophotography does not have to be complicated or expensive. Most of us can drive an hour, get away from city light pollution, and take photos of bright objects like the moon simply by placing a cell phone camera on the eyepiece of a telescope.

DSLR image of the Andromeda Galaxy

Naturally, the quality of images will not be comparable to what is possible with more sophisticated gear but there’s a lot of astrophotography that can be accomplished with every day photography equipment. Beyond that, the sky is literally the limit depending on your interest and budget.

KEEPING IT CHEAP AND SIMPLE

Star Trails

Photographing star trails is one way to engage in astrophotography with basic photography gear. All you need is a camera body capable of long exposures (Bulb mode); a wide angle lens; a tripod; and a moonless, clear night at a location free from as much light pollution as possible.

An intervalometer is well worth the investment but not essential. This device will automate the imaging process by allowing you to program shutter speeds, number of exposures, and exposure intervals. A new Nikon intervalometer is pricey - over $150. I've had great luck with the aftermarket version made by Phottix (new - $50).

Once the imaging sequence begins, an intervalometer does the rest in triggering all the exposures you'll need. All that’s left for you to do is replace the camera’s battery if and when needed.

For circular star trails, locate Polaris (the North Star) and compose the image with Polaris in the frame. All other stars will appear to revolve in a circle around Polaris.

Eiffel Tower star trails composite

I created my Eiffel Tower composite using a Nikon D600, a 15mm Sigma f 2.8 fisheye, a Phottix TR-90 Intervalometer, and a tripod. The star trails consist of twenty four 15-minute exposures ISO 1600, f2.8, layered together. The Eiffel Tower image was shot at f2.8, ISO 1600, and 1/40^th second.

As an aside, I also shot some "flats", "darks", and "bias" frames that were included in the pre-Photoshop processing of images. I shoot these frames for all my astro images. The pre-Photoshop process is called "stacking" and it's accomplished in software designed to combine a number of astro images together, i.e., Nebulosity and Deep Sky Stacker. I'll delve into "darks", "flats", and "bias" frames in a later post but if you're anxious to see what these are just Google the terms and you'll find a wealth of information about them and how to shoot them.

Meteor Showers

The technique used to shoot star trails can also be used for capturing images of meteor showers. Because of the sporadic appearance of meteors, numerous exposures are necessary to capture enough light streaks in the sky. To create a meteor shower in one image, shoot as many images as you can, select the ones with light streaks, and then layer them together while brushing out everything but the light streaks.

Perseid meteor shower composite

My Perseid meteor shower composite was created with a Nikon D800E and a Nikon 17-35mm f2.8 lens piggybacked atop my Celestron SE 8 telescope to minimize blurry stars. Absent a motorized piggyback telescope, keep exposures to a maximum of 30 seconds. I used ISO 1600 at f2.8 with my intervalometer set to 60-second exposures every 3 minutes for 6 hours on two successive nights. I added a few longer exposures of the sky to capture the Milky Way. The foreground image was shot during the day and then converted to simulate night in Photoshop, adding a faux light painting effect.

The Milky Way Galaxy

The Milky Way is another astrophotography image that can be captured with basic photography gear. At a clear, dark site on a moonless night locate the Milky Way in the night sky. A quick search on the web should help you find it. The best views in the Northern Hemisphere are from February through September.

The Milky Way

Using a tripod mounted camera, start with ISO 3200, f2.8 and a 25-second exposure. Next, shoot several over and underexposed images that bracket this exposure. Images shot with a shutter speed in excess of 30 seconds will show some blurring in the stars but no worries.

Finally, layer your images one on top of the other. Brush out the poorly exposed portions from each image. Do the same for any blurry stars from the slow shutter speed images. Then, merge your layers and make final processing adjustments.

Part II - Imaging the Solar System

In Part II, I will take you to the another level, which I consider to be the next logical step in astrophotography - imaging the moon and planets. Stay tuned.