So you’ve enjoyed views through your telescope and you feel that your eyes have seen as far as they can see. Yep! It’s time to get into astrophotography!
Astrophotography is practically a new level of observing the sky. While you may not be directly seeing the object with your eyes, your camera will reveal things that you previously couldn’t see! Plus, it’s YOUR equipment that makes this possible!
When you get the focus precise, the exposure settings, and the object(s) in the correct spot for the image, astrophotography is a rewarding experience!
When looking at deep sky objects, even with larger telescopes under ideal skies, you can get disappointed because they don’t look like the images you see in science books. This is by sheer virtue of the objects being too far away, and your eyes not adapting to color in low light settings. Your exit pupil under perfect conditions is still 7 mm wide, is constantly shuttering like a camera at 1/50th of a second on average… therefore your eyes can only allow so much light.
Cameras have one major factor – you can set their shutter speeds as long as you want! Therefore, they allow much more light into their sensors than a human eye ever could – revealing details that you previously could never see!
As far as the late 19th century, astrophotography became the preferred research tool, and it is still done today for data analysis as well as new discoveries.
The 48 inch Samuel Oschin Telescope at Palomar Mountain is strictly a camera, remotely operated by CalTech in Pasadena. It can photograph the entire sky in three days – of which small changes days apart can be detected and further analyzed with their 200 inch Hale telescope. This is how KBO’s like Eris and Sedna were discovered!
So, you think you’re ready to join the community? Here are some major bits of advice for those just starting out.
Know How to Work A Telescope!
If you don’t know how to get your telescope precisely pointed at the object you’re trying to view, how do you expect to get a picture of it?!
Astrophotography is literally the next level of observing, and if you don’t even know how to work a telescope, then don’t consider trying to do astrophotography through a telescope just yet!
Ditch the Smartphone – Get an ACTUAL Camera!
Yes, don’t depend on your smartphone for long exposure photography. With dedication, you can still get decent lunar, solar, and planetary shots… but that’s it! If you want to start taking great pictures of the deep sky wonders, you need an actual camera.
Astronomers in the digital age use Charge Coupled Device Cameras (CCD) which are much more light sensitive than film. Their exposure times can be relatively short versus film, and be used for different purposes like photometry.
DSLR’s on the other hand are much more commercially affordable and readily available. Even entry level DSLR cameras can get the job done. While they may get more noise than a CCD, there are techniques you can learn to reduce the noise.
There are some pros and cons with each type of camera, but at this point it’s not about you getting the best equipment possible, it’s you learning the ropes with what you get!
With DSLR’s – Stick With One Brand
Nikon, Sony, Canon… the list goes on. If you choose a particular brand, then you need the proper T-ring adapters for that brand so that they can be mounted into your telescope for prime focus photography.
The same applies with camera lenses, as you’ll find yourself wanting/needing a particular lens with different f/ stop settings or zoom capabilities. All Nikon dslr lenses are interchangeable between Nikon cameras, thus if you one day get a better camera, your old lenses and adapters can still be used.
Milky Way Shots Are Easier Than You Think!
While having a mount with a clock drive that tracks with Earth’s rotation is a plus, to get wide angle shots of the sky, even the Milky Way, all you need is a stable tripod and a remote shutter.
Just make sure the stars are in focus, which can be tricky but there are techniques you can do. One is simply looking through the viewfinder and getting the brightest stars in focus, the other is by shining a light such as a laser on a distant object, and focusing on that bright dot.
The two key things to look for are of course how low you can get your f/ stop (the lower the focal ratio, the faster light travels into the camera), and how long you can realistically set the exposure time before the stars start trailing off. The other part is how much ISO you want to set it to. While some cameras with high ISO settings give grainier images, some DSLRs have noise reduction features that help combat it, and it can be further fixed with image processing software.
Your Telescope NEEDS an Equatorial Mount
While Alt Az mounted telescopes may have GoTo drives and can track any object, the longest you can get exposures with such telescopes will be less than 20-30 seconds before the stars near the edge start to trail off due to field rotation. Even if the centered object is being perfectly tracked, the stars around it will appear to create circle trails, similar to those shots of star trails around Polaris.
Having an equatorial mount can help eliminate that issue, and give you longer exposures. However, lunar and planetary shots that don’t require long exposure are still fair game for any type of mount!
Your Polar Alignment Needs To Be Perfect
Besides having an equatorial mount, one of the biggest requirements is the alignment needs to be perfect. Poorly aligned equatorial mounts will also result in some field rotation, and limit how long you can expose before the starlight trails off. Unless the mount is perfectly aligned, there will be some degree of field rotation.
The procedures to do this can be time consuming, but necessary for your images to stay as sharp as possible. Some telescope mounts have polar alignment scopes, or are compatible with them. There are also polar alignment cameras you can purchase that adapt to your mount and get you to within arc-seconds of perfect alignment.
Autoguiders Are A Must For Longer Exposures
Even if you can get your polar alignment to be dead perfect, one more issue may arrive. To get a sharp image from a longer exposure, you must keep a guide star centered on cross hairs for the entire time the shutter is open.
The drifting can be caused by many factors, usually by periodic errors in the motor gears. While you yourself can keep correcting the minute changes by keeping track of the guidestar in the eyepiece and making small adjustments by hand controller, to help eliminate the hassle, you may want to get an autoguider and guide scope to have it do the work for you.
This is especially true if you are wanting to take pictures of smaller and more distant objects.
The Shorter the Focal Ratio, the Shorter the Exposure
Telescopes with a focal ratio of f/5 or lower are essentially “fast” telescopes, and because the light travels faster, your exposure times don’t need to be as long. Newtonian reflectors with moderate focal lengths typically have lower focal ratios. However, this also means the images will typically not be as big.
Telescopes with longer focal lengths, such as refractors or SCT’s, will have higher focal ratios, or “slower” telescopes. While it will take longer for the amount of exposure needed for the image, the image will be larger because the longer focal length means you’re zoomed in more.
There’s No Wrong Way To Photograph The Sky
The simplest method of photographing the sky is by piggybacking your camera to the top or side of your telescope, and using your standard camera lenses.
One main method known as “prime focus,” where you thread the camera onto the telescope focuser and the camera becomes the eyepiece. Depending on the focal length of the telescope, the telescope essentially becomes the camera lens – If your telescope’s focal length is 1000 mm, then your telescope is the equivalent of a 1000 mm focal lens with the light gathering power of your telescope!
Another method is “projection,” where an eyepiece is used to project an image into the camera’s light sensors. This is much more narrow and magnified, so it’s used more for lunar and planetary.
Certain objects require different focal lengths to capture the entire celestial sight. While the Orion Nebula fits well inside a 1000 mm image, objects like Andromeda Galaxy and the Pleiades are so wide that a 1000 mm focal length is too narrow for photography, but shorter focal lengths will easily capture it. On the other hand, small objects like distant galaxies and planetary nebulae require much longer focal lengths for the object to appear large enough in the image. Adding a Barlow can help with that if your scope has a shorter focal length.
NEVER Stop Shooting!
The only way to get better is to keep shooting! Everyone starts with an out of focus test image, or an image that looks amazing in the 2 inch preview screen, but clearly shows burry or grainy objects when viewed on a larger screen.
This is a new level of observing, and you’re only going to get better with each shot! You’ll figure out how to keep the stars in focus no matter what method you use, and if you end up getting a perfectly aligned Go To equatorial mount, you’d be quite surprised of how many images you can take in a short amount of time!
Thanks to the digital age, you can take thousands of shots, and always find a hidden gem or delete the bad images and try again!
Sometimes, the simplest shots are the best, and you’ll find that there’s people who love different images. Many of my best images are “lucky” shots where I have the correct amount of exposure, light, and barely have to do any processing to polish it.
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