Astrophotography
Basics |
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Astrophotography is a blast! I love looking through telescopes, but each viewing moment is isolated and the memory of the image often fades quickly. Being excited and fascinated by what I see, I've wanted to share it with others. Those reasons alone were enough to get me interested in astrophotography, but then I discovered that photographing celestial objects greatly enhances their sharpness, clarity and color! Our eyes don't have the ability to collect photons over a period of time but a camera can! In fact, you can take pictures of objects that you can't even see when you look through the telescope! The digital camera revolution has made entry into astrophotography easily affordable. In fact, many of the most basic point and shoot digital cameras have the ability to set the shutter to stay open for several seconds. That's enough time to take some really nice shots of constellations and star fields. With a fairly basic point and shoot camera (Canon PowerShot A620) that we already owned, I kept myself entertained for nearly a year shooting constellations and the moon.
To take pictures of nebula and galaxies, you'll probably want to shoot through a telescope, but if you already have a telescope that doesn't have to be expensive either! While you can take pictures through a telescope with a point and shoot camera (I got some pretty decent moon shots this way), a much better approach is to use a Digital Single Lens Reflex (DSLR) camera. A DSLR camera is a camera that allows you to detach and change lenses. That way you can use higher magnification lenses if you want, but the biggest advantage is that it makes taking pictures through a telescope a snap. If you only want to shoot through a telescope you don't need
to buy any lenses at all! The Canon Digital Rebel XT (350D) is a very
popular DSLR camera for astrophotography and is easily affordable
(prices last checked December 2007). All you need is the camera body ($199),
a T adapter, which slides in place
of the telescope eye piece ($18.65) and T ring for your particular camera ($8.95).
Make sure that you get a battery for your camera if it doesn't
come with the body. Also, if you do want to get some
lenses you can save a lot by taking advantage of the package
deals when you buy the camera.
If you have a telescope (or access to one), you can take some great shots for less than $230! The T adapter simply slides in where the telescope lens normally goes and the T ring attaches your DSLR camera to the T adapter. The telescope itself becomes the lens!
Astrophotography can be easy and affordable or challenging and expensive. It all depends on your goals, what you want to put into it and what you hope to get out of it. The beauty is that anyone can try astrophotography with very little expense and then decide how far they want to pursue it. If you are like me, you'll find it an extremely pleasant, fun and rewarding hobby! Steve put together the
following tutorial for the next steps in getting started: Astrophotography
Basics Stepping into the realm of astrophotography can be daunting. Astro imaging can be both expensive and complex, leaving your head spinning faster then a Neutron star. Well relax, it can also be relatively simple and easy on your wallet. Astro imaging will test your patience, tax your mind and challenge your endurance. But this is what makes astrophotography such a great hobby. At the end of a session to have captured an image of a Nebula or Galaxy that is millions of years old can be quite thrilling. "So how do I get started?", you ask. Well, expensive telescopes, mounts or cameras are not always needed to take great images. If you already own a telescope, a cheap web camera can be had with software for less than $100.00. Quality DSLR cameras start at around $500.00 and are employed by amateur and professional astrophotographers alike. A DSLR camera unlike a web cam, may be used alone, on a tripod or piggybacked on a telescope with a tracking mount. The use of a T- Adapter, T- Ring and Tele- Extender allows a DSLR camera to be attached to the back of the telescope for Prime Focus and high magnification Eyepiece Projection astrophotography. At the SVObservatory (Sola Virus Observatory), I use digital SLRs for both deep-sky and planetary imaging and a NexImage camera for Solar System imaging only. Among DSLRs I prefer the Canon Rebel XT (350D). Like many newer digital SLRs, the Canon Digital Rebel XT(EOS 350D) works surprisingly well as a deep-sky astro camera without any cooling devices, particularly when exposures are kept under 10 minutes and dark frames are subtracted. Colder weather goes along way in extending those exposure times to the 10 minute mark and beyond. The Canon 350D also has low noise, can take Pentax and Nikon mounts (with adapters), works well in light polluted skies and can be completely computer controlled. This is the imaging train I have been using. A Canon 350D attached to the scope via a T-Ring adapter along with a ScopeStuff TA2P which contains a f/6.3focal reducer and connects the camera to the microfocuser on the C11 telescope.
Beginning astro-imagers, myself included, expect our first imaging session to be a "Super Terrific Happy Hour" full of Super Galactic images. Obtaining quality images rarely happens by accident. Next we will discuss proper DSLR camera settings and a few techniques that will have you one step closer to successful imaging. Basic DSLR Camera Settings for Astrophotography
You will find the settings menus like the one above within the camera program and/or the camera controls on the camera body. Consult the manual supplied with the camera for more detailed information. Instead of listing the many parameters and settings here, you can find them in this article by Jerry Lodriguss. For the most part these settings are very accurate, however the ISO speed settings and White Balance settings are not set in stone. I have imaged deep space targets at ISO 200. The generic White Balance set to daylight is not always appropriate. Experiment and see what works for you. Are We Ready To Image Yet? There are just a few more basics to discuss. Equipment: DSLR or Film Camera, Web Cam ( telescope required) You can take the list from here, for the sky's the limit. But with this basic equipment list you can begin to capture our own Luna Moon or the wonders of the universe from your own backyard. Polar Alignment If you will be using your camera with a telescope, then not enough can be said about polar alignment. Having a good polar alignment or drift alignment (the most accurate method) is a must for successful astro imaging. A rough polar alignment will suffice for viewing but not for astro imaging. Also important is to make sure your mount or tripod is level. Focusing Without critical focus your images will be a bit of a disappointment. Focusing the DSLR camera especially when attached to the telescope can be a challenge and a true test of patience. Focusing by eye thru the viewfinder is awkward to say the least, making you wish your body moved like Gumby. Right angle attachments can make things somewhat easier but the view of faint objects has now become more dim. A Hartmann Mask is a nice simple tool that can assist you in achieving critical focus and are easy to make. Many of today's DSLR cameras have an Auto Focus feature and when used with auto focus lenses can achieve some amount of critical focus. Knife edge focusers and focusing on Diffraction Spikes work for some astro imagers. Using a Flip Mirror in your imaging train may help also, however I'm not a big fan. While there are many other methods of achieving focus, the two I use most often at SVObservatory is focusing software and a Slider Microfocus. I use Images Plus, DSLR Focus or DSLRlite focusing software. Most focusing software take the many variables of critical focus into account including the effects of temperature on the imaging train. On the downside there is the added cost, the learning curve of the software and portability as focusing software requires a PC next to the scope. Capturing Images What about Flats, Darks, Lights, Noise Reduction, Color Space, RAW, Mirror Lock and so many other terms. Do we need to know all of these? Well of course, but for basic astrophototography we will focus( did you get that) on a few for now. Raw Mode or JPEG, which one should I choose? JPEG is easier for beginners. No worrying with dark and light frames, flats or too many parameters. If you have too many hot pixels or noise on your images, just resample your image to 25% of the original image. RAW mode is the best format to image in and allows the greatest manipulation of your images during processing. RAW mode saves the data recorded by the CMOS or CCD sensor in a high bit format. Noise reduction technology reduces the amount of errant thermal signal. Most DSLRs have in-camera long exposure noise reduction built in. Using in-camera noise reduction will increase your imaging time due to the fact that the camera will be taking dark frames automatically after each image, but it is one less thing for the beginning astro imager to worry with. Mirror Lock, if you have it on your camera, great, if not it is not the end of the world. Normally for long exposures on a good mount it is not needed. The way I usually go about imaging at SVObservatory is to begin with taking flats sometime around dusk when the sky is evenly illuminated. I also use a light box panel and even the dome wall. Taking flats help you detect any contaminates on the sensor or optics that can be subtracted later as well as determining the amount of vignetting or dark edges. After imaging I will take all my dark frames. I average the dark frames from my shortest and longest exposure times. Take your darks in odd quantities like 3, 6, 9 etc. When combining later during processing the software picks up on the odd numbered choices. *Quick Tip, for anyone who wants to do their own darks and their cameras are not controlled by software, just leave the lens cap on, turn in-camera noise reduction off. Be sure to cover the view finder window, you could get errrant light leaking onto the sensor and take a minimum of 3 dark frames. Do this under the same condtions and at the same length of your longest image, i.e. 5 minute image, take a 5 minute dark frame.* For deep-sky imaging I usually image in sets or subs, taking multiple frames of varying exposure times. For example: 30: 30 second subs, 3: 4 minute subs etc. Don't be afraid to mix it up either. I have occasionally taken long single exposures of 5 minutes or more. Taking multiple exposures however will increase your success and later during processing you will stack and align these frames using software such as Registax. Image Processing Now you have your images and you think you are done..... Next you have to process those hard earned bits of data into something you can show off to friends, family or maybe here at MidAtlantic Astronomy. Registax, Gimp or IRIS are all good programs and they are all free. I use Registax, K3CCDTOOLS and IRIS for processing images at SVObservatory. The many facets of image processing are too much for me to cover here. But you will find a decent tutorial on the web site of fellow astronomer David Nash from the U.K. Mr. Nash takes you thru the steps of processing an image he captured using K3CCDTOOLS and Gimp. Any questions? Why of course you do. The journey has
just begun...... This is the end of Steve's article. To learn more, check out the great tutorial for getting started in astrophotography that Jerry Lodriguss has put together! Here are some free software programs for getting the most out of your images: Gimp (Free imaging software that rivals Photoshop) Deep Sky Stacker (Automatically aligns and stacks multiple images) RegiStax
(Another free stacking program)
A special thanks to Bryan at DataMasters, Inc for hosting this site!
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