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Here you will find articles on many how to topics.

Astrophotography Basics
by SVObservatory

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, at prime focus 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. 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). It is reasonably priced, are easily modded and 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.

My basic imaging setup is 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 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)
Cable Release
Tripod
EQ Wedge or Mount  (if using telescope)
Telescope (optional)
Image Processing Software
Extra Camera Battery
Power Source

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.

next step is Focusing  continued at top of page......

 

 

Observatory Environment Control

by SVObservatory

Temperature and humidity control inside an observatory, excluding roll off roof designs, is often overlooked. The first trip my observatory took thru a Maryland summer, affectionately know as "Ol' Dragon Breath" aka the "Bermuda High" was quite the experience. While the scopes were in no real danger, computers, webcams, UPS systems and other electronics as well as books and manuals were all fair game.
 
The SVObservatory sits on 3 acres in full sun, ouch!  The fiberglass shell of the observatory came with a nice reflective white gel coat which went a long way in keeping the inside temperatures from reaching "Hells Kitchen" proportions, still too close to the maximum operating range for most of my electronics. It also afforded no defense against humidity. Controlling temperature and humidity required a three pronged attack, literally. 
 
No observatory should be air tight, you want them to breathe. Elevating my observatory above ground level allows cooler air to circulate underneath the floor, in this case a deck structure, and to be drawn up into the OB by natural or mechanical means. I installed a 6 inch duct fan controlled by a FanTech speed controller which in turn is bridged to the OB computer for auto turn on at a preset temperature. This works quite well for controlling excess heat build up during the day and bringing the OB to ambient temperature rapidly for observing. Humidity control however was not completely addressed.

Installing air conditioning in an observatory seemed insane at the time, after all we are trying to remain near ambient temperature not make a penguin habitat. I remember reading article after article, one in particular denouncing the very thought of installing such a thing in an OB and another stating it was heresy. After careful consideration and sizing, using an A/C unit no longer seemed rediculous. I chose a Mitsubishi unit that I modified to work in the observatory. I liked this unit due to its tri-mode capabilities. This unit can operate as a dehumifiier, a/c unit or fan only as well as full auto mode where it will switch to whatever mode is best suited for the current conditions. I found the onboard humidity sensor lacking in accuracy so I use an aftermarket hygrometer control connected to the OB computer for more accurate humidity control. Another unit I found interesting, is one from PetCool, made for dog houses that heats and cools. I had some reservations about a unit like this but they seem to perform quite well and may be a future upgrade.

 

The key idea here is to control environmental conditions not turn our observatories into HVAC nirvana. With less than $350.00 and a few hours of my time the SVObservatory now tracks at or very near outdoor ambient conditions. The observatory computer monitors the interior condtions and you can find them here. During the winter months the duct fan is used on rare occasions to bring the observatory to equilibrium.     SVO

 

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 conditions 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 at MidAtlantic Astronomy Yahoo Groups.

Registax, Gimp or IRIS are all good programs and they are all free. I use Registax, K3CCDTOOLS and IRIS for processing images.

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.....  SVO

 
 
 
 
More Articles
 
 
Satellite Imaging  (courtesy of Brian Webb)
 
 
Webcam Astrophotography   (Ray Shore)
 
 
Kochab Clock Polar Alignment  (Doc Clay)
 
 
Drift Alignment   (Ian King Imaging)
 
 
Controlling Heat Currents   (Doc Clay)
 
 
SCT Collimation   (AstroChris)
 
 
Optics Cleaning  (Doc Clay)
 
 
 
 
 
Go To Links Page  
 
 
 
 
 

Seeing Is Believing, Or Is It?
                       by SVObservatory
 
Lately I've been asked, "What can you see thru your telescope?" Well it all depends. Our atmosphere is a gift and a curse. You may have heard the terms seeing, transparency and darkness along with a few others bantered about or perhaps you may have come across them on my Clear Sky Clock.
 
Seeing relates to how steady or turbulent our atmosphere is. Notice when the air is relatively calm, stars shine steadily with little to no flicker. Seeing is often rated using scales such as The Pickering Scale or The Antoniadi Scale.
 
A turbulent atmosphere will often limit magnification to low powers. Collimating telescope optics will be made more difficult, often the airy disc cannot be discerned clearly.The detail of the moon and planets will be diminished, sometimes they may even appear to boil. Stars will be jittery, endlessly dancing about, morphing into fuzzy spiked blobs. However, even in bad seeing conditions a brief window of good seeing will reward the patient observer.
 
Viewing in the hours after midnight will generally find you with a more steady atmosphere. The first night or two after a storm or weather front has pushed thru will often yield very clear skies, but very turbulent air.
 
Transparency is a measure of the sky's darkness and clarity. A transparent sky allows us to see far more faint or dim objects. A dark sky allows our telescopes too reach further in magnitude and deeper into the universe. Things such as pollution,water droplets,aerosols, dust, even smoke from a distant forest fire can scatter the available light trying to reach our telescopes. Water vapor has an annoying effect of reflecting light pollution from ground based sources. Sometimes this reflected light is worse then moon light. Take the same water vapor and our all too common smog and all but bright objects are out of reach.
This is one of the main reasons large observatories are placed at higher elevations above these limiting conditions.
 
So there you have it in your basic nutshell. We cannot always place the blame on our telescopes. The Earth is a complex machine from which we gaze.   SVO
 
 
 
 

 

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