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Introduction to DSLR Astrophotography
• Relatively simple and inexpensive. – No guiding required. Using consumer Canon DSLR’s.
– Home use camera: Canon t3i, 18 MP• No field laptop required. • ISO up to 6400, 30 sec or bulb exposures, swivel screen, zoom live focussing• Sensitivity diminishes in the red “Ha” emission wavelength.
– Fast Reflector vs APO• Larger aperature, faster f/#, no chromatic aberration, dewing takes longer, affordable.
– Stack of multiple shorter exposures vs single long exposure• No guiding required (no AG mount, separate guide scope & camera, or laptop)• Freeware “Deep Sky Stacker”, process images on a cloudy or rainy night
– Polar Aligned Equatorial Mount• Decent unguided 60-90 second exposures at 800 mm using Celestron CGEM
– “Local” Dark Sky sites• Blackbird SP, Tuckahoe SP, Cherry Springs SP, Cape Hatteras NC
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Celestron CGEM mount with Go-To and Autoguider $1500 new
Astro-Tech $ 450
8” f/4, 800mm fl
To Polaris
Polar alignment scope with offset
Imaging Setup, 8” f/4 on Celestron CGEM
Hand Controller with 40,000 object Go To Data Base.
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Camera Setup and LPR Filter Transmission
T Adapter
2” Baader MPCC
2” Hutech LPR Filter
Programmable shutter timer. Bulb Mode. N x 90 secs
UV and IR Blocking with notch filtering of Orange Street lights and transmission of Ha light
Swiveling Live Focus Screen
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Step by Step Procedures: Setting Up Scope• Laser collimate Telescope at Temperature
• Level Telescope Tripod.
• Balance DEC and RA Axis with camera attached (counterweights and dovetail)• Polar Align and center 2 or 3 alignment stars. No drift alignment needed
On Primary Center Mark
“Centered” on secondary
Returns to laser aperature
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Imaging Procedures• Camera Setup
– Manual Mode, 90 sec exp, 1600 - 6400 ISO, RAW Mode for stacking.
– Focus on bright star or Jupiter using “Live Zoom” feature
– If not “go to” equipped, find what object you’re looking for• Star Maps and TelRad or finder scope. Start with easier, brighter objects.
– Take lots and lots of “light” frames, many will be unacceptable for stacking
1 x 75 seconds @ ISO 6400.
Note lots of noise in raw images
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Screenshots from Deep Sky Stacker. M3 Cluster
8 x 75 secs @ 6400 ISO Light Frames Only. No flats or darks. Best images without trails or periodic error.
Stacked Image, no post processing
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Single 75 sec light frame9 x 75 sec light frame stack @ ISO 1600 using modified DSLR
PS adjust levels, contrast, sharpen, vibrance
Using Deep Sky Stacker http://deepskystacker.free.fr/english/index.html
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Objects imaged with light frames only (no flats, darks, or bias frames) Unguided stacks @ 1600 ISO. Levels adjusted and sharpened using Photoshop.
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Miscellaneous and other details• Maximize “SNR” or Signal to Noise Ratio
– Signal: Photons you want to keep• Good focused images long exposure images
– Noise: Artifacts you don’t want– Light pollution (orange street lights).
• Use LPR filter– High ISO noise (most common)
• Take lots of light frames and stack– Dark Signal (removed by dark frames)– Vignetting, dust or smudges (removed by flat frames)– Dew. Newtonians better than SCT’s
• Optional Accessories: Many available at AstroMart (http://www.astromart.com)
– Coma corrector for fast Newtonians• http://www.optcorp.com/product.aspx?pid=10026
– LPR Filters (especially in light polluted “orange” skies)• http://www.optcorp.com/product.aspx?pid=105-156-840-1155-850-4172
Next Talk: More Advanced Astrophotography Techniques: Autoguiding, Flats Fields, Dark Frames and Dithering