introduction to dslr astrophotography

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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