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Astrophotography

The Basics. Astrophotography. Image Capture Devices. Digital Compact cameras Webcams Digital SLR cameras Astronomical CCD cameras. Disadvantages Lens not replaceable Often, automatic modes cannot be switched off Mounting to telescope not easy. Digital Compact Cameras. Advantages

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Astrophotography

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  1. The Basics Astrophotography

  2. Image Capture Devices • Digital Compact cameras • Webcams • Digital SLR cameras • Astronomical CCD cameras

  3. Disadvantages Lens not replaceable Often, automatic modes cannot be switched off Mounting to telescope not easy Digital Compact Cameras • Advantages • Inexpensive • Easy to use • Small size • Low weight • No computer or external power supply needed

  4. More Disadvantages Lack of features No bulb setting Limited to 15 to 30 sec. exposure Digital Compact Cameras • More Advantages • Fast, automatic operation

  5. Disadvantages Tiny sensor, small field of view No bulb exposures possible No cooling to reduce noise Huge amounts of data Webcams • Advantages • Inexpensive • High sensitivity, short exposure times • High resolution, sharp details • Color images

  6. More Disadvantages Losses through data compression Operation impossible without computer Operation without telescope not reasonable Webcams • More Advantages • Good focus control • No cable release tangle • Unbeatable for planetary imaging

  7. Disadvantages Relatively high noise for long exposures High power consumption Difficulty focusing using LCD screen Digital SLR's • Advantages • Easy to use • No computer necessary • Versatile • Color images • Suitable for large objects

  8. More Disadvantages Due to color data, lower resolution than black and white CCD camera Limited red sensitivity through IR blocking filter Digital SLR's • More Advantages • Results can be viewed immediately • Automatically records exposure data • Flat exposure surface as opposed to film

  9. More Disadvantages In camera image processing that is detrimental to astrophotos (even in raw) Digital SLR's • More Advantages • Easy adjustment of ISO speed

  10. Disadvantages Complex handling Computer required Time consuming for color shots Use limited to astrophotography Difficulty in setting and focusing Astronomical CCD Cameras • Advantages • Low noise due to sensor cooling • Large dynamic range • High resolution with monochrome sensor • True raw data

  11. More Disadvantages High priced Astronomical CCD Cameras • More Advantages • High spectral sensitivity, shorter exposure • Good guiding capabilities • No camera shake due to hands off operation • Maximum image quality

  12. Notes and Tips • Digital cameras allow for shorter exposure times than film cameras • You can find samples of pictures taken with different camera types at: www.astromeeting.de/astrophotography_digital.htm • Telescopes with focal lengths of 500mm – 1000mm are recommended

  13. Step by Step Path to Astrophotography • Scenic snapshots – Tripod and camera • Piggyback – Mount camera on telescope tube • Images though telescope eypiece – Afocal photography • Webcam through telescope • Deep-Sky Images • DSLR • Astronomical CCD • Tracking mount

  14. Notes and Tips • Large focal ratio (F-Stop number is larger) telescopes are best suited for planetary photography • Low focal ratio (F-Stop number is smaller) telescopes are best suited for deep-sky photography • For astrophotography not only are the number of megapixels important, but also the dimensions of the sensor and the dimensions of the individual pixels

  15. Resolving Power of Telescopes • 60 mm = 2.2” • 80 mm = 1.6” • 100 mm = 1.3” • 130 mm = 1.0” • 150 mm = 0.9” • 200 mm = 0.7” • 250 mm = 0.5” • 300 mm = 0.4

  16. Angle of View • To get the best results for your astrophotography you need to know the angle of view for a particular combination of lens, telescope, and camera combination.

  17. Angle of View Formula • If you know the edge length of the image sensor and the effective focal length of the optics you can determine the angle of view with this formula: • Angle of View = 2 x Artan(L / 2*F) • L = edge length of imaging sensor • F = effective focal length in mm

  18. Focal Length Formula • If you want to determine the focal length needed to fill your frame you can use this formula: • F = L / 2*Tan(Angle of View / 2) • F = Focal length • L = Edge length of imaging sensor in mm • Angle of View = Angle of view of object you are trying to photograph

  19. Ideal Magnification for Planetary Astrophotography • N > Dpixel / .2805 • N = Dnominator of focal ratio (F-Stop) • Dpixel = edge length of a single pixel in micons (um) • Gives you the optimal focal ratio to get the maximum resolution from your telescope (see telescope resolution slide) when taking astropohotos of sun, moon, or planets

  20. Ideal Magnification for Deep-Sky Objects • F = 413 * Dpixel / S • F = Focal length in mm • Dpixel = Edge length of a single pixel in micons (um) • S = Maximum expected resolution in arcseconds on a particular night, due to atmospheric turbulence (seeing). If you do nhot have an excellent dark-sky observing site, then you should estimate a maximum resolution of 4 arcseconds.

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