Astrophotography

1
Astrophotography

• The Basics

2
Image Capture Devices

• Digital Compact cameras
• Webcams
• Digital SLR cameras
• Astronomical CCD cameras

3
Digital Compact Cameras

• Advantages
• Inexpensive
• Easy to use
• Small size
• Low weight
• No computer or external power supply needed

• Disadvantages
• Lens not replaceable
• Often, automatic modes cannot be switched off
• Mounting to telescope not easy

4
Digital Compact Cameras

• More Advantages
• Fast, automatic operation

• More Disadvantages
• Lack of features
• No bulb setting
• Limited to 15 to 30 sec. exposure

5
Webcams

• Advantages
• Inexpensive
• High sensitivity, short exposure times
• High resolution, sharp details
• Color images

• Disadvantages
• Tiny sensor, small field of view
• No bulb exposures possible
• No cooling to reduce noise
• Huge amounts of data

6
Webcams

• More Advantages
• Good focus control
• No cable release tangle
• Unbeatable for planetary imaging

• More Disadvantages
• Losses through data compression
• Operation impossible without computer
• Operation without telescope not reasonable

7
Digital SLR's

• Advantages
• Easy to use
• No computer necessary
• Versatile
• Color images
• Suitable for large objects

• Disadvantages
• Relatively high noise for long exposures
• High power consumption
• Difficulty focusing using LCD screen

8
Digital SLR's

• More Advantages
• Results can be viewed immediately
• Automatically records exposure data
• Flat exposure surface as opposed to film

• More Disadvantages
• Due to color data, lower resolution than black
  and white CCD camera
• Limited red sensitivity through IR blocking filter

9
Digital SLR's

• More Advantages
• Easy adjustment of ISO speed

• More Disadvantages
• In camera image processing that is detrimental to
  astrophotos (even in raw)

10
Astronomical CCD Cameras

• Advantages
• Low noise due to sensor cooling
• Large dynamic range
• High resolution with monochrome sensor
• True raw data

• Disadvantages
• Complex handling
• Computer required
• Time consuming for color shots
• Use limited to astrophotography
• Difficulty in setting and focusing

11
Astronomical CCD Cameras

• More Advantages
• High spectral sensitivity, shorter exposure
• Good guiding capabilities
• No camera shake due to hands off operation
• Maximum image quality

• More Disadvantages
• High priced

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/ast
  rophotography_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 / 2F)
• 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 / 2Tan(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 gt 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.