Getting started with Digital Astrophotography - Part II Rodger King - Dec 2016

Transcription

1 Getting started with Digital Astrophotography - Part II Rodger King - Dec 2016

2 RECAP Getting started with Digital Astrophotography - Part I Rodger King - May 2016

3 Visual Astronomy Equipment Telescope Tripod Eyepiece

4 Question Visual Astronomy What is the frames/sec of the human brain/eye? Answer - it varies ~ 200/sec for very bright images, fast moving ~ 30-50/sec for normal images Slowest speed of few seconds per frame for very faint images

5 Digital Astrophotography No Limit To Exposure Time (KEY DIFFERENCE) ~11 times diameter ~120 more light collection What you can see = Hubble telescope = 2.3m My telescope = 0.2m Light Collection x Exposure Looking through the Hubble telescope is similar to a 300 second exposure using a camera on my telescope

6 Digital Astrophotography Now the problems start

7 Astrophotography Problems part I 1. Most Astronomical objects are faint 2. My telescope shakes and spoils the picture 3. Objects are moving 4. Light Pollution 5. Seeing the results 6. Wished I had taken multiple pictures 7. Cannot focus accurately 8. Is one telescope enough? 9. I cannot find what I want to see

8 SMALL MEDIUM TELESCOPE DSLR MOTORISED GOTO SYSTEM HEAVY TRIPOD LAPTOP or TABLET

9 Part I

10 DSLR using 8 Reflector

11 DSLR using 3 Refractor

12 Not able to take this yet We need Part II

13 Digital Astrophotography The problems continue

14 Astrophotography Problems part II 1. In Manchester the sky is poor, the weather is poor 2. I would like to take an even longer exposure 3. How do I combine multiple pictures? 4. Controlling the telescope 5. The results are grainy 6. The Picture is too small or too big 7. The Picture doesn t look the best?

15 Astrophotography - Problems In Manchester the sky is poor, the weather is poor Contrails from aeroplanes Other dirt and dust in the atmosphere Light Pollution Clouds, Rain, snow, windy, just too cold ANSWER : Move Be Mobile - Travel

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17 Astrophotography - Solutions Travel Options Abroad (better skies and weather) Canary Isles Tenerife La Palma Europe Tuscany Umbria Provence Others U.S.A Australia 5-9/ /10 5/10 7/10 5-9/10 Only bettered by: Hawaii, Chile

18 Astrophotography - Problems Travelling Abroad problems Costs All the equipment weighs a lot Airline allows 30KGs each to La Palma The mains A/C power supply is un-reliable Use a Power-pack/Battery Cant take it on the plane Buy it in Tenerife Ship it to La Palma Store it in La Palma ~ 40 ( ~ 33KGs)

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21 Astrophotography - Problems I would like to take a longer exposure Motors have jerky movements due to the gears and cogs Internal accuracy limited Reduces with more weight to carry Tracking accuracy maximum of : ~ 200 seconds

22 Astrophotography - Solutions I would like to take a longer exposure Feedback signal to the tripod to correct errors Period Error correction (PEC) Compensates for the gears and cogs

23 Astrophotography - Solutions I would like to take a longer exposure Feedback signal to the tripod to correct errors Guiding Compensates for all inaccuracies Use a second camera (video camera) looking at the same scene Takes a picture every 2-3 seconds.

24 Astrophotography - Solutions Guiding Off-axis Guider Second Telescope Or use the finder

25 Astrophotography - Solutions Guiding Connect signal cable from Video camera to tripod (ST4/Autoguiding port) Look at the Video feed from the guider Pick one star and mark it with crosshairs If the picture moves it will feeds back a signal to the tripod Accurate to 1/5 th pixel of the video camera Tracking accuracy increased from ~ 200 secs to? > 3,600 secs

26 Astrophotography - Solutions ~ 200 ~ 0

27 Astrophotography - Problems Why do I need to take multiple pictures? One picture may have movement One picture may have contrail or other mistake One very long exposure still may have light pollution ANSWER : Take many shorter exposures Delete the ones that are not good Align + Combine into one picture

28 Astrophotography - Solution Combining pictures Take 3 mins (180 secs) minute exposures Take 20 pictures Combine is the same as 60 minute (1 hour) exposure You can ignore/not use the bad one(s) Signal/Noise is improved Star signal adds up Noise remains random You need Software to do this Aligns images in case there has been movement Combines images (add signal together)

29 AstroArt ~ 100

30 Astrophotography - Problems Controlling the telescope using the handset Wire is to short Can t visualise where to go ANSWER : Use virtual (computer) handset 0 Use wireless handset Use planaterium software ~ 20 + handset 0

31 Astrophotography - Solution Virtual Handset X

32 Astrophotography - Solution Wireless Handset X

33 Astrophotography - Solutions Planatarium Software Click on an object Press go ~ 0

34 Astrophotography - Problems The results are too grainy S/N is too high DSLR cameras too noisy when warm ANSWER : Use dedicated Astronomical CCD camera ~

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37 Astrophotography - Solution Astronomical CCD Camera Black and White (B/W) Camera (some are colour) 1 4 Mega Pixels Cools to 25C - 35C below outside temperature B/W needs a filter wheel with Red/Blue/Green Combine colours in PC software to make colour

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39 Astrophotography - Solution Combining mono CCD images pictures Take 2 minute exposures Take 5 pictures for red, blue and green Take 15 pictures with no filter (B/W) Combine is the same as one 60 minute exposure Signal/Noise is much improved PC Software Aligns images in case there has been movement Combine each filter images to just 4 images Create a 3-channel (RGB) single colour picture Add the B/W picture to improve S/N ratio

40 Astrophotography - Problems The picture is too small or too big Change the Telescope Longer the Focal length the more zoomed in Small Telescope (500mm) wide angle Medium Telescope (1000mm) zoomed in Large Telescope (1500mm) more zoomed in Change the Camera DSLR (bigger CCD chip) wide angle CCD Camera (smaller CCD chip) zoomed in WebCam (very small CDD chip) more zoomed in

41 DSLR using 3 Refractor La Palma

42 CCD using 3 Refractor La Palma

43 Astrophotography - Problems Picture doesn t look the best? Light pollution Plane passed through the image Stars are a bit blurred ANSWER : Post Processing

44 DSLR using 3 Refractor La Palma

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47 DSLR using 3 Refractor La Palma

48 DSLR using 3 Refractor La Palma

49 Part II

50 DSLR using 8 Reflector Timperley

51 CCD using 8 Reflector Timperley

52 CCD using 8 Reflector Timperley

53 DSLR using 3 Refractor La Palma

54 DSLR using 3 Refractor La Palma

55 CCD using 3 Refractor la Palma

56 DSLR using 3 Refractor La Palma

57 DSLR using 3 Refractor CCD using 3 Refractor la Palma

58 CCD using 3 Refractor la Palma

59 CCD using 3 Refractor la Palma

60 of Part II