Digital Video Planetary Imaging with a Dobsonian Telescope · 7 Film Camera - late 1800s to ~1980s...

Digital Video Planetary Imaging

with a Dobsonian Telescope

WOLAS 10-6-2012 © Martin Lewis Nov. 2015 1 Martin Lewis (www.Skyinspector.co.uk)

Planetary Imaging

• Methods of Recording Planetary Details

• Lucky Imaging of Planets with Digital Video Cameras- Overview

• Video Planetary Imaging with a Dobsonian Telescope?

• Progressive Refinement of Imaging Methods

Recording Planetary Surface Detail- Methods

Recording Planetary Surface Detail – Methods

• Sketching at the Eyepiece

• Film camera

• CCD camera

• Digital camera

• Digital Video imaging

Sketching at the Eyepiece - 1600’s to present

• Low tech, low cost

• Able to make the most of fleeting moments of good seeing to pick out fine detail

• Brain is able to effectively average out some of the movement effects of a turbulent atmosphere

Giovanni Cassini 1677 Sketch of Jupiter

Sketching at the Eyepiece - 1600’s to present

Jupiter 9/6/93, 10” Dob. ML

• Can be difficult to quickly record fine details accurately before planetary rotation becomes significant especially for Jupiter

• High levels of skill needed to make quick and accurate drawings of planets – can take years to develop this skill

• Prone to subjectivity and suggestion - Martian canals

Film Camera - late 1800’s to ~1980’s

• Less subjective than sketching

• But generally, can see much more by eye at eyepiece than can record on film

• Small image size at prime focus and scattering of light in film causes loss of contrast unless use eyepiece projection or barlow to enlarge image then longer image exposures cause blurring

AA Common 1867; 1st known photo of a planet showing surface details

Film Camera - late 1800’s to ~1980’s

• Dimness esp. due to enlargement, necessitates exposures of several seconds making method prone to blurring by movement of atmosphere and placing big demands on tracking accuracy.

• Have to estimate position of best focus - lot of luck required

Pic du Midi 1m scope 1988

200” Hale telescope

CCD Imaging - 1980’s to ~2000

• CCD are like reusable electronic film

• No emulsion scattering issues and higher sensitivity compared to film which allows short exposures at reasonable image scale – so reducing blurring by atmosphere

• Can take many more individual images than with film and reject most- with this method one can readily home-in on the position of best focus

• Electronic image so easier to carry out imaging processing techniques that allow image enhancement and methods like stacking of individual images

• Electronic medium allows easy distribution of images

• CCD cameras relatively expensive

Digital Camera - 1990’s to present

• Similar to CCD imaging with similar advantage but much cheaper than CCDs now- no need for cooled chip of CCD as exposures so short

• Quick to see results and so quick to home-in on focus

• Recent camera developments allow live view and video imaging at high fps

Digital Video Imaging - ~2000 to present

• Has the potential to pull out significantly more detail than any other method

• No other method comes close to video imaging in terms of accuracy and detail

……. and still evolving with better cameras and processing methods coming along all the time!

12 © Martin Lewis Nov. 2015 © Damian Peach

Digital Video Imaging – Introduction

• Low-cost uncooled CCD digital video camera (webcam) used to take thousands of separate frames of planet which are combined to make one final combined image

• Not just the recording method. The whole process relies on the combination of video camera AND special processing software.

The venerable and once very popular Philips Toucam webcam with its colour Sony 098 chip ready for action!

• Video imaging method uses software to;

• Align separate frames

• Put frames in quality order

• Reject worst frames

• Stack the best frames to produce an averaged and low-noise image where atmospheric disturbances is averaged out

• Stacked average image can then be image-processed revealing detail which was initially hidden

Digital Video Imaging - Advantages

• Video camera fairly low cost and key processing software is free!

• Relatively simple to get started

• Good results possible with fairly minimal learning but great capacity to take further

• Best planetary imagers need to develop skills in a wide range of different disciplines and this makes it really challenging and interesting;

• optics

• video processing

• still image processing

• mechanics

• thermal management

• weather/atmosphere

Digital Video Imaging - Overview of Method

Digital Video Imaging Overview – Min. Equipment

laptop

Firewire/USB/Ethernet

connection for high data

transfer rate

camera Filter wheel (for

mono camera)

Barlow or

Powermate

Motorised

Focusser

Plus •1.25” to camera adaptor •IR/UV filter

Tracking Mount

TELESCOPE

Digital Video Imaging Overview - Lucky Imaging

Overview of the Lucky Imaging process

• What a real planetary video looks like

• Unprocessed Video of Mars (red filter) from 26th Jan 2010.

• 2000 frame video

• See how the brain picks out the fleeting details

20 © Martin Lewis Nov. 2015

Lucky Imaging – Quality Sorting

Best red frame out of whole avi of 2000 frames

-not as good as ‘mentally filtered’ impression!

Lucky Imaging – Quality Sort

Best of 2000 frames

Worst of 2000 frames

1201st Worst Frame

Align and Stack this Range

• Registax or AutoStakkert!2 sorts the frames of the video in quality order

• Pick the best 1200 out of 2000 total frames

1200th Worst Frame

Reject this Range

Lucky Imaging – Align and Stack

Best of 2000 frames Worst of 1200 stack

Stack of 1200 frames

• Align and Stack best 1200 frames

Aligned Stack of 1200 best frames. -Noise reduced -Atmospheric turbulence averaged out

Lucky Imaging – Wavelet Processing

Stacked image wavelet processed in Registax (Red)

Stack of 1200 best frames.

Lucky Imaging – Colour Images

Taken through Blue filter

–quality sorted/aligned/stacked image wavelet processed

Taken through Red filter

Taken through Green filter

Video Imaging – RGB Colour Method

Video Imaging – Two Methods of Getting Colour

• Traditionally Monochrome video cameras with changeable colour filters in front produced superior results;

• Superior dyes in dedicated filters with more controlled band-pass

• 3x as many pixels for each colour so better resolution

• More light per colour per frame so less noise

• Colour video cameras with colour filters incorporated into the chip are simpler and much quicker and now much improved

Colour Camera Mono Camera + RGB filters 1/3/2012

Video Imaging with a Dobsonian though??

The Dobsonian Design

•To help popularise astronomy, John Dobson, a Californian monk, invented a simple low cost alt-azimuth mount for a Newtonian reflector to allow the largest aperture to be built for the lowest cost •The ‘Sidewalk Astronomers’ took the scopes around the streets of San Francisco at night showing people the heavens

Dobsonian Design

The mount revolutionised astronomy and made large aperture scopes much more affordable •Very stable alt-az mount •Undriven •Push-To follow with no tracking

Dobsonian Variants

Traditional solid tube

Truss tube

Ultra-light

Original

222mm Dobsonian ‘Mr. Orb Inspector’

Video Imaging with a Dobsonian

• The frame to frame alignment capability of Registax and AS2 means that there is not the requirement to keep the planet absolutely stationary in the field during recording of the video

• Planet’s image just needs to be somewhere in the field

• But a Dobsonian telescope has no drive capability at all so image will drift out in a few seconds won’t it ??

Video Imaging with a Dobsonian – Drift Method

Drift Method (May 2005)

• Allow planet to drift through field and record video as drifts from one side of field to other side

• Reposition scope to start and repeat drifts until have a few hundred frames

• Process videos in Registax as a set

• Drift video 22th June 2005

Jupiter using drift method June 2005 with colour Toucam

• Very simple method to get you going on any undriven scope

• Field drift approx. 15” per second

• Short exposures of <1/30 sec give <0.5arcsecs of smear

• Small image size otherwise get too few frames per drift

• Need to work quickly to minimise rotation of planet (esp. Jupiter)

• No compensation for field rotation

Video Imaging with a Dob. – Eq. Platform Method

• Drift method can only take you so far

• Image scale is low

• Noisy images as too few frames

• In Autumn 2005 decided to improve my imaging by designing and making an equatorial platform

• With my Dobsonian mounted on this platform it should allow me to track the planet

• Targeted the 2005/2006 apparition of Mars for completion of equatorial platform

• Platform has a virtual rotational axis which has to be carefully aligned with the earth’s axis – it must point at the Celestial Pole

• Anything placed on the driven platform follows the rotation of the sky

• Very stable as bearing surfaces so far apart and very low

• Retains the easy alt-az scope movement that is so appealing with a Dobsonian scope but with the benefits of tracking

Equatorial Platforms – Simples

Lat=52°

•Large Cone with base angle = 2x latitude

•On ground with axis at latitude angle

•Constrain with rollers on brackets on each side so cone can only rotate about axis

•Point axis at celestial pole and rotate with sidereal period to match stars

•Cut off parallel with ground and fill scoop shape to make a flat and level platform

•Anything placed on platform will follow the stars

Commercial Equatorial Platforms

• Tom Osypowski, California, US, www.equatorialplatforms.com @ $1000+

48 © Martin Lewis Nov. 2015 48

Mars 18th Nov 2005

First images of Mars with scope on Eq. Platform

with Toucam Colour camera

Equatorial Platform 11th May 2006 Drift Method 22nd June 2005

• More frames in given time so lower noise

• More frames and larger images scale so more detail visible

Refinement of the Imaging Method

• Color video cameras simpler to use and quicker to get results

• But B&W (mono) video cameras with changeable colour filters in front produced superior results

• Superior dyes in dedicated filters

• 3x as many pixels for each colour

• More light per colour per frame

• Mono-rechipped Toucam bought in early 2006

Further Improvements to Method – From Colour to Mono

Eq. Platform and Mono-rechipped Toucam (610nm filter)

Eq. Platform and Standard Colour Toucam

Both 17th Feb. 2006

Further Improvements – Addressing Vibration

• Improvements made to eq. platform motor vibration (2009)

Further Improvements to Methods – Vibration

• Very low motor vibration is a key characteristic of any tracking mount when video imaging planets. Much less important than tracking accuracy

• Normally won’t even notice vibration Visually or Deep Sky work but when need resolutions of <0.5” for high resolution planetary imaging the impact can be large

• Should certainly be no vibration felt in body of scope and very little by motor

• Detection presence of vibration problems by ‘star dance’ method

Tapped eyepiece at high power - no vibration

Tapped eyepiece at high power – vibration present

• Stepper motor replaced with turntable synchronous motor driven under-voltage

• Introduced worm and wheel into gearing path to improve mechanical isolation

• Motor is spring isolated

• New design of low power synchronous motor drive electronics designed by work colleague (Steve Markham)

58 4th May 2010 Edge-on Saturn after improvements to platform vibration

Further Improvements to Methods – Sensitivity

• Increasing the image surface brightness allows one to push forward in a number of ways to improve image resolution;

• Larger image size without excessive reduction in surface brightness

• Faster frame rate without being limited by exposure time. More frames = less noise and better averaging

• Less shot noise

• To improve image brightness

• Get a larger scope - also improves inherent resolution ££££

• Get a more sensitive camera - Sony 618 chip has twice the sensitivity of previous popular chips

60 21st Sept 2010

Jupiter with 618 chipped Imaging Source camera showing detail in Ganymede

Saturn 10th April 2011

Further Improvements to Methods – Image Scale

• Improved sensitivity allows improved image scale

• f35.7 = 7.9m fl & f22.3 = 5.0m fl

Further Improvements to Methods – Use of ADC

• Prismatic effects of atmosphere especially at low altitude means a positional offset for R, G and B

• Registax can realign the separate R,G &B channels BUT

• When the dispersion is bad then you get vertical smearing within each colour band

Polaris (alt 52°) showing dispersion effects

Further Improvements to Methods – ADC

• Severity of dispersion effects depends on object altitude, wavelength and the width of filter bandpass

• Colour filters reduce dispersion effects but are significant in blue for all planet altitudes from UK (<60°)

0.4” resolution limit

• Atmospheric Dispersion Corrector (ADC) to correct for prismatic effects of atmosphere by applying opposite dispersion to that caused by atmosphere

Astro Systems Holland

Pierro Astro ZWO

Jupiter & Callisto 13th Jan 2012

Jupiter 22nd Nov. 2011

Smallest features ~0.4” across (image scale=0.18pix/arc sec)

Mars 2012 Albedo Maps

Mars –Opposition, Winter 2007/2008

Winjupos to unwrap globes and form map

Mars –Winter/Spring 2010

Mars –Winter/Spring 2010 (top) v Spring 2012 (bottom)

26th Jan 2010 14.1” after vibration fixed

24th Mar 2010 13.1” with 618 chip & ADC & Pipp

Mars –Spring 2012

Mars – Spring 2012

Mars –Spring 2012

Further Improvements to Methods – Winjupos Derotation

Winjupos is a multipurpose Swiss Army knife for planetary imaging. Originally designed to map the movements of Jupiter’s cloud belts the program can now do all sorts of other useful things; •Ephemeris for planets and their moons with graphical representation •Creation of planetary maps by unwrapping globe •Creation of rotational videos based on standard or created maps •Derotation of videos •Derotation of RGB images

Derotation feature is especially useful for Jupiter. Rotational period is so short that to prevent blurring of the image all videos need to be gathered within about 2mins. Derotation feature allows you to extend the time window enormously

•R 1min 3600 frames at 60fps •G 1min 3600 frames at 60fps •B 1min 1800 frames at 30fps •R 1min 3600 frames at 60fps •G 1min 3600 frames at 60fps •B 1min 1800 frames at 30fps •R 1min 3600 frames at 60fps •G 1min 3600 frames at 60fps •B 1min 1800 frames at 30fps •Process each video to create R, G or B images •Combine all Reds using image derotate •Combine all Greens using image derotate •Combine all Blues using image derotate •Finally Combine R, G & B with RGB derotate

22nd June 2005 17th Dec 2012

Same 8 ¾” Telescope!

Drift Method with Toucam Eq. Platform (vibration reduced), Sony 618

chip camera, ADC, + Winjupos derotate

Where Then?

In early 2013 decided that had reached the limits of my 222mm scope but not the limits of my ambition! I needed a bigger planetary scope!

Where Then?

In early 2013 decided that had reached the limits of my 222mm scope but not the limits of my ambition! I needed a bigger planetary scope! Fortunately I had one.....

Fossil Light 444mm Dobsonian

18” on equatorial platform- 1st try on 9th Jan 2013

18” on equatorial platform- 1st used 9th Jan. 2013

2013 season

•Jan. 2013 was right at end of 2012/2013 Jupiter apparition 2012/2013 •Saturn that year I used my trusty 222mm Dobsonian and a newer, faster higher sensitivity colour CMOS based camera that had been recently launched by ZWO in China •Even though colour camera it gave great images when used with the ADC -even for Saturn at 27°

•Decided to use 18” as much as possible on Jupiter and Mars in 2014 •Colour versus mono comparisons kept defying received wisdom that you get the best colour images using a mono camera and filters

ASI120MC (colour) ASI120MM (mono + RGB filters)

ZWO ASI120MC colour camera gave great images & much less trouble than mono RGB

ASI120MM (mono + RGB filters)

•With the good results on Jupiter with the 18” + colour camera + ADC combo I decided to use this combination for Mars apparition in 2014

15th April 2014 15th May 2014

•Saturn was still better with the 222mm scope but the lower altitude was making imaging it difficult

Best of 2014 (23° alt.) Best of 2013 (27° alt.)

•After Saturn had gone from the evening skies there would be a long break until Jupiter came round

•Took the opportunity to get Es Reid to improve the figure on my mirror –removing ~1/6 wave of overcorrection •Did a lot of work on improving the thermal management of the scope as well as big improvements to the mirror edge support which I think was causing issues with low alt. planets like Saturn.

•Jupiter with new larger format colour ASI camera with larger pixels (ASI174MC)

Jupiter and Ganymede 14th April Jupiter 23rd April

•Colour camera versus mono RGB again!

ASI174MC colour ASI174MM mono RGB

•Also experimented with better barlows including a lovely 2.7x APM barlow which was better corrected than my 3x TV and 2.5x and 5x Powermates •Doubled-up, two 2.7x APM cells together give 6x magnification

•Also experimented with IR imaging using a new Astronomiks 642nm filter

•Methane filter (890nm 10nm bandpass) from ZWO on Jupiter well past its best

•ASI174MM did well in UV and IR on Venus

•Venus in UV and IR in 2015

9th July

13th May 3rd June 23rd June

30th July

•The ASI174 when combined with the refigured mirror and improved mirror support gave my best ever Saturn image at an altitude of only 20°!

•Another new camera from ZWO was the highly sensitive and ultra low noise ASI224 colour camera which is very sensitive in the IR

•Venus best at end of year •Mars close, but very low at opposition at alt. 16° •Make the most of Jupiter 44° alt. at opposition •Saturn very low at opposition at alt. 18°

Planetary Imaging of DSOs?

•An exciting new possibility with the ASI224MC is to use thousands of short exposure photos and high gain to take shots of DSOs using planetary imaging align and stack techniques

Digital Video Planetary Imaging with a Dobsonian Telescope · 7 Film Camera - late 1800s to ~1980s...

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