Transcript First Steps In Astrophotography
First Steps In Astrophotography
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
First Steps In Astrophotography
• Cameras and what they can do • Short exposure imaging • Long exposure imaging • Processing • Some tricks 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Cameras (and what they can do)
• Camera types • Strengths and limitations of camera types • Best subjects for camera types 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Camera Types
• Digital or Film • Simple “point & shoot” • More complex Point & shoot • Single Lens Reflex cameras • Webcams • CCD Cameras 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
An (Important!) Aside!
• Start with what you’ve got • Get a camera which isn’t just for astronomy • Get a tripod 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Digital or Film
• Film – bit old hat but still good for some subjects • Digital – rapidly improving format with lots of variations 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Film
• Good cameras are very cheap on e-bay • Film processing takes time • High “Dynamic Range” (about 16-20 bits) • Large “sensor” (35mm) • 35mm film is equivalent to about 20 M Pixels • Further processing requires scanning 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Digital
• Prices for “high end” cameras reducing quickly.Cheap cameras aren’t really coming down in price (just increasing pixel count) • “Instant” results • Limited dynamic range (8 to 14 bits) • Small sensors (typically 10mm across) • Easy digital enhancement and stacking 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Simple Point & Shoot
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Simple Point & Shoot
Auto Exposure only Auto Focus only Small Sensor and dynamic range Nearly always have a “live view” on LCD screen (WYSIWYG) Light and cheap (£50 up) Probably have one already!
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
More complex Point & Shoot
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
More complex Point & Shoot
Exposure Control Probably no focus control Up to APS (26mm) sized sensor Limited Dynamic Range (8 bit jpg files) Live View Fixed Lens Has a Filter Ring Becoming bulky and more expensive. £150 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Digital SLR
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Digital SLR
Pricey – Typically £400 with lens but good 2 nd hand market Full exposure and focus control APS or 35mm sensor 12 or 14 bit dynamic range (Raw file) No Live view except on most recent models Removable lens so can attach to telescope 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Webcams
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Webcams
Take a video stream that can be stacked into a single image Dead cheap (£30 - £60) Very small sensor Limited to bright subjects CCD Type best (ToUcam, SPC 900NC) Cheap adaptor connects to telescope 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
CCD Camera
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
CCD Camera
£400 up (and up..) Good 2 nd deals hand Cheap T Adaptor to connect to scope Needs capture software (maybe bundled) Low noise High sensitivity and dynamic range Specialised astro gear 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
What can they do?
• Daytime pictures (Sunrise/set, halos, sundogs, etc) • Constellation and wide field • Moon • Planets • Long exposure telescope imaging 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Daytime Pictures
Auto Exposure Point & Shoot Manual Exposure Point & Shoot Digital SLR Good. Convenient to carry for the unexpected Very Good. Allows “bracketing” of exposure Very Good Webcam CCD Camera No No 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Moon
Auto Exposure Point & Shoot Manual Exposure Point & Shoot Digital SLR Webcam CCD Camera Good Using Afocal method Potentially Very Good if coupled using filter ring Very Good if using telephoto lens or scope Excellent through scope Small field of view OK but usually too sensitive 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Planets
Auto Exposure Point & Shoot Manual Exposure Point & Shoot Digital SLR Webcam CCD Camera Planet too small for reliable results Planet too small for reliable results Possible using eyepiece projection but not good Excellent through scope Can get very good detail Too sensitive and planet too small 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Constellation & Wide Field
Auto Exposure Point & Shoot Manual Exposure Point & Shoot Digital SLR Webcam Poor. Usually limited to short exposures OK if 10 to 30 second exposure allowed Good if undriven, very good if driven No CCD Camera Very Good if matched with “T” SLR lens 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Long Exposure Telescope Imaging
Auto Exposure Point & Shoot Manual Exposure Point & Shoot Digital SLR No No Very Good Webcam CCD Camera No Excellent 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Daytime exposures (with “normal” lens)
• Views and phenomena • Sunrises & Sunsets • Moon • Eclipses • Tripod a good idea • Bracket exposures 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
9 th January 2008 Moon and Venus 2008/01/05 07:30 Canon 300D 55mm 1/10s F/5.6
800ISO Tripod Terry Evans, Bridgwater Astronomical Society
9 th January 2008 Partial Lunar Eclipse 2006/09/08 21:00 BST Canon 300D 400mm 1/160s F/4.5
800ISO Tripod Terry Evans, Bridgwater Astronomical Society
Noctilucent Clouds 2006/07/14 22:44 BST 9 th January 2008 Canon 300D 27mm 2.5s f/8 800ISO Tripod Terry Evans, Bridgwater Astronomical Society
Moon 22° Halo 2007/01/05 22:07 9 th Canon 300D 22mm 10s f/5.6 800ISO Tripod January 2008 Terry Evans, Bridgwater Astronomical Society
Moon and Venus 2004/01/24 17:44 Minolta Dimage-X 17mm Auto-exposure f/3.6 200ISO Wedged 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Short Exposure Imaging with a Telescope
• Moon and Planets • Sun with solar filter • Need to provide high magnification for planets and crater detail • Use eyepiece projection and “afocal” imaging 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Afocal Imaging
• Point camera with lens through telescope eyepiece!
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Lots of vignetting and need to be careful with focus. Starts like this 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
But careful composition and focus gets you this with an afocal DSLR 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Or this with a simple point & shoot camera 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Or this with a camera phone (not mine) 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Improving Afocal images
• PVC tube over the eyepiece • Camera attachment 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Improving Afocal images
• PVC tube over the eyepiece • Camera attachment • Filter ring attachment 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Webcam Imaging
• Best way for planets • Attach to scope with 1¼ inch adaptor • Essential to replace IR filter 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Webcam Imaging
• Need a computer!
• Use Webcam software to record about 10s AVI • Use Registax to stack the AVI
http://registax.astronomy.net
• Fiddle with Wavelets to bring out detail Registax Demo 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Constellation and Wide Field
• Need a camera which allows 10 to 30s exposures • Need a tripod • Lens of about 50mm (35mm equivalent) • Stacking software (DeepSky Stacker) 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Trailing
The Earth rotates about its axis every 24 hours The stars appear to rise in the East and set in the West The amount of motion detected on the sensor is proportional to the magnification and the duration of the exposure 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Trailing Formula
Trail Length = F*E*T*cos(D)/ Pixel size where: F = Focal length of lens/scope (mm) E = Exposure length (Sec) T = 2* /86400 D = Declination of the star 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Star Trail Lengths on Canon 300D Pixel size 7.1 microns Focal Length Exposure 55mm 24mm 55mm 55mm 24mm 400mm 30s 30s 10s 30s 10s 10s Declination 0 0 0 60 60 0 Trail Length 17 pixels 7 pixels 5 pixels 8 pixels 1.2pixels
123 pixels 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Orion 10s @ 35mm fl 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Closeup of the Belt Stars 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Tracking the Stars
• Piggy-back on a telescope 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Tracking the Stars
• Piggy-back on a telescope • Dedicated Camera tracker 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Tracking the Stars
• Piggy-back on a telescope • Dedicated Camera tracker • Barn Door Mount 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Long Exposures with a Telescope
Need: • SLR or CCD camera (prime focus) • Coupling between camera and telescope • A way to take pictures • Good solid driven mount • Way to focus accurately 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Coupling to Telescope
• Coupling via T mount and T-eyepiece adaptor “Nosepiece” • Fully Screw-in system more robust but less flexible (e.g. SCT coupling) • Focal Reducer can be used to widen field of view 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Taking Pictures with Digital SLR
Stand Alone Computer Control You control the exposures directly Set up a sequence and let the computer do the exposures Feedback is through the LCD screen Images stored in the camera memory card Can display first exposures to make sure they’re right Can save in the camera or download to computer Needs lots of batteries but can be done anywhere Need power supply for the computer 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Stand-Alone DSLR shooting
• Need remote shutter release (can be wireless!) to avoid shake (£15) • Set shutter speed to longest available if no “bulb” • Set Mirror lockup if available • Set resolution to “RAW” or best available • Need lots of room on the memory card 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
DSLR Remote Control H/W
• USB cable for control and download • Probably need separate cable for “bulb”, about £15 for a serial cable http://www.astronomiser.co.uk/ 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
DSLR Remote Control S/W
Remote control using camera software or dedicated astro-sw, e.g.
• DSLR Focus (£25) http://www.dslrfocus.com/ • DSLR Shutter (Free) http://www.stark-labs.com/DSLR_Shutter.html
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Good Solid Driven Mount
• Needs to be solid enough for the telescope
plus
the camera • Need to get the balance right and may need more counterweight • Longest exposure dependent on polar alignment (Field Rotation) • Alt-Az OK for short exposures. Automated stacking takes care of field rotation 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Accurate Focus
• Remote control software has focus mode • Use bright star for focussing • Live View cameras make this easy (zoom) • Hartmann Mask / Diffraction Spikes 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Processing
• Can’t put back what wasn’t there!
• Stacking to increase Signal to Noise Ratio • Aligning to minimise tracking and field rotation issues • Post-processing to enhance the signal 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Stacking
• Adds (or averages) a number of images • Produces in increase in S/N ratio • Makes the image smoother • Mimics the effect of a longer exposure Exposure Effective = Num exposures*Exposure • Short exposures reduce: – Tracking errors – Lost Exposures because of cloud or satellites 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Aligning
• Makes sure each image aligns with the others for stacking • Manual 1 star alignment for tracking • 2 star alignment for tracking and rotation • Automatic star matching • Correlation (Registax) 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Aligning & Stacking Software
• Registax (Free) http://registax.astronomy.net • DeepSky Stacker (Free) http://deepskystacker.free.fr/english/index.html
• IRIS (Free but very complex to use) http://www.astrosurf.com/buil/us/iris/iris.htm
• Images Plus ($200) • Astroart (£120) • MaximDL (expensive but best $459) 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Post-Processing
• Photoshop (in its various guises) • Paintshop-Pro • Images Plus, Maxim & Astroart have some nice features (DDP & FFT filters) 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Photoshop
• Various versions • CS3 (hugely expensive, student version) • Elements (£60) but sometimes free with equipment • Various older versions (typically 8 bit) 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Photoshop Manipulation
• Levels • Curves • Sharpening filters • Noise / blur filters • Layers and masks 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Blurred layer to remove gradients
• Duplicate as new layer • Use “Dust&Scratches” to remove stars • Change mode to Difference 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Wash Layer to Increase Colour
• Duplicate image as a layer.Select layer • Filter Median and Gaussian Blur • Increase Saturation • Change mode to Color (sic) 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Layer Masks to Increase Range
• Duplicate image • Manipulate with curves, etc • Layer on original (ctrl-A,ctrl-C and ctrl-V) • Create a mask, select (alt click) and ctrl-V • Gaussian blur the mask (~10 pixels) • Select the layer 1 image • Merge down when happy 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Buying Second Hand
• Active upgrading so not just throwaways • http://www.astrobuysell.com/uk Very active site (15 listings per day) • http://www.astronomy-uk.co.uk/ Less busy but all good stuff • E-bay Some gems but 99% tat • American sites for the adventurous 9 th January 2008 Terry Evans, Bridgwater Astronomical Society
Things I’ve Left Out!!
• DSLR H-Alpha response and modification • Bias, Darks & Flats • Polar Alignment • Guiding • Motorised focussing • CCD imaging • And lots more… 9 th January 2008 Terry Evans, Bridgwater Astronomical Society