BASIC DSLR ASTROPHOTOGRAPHY

 

Updated 2017 January 16

 

Contents

 

Introduction

 

This tutorial describes three methods of astrophotography using a Canon 550D DSLR;

a) Mounted on a fixed tripod

b) Attached to a telescope focuser (10”/25cm Newtonian reflector)

c) Mounted on a goto mount (same as that used with the 10” Newtonian)

In all cases the camera is controlled by the EOS Utility Camera settings/Remote shooting software packaged with the camera. Remote Live View Shooting is covered in detail in the manuals which accompany the camera.

 

Processing the images is also covered;

- stacking using DeepSkyStacker

- further processing using Iris

 

Celestial objects used were – the Moon for (a), open clusters for (b). Item (c) will be covered when the dark nights return later this year.

 

Imaging

(a) Camera mounted on a fixed tripod

 

Equipment set-up

 

For this exercise, carried out when the moon was suitably positioned, I mounted my camera on a mini-tripod stood on my desk and pointing through an open window – Figure 1. The controlling laptop, connected to the camera via a USB cable, was positioned on a separate unit to avoid vibrating the camera during exposures.

 

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Figure 1. Equipment setup

 

Computer set-up

 

Open the EOS utility and select ‘Camera settings/Remote shooting’ – Figure 2.

 

Figure 2. EOS Utility

 

This brings up the EOS550D window – Figure 3.

 

Figure 3. EOS550D window

 

Imaging set-up

 

Images of the Moon were obtained as follows;

 

In the EOS550D window the values listed below were set;

- exposure time           1/1250 sec

- f number                   6.3

- ISO                           800 (for fainter objects set ISO to its maximum value)

- image quality            L (would advise using RAW + ΔL)

- Focal length              300mm

 

- click the ‘tools’ (hammer and spanner) button

- click on ‘Live View/Movie func set’ button.

- select ‘Enable’ and then ‘OK’ in the Live View/Movie func. set shoot window

- click the ‘Live View shoot’ button

 

The image is then displayed in the Remote Live view window as shown below. Position the camera so that target is in the centre of the image (it may be easier initially if the lens is set to minimum zoom and then to maximum once the target is centred).

 

Note that for precision astrometry it is important that the correct time is recorded for each image. First ensure your PC time is correct by installing software such as Dimension 4. Click on Date/Time In the EOS550D window and, in the Date/Time Setting window, Figure 4, select ‘Always match the computer time’, click on the ‘From PC’ button and then ‘OK’. The time recorded in the image info is for the start of the exposure.

 

Figure 4. Date/Time setting window

 

Focusing

 

Obtain focus initially with the lens in Manual Focus mode and then switch to Auto Focus mode. Drag the box to the section of the image to be enlarged – Figure 5

 

Figure 5. Focusing

 

Clicking on the magnifier button at the bottom of the window displays the selected area in the Zoom View window – Figure 6.

 

Figure 6. Focusing – Zoom View window

 

Using the arrows at the edges the image move the box to an area of the image which contains features which can be used for focusing and select 200%. The image can now be brought into focus using the arrow keys in the Focus section of the Zoom View window – Figure 7.

 

Figure 7. Focusing – Zoom View x 200

 

To return to the original size image deselect ‘200%’ and click the ‘Fit in window’ button below the right-hand edge of the image.

 

Imaging

 

Once the target is in focus further images can be obtained using the Shoot button in the top right-hand corner of the EOS550D window. Images, obtained in dual RAW and jpeg format (RAW+L), are transferred form the camera to the PC and displayed in the Quick Preview window. Digital Photo Professional starts automatically and records the images – Figure 8.

 

Figure 8. Digital Photo Professional start-up window

 

Various settings were tried for a series of images and these can be displayed by selecting a thumbnail image and then clicking on the ‘Info’ button. The combination which produced the best image, Figures 9 - 12, was;

- exposure time                       1/1250 sec

- f number                   6.3

- ISO                           800

- Focal length              300mm

 

Double clicking on an image in the DPP window, Figures 8, shows it full size, Figure 9, The Field of View is approximately 3.7 x 2.6 degrees.

 

Figure 9. Full size image

 

To produce an enlarged image select ‘Tools/Start Trimming/Angle Adjustment tool’ and draw a box around the section of the image you wish to enlarge, Figure 10, (clicking over the box or on the corners allows it to be repositioned).

 

Figure 10. Selecting an area of the image to be enlarged

 

Click ‘Center on Screen’ and then ‘OK’. The result is shown in Figure 11.

 

Figure 11. Enlarged image

 

To save the enlarged image select ‘File/Convert and save’.

 

Any fuzziness is probably due to the warm air passing from my study past the camera and through the open window above.

 

The image of the Moon shown in Figure 12, was obtained in twilight at the Hampshire Astronomical Group’s Clanfield observatory. The camera was set up outside so no problems with columns of warm air. Settings were;

 

- exposure time           1/1000 sec

- f number                   6.3

- ISO                           1600

- Focal length              300mm

 

Best Moon

Figure 12. The Moon in twilight from the Hampshire Astronomical Group’s Clanfield observatory

 

Please note that none of the images were processed in any way neither were the images calibrated using dark frames and flat fields.

 

The Bright/RGB box at the bottom right of the Remote Live View Window, Figure 13, can be used to set the correct exposure. An image of Mars from the Compact NASA Atlas of the Solar System was used to illustrate this point (with the way the weather is at the moment this is the best I can do !!!). The height of the curve at any point indicates the number of pixels existing at that particular brightness level. Adjusting the exposure time/ISO setting to minimise the number of pixels on the extreme left (under exposed) or right (over exposed) should produce the best image. Clicking on ‘RGB’ will produce a similar display for each colour.

Figure 13.  Setting the correct exposure using the Bright/ RGB box

 

The Tool palette, allowing image manipulation, can also be displayed by clicking on the button of that name in the main DPP window – Figure 14.

 

Figure 14. Tool palette

 

(b) Camera attached to a telescope focuser (10”/25cm Newtonian reflector)

Equipment set-up

 

Figures 15 and 16 show an eyepiece and DSLR camera respectively attached to the focuser of my telescope, a 102/25cm f6.3 Newtonian reflector. For the former the focuser is at one extreme of its travel and for the latter the other. It may be necessary to insert a Barlow lens between camera and focuser to obtain a good focus (as is the case with the Hampshire Astronomical Group’s 24”/61cm reflector).  I do need some form of safety strap to ensure that, if the camera were to make a bid for freedom, it can’t go too far.

 

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Figure 15. Telescope with eyepiece in place

 

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Figure 16. Telescope with eyepiece replaced by DSLR camera

 

The standard USB cable proved to be a little short necessitating placing my laptop on a chair close to the telescope so an extension lead has been purchased allowing for more secure and comfortable positioning of the computer.

 

Focusing and imaging

 

Similar to the camera with its own lens mounted on a fixed tripod except that focusing has to be done manually using the telescope’s focuser. A good focus was achieved by adjusting for the smallest stellar image – I have yet to use a Bahtinov mask for that purpose.

 

The constellation of Cancer being well placed I imaged the open clusters M44 (Beehive Cluster) and M67. In the images of both clusters below, Figures 17 and 18, the faintest stars are approximately magnitude 14.5. Exposure details are;

- exposure time           15 sec

- ISO                           1600

 

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Figure 17. M44 – the Beehive cluster

 

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Figure 18. M67

 

(c) Camera attached to goto mount

 

Please note that this is the way I do it but, depending on your circumstances, you may arrive at the end result (ready to image) by a different route. I strongly recommend that once you have  worked out your preferred method you commit it to paper – nothing beats a checklist !!!

 

Equipment

 

The various components used are shown in Figure 19. Clockwise from top left they are;

- 75-300mm lens

- USB cable

- USB cable extension

- camera mains adapter and cable

- tools required for assembly

- lens hood

- red dot finder

- camera hot shoe adapter for red dot finder

- dovetail bar, attachment bolt and washers

- Canon EOS550D DSLR with 18-35mm lens attached

 

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Figure 19. Components

 

Figure 20 shows all the components attached to the camera while Figures 21 and 22 show the camera ttached to the goto mount and the observatory. The rectangular white box next to the laptop is a Devolo wifi power line adapter which plugs into a mains socket and is used to connect the laptop to the internet.

 

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Figure 20. Camera assembly

 

 

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Figure 21. Camera assembly attached to goto mount

 

Camera set-up

 

The various components are attached to the camera as shown in Figure 20. Assuming a good weather forecast I do this late afternoon so as not to eat into imaging time.

 

Camera settings as gleaned from various sources;

- Mode set to Manual

- High ISO speed noise reduction on

- Long exposure noise reduction to strong

- Mirror lock-up to Enable

- Self-timer set to 2 seconds

- White balance set to Auto (AWB)

- ISO set to 800 (or 1600 for fainter objects)

- f.no set to 5.6

 

Again to make the best use of your imaging time targets should be selected at this time.

 

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Figure 22. Observatory

 

The next stage is to attach the camera to the mount, camera to laptop, plug in the mains adapter and fire up the laptop and power line adapter.

 

Laptop set-up

 

If timing is important I use Dimension 4 to accurately set the PC clock..

 

To check that I am properly aligned on the target I bring up Megastar, a planetarium program. Any similar software such as Guide or Stellarium will do the same job.

 

Next start up EOS Utility to be able to control the camera from the laptop (an alternative is BackyardEOS). The use of this software and Canon Digital Photo Profssional has been described earlier so will not be repeated here except to mention that images should be saved to both camera and laptop.

 

Alignment and focussing

 

The need to polar align and/or 3-point align will depend on your circumstances. For me I just need to do a 3-point alignment which takes into account any small errors in polar alignment.

 

The red dot finder can be used for 3 point alignment and Live View if the alignment star is quite bright (as alignment stars usually are).

 

Imaging

 

My first attempts with this setup were of constellations. The size of the constellation will dictate the lens used. The 75-300mm lens was suitable for Delphinus, Equuleus, Lyra and Sagitta.

 

One needs to experiment with exposure time  so  I tried 10-60 secs in 10 sec steps and found that light pollution started to show its hand at 60 secs. More experimentation with f.no and ISO is required.

 

Figure 22 is an image of Lyra and Figure 23 is a stack of images processed with Deep Sky Stacker and Iris as described in the article by Ian Morrison in the 2015 November issue of Astronomy Now and below.

 

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Figure 22. Lyra. 50sec exposue, f/6.3, ISO800, FL 75mm

 

Lyra sblur IRIS

Figure 23. Lyra, stack of 5 images processed with Deep Sky Stacker and Iris

 

 

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Figure 24. Part of Figure 22 showing M57, the Ring Nebula, in the centre. The faintest stars in this image are around mag 11

 

Image processing

DeepSkyStacker and Iris

 

DeepSkyStacker can be accessed at http://deepskystacker.free.fr/english/index.html and the User Manual via the same URL.

 

Both DSLR RAW and CCD FITS images can be stacked as demonstrated below. In these examples only light frames are processed.

 

a) DSLR RAW images

Deep Sky Stacker

Start DeepSkyStacker and click on ‘Open picture files’. The selected files are listed as shown in Figure 25. These are images of Lyra taken with the DSLR camera on the goto mount and of  exposure times 20, 20, 30, 40 and 50 secs. (to be redone with images of same exposure times).

 

Figure 25. RAW images loaded into DSS

 

To register and stack images;

- select Check all

- select Register checked pictures and OK on the two windows which then appear

  in succession (options will be covered later).

- select Stack checked pictures

 

After much churning the stacked image appears - Figure 26. The RGB sliders were  adjusted slightly to better show the stars

 

Figure 26. Stacked DSLR RAW images

 

Running under Windows XP (and possibly other operating systems) I found that I had to save the images as ‘TIFF Image (16bit/ch)’ to be able to recover them. To do so click on ‘Save picture to file…’, save as type previously mentioned and complete the other usual Windows boxes.

 

Iris

 

Start up Iris and load the TIFF image saved after DSS processing. The image can be manipulated using a View/Logarithm and the Threshold sliders – Figure 27.

 

Lyra stack IRIS

Figure 27. Image after processing with Iris

 

To bring out the star colours load the TIFF image from the DSS processing and invoke the SBLUR command, SBLUR 10 4, via the command line window – Figure 28.

 

Lyra sblur IRIS

Figure 28. Image processed with Iris including the SBLUR command

 

b) CCD FITS images

Start DeepSkyStacker and click on ‘Open picture files’. The selected files are listed as shown in Figure 29. The images were of comet 29P obtained on 2015 July 17 using the Warrumbungle robotic telescope (part of the SSON network).

 

Figure 29. Selected FITS images.

 

To register and stack images;

- check required images

- click on ‘Register checked pictures’ and OK on the two windows which then appear in succession (options will be covered later).

 

After much (but less than for RAW images) churning the stacked image appears - Figure 30. The RGB/K level slider was adjusted to better show the comet.

 

Figure 30. Stacked images of comet 29P

 

Running under Windows XP (and possibly other operating systems) I found that I had to save the FITS images as ‘FITS Image (16bit/ch)’ to be able to recover them. To do so click on ‘Save picture to file…’, save as type previously mentioned and complete the other usual Windows boxes.

 

c) Comet stacking

DSS offers three stacking modes for comets;

1) Standard stacking - the comet position is ignored. The comet is fuzzy and the stars have no trail.

2) Comet stacking - the image is aligned on the comet and the stars are trailed. Star positions are used to compensate any field rotation.

3) Comet and stars stacking - the comet position is used. A first stack is created to extract the comet from the background. Then a second stack is created to freeze the star (the comet is subtracted from each calibrated and registered light frame before stacking it). Last, the final image is obtained by inserting the comet back in the image.

 

For this example images of comet C/2014 Q2 obtained with the SSON robotic telescope on 2015 July 29th were used.

 

1) Standard stacking

Open the required images

Register the images by;

- checking the images

- selecting ‘Register checked pictures…’

Under the Register Settings/Actions tab;

- enter 100% in the ‘Select the best’ box

Click on OK

 

Return to the Main window, Figure 31, by clicking on ‘Open picture files…’

 

Figure 31. Main DSS window

 

Register the comet centre for by selecting each image in turn and using the Edit Comet Mode, Figure 32, and save the change by clicking on the floppy disk symbol below the comet symbol in the toolbar. When the comet position is set a + (C) will be added to the star count in the #Stars column in the list of images in the bottom half of the screen.

 

The number of stars can be varied by adjusting the Star detection threshold in the Register Settings window under the Advanced tab. This is accessed when ‘Register checked pictures’ is selected.

 

Figure 32. Registering the comet centre

 

Select the images you wish to use and then ‘Stack checked pictures’. Click on ‘Stacking parameters’ in the Stacking Steps window – Figure 33.

 

Figure 33. Stacking Steps window

 

Under the Comet tab select Standard Stacking, Figure 34, and under the Light tab select Average, Figure 35, and then OK twice. The result is shown in Figure 36.

 

Figure 34. Stacking Parameters window

 

Figure 35 Stacking parameters, Light tab

 

Figure 36. Result of Standard Stacking (stacking on stars) – the positions of the comet are shown

 

The brightness of the image may be varied by moving the slider and clicking on ‘Apply’

 

Under Processing select ‘Save picture to file…’ and save as ‘TIFF Image (16bit/ch)’ or FITS Image (16bit/ch) (see comment under Figure 30 above).

 

2) Comet Stacking

 

Proceed as previously but, under the Comet tab in the Stacking Parameters window, select Comet Stacking and select Average under the Light tab The result is shown in Figure 37.

 

Figure 37. Result of Comet Stacking (stacking on comet) – star trails are shown

 

3) Stars + Comet stacking

 

Proceed as previously but, under the Comet tab in the Stacking Parameters window, select Stars + Comet Stacking and select Average under the Light tab The result is shown in Figure 38.

 


Figure 38. Result of Stars + Comet Stacking

 

 Resources

 

Many of the resources listed below came to light at the BAA Observers’ Workshop held at Burlington House 2013 September 22.

 

Introduction to DSLR Astrophotography by Tony Morris and available from the BAA Office.

 

Graham Relf’s ‘Photography – creative and technical’ website  at http://www.grelf.net/index.html

- GriP software - http://www.grelf.net/grip_intro.html

 

When imaging constellations for example it is useful to work out beforehand the size of the required field of view. A tool can be found at http://www.howardedin.com/articles/fov.html  which will calculate the field of view for a given camera/lens focal length combination or produce a table of FOVs for different focal lengths of a given lens.

 

One wants a long exposure time to bring out fainter objects but a short one to avoid trailing. An exposure calculator can be found at http://www.sceneplanner.com/tool3.php

 

Camera control software

- Astro Photography Tool - http://www.ideiki.com/astro/     

 

Image processing software

- Raw Therapee - http://rawtherapee.com/blog/features                                            

- Irfanview - http://www.irfanview.com/                                                                  

- Adobe Photoshop - http://www.adobe.com/uk/products/photoshopfamily.html

- DeepSkyStacker - http://deepskystacker.free.fr/english/index.html           

- AIP4WIN - http://www.willbell.com/aip4win/aip.htm

- PixInsight - https://pixinsight.com/

- IRIS - http://www.astrosurf.com/buil/us/iris/iris.htm

- Images Plus - http://www.mlunsold.com/

- Maxim DL - http://www.cyanogen.com/maxim_main.php

- Nebulosity - http://www.stark-labs.com/nebulosity.html

- Astro Stack - http://www.astrostack.com/

- Astroart - http://www.msb-astroart.com/

- Gimpshop - https://www.gimpshop.com/ (this is the correct address but it wont open from this page so suggest you type it into your browser)

- PaintShop -  http://www.corel.com/corel/allProducts.jsp

 

Software for creating mosaics

- iMerge - http://jaggedplanet.com/iMerge.html

- Microsoft Ice - http://research.microsoft.com/en-us/um/redmond/groups/ivm/ice/

 

Bahtinov masks - http://www.morris-engraving.co.uk/bahtinov.htm

 

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