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Bizibilder

Simple white light Solar imaging

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Most people consider Astronomy to be a “night time” hobby, however this is most definitely not so! The Sun offers us plenty of scope for daytime observation and imaging. Its brilliance does present some problems (and dangers!) but it shows us a disc that is never the same from one day to the next. My intention here is to describe how to go about simple Solar imaging, using basic equipment. This is a description of the methods that work for me – it is not meant to be an in depth tutorial on every aspect of Solar imaging. Simply a guide for the beginner seeking to obtain straightforward, full disc, images of the Sun that record all the basic features visible in “white light”. Some parts of this go into a bit of detail – these are in response to questions asked on the forum over the past few months – where beginners have asked for step-by-step instructions.

By the way, exactly the same equipment and techniques can be used for full disc images of the Moon – Just remember to take the Solar filter off first!

I have listed my own equipment, where appropriate, so you can see the sort of things needed – there is plenty of other equipment out there which will do the job just as well.

Let us deal with the dangers first: NEVER look directly at the Sun and NEVER look at the Sun through any kind of optical device (telescope, binoculars, lenses etc) without having first fitted the correct filter(s). These can be obtained, ready made, from reputable Astronomical equipment suppliers or can be constructed at home from the appropriate materials following the instructions provided by the filter material manufacturers.

Equipment:

Telescopes:

Refractors – These are probably the easiest to use. You will need an aperture from 80-120mm and a focal length of around 1000mm. This will give a decent sized image of the Sun on the camera sensor (a focal length of 1metre gives an image of roughly 1cm on the sensor). An achromatic refractor is quite adequate for work of this kind.

Reflectors: Reflecting telescopes are also suitable, if a little more awkward to use. You can use the full aparture up to around 100mm, after that you may prefer to make a filter that fits over the “little cap” on the main end cap of the telescope (so that’s what it is for!!) – Just make sure that the main cap is well secured to your scope – many are quite loose and can fall off. Again a focal length of around 1000mm is suitable.

My own Solar imaging kit is a 120mm refractor (I use both an Evostar achromat and an ED APO – there is no discernable difference in the final images!). My own scopes are “stopped down“to 100mm (i.e. the aparture of the filter is 100mm diameter). On each I have a motorised drive fitted to a dual speed Crayford type focusser - this is an extremely useful accessory but is certainly not essential.

Mounts:

An equatorial mount is probably the most useful type, motor driven is convenient but not absolutely essential. You should look for a mount that is sufficiently steady and solidly built. Even for smaller scopes I would recommend at least an EQ5 sized mount. I use both a portable EQ5 and fixed HEQ5.

Camera:

You will need a camera that can have its own lens removed and be attached directly to the telescope. A DSLR type with a “t-ring” and adapter will suffice (I use a Canon 1100D). If your telescope will accept them 2” fittings are much more substantial than the smaller 1.25” type. Ideally your camera should be controlled by a laptop or netbook – but you can work without, its just a little awkward to see what’s going on. I use Canon EOS cameras that come with their own operating utility software – this description uses this software (again other software is available on the web). This makes setting up much easier, allows complete control of the camera and image acquisition, easier focussing and- very important when solar imaging – allows you to actually see what is going on, especially if you build a viewing box to shield the laptop screen from the Sun.

My homemade viewing box (from MDF sheet):

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A solar filter:

This should be either a ready made solar film filter or one that is bought in sheet form for you to make your own holder. If you can cope with simple cardboard and sticky tape DIY then it is quite easy to make your own filter holder. If you are unsure of your own DIY abilities then I would suggest buying ready made – if you tell your supplier which telescope you have they will supply the correctly sized filter. Just a note – Baader Solar film (there are others) should not be tight when assembled into the filter holder – which is why a correctly made filter often looks “floppy”. The filter should be treated with great care – it is made of tough material but should be kept in a suitable box or container that is padded to prevent any possible damage to the filter. ALWAYS check your filter is undamaged before EVERY use.

Homemade filter in plastic ventilation pipe holder:

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Setting up:

Set up your telescope and mount - which should be polar aligned- and put the filter onto the scope FIRST! Then assemble the camera and its link to your laptop. When you are set-up and have checked everything is correctly fitted – especially the filter! - aim the scope at the Sun and turn on the motor drive. If you open your camera control software and switch to “live view” you should see the disc of the Sun on your laptop screen. Believe it or not it can be quite tricky to find the Sun! You can either make up a simple finder or use the shadow of the telescope itself to help you.

Orientation:

Once you have the Sun’s image on your screen you will need to orientate the image so that it tracks precisely across the field of view. (I usually set the exposure on the Canon utility software to a value where I can easily see a bright imager on the screen – often 1/1000 sec works for my own set-up). For this task I use “Al’s reticule” which is freeware. It draws a disc and cross reticule on your computer screen which will always be on top of any other open windows. To orientate your image move the reticule to place a convenient sunspot (you will need to rough focus first) on the horizontal reticule line and use “fast” RA slew to move the image of the Sun backwards and forwards across the field of view (or simply allow the image to drift across the field of view if you have no motor drive). At first the sunspot will probably zoom off at an angle to the line! Rotate the camera an appropriate amount, realign the reticule and repeat the slew – it will not take you long to get the Sunspot to travel perfectly along the horizontal reticule line.

Image orientation:

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You are now correctly orientated – but NOT North at the top! See “Adding Longitude and Latitude lines “below:

What do you do if there are no sunspots? You can run the top or bottom edge of the Sun’s disc along the reticule line to get orientated.

Focussing:

After that you should spend a little time getting your focussing perfect – It’s not easy as the Earth’s atmosphere constantly “boils” your image into and out of focus. I use the Canon utilities zoom feature to get a decent sized image to work with. Keep the exposure setting to a value where you can see a good image that is not too overexposed. This is where a motorised focusser comes into its own – you can adjust the focus with no vibration or movement of the image at all. It is critical that you get your focus as good as you can – your final image quality will depend on it. Then align your image in the centre of the field of view.

Centering using the Canon Utilities grid:

post-4502-0-37668800-1340138488_thumb.jp

Sun in focus:

post-4502-0-63740000-1340138517_thumb.jp

Taking your images:

You are now ready to take your images – set the ISO value, exposure and set the capture folder for your images on your laptop. I always set my camera to take “Large JPEG” images – Yes, I know this is all wrong! But it works for me. RAW images – which are the ones you are supposed to use – cause all sorts of problems when stacking, probably due to the comparatively huge file sizes involved.

Ready to go!

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The ISO should be the lowest available – usually ISO100. The exposure is tricky but it is better to under expose than to over expose. The live view image on the laptop screen will appear quite dim when the exposure is correct. With my 1100D I usually use somewhere between 1/2500 sec to 1/4000 sec. My older 1000D was normally set at around 1/1000 sec. Take a test image and look at it on the laptop screen full size. Is it in focus? It may well be a little fuzzy as the atmosphere will play havoc with your image quality – experience is the best judge of this. Can you see a hint of the surface granulation and some bright marks near the edges of the Sun’s disc? These are faculae and, if they are present, you should easily be able to see them on a correctly exposed image. If the image is pure white with just the sunspots visible – you have overexposed the image and need to drop the exposure. When you are happy take between 40 and 100 frames. I usually take 64 frames (or more if the seeing is poor – the idea is to have a final stack of around 60 frames). Job done!

Ready to go! The camera, focusser and wires everywhere:

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Processing:

First take a quick look at your images, large thumbnails will do, and delete any that show obvious clouds. With UK weather I often image during small gaps in the clouds so this step may be necessary more often than you may think!

The first part of processing is to stack your images. For this you can use the freeware “Registax5”. (I much prefer Registax 5 to the newer version 6). Open the program and click the “select” button at the top left. Find your image folder and open all the images you want to stack.

Registax screen 1 & 2:

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The first image will appear on the screen – or rather only part of it will. You will have to use the sliders to get the image centered. Find a decent sunspot and get it in the middle of the screen. As you move your cursor around you will find that it has a square box attached to it – this is the “region of interest box”. In the left hand menu you can set the size of this box – set it to 256. Use the cursor to put the centre of the box over your chosen sunspot and click once. A box will be fixed on your image. Do not set any more boxes! Make sure the “lowest quality” box (left hand side) says 95% - use the arrows to move the number up or down – or simply enter the number manually. You will find the Align button (top left) will now be underlined in green. Click it and Registax will start to align your images – you can follow progress in the bar at the bottom left of the screen.

Registax screen 3 & 4:

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Now look at the numbers at the bottom centre of the screen. Stacksize 82/123 (or similar) – the first number is the number of frames that Registax has chosen to stack (82) and the second number is the number of frames you opened (It must have been poor seeing that day as I had taken 123 images). If you raise or lower the “lowest quality” setting you can increase or decrease the number of frames that Registax will use for your stack. Hopefully you can get Registax to show at least 60 out of your total number of frames before the quality number gets lower than 85%. If this is the case it means that Registax will stack all 60 of your frames and you aren’t trying to stack any really poor frames. Click the “Limit” tab – top left and underlined in green. The Registax screen will change to the optimise screen. There is nothing to change here – go to the top left and let the cursor hover over the “optimise and stack” tab – it will turn yellow – click once and Registax will start to check and then stack your images.

Registax screens 5, 6 & 7:

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Depending on the capacity of your computer this could take several minutes – there is a time remaining estimator in the bottom bar of the screen and a progress bar at the bottom left.

When stacking is complete the screen will change again to the “wavelets” screen. You will have to re-centre your image and again find a sunspot to concentrate on – put it in the middle of the screen and click on it once (this is important as it places the preview area centered on your chosen sunspot – otherwise the preview area will be simply be set by Registax and any wavelet changes you make will not appear to have any effect unless you happen to have the preview area within your screen area). The final part of the processing in Registax is to apply image sharpening “wavelets” to tease out the detail from your hard-won data.

Registax screen 8:

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It’s wavelets playtime! There are no strict rules for wavelets and settings can and do change from image to image – so have a play with the sliders and don’t be afraid as you can reset them either by right clicking on each in turn or by clicking the reset button which is top centre above the image box.

Registax screen 9:

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I usually use something similar to the settings shown – work down the sliders – optimise the first before moving on to the second etc. You may well only need to move the top two or three, any more may lead to artifacts and “over-processing” of your image. Less is often more with wavelets. When you are happy with the wavelet settings for your image click “Do All” at the top left and Registax will process your wavelets across the whole image – this may take some time – there is a progress bar at the bottom left of the screen. Save your image using the “save image” button. I generally save as a (TIFF 16BIT *RGB). Close Registax.

Now we come to the final part of image processing. The image that you have produced from Registax could do with a bit of “tweaking” to make it more presentable. This can be done in a photo-editing program like Photoshop (or its freeware equivalent GIMP, which should be capable of doing the same tasks). I quickly discovered that I did pretty much exactly the same thing to every image that I processed! So, being lazy, I have written an “Action” to do my processing. The action is listed below so that you can process your own images by following it line by line. Please feel free to change things as you gain more experience! I can provide (for free) the action as a file if you wish but you will learn far more about what is going on by manually following the process and maybe recording it as your own action – complete with any personalised additions or changes. (Note: Photoshop processing for images of the Moon is quite different!)

Open the image in Photoshop:

Open in Photoshop

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Crop the picture to give a Solar image with a small dark surround (Mine is an 1800px square but yours will be different depending on your scope and camera).

Cropped and Auto-coloured:

post-4502-0-68939200-1340138873_thumb.jp

Then this is Bizibilder’s “Action”:

Image > Autocolour

Image > Adjustments > Levels Move the mid slider to 0.5

Image > Adjustments > Curves fix the centre of the line (click on it but don’t move it) then click “half way” to the bottom and set that point at 64/55. Click half way to the top and set that point to 187/197. (Note: first number is input value/second number is output value)

Image > Adjustments > Colour Balance Move the sliders (Midtones) Cyan > Red to +50 and Yellow > Blue to -70

Image > Adjustments > Vibrance Set the Saturation to 10

Image > Adjustments > Exposure Set the Gamma Correction to 0.75

Image > Adjustments > Photofilter Set the colour to R=220, G=170, B=30 and move the density slider to 50%

Filter > Sharpen > Unsharp Mask Set Radius to 250 and amount to 10%

Filter > Sharpen > Unsharp Mask (i.e. Do a second unsharp mask). Set Radius to 1.5 and amount to 50%

Filter > Blur > Gaussian Blur Set the radius to 0.4px

Resize your image to something like 1024x1024 (or whatever other value you like)

Done!

After running Bizibilder’s Action:

post-4502-0-70172700-1340138902_thumb.jp

As you will see this produces an image that is distinctly pale orange in colour – some folk like this and others say it’s wrong as it is false colour. My own view is that the “plain white” image does not look very good on a computer monitor – where 99.9% of the time it will be viewed – due to lack of contrast and the fact that many monitors are not very well set up for displaying good colour! So colour it is! – but feel free to omit the colouration processes or change them if you wish.

I save this first image as a JPEG and then annotate a copy of it which is also saved. I use the text tool in Photoshop for this. Sunspot numbers can be found here: http://www.solen.info/solar/ I have also made a “Little Earth” to show the relative size compared to the Sun – get an image from the web and reduce it until it is: Sun’s diameter in pixels divided by 106. Keep the reduced image and copy and paste it onto your annotated image.

Little Earth:

post-4502-0-30433100-1340138928.jpg

Adding Longitude and Latitude lines:

I like to add a Longitude and Latitude grid to yet another copy of my own image and for that I use the freeware “Tilting Sun”. This has an excellent tutorial of its own that explains how to use Photoshop to put the grid in place. The only thing it doesn’t tell you is that the maximum whole disc grid size you can produce is around 600px diameter (at least it is on my monitor – yours may be different). To fit this to your image you have to prepare an image of this size from your original. Measure the diameter of your image of the Sun (using the ruler tool in Photoshop) so that you can resize it (“600 divided by your image diameter in pixels multiplied by 100” will give the percentage reduction required – put this value into: Image>resize to do this). This will produce a disc that the “Tilting Sun” grid will match with perfectly.

(Note: For processing images of the Moon just apply Image>Autocolour and then a simple unsharp mask with the radius between 80-150px and the amount 10% followed by a second unsharp mask with radius between 1-2px and the amount 30-60% - each image will respond differently so you will have to experiment.)

Finally:

Solar disc image, Annotated disc image and image with Longitude and Latitude

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Please post your images on the forum for everyone to see – you will quickly build up a good series of pictures of the ever changing face of the Sun!!

I seem to have gone on a bit!! If there are any questions or errors and omissions please ask and I will try to answer them.

Appendix: Taking Flat Frames in Registax.

Taking Flat frames and processing them with your images (Light Frames) will get rid of gradients and dust bunnies that mar your images. These problems are usually caused by dust and smudges etc on your camera sensor. The process also deals with vignetting – where the edges of your image are darker than the centre of the image – this often manifests itself in the top and bottom of the Solar disc appearing darker than the left and right side (assuming landscape orientation of your image).

How to do it:

Firstly take your normal “Light” pictures of the Solar disc with your DSLR (or other) camera. Then swing the telescope to a part of the sky that is WELL AWAY FROM THE SUN. Remove the Solar filter and de-focus the camera by moving the focusser at least ½ an inch (1cm) or a little more. DO NOT allow the camera to move/rotate – other than the change in focus. Switch the camera (for Canon) to the Av setting – on the 1100D it is next to M – this will tell the camera to select a suitable exposure automatically. Take around 10-20 frames. These will appear bluish-grey as they are out of focus pictures of the sky. (I need to experiment here with things like t-shirts and translucent acrylic sheet for the best results – I will update when done). Remove your camera from the scope – remember the Solar filter is OFF!!!

All done – that was the difficult bit!

Open Registax (For this example I am using Registax 5).

Click Select and open your flat files only.

Click on the Flats/Darks/Reference button and select “Create Flat Field”.

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Registax will start to process your flats. It will show the stack screen

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When done - Click on Save Image and give the file a name – it is a .bmp file. Don’t change it.

That is your flat frame created.

This example is a flat I generated from 10 frames. I have enhanced it by putting it through curves in PS so you can see the dust bunnies and vignetting!!

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Open your light frames in Registax in the normal way.

Before you do anything, click on Flat/Dark/Reference and click “Load Flatfield”

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Select your flat and click “Open”

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If you click on the Flat/Dark/Reference tab you will see that “Use Flatfield” is checked and the name of your flat is shown.

Then carry on with Registax in the usual way by setting your align box etc.

Remember that the flat that you created will only work for the set of images associated with it. You will have to take a new set of flats for every imaging session.

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Hi Roger ,

Thankyou for the great tutorial , not often you find one so well written and easy to follow .

All the best ,

Steve.

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Thanks for posting that, Roger. Now I have a clue where to start I shall certainly be trying out some solar imaging as soon as I have the opportunity.

James

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Thanks for your comments folks - I have amended a couple of errors that had crept in. If you have copied the "Action" you may need a new copy! (I'd muddled up Red Green and Blue!!). The tutorial is now the corrected version (until someone finds another bug in it!)

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Any tips on making the clouds go away Roger? :smiley:

Seriously though, that is one quality guide.

Edited by JamieW

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Great tutorial Bizibilder - thanks for putting it together. I know how long it takes to craft these, so thanks for the effort it is much appreciated.

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Roger I have only just read this thread of yours on solar viewing and imaging. I think it should be pinned because of the excellent info that it contains.

Mark

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Fantastic. I've been thinking about trying this in the summer time to save staying up so obscenely late for star shots.

Great tutorial. Thanks.

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The OP mentions that reflectors UP TO 100mm are suitable for solar imaging. Is there any reason why this is so?

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That was "full aparture" for reflectors up to around 100mm. You can, of course, use a larger aparture but you won't see much more with it. The reason being that the resolution of a Solar image (visual or photographic) is 99.99999% governed by the atmospheric seeing rather than the optical quality of your scope. The "cut off" where you get little or no benefit by increasing the aparture is around 100mm.

If they have a larger scope you will find folk tend to restrict the aparture to around this figure. It has a couple of additional advantages - you can reduce aparture and collect your image from between the secondary supports with a reflector and, secondly, you can make at least two filters from a single sheet of "A4" Baader film (which, by the way, is somewhat smaller than A4 when you buy it!). if you are a bit tight with the pennies (like me) then "every little helps" :p .

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Awesome tutorial.

Finally I could work with my pictures of the sun and process them.

Now they look close to what I wanted.

Cheers

Tom

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Roger

I have just found this thread. Can't thank you enough, all the information you have put into this thread and so well set out. Cant wait to try putting this into practice.

Clear Skies

John

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Well Roger I followed your instructions and ended up with this first go at Solar.

Solar 3108130 130

Taken with a Canon 1000D Afocal on SE8 Nexstar

I need to get a better cover to shade the laptop screen to aid in focus adjustment during eos live view, either that or a longer pair of arms to reach the laptop in the shed and focuser at the same time :laugh:

Thanks again Roger

Regards

John

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Sorry I can't upload action files to the forum - if there is a way then I'm quite happy to do so.  You can easily create an action by following the tutorial whilst recording what you do in PS.

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An excellent write up Roger, thanks a lot for that. I can't believe I have missed this one.

I like the bit about the flats too, might have to try that one.

A thought just occurred to me about my dslr settings, I normally have all my in camera settings switched off, like noise reduction, etc for night photography. Whether that is right or wrong I guess it depends on what you read.

Anyway it strikes me it may be better to switch them back on for Solar(lunar too?) work, what does everyone else have their settings at?

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I turn all the setting off (noise reduction etc) and now use RAW images rather than JPEG's - the rest of the technique is the same but I first put the RAW images through PIPP https://sites.google.com/site/astropipp/  (usual disclaimer) and use that to sort and crop them.  It makes the processing in Registax very much quicker!

If the weather is lousy and I have only a little time then JPEG's will do the job - you can take 100 JPEG's in 90 seconds, 100 RAW will take several minutes as the image download time is much slower.

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Excellent, thanks for that clarification. I have everything turned off anyway and always take both RAWS and JPEGS at the same time so it seems at least that part is right.

I have just started using PIPP and it's a fantastic program, definitely simplifies the process compared to what I was doing.

While I'm at it, with a continuum filter if I was to use it with the standard SW150PL foucuser and dslr I guess you use the 2" one and does it get in the way of the t-ring or sit in it somewhere, what part of the image train does the filter sit in?

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The filter should screw into the end of the adapter that fits into the focusser - either 1.25" or 2" will do the job.

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