Solar Imaging

Photographing the sun without the correct equipment is not recommended.

However, using a Coronado PST Solarscope highly detailed Hydrogen Alpha images of the sun can be taken using normal DSLR camera or preferably a mono CCD camera.

Latest solar images can be seen here

My setup for solar photography is a Coronado PST solarscope mounted on a Acuter Merlin motorised mount with the photographs captured with a Canon 7D fitted to the back of a Baader Hyperion 8-24mm zoom eyepiece using a threaded adaptor. To ensure that the focus and tuning of the PST is as good as possible I connect the Canon 7D to a laptop so I can monitor the live view from the camera while I’m adjusting focus on the solarscope.

Alternatively I use a Imaging Source DMK41 USB mono CCD camera fitted with a short (less than 20mm long) nosepiece. It is important to remove the C/CS thread adaptor from the camera body and to make sure that the nose piece can slide fully into the PST eye piece tube so that the DMK41 camera housing touches the top of the eye piece tube. If the DMK41 camera housing doesn’t touch the top of the eye piece tube it will be difficult, if not impossible, to achieve focus without the aid of a barlow extension tube or Powermate.

As a quick ‘grab and go’ setup the PST and Merlin mount is ideal, you can be viewing the sun within a few minutes and it is stable enough for photography.

Your first image taken through this PST solarscope is very likely to be similar to mine.

It will be very RED

and to be honest I thought it was a reasonable image until you see what the experts can produce.

It is also worth knowing that the sun is approximately 108 times larger than the earth so the prominence at 3 o’clock in the image above is larger than the diameter of the earth!

The Hydrogen-alpha frequency is only captured by the red channel of a DSLR camera, the green and blue channels only muddy the final photograph as you can see in the image above. For this reason the seasoned solar imagers use monochrome CCD cameras and process a captured video through a programme like Registax to get the highly detailed images that can be post processed to introduce the colour.

For DSLR solar imaging it is very important to use the histogram during the image capture. The histogram will allow you to assess the signal on each of the R, G and B channels and adjust the exposure to maximise the signal on the red channel without overexposing it. If the red channel is overexposed all of the detail in the disk will be lost even if the prominences show up well.

One or two images can be used to make the final composite image. To process the captured image(s) it should be split into individual colour channels and normally the blue and green channels are discarded.

The red channels of the images can then be processed, as grey scale images, to produce two images, the one highlighting the surface detail can be processed using the wavelet function in Registax or PixInsight to enhance all the detail in the image.

and the second one to highlight the prominences.

The surface detail of the disk can then be pasted accurately over the prominence image to produce a composite grey scale image.

To re-colour the image it needs to be converted back to a RGB colour image and then using colour balance and hue/saturation controls the false colour is re-introduced. Layers should be used for these operations, if your software supports them, so you can go back and adjust them if you want to tweak the final image.

This image was taken at the same time as the image shown earlier but processed ‘correctly’. To remove the black line around the edge of the disk you can adjust the selection slightly by contracting the selection and then smooth and feather the edge before pasting over the proms image.

Typical values for colour balance are:

Highlights

  • Red  +30
  • Green -20
  • Blue -40

Midtones

  • Red +20
  • Green +0
  • Blue -60

Shadows

  • Red +50
  • Green +10
  • Blue -100

make sure ‘Preserve Luminosity’ is checked during the colour balance operation

Depending on how you have applied the colour balance you might find you need to adjust the Hue/Saturation to finish the image but typically it should be desaturated by about -30.

To compensate for the inversion of the image orientation through the PST I flip the image on the horizontal and vertical axes and then apply a -40 degree rotation to the image.

Since posting this blog I’ve progressed to a Lyra Optic 4″ f/11 refractor modified for Solar H-a imaging and observing

15 Responses to Solar Imaging

  1. Daniel says:

    Kev,

    Great post and astounding images! I am especially grateful for the section on image correction and the color correction data; I referenced your post in my own humble post.

    Thanks
    Dan

  2. Pingback: Solar Observation | Dan's Blog

  3. Pingback: AP with the PST?

  4. Dan says:

    Superb pictures congrats ! I’ll receive soon my PST, it opens new possibilities…

    I’ve a question : I’ll buy a fixed focal length hyperion (the zoom is to expensive for me), I have to chose which one. Which focal setting do you use for prominences pictures like this beautiful one ?
    http://www.photosbykev.com/wordpress/wp-content/gallery/solar/115852_processed.jpg

    Thanks a lot !

    Dan

    • photosbykev says:

      The PST comes with a 20mm EP from memory so I would be looking for a 2nd EP around 8-10mm

      • Dan says:

        Thanks a lot ! I’ll probably buy the 8mm then.

        Which length of T2 extension tubedo you use between the T2 adapter atop the zoom and the T-ring for imaging with the DSLR ?

        thanks again,

        Dan

        • photosbykev says:

          With the Baader 8-24 zoom there is a T2 thread directly on top of the EP which the camera connects to with a T-adaptor. No extension tubes were required. Please be aware that the PST is very fussy about what can be used to focus, and what works and doesn’t work, and it seems to change from PST to PST.

  5. Alex Dzierba says:

    Kevin,

    I had emailed you a while back asking about how you mounted your cameras on your PST. Since then I’ve been taking nice pictures with my Canon T3i on a Hyperion click stop zoom! I love the results! The DMK41 I ordered has been on back order for three months. It finally arrived in the mail today. I already have the short 1.25 in.
    eyepiece adapter, with no shoulder, that you helped me find. Hopefully I won’t have to wait all the way to the weekend to do some imaging of the sun with the new DMK41. I’m going to like having a monochrome camera with no IR cut filter, and that is lighter.

    Just wanted to send you a “Thank you” for getting me on my way imaging through the PST.

    Aloha,

    Alex
    Honolulu, HI

  6. Ron Cottrell says:

    I have been imaging the sun with a 40mm PST and a Philips webcam for a few years. I recently purchased a DMK 41 and really like the improvement in the disk features. I usually add color. However, adding color to the prominences has not been that successful. A large prominence captured with the webcam turns out better.

    Can you elaborate on how I should be adding color to prominences?

    Thanks, Ron

  7. John Hicks says:

    I use two methods to capture the entire solar disk
    a) I use a Pronto 70 mm Televue Refractor attached to a Lunt 50 mm h-alpha filter. The 2″ focuser terminates with an AstroSystems 2″ to 1-1/4″ Ultra Low adapter into which I can fit the Lunt 1-1/4″ blocking filter diagonal nosepiece. A DMK on the other end with a standard nosepiece easily fields the whole sun. Very Good Detail.
    b) The other method is to use 325mm century brand telephoto lens – attached to a Lunt H-alpha filter (which will thread right into the lens hood beautifully – finally someone thought ahead at Century Optics and created a Universally accepted thread),
    then cut off the antiquated 2″ barrel and insert a Sky Research 1-1/4″ focuser into the remaining tube then add the DMK with short barrel or factory barrel.

  8. Jonny says:

    Hi!
    Great guide! and nice picture!
    Do you use a standard P.S.T and the zoom okular with no extra gear?

    Jonny

  9. Pingback: » PST Solar Imaging » PhotosbyKev

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