Shooting a Complete Solar Eclipse with m43 and how to process the data!

jimchungblog

In case you haven`t heard, there is a complete solar eclipse happening on April 8th and it can be seen in many of the most populated regions across North America, from Mazatlán in Mexico to St. John’s in Newfoundland. If you have never experienced witnessing this phenomenon, it is often on people`s bucket list and is certainly worth seeing if you happen to live in close proximity to its path of totality (and can also get that Monday off work!).

Every total solar eclipse is different which is why there are legions of eclipse chasers who try and see each one by travelling across the globe.  They occur about once every 18 months, but since most of the planet is water, they will often occur only over the oceans making it very difficult and expensive to see those apparitions.  The next one to occur in North America (and only in limited areas of the western part of the continent) will be in 2044, and I might not be around. 

The 2024 total solar eclipse will be unusual for two reasons.  The moon will be relatively close to the Earth in April causing totality to occur for 4.5 minutes (although for us Canadians, the length will be down to about 3 and a half minutes).  This is two minutes longer that the Great American Eclipse of 2017, which I attended.  The Sun will also be close to its peak of solar activity so there could be multiple plasma containing prominences projecting from the solar surface and visible along the perimeter of the Moon.  Unlike 2017 however, the Sun will not be at its peak height in the sky but descending into midafternoon in April so not the optimal position for best photography.  And April tends to be a very cloudy and rainy month, so check the forecast in the days leading up to the event because it might very well be a blow out. 

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The ideal focal length to shoot a total solar eclipse with a m43 sized sensor is 500mm (or a 1000mm for a full frame sized sensor). This gives you a high magnification view of the sun as well as enough room around the sun to see the solar corona. You could use the Sigma 500mm f/4.5 on the left but that would require a large telescope style equatorial mount to carry. Or the very compact 500mm Olympus f/8 mirror lens on the right which can be easily carried by a much small Star Tracker style mounts.   You do need a motorized mount to keep the sun relatively centered at this demanding focal length during the eclipse and you will not have time to make constant corrections with a manual mount.  Unless you polar align your mount the night before, it will still work if you do a rough alignment to the North and set the angle at 90º – your latitude (in degrees).  I think I might try shooting also in high resolution mode.

I used a phone app to change the shutter speeds and trigger the shutter release without touching the body and disturbing the tracking mount.  I’m sure there are better apps availabIe today that can be preprogrammed to entirely automate this procedure and allow the individual to enjoy the eclipse experience.  In 2017, I used the Olympus EM-1.2 at base ISO 200 and shot at 1/4, 1/100 and 1/400 of a second shutter speeds to capture the entire dynamic range of the corona.  Multiple exposures were captured at each shutter speed and stacked to improve S:N response.  You can use software called Nebulosity by Craig Stark which is now available in the public domain.

The processing of all this data follows the technique first published by Fred Espenak in 2000.  Fred is an astrophysicist well known for his singular focus on solar eclipses and was a frequent contributor to Sky & Telescope magazine.

From left to right, stacked images taken at 1/400, 1/100 and 1/4 s.  It is crucial that the images are centered in both horizontal and vertical axes.  You can do so by Show Grid under the View menu in Photoshop and determining how much to crop off the sides to bring the central disc into the center.  Alternatively you could use the Rectangular Marquee tool to measure the distance from disc to sides by reading out the pixel position and cropping accordingly.  It is best to process all images at this point in .tifs

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The solar corona’s brightness is radially symmetrical in the first order.  Choosing Radial Blur under the Main Filter menu and Blur submenu in Photoshop, set the amount to 10 degrees and save the results as shown here.
The Blur images are subtracted from the original images using Apply Image under the main Image menu to produce this trio of images and are saved.

 

Using Apply Image as shown to subtract the blurred image from the original image, note that Offset must be at 128.

 

Finally, the Original image is multiplied by the Subtracted image again using the Apply Image function to reveal enhanced coronal detail.

 

The 1/400 s data is blended with the 1/100 s data. This is then blended with the 1/4 s data to produce this final composite image of the solar corona.  The corona can reach temperatures of over a million degrees C whereas the surface of the sun is only about 5,500ºC!

It is perfectly safe to shoot the eclipse during full totality with no filter.  It is also safe to look at it at this point with your naked eye.  In fact you won’t see anything unless you remove your eclipse glasses and solar filters off your camera.  But as soon as Totality is over, filters must go back in place to prevent permanent damage to your camera sensor and your eye. 

Published by jimchungblog

I have degrees in Biochemistry and Dentistry and practice clinically 2 days a week. The rest of the week I devote to photography and bringing you the very best writing in this blog.

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