Monday, 30 April 2012

Eclipse Chasing

In doing some research into early eclipse observations from aircraft with Bob Morris I uncovered an article from 1914 in the NY Times. At the time there was an eclipse chaser named David Todd who was an astronomer at Amherst College. It seems he either had a fan at the Times or maintained regular correspondence with them regarding astronomical items of interest and his eclipse pursuits.

In 1914 David Todd proposed to follow the eclipse in Russia using an airplane capable of 120 miles per hour. He hoped to induce more speed from the plane by descending rapidly. His goal was to increase his observation time by several minutes. Towards this end he arranged for the equipment and started his journey.

The article caught my eye because it says his proposal was akin to "chasing the sun" - the earliest use of the word chasing with relation to solar eclipses that I've found in published media.

Sunday, 29 April 2012

Don't Do It Yourself

A recent discussion on the Solar Eclipse Mailing List caught my eye as something that should be shared with everyone. It is about one of those things that I thought had been put to rest a long time ago. The simple fact is: you cannot build your own SAFE solar filter by stacking sunglasses or neutral density (ND) filters.

The reason is these filters (sunglasses are in filters) are for visual light only and do little or nothing for radiation outside the visible spectrum. Ultraviolet and infrared radiation can damage your eyes.

For photographers, stacking filters presents a different problem - flares. Reflections between the filters will be picked up by the camera and look like flares in the images.

It is important to use the right tool for the job. For cameras, purchase a dedicated solar filter. This is even more important for telescope owners. And make sure the filter goes on the front of the optics - you don't want a filter over heating and ruining your vision! Click here for more information about filters and photographing the Sun.

A further consideration is that commercial ND filters are absorptive and can get warm when exposed to the Sun for a prolonged period of time. Gelatin filters may melt or deform under the heat.

Check out the Solar Filters for sale at Amazon.Com

Friday, 27 April 2012

Eclipse Photography Thoughts 2

For the Annular Solar Eclipse on the 20th of May (USA) we are considering a location in a public park with other eclipse chasers who live in the area. While I'd enjoy taking a series of images through the Coronado telescope of the entire event (1st through 4th contact) it seems wrong to not allow others a peek through the telescope. And being in a public park could present difficulties as we are most likely to draw curious onlookers.
I will be the guy in the silly safari hat.

My plan is to use the telescope as a public education tool and share the view. If there is an opportunity I will take some images but I think I will get far more fun and interesting images with a regular camera. One of the best features of an annular solar eclipse are the shadows and pinhole images of a round light source (the Sun) appearing everywhere. It is an "Alice in Wonderland" sort of view when the right objects are casting shadows. My favorite is look on sidewalks where tree shadows fall. Sometimes it looks like a pile of translucent crescents or rings piled atop each other.

Image by Andy Hinds during the 2005 Annular Solar Eclipse

The key to finding good shadow projections is a porous shadow against a light background as seen in the image above by fellow eclipse chaser Andy Hinds.

Since we will be somewhere in northern California (weather will dictate where we set up) the annular phase of the eclipse (between 2nd and 3rd contacts) will last well over four minutes. This will hopefully provide plenty of time to find some interesting views to share.

Thursday, 26 April 2012

Transit of Venus Cartoons

A couple of cartoons about the Transit of Venus and solar observing are presented below. These were drawn for fun and are not artistic in any way.

Babylonian Astronomer busy writing up the evening's observation report misses the transit of Venus across the disk of the Sun on a hazy morning. 

Mayan astronomers are summoned to explain a big round dot on the solar disk. It was not an eclipse of the Sun nor was it a cloud - best guess was a big round bird.

Sailors in some bronze age ship notice a dot against the Sun as it sets over the water. This leads to a philosophical debate about the nature of the solar system and because the captain is a 'geocentrist' they decide not to report the observation.

In 1761 there was a world war going on. Astronomers had a problem getting around the national interests and often found themselves in the wrong place at the wrong time. 

DO NOT STAND or put anything near the eyepiece when no filter is in place.

A French astronomer in Siberia. They thought his equipment was causing the unseasonable rains and subsequent flooding. Of course, he wanted clear sky for his observations. This is based on a true story where soldiers had to be called in to quiet a potential riot.

Fr Hell of Austria went to Norway to watch the transit of Venus in 1769. He spent about a year there getting his equipment ready. You know it is cold there.

Ancient archers take credit for putting a hole in the Sun.

All cartoons by Bill Kramer. All rights reserved.

Eclipse Photography Thoughts

A question I am frequently asked by eclipse photographers is what exposure setting works best. The answer to that question is not easy as it depends on a number of factors - some you can control and others you cannot.

a) Optical system: The optical system is your camera plus the lens (or telescope). You can obviously control this aspect of your photography mission. There are tools online for estimating exposures. These are based on the focal ratio of the optics and sensitivity of the camera to light. Focal ratio is simply the focal length of the optical system divided by the aperture (front lens size). The lower the focal ratio, the faster the system. The faster the system, the shorter time required for an exposure. Light sensitivity in cameras is measured in terms of 'speed'. This speed value is often expressed using the acronym ASA or ISO (standards organizations). The higher the speed, the faster the light can be recorded.

b) Weather: You can't control the weather but you can work with it. If the sky is clear and the Sun is bright then you can get details of the solar surface. Light clouds or haze will block a lot of sunlight making some filters almost useless in terms of seeing solar surface details such as sunspots. Of course, during a total solar eclipse you want few or no clouds anywhere near the Sun and Moon! A clear blue sky is best - just not always achievable.


To figure out the best camera settings, practice with the system before the eclipse (or transit) event. Try a variety of exposures and try them under different weather conditions. Pretty soon you will develop and almost intuitive feel for the "right" exposure setting.

For the transit of Venus and annular eclipse, the pace is comfortable. You can shoot a variety of exposures and work with them later on the computer. A total solar eclipse on the other hand is almost frantic when it comes to photography. You cannot really practice the stress condition. But you can practice enough to become confident in your skills (for totality practice, take pictures of the Moon).

Just make sure the camera and lens are focused. This is probably the hardest part. So here are some tricks I've picked up over the years.

a) Use a dark hood. Using a small blanket or towel over your head that covers the camera makes the view in the finder stand out better. You can see finer detail and achieve a better focus.

b) Mark the focuser. If you are using a telescope this is very handy. Most manual lenses have approximate focus distances marked on the lens. In the case of a telescope we are focusing at infinity so only a single mark is needed to indicate about where that sweet spot is located. Use a light colored nail polish or permanent marker to indicate where the focus point is located. THEN ADJUST based on the weather and optical condition (normally a very small adjustment is all that is needed).

c) If you wear glasses, or worse, bifocals - use the longer distance side to focus the image when looking through the camera. Believe it or not, this takes a bit of practice and you will find yourself looking through the close up side if you are not careful.

And remember, at the end of the eclipse, you can always trade images with others should yours not come out great or only show a portion of the features visible.

Wednesday, 25 April 2012

Less than a month to go before the Annular Solar Eclipse across parts of China, Japan, and the USA. The general rule of thumb in eclipse chasing is that a total is worth any effort, an annular is worth a short trip, and a partial worth setting up in the yard. So for this eclipse, we make a short trip. Out to California to join some fellow eclipse chasers.

An annular solar eclipse is a great practice for a total solar eclipse photography. Rare events that provide a sharp contrast across the solar disk are wonderful. Time this just a few short days before the Transit of Venus and we have a "must photograph" situation in my book.

I am considering the use of my Coronado 40mm hydrogen-alpha telescope. To image I need to use the 2x barlow and negative projection. This fills the image frame nicely. Testing this set up produced nice images with exposures of about 1/60th of a second on up. Longer exposures (over 1/4 second) shows prominences around the edge of the photosphere. The longer the exposure, the more prominences that showed up in the images. For this configuration, tracking is essential at exposures over a quarter second. For more details about whether you need tracking (or not) see

After a lot of dump shots, I got a few that took to the computer and tried to merge with Photoshop. There are a couple of things to note. The above image consists of two images laid on top of each other. The grey image is the shorter exposure. I colored it grey. The color of hydrogen-alpha is a deep red, more like the outer image which is a clipped with a black circle and placed behind the grey image.

A couple of things I learned are that I need to account for the solar disk darkening about the edges by adding more images with exposures in between the extremes. This is will be difficult as the solar disk has low contrast and will fade out as more images are added - more fun with Photoshop awaits!