Eclipse Prep Notes

Wow - I turn around and suddenly we are down to two weeks to go for the Total Solar Eclipse (TSE)! While I have been trying to read, prepare, and bullet-proof (except for weather - that's the wildcard) for the event there's still things to do on my checklist. Among the things I have checked off my list are the following:

Solar Filter: Glass or Film?

Partial Phase - Aug 21 2017

For the 2017 TSE I purchased a Seymour glass solar filter for my 80mm Vixen. That worked out pretty well, allowing me to capture photos with my Canon t6i with good clarity (click the image at left to enlarge). However, this time around in an effort to capture even more of what promises to be a stunning corona near sunspot maximum, I have purchased a used full-frame Canon body. The solar disk is smaller so I'll need sharp focus to enable enlargement without degradation.

One question in my mind was whether a good quality mylar solar film type  might yield sharper images. I invested in a Baader filter from Aegna Astro and did a side-by side comparison a couple weeks ago. The glass filter gives a slightly better color (yellow-orange) but of course our star is actually closer to white in appearance - which is how it looks with the Baader. While not a ton of difference between them, the Baader may be yielding a slightly crisper rendering of the sunspots. But on the other hand the Seymour is easier to slip on & off the scope. 

Comparing Baader film (white) to Seymour (red)

Filtered Smart Phone

At the HAL meeting the other week I mentioned that a simple, low-tech hack for getting images of the partial phases might be trimming one of the eclipse viewing glasses into a makeshift filter taped to your smart phone. The phone I used for this was an older Motorola (Android) that I recently replaced. I cut around the filter of one of the eyeglasses and taped it to cover the camera lens, very simple and quick. Unfortunately, all my attempts to capture the Sun were wildly overexposed. The phone's camera interface supposedly did allow me to adjust the ISO and camera shutter in "Pro" mode, but I was hard pressed to see any difference. While it didn't work for me, it is still an inexpensive and easy modification to your phone, and some better phones (I am quite frugal in what I'll spend for a phone), like an Apple iPhone or Google Pixel, might allow shutter speeds that will render a proper looking Sun. I will say that it is hard to see the Sun on the camera's screen when pointing it at the Sun, so rigging up some sort of shield might pay dividends if you find your camera can snap solar images.

SETnC Trial

If you've been doing some reading about photographing an eclipse you have probably come across the advice of "don't do it, just enjoy those precious moments!" And there is truth in that statement. At the 2017 event I spent a lot of time looking at the eclipse via my pad through which I was controlling the camera. I still took time during totality to soak in the corona and twilight horizon, but not as much as I might have liked. Part of the issue was that a week before the eclipse I decided that the software I was hoping to automate taking the photos to free me up was a little to unpredictable, so I opted to go the manual route. And to be sure, I treasure those shots I took that day.

This TSE will hopefully be different. I came across the Solar Eclipse Timer and Camera controller application (SETnC) and, although the interface is a little "busy", it seemed quite straightforward and nicely programable for firing off shots during the eclipse. You specify your location and the software identifies the C1 - C4 times and provides an Excel-style grid where you define what exposures to take at specific times during the eclipse.

True to forecasts, Sunday was a cloudless day that was perfect for a full dry run - all the equipment set up as if it were the real thing. The only difference is not taking the filter off during "totality"! 😉I began the session about 12:25 pm, roughly when it will start in Texas the day of the eclipse. The software worked flawlessly, so I feel very comfortable turning over the picture taking to it during totality. I did find that while the camera battery and Celestron Power Tank for the mount lasted throughout the simulated eclipse, my laptop would come close to running out of juice near C2. That was solved by my small Jackery 300 portable battery generator.

I also discovered that the HEM27 mount gradually began to struggle tracking the Sun once it had crossed the meridian. I found to my surprise that doing the meridian flip was not as horrific as I had imagined. The main thing was picking up the laptop and walking it to its new position once the slew was finished, plus re-centering the Sun. If you haven't practiced the meridian flip and are planning to take photos, I'd strongly suggest you practice this at least once in case you find you need to do it.

Tip: Sun Centering & Solar Projection

One of the challenges in Solar observing with a telescope (or binoculars mounted on a tripod) is centering the Sun in the field. One great technique that I learned as a teenager is that by watching the shadow of your telescope/binoculars on the ground and adjusting your instrument to create the smallest possible shadow, the Sun will pop into view. Here is a video I created demonstrating the technique. 

At the March HAL meeting I also mentioned that using Solar Projection was a time-honored technique for sharing a view of the Sun with a group of people. In short, you pop in an eyepiece and direct the sunlight emerging from the eyepiece onto a white surface. You focus until you have a nice, crisp view of the Sun for all to see. This technique also works for binoculars as well, especially suitable if they can be mounted on a tripod. The main caveat is to occasionally give the telescope's optics a break and move it off the Sun for a few minutes. You can see a video of the technique here.

Activities for Maryland

Even if you are not able to get into the totality line, there are some interesting observations you can make with a deep partial eclipse such as what Maryland will experience. First, as you hit maximum eclipse (about 3:21 pm in central Maryland), can you detect any Purkinje Effect? In brief, due to the diminished sunlight, the cones in your eye are used less and the rods begin to come into play. Because the rods are more blue-light sensitive, you may notice that red and green colors lose some of their saturation. See the video below for a fuller explanation:

The second phenomenon to observe is how a thin crescent Sun will impact shadows on the ground. Shadows are normally a bit fuzzy on their edges because the Sun appears as a significant disk in our sky, not a point source. That’s in part why the shadow of one of Jupiter’s moons on its clouds is much sharper than our Moon during an eclipse since the Sun is much smaller as seen from Jupiter. If you have a rod/stick oriented tangential to the crescent, and another perpendicular to it, then the tangential one should have a sharper shadow. Check out this video for more information on this effect.

Whether you are heading out to catch totality or staying put to enjoy the deep partial eclipse, my hope is for clear skies and my #1 tip is to be sure you do your observing safely. With any luck we'll all have some wonderful stories and photos to share at HAL in upcoming meetings!