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Thursday, 07 June 2012

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At first I thought the lines represented a modern attempt at the triangulation used by astronomers in the 18th century to measure the earth to sun distance.

The family and I spent a wonderful afternoon & evening just a ways west of Milwaukee at the Yerkes Observatory in Williams Bay, WI. Thanks to all the volunteers, there were many telescopes set up as well as projection viewers. My favorite was viewing through a Hydrogen-alpha scope where one could also see prominences erupting from the sun.

So Nicholas, you could take two steps right or left to get rid of the lines?

just kidding... great shot!

I do a bit and post some photos on flickr. It is totally unprepared as it is my son who want to do it but only told me just before I slept the night before. I like astro but only DSO e.g. via iTelescope. But not much interest on the sun. But, well, have to do it for him.

It was a total failure visually in the next morning as you cannot project easily the son on paper. I dare not to risk my telescope without the solar filter. (He later did it use a sporting scope by projection at school. I have warned repeatedly about the blindness issue if he simply try to look/focus using the scope.)

Finally I decide to take risk with my Nex5N and just photo and video the sun. With a ND4/8 plus some red filter (for my 8x10), it seems ok. Then add the NDvariable (up to 300), it seems much better to control the light and the focus. I assume the worst but so far I cannot find anything wrong with Nex5N afterwards. Most people like the green filter ...

It is just a dot if one think about it. But it is quite nice to take your pic. I guess my next re-birth 105 years later would be more prepared.

Risked shooting with just an R72 filter on a D7000. However, only using a 90mm lens, so had plenty spare sensor to act as a heatsink. Also small and light enough to handhold and therefore not pointed directly at the sun for long.

Got me planning for a solar eclipse due later this year!

My results look pretty much like Nick's, but without the lines. I used my Nikon D300 with a Nikkor 70-300mm D lens, part of the time with a Tamron 2x teleconverter I bought for the 1991 eclipse. To reduce the sunlight, I used a Thousand Oaks solar filter, also purchased for the 1991 eclipse, mounted in a modified Cokin filter holder.

Since the filter holder didn't fit the current lens, I drove over to National Camera Exchange to try to find one with a 62mm thread. I was surprised to find that they no longer carry Cokin products (does anyone?), but they found a step down adapter that worked fine for the purpose.

In 1991 I used a waist-level finder on my F3 to adjust my aim and focus, then locked up the mirror before each exposure. This time I used Liveview in tripod mode, which worked great except for draining the battery quickly. But there's one thing I still haven't figured out: In tripod mode, does the mirror flip down and then up again before each exposure, or does the mirror remain up until the exposure is finished? (I was using manual focus and exposure.) If the latter, this would be a neat way to minimize vibration, though not as good as the old-fashioned lockup.

The interesting thing is that during parts of the video (this is more obvious with some wavelengths) Venus appears translucent - you can actually see some highlights behind it as it travels across the sun.

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