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  #1  
Old June 5th, 2012, 07:38 AM
Doug Kerr Doug Kerr is offline
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Default The Transit of Venus

No, it's not the latest romance novel by Barbara Cartland. The transit of Venus refers to the fact that the planet Venus will pass in front of the sun's disk "today".

This will be visible in much of North America late in the afternoon or near sunset on Tuesday, 2012.06.05.

Carla and I plan to attend a watching party held by a local astronomy club at a nearby state park. I didn't make good preparations for photography in advance, but I plan to pick up a piece of shade 12 welder's glass shortly, which I will use as an ND filter.

The nominal density of shade 12 welder's glass is 4.71, which corresponds to 15.6 stops. Shade 14 (18.5 stops) is usually recommended for direct viewing, but that is a special order item at the local welding supply shop, and the supply they ordered for the annular eclipse a couple of weeks ago was depleted then.

For those who are interested, the (optical) density, D, of welder's glass of shade number S is given by:

D = 3/7 (S-1)

The equivalent attenuation in stops (A) is given by:

A = 1.42 (S-1)

Best regards,

Doug
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  #2  
Old June 5th, 2012, 05:19 PM
Asher Kelman Asher Kelman is offline
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Well, I have no idea where the local welders supply store is! I hope you will post some pictures of yours later tonight!

Asher
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  #3  
Old June 5th, 2012, 05:56 PM
Asher Kelman Asher Kelman is offline
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Doug,

With 15.6 stops, what ISO, aperture and speed would you choose?

Asher
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  #4  
Old June 5th, 2012, 07:20 PM
Doug Kerr Doug Kerr is offline
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Test made before the start of the transit revealed that the 12 shade welder's glass did not make a good filter for photography. I suspect the problem is excessive dispersion, but haven't had time to diagnose it. In any case, I could not get a sharply focused image at all (using a Canon EF 70-200mm f/4L IS with a Canon EF 1.4X focal length converter on my Canon EOS 40D).

Here is a crop of a shot with that filter of the actual transit, ex camera (Venus is in the upper-right corner of the solar disk):


Douglas A. Kerr: Transit of Venus through 12 shade welder's glass

So I resorted to using a piece of the filter material from the direct viewing glasses supplied by NASA via the event hosts. I have no idea what its density is.

Here is a crop of a shot with that filter of the actual transit, also ex camera, with the same setup otherwise:


Douglas A. Kerr: Transit of Venus through "viewing glasses" filter

Note that Venus is only about 15 pixels in this setup.

We also see some sunspots.

I'll post a sweetened version of the image shortly.

The viewing party hosted by the Amateur Astronomers Group was held at Oliver Lee State Park, about 15 miles southeast of Alamogordo, in a nice level area with a shady "tent". Turnout was very small compared to that for the recent annular solar eclipse held at the Alamogordo Space History Museum, in town. The members were very grateful to see Carla and me there.

Here's an overview of the setup:


Douglas A. Kerr: Amateur Astronomers Group viewing party

Carla can just be seen at the right margin, under the "tent".

Here we see Carla viewing the transit through the 11" Schmidt-Cassegrain catadioptric telescope (I had erroneously reported its objective size as 14" or 16" in my report of the recent annular solar eclipse, at which it was also used).


Douglas A. Kerr: Carla at the Celestron 11" Schmidt-Cassegrain

Best regards,

Doug
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Old June 5th, 2012, 08:02 PM
Asher Kelman Asher Kelman is offline
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Good job and look what a great Astronomer looks like in lilac!

You two are having fun! Who ever would have thought you actually just moved!

Asher
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  #6  
Old June 5th, 2012, 08:31 PM
Doug Kerr Doug Kerr is offline
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Hi, Asher,

Quote:
Originally Posted by Asher Kelman View Post
Good job and look what a great Astronomer looks like in lilac!
Indeed! She is expected at each astronomical event here.

Quote:
You two are having fun! Who ever would have thought you actually just moved!
And in fact from last Thursday through Monday we were near our former home in Texas, attending Carla's grandson's high school graduation (to be covered in some other threads to come).

It's about a 9-hour trip by car each way, not tough but still long and tiring, especially twice in a few days.

And when we got back about suppertime Monday we were too tired to go that night to the Full Moon Concert at White Sands National Monument.

Best regards,

Doug
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  #7  
Old June 5th, 2012, 09:54 PM
Doug Kerr Doug Kerr is offline
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A review of Internet sources for solar viewing glasses suggests that an optical density of 5 is the most common "minimum" density for such glasses. That corresponds to 16.6 stops. It also corresponds to welder's glass shade 12.67.

Best regards,

Doug
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  #8  
Old June 6th, 2012, 08:56 AM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by Doug Kerr View Post
A review of Internet sources for solar viewing glasses suggests that an optical density of 5 is the most common "minimum" density for such glasses. That corresponds to 16.6 stops. It also corresponds to welder's glass shade 12.67.
Doug,

Thanks, but what about the settings on the camera with ISO 160 and no filter for film and without burning out the sensor in live view!!!!

For your interest and the record, here's the BBC collection of Venus Transit pictures.

Asher
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  #9  
Old June 6th, 2012, 09:01 AM
Asher Kelman Asher Kelman is offline
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My 4 year old grandson was really concerned when I showed him pictures of the transit across the fiery picture of the sun. He asked,

"Will Venus go back to being a planet now? I really like Venus. It's my favorite planet."

Taking more of his ice-cream.

"Not like Pluto which is not big enough to be a real planet. I was a planet but maybe if it gets bigger it can be a planet again."

Doug, that's the beginning, I think, of your potential understudy.

Asher
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  #10  
Old June 6th, 2012, 09:13 AM
Asher Kelman Asher Kelman is offline
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Watch the transit as no humans have seen it before!

NASA movies!
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  #11  
Old June 6th, 2012, 09:32 AM
Doug Kerr Doug Kerr is offline
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Hi, Asher,

Quote:
Originally Posted by Asher Kelman View Post
Thanks, but what about the settings on the camera with ISO 160 and no filter for film and without burning out the sensor in live view!!!!
What kind of film camera has Live View? Or are those two different questions?

I did no planning for film usage.

I didn't use Live View. I didn't have a handy focusing cloth available, and when I used a windbreaker to fake it, I found I had problems getting the live view to work properly.

By rights, I should have perfected the setup well before the event, but I didn't do so before we left for our trip to Texas and there was little time for that after we returned.

But I think there would hardly have been a problem with "burning out the sensor" with what I estimate to be a 16.6 stop filter in front of the lens (transmission of about 1E-05).

Quote:
For your interest and the record, here's the BBC collection of Venus Transit pictures.
Thanks so much.

Best regards,

Doug
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  #12  
Old June 6th, 2012, 10:05 AM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by Doug Kerr View Post

But I think there would hardly have been a problem with "burning out the sensor" with what I estimate to be a 16.6 stop filter in front of the lens (transmission of about 1E-05).
But what was your ISO, aperture and speed?

Asher
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