Observing Transit of Venus

Discussion in 'Large Format Cameras and Accessories' started by JamesDean, Jun 3, 2012.

  1. JamesDean

    JamesDean Member

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    Hi all,

    By chance, I'll be in Florida on Tuesday when Venus is scheduled to transit in front of the sun. It should be visible from about 6pm onwards.

    I thought that a 4x5 view camera might make a good viewer. I've experimented with a pinhole mounted on a lensboard and can make fairly poor images of lightbulb filaments on the ground glass. I'd rather use a lens, but worry about how safe it is. I presume the dangers are targeting a bright light into my eye, overheating the ground glass or damaging the lens. That said, I have taken plenty of pictures with the sun in shot them and not had any problems.

    Any thoughts?

    James.
     
  2. mjs

    mjs Member

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    Unlike an eclipse, a transit will not appreciably reduce the amount of light coming from the sun. Venus will be a very small dot crossing the upper right quadrant of the sun, so you will need a long focal length and expose as though you were photographing the Sun. The eclipse will still be in progress as the Sun sets from Florida, so if possible you will want as low a western horizon as possible. You should have an hour and a half to two hours (depending on your western horizon) or so from the beginning of the eclipse at 6:04 EDT until the sun sets, so there's plenty of time for multiple setups, exposures, etc. -- no need to hurry with this one!

    As always, do not look at the sun without adequate eye protection! Use a #14 welder's glass, a purpose-made solar shield or solar glasses, etc. Exposed film and neutral density filters do not block enough solar radiation to protect your eyes -- don't use them! Do not look through a lens at the sun, even for a moment: eye damage will result instantaneously. Do not look at the sun's image on your ground glass with a loupe or magnifier -- you will damage your eye!

    Be safe and good luck!

    Mike
     
  3. Maris

    Maris Member

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    If you intend to use a lens or pinhole to form an image of the sun remember that the diameter of the sun image is the focal length/focal distance in millimetres divided by 100.

    To get a 50mm diameter sun disk you need a 5000mm lens! In practice using a telescope in eyepiece projection mode is the way to go. That's what I'll be doing. And I won't be letting any direct rays from the sun or it's image get into my eyes.
     
  4. Poisson Du Jour

    Poisson Du Jour Member

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    The first problem is getting clear skies!! All this rain coming down from Queensland — not funny!
    I think there will be a huge number of people with ruined cameras just going out and poking their camera up at the sun. Excellent way to fry lenses, mirrors and shutters...
     
  5. docchilie

    docchilie Member

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    Do you have an infrared filter?

    When the solar eclipse happened a couple Sunday's ago, the weather was such that I thought I wouldn't see it at all so I didn't set up the telescope. I scrambled when it finally cleared to get something and I grabbed my infrared filter. I put that on my d****l and took a few quick shots to see what would happen and got awesome results. Unfortunately, when I switched it back to my K1000, it was loaded with infrared film which was a huge mistake. If I would have had 25 ISO something in there other than infrared the shots probably would have been great.

    Note that what I just described is safe for the camera, but not you. The infrared is really bad for your eyes too and you really shouldn't look through the viewfinder. I pretty much just glanced in there to make sure I was on target.

    For the transit, I'm actually aligning the telescope tonight and rubber strapping some sheets to it (I have a solar filter).
     
  6. Bill Burk

    Bill Burk Subscriber

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    Dang it all. I actually drove past the telescope factory Saturday and didn't pick up a solar filter while I was in the neighborhood. What was I thinking?
     
  7. holmburgers

    holmburgers Member

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    Hey guys; I'm kind of excited myself about getting a picture that won't be possible for another century.

    My longest lens is a 180mm/315mm S&K Symmar convertible. It should be clear skies here in Kansas this evening, and there's a lake nearby that will provide an excellent horizon.

    I need to look at all my Wratten filters, but I'm thinking I can just stack 2 opposing color separation filters and give it hell at f/45 and 1/200th, with TXP320 @ 200.

    Any thoughts?
     
  8. polyglot

    polyglot Member

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    Disc of the sun is EV33.6 (from my Venus thread), i.e. 19 stops more than Sunny-16; you can maybe do your exposure calculations from that.

    2 opposing filters will obviously give a fair amount of attenuation but not (I think) predictably. Most of them don't cut UV very well, and with a direct image of the sun I suspect that UV light is going to have a big impact on your exposure once you've cut out a lot of visible light.
     
  9. Mike Wilde

    Mike Wilde Member

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    I have a supply of theatrical neutral density gel in my studio flash kit.
    With a pack and head rig in some situations you can't always just dial back one head, and you don't always want to pull back with certain light modifiers, so a bit of ND across part or all of the tube output is the cats meow for that situation.

    I folded a couple of thicknesses of ND9, ie a three stop neutral density a few times back onto itself until the digithing I was using to meter on the fly started to show a reasonable exposure solution.

    I know multiple acetate filters are not the prefered optical solution, but the results from the digi via the occular of one side of a pair of binoculars yielded a pretty good image. I have yet to process the film I shot.
     
  10. Hatchetman

    Hatchetman Subscriber

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    I used a pair of free solar glasses the kids got at the Adler Planetarium yesterday. Made a filter out of one of the lenses, an index card, and duct tape. LOL.

    You can see the non-film shot here: http://www.flickr.com/photos/22953190@N07/7343334668/in/photostream
    I also used Ektar with a Pentax 6x7 & 300MM. We shall have to wait for that.
     
  11. RalphLambrecht

    RalphLambrecht Subscriber

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    a pinhole to view the sun's projection is very safe to operator and equipment as long as you don't look directly into the sun.
     
  12. RalphLambrecht

    RalphLambrecht Subscriber

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    i doubt,you gonna see it in florida.the sun will have set before the transit begins.australia'seast coast is best,but they have 90% cloud cover today. well, all they hcan do is wait ubtil june 2016 fo the next venus transit!
     
  13. polyglot

    polyglot Member

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    Sorry Ralph, it's 105 years until the next one.
     
  14. RalphLambrecht

    RalphLambrecht Subscriber

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    not according to my astronomy software, voyager4:june2016,which still is a long time.this software has proven to be extremly reliable
     
  15. polyglot

    polyglot Member

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    December 11, 2117 according to NASA. Perhaps your software is ignoring the fact that Venus' orbit is inclined with respect to ours and is counting transits where the shadow misses Earth, passing above or below the plane of the ecliptic?
     
  16. RalphLambrecht

    RalphLambrecht Subscriber

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    i'll erite a note to the software developer. it's hard to argue with nasa data