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  1. #31
    Lee L's Avatar
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    Quote Originally Posted by reub2000 View Post
    Acording to the map the best place to shoot would be in the middle of lake michigan.
    The middle of Superior would be even better. Arizona is a better place to set up a tripod. Some of the cities there even have rules about stupid lighting.

    Lee

  2. #32
    copake_ham's Avatar
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    Quote Originally Posted by Lee L View Post
    The middle of Superior would be even better. Arizona is a better place to set up a tripod. Some of the cities there even have rules about stupid lighting.

    Lee
    Lee,

    My alternative self has a house in Tucson - itself is too close in to avoid city lights - but near enough to real dark that I want to try it there too.

    But getting back to wintertime dark skies in the northern climes - I was thinking of a heater of some kind across the lens (e.g. hair dryer). But would this create "distortion" due to the warmed air in the immediate front of the lens on a sub-freezing night?

  3. #33
    Jim Jones's Avatar
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    Quote Originally Posted by copake_ham View Post
    . . . I was thinking of a heater of some kind across the lens (e.g. hair dryer). But would this create "distortion" due to the warmed air in the immediate front of the lens on a sub-freezing night?
    That would be overkill. Resistors dissipating a Watt or two beneath the camera lens and within a large lens hood sufficed for northern Missouri. Convection put the warmth where it was needed.

  4. #34
    Lee L's Avatar
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    Quote Originally Posted by copake_ham View Post
    Lee,
    But getting back to wintertime dark skies in the northern climes - I was thinking of a heater of some kind across the lens (e.g. hair dryer). But would this create "distortion" due to the warmed air in the immediate front of the lens on a sub-freezing night?
    George,

    You can use a hair dryer to warm up optics for visual observing, but it may not last long enough to get the exposure you need. It would likely create enough turbulence during the shot to ruin the image. Hair dryer elements can also glow if hot enough.

    See my note about 9 postings before yours for "dew chaser" comments.

    String enough resistors in series to draw about 2 Watts from a battery, make sure they are electrically insulated, and wrap the string of resistors around the lens barrel near the front element. Use a lens shade, and you can even wrap some closed cell foam around the outside of the resistors to hold in the heat. A couple of Watts will keep the lens just above the dewpoint without creating turbulence. Figure out how many hours you want it to run and use a lead acid, deep cycle, or power supply with sufficient amps or amp/hours for the task. Some people use gutter heating tape of the right length/resistance to generate a couple of Watts. I use one that was given to me that I can wrap around two lenses at once. You can use a cigarette lighter plug for 12V (well... 13.8V) from a car battery.

    One of these http://www.sciplus.com/singleItem.cfm?terms=2945 will also work off 12V, giving you about a Watt. (DON"T USE IT ON MAINS VOLTAGE TO WRAP YOUR CAMERA!)

    Since you're a ham, I know you don't need the math spelled out for you, or that last warning. You can google for more options or ideas.

    Hope this helps.

    Lee

    Here's a link with DIY instructions. For most camera lenses one Watt is likely sufficient, but two won't hurt unless you need to stretch battery life.
    http://skytonight.com/howto/diy/3304231.html
    Last edited by Lee L; 11-11-2006 at 10:47 PM. Click to view previous post history.

  5. #35
    Jim Noel's Avatar
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    You need to remember that the earth takes 24 hours to revolve 360 degrees. Therefore it takes 1 hour for the stars to intercept an arc of 15 degrees. A one hour exposure then would give you a very short streak.

    To learn how long it takes for a streak the wength you would like, dran one and then measure it with a simple protractor. You probably are thinking of streaks which require 3+ hours of exposure.
    [FONT=Comic Sans MS]Films NOT Dead - Just getting fixed![/FONT]

  6. #36

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    Not quite on the exposure issue, but if you use neg film you'll want to make even more sure than usual that the negs are absolutely clean when you print them, because the smallest dust spot will stand out like the proverbial sore thumb against a black sky. It's less of an issue with slide film where dust prints black, but there, of course, exposure becomes much more critical.

    David.

    p.s. Helen, that was a lovely shot.

  7. #37
    Jim Jones's Avatar
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    Success in long star trails requires dark skies. f/11 on T-Max 100 film works fairly well for 8 hour exposures on a good midwestern night. This was 8 hours at f/6.6 on Kodak Tech Pan developed 6 minutes in print developer for enhanced speed and contrast. A dew cap somewhat like Lee described was used.

  8. #38
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    Hi Jim,

    Nicely done.

    Rich
    Richard A. Nelridge
    http://www.nelridge.com

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