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  1. #11
    naturephoto1's Avatar
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    You may wish to get a Black Cat exposure guide or really long exposures including Star Trails photos. It is a small package that you can take out into the field very easily.

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

  2. #12
    glbeas's Avatar
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    One point to remember is the longer the focal length in your format the longer the star trails for any particular length of time. Therefore a wide angle will allow a longer exposure without the stars seeming to move, which will be desireable if you are aiming on capturing any emission nebulae such as the North America Nebula. Use a higher speed film when going for these, making a tradeoff between detail and brightness.
    Gary Beasley

  3. #13
    Lee L's Avatar
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    Quote Originally Posted by Sparky
    SKY FOG?? Ain't got nuthin' to do with SKY FOG. You mean light pollution - if you were referring to the earlier comment about fogging being a major concern - I was talking about LENS fogging. It's kind of hard to get any kind of shot without some kind of lens heater. See the article. It's pretty informative. Light pollution is light pollution - we just do with what we have. It can be pretty, even.
    Sparky,

    You misread me. My comments were in no way a reference to your lens fogging concerns. "Sky fog" has long been a vernacular term among astrophotographers for light pollution levels in combination with film characteristics that determine how long an exposure you can make without the film being "fogged" by stray (mostly manmade) light, rendering the sky lighter than is acceptable. Atmospheric moisture plays a role in this, but the term doesn't refer specifically to that. As a matter of interest, films with greater reciprocity failure can allow longer exposures because they don't "fog" from scattered light as quickly.

    Think of the term "sky fog" as a reference to film being fogged by stray light (just as it can be fogged by x-rays, heat, or other radiation) that renders the base denser than it should be, rising close to the density of the subject you're really trying to photograph, which is beyond the local sky.

    Lee

  4. #14
    Tony Egan's Avatar
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    Re lens fogging I have read recommendations to carry a small battery operated fan which can be attached to another tripod to direct a current of air across the face of the lens from one side. Apparently while the air is moving there is a much lower chance of condensation forming on the glass. I have not tried this but I have certainly experienced lens condensation problems attempting star trails in the cooler months in Australia.

  5. #15
    Lee L's Avatar
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    A battery powered fan will certainly help with dew on cameras and lenses. Small hair driers are more commonly used when electricity is available. The hair drier has the advantage of heating up the lens, which prevents dew formation for a longer time, until the lens drops to ambient air temperature or below.

    A search on "dew heater" or "dew chaser" will also get you some information on commercial and DIY heater tapes or strings of resistors used to raise the temp of the lens just above ambient. This will prevent dew forming on your optics. I use a short section of gutter tape (used to keep house gutters from freezing) and 12VDC from a battery or power supply to keep lenses and telescopes free from dew. I also use commercial dew chasers in a couple of observatories.

    Lee

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