Help with star trails.

Discussion in 'Exposure Discussion' started by nlochner, Aug 14, 2006.

  1. nlochner

    nlochner Member

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    Greetings,

    I am going to the northern area of michigan were there will be little ambient light, and more stars, and i will be on lake michigan, so i thought this would be a good opportunity to experiment with photographing star trails. My format is 35 mm, and i plan to use color film.

    Does anybody have any quick rules of thumb or tips for me? Thanks a lot to all that do,

    nlochner
     
  2. Sparky

    Sparky Member

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    I'd say just use common sense... the length of the trail will be based on the rotation of the earth - so for each hour the shutter is open, the trail will traverse 1/24 of 360 degrees (which probably look bigger than you think).


    Here's a google image search showing star trail photos with the search term "minutes" - so the exposure length should be indicated on them. Probably a medium-speed film would work best (too slow a film may not get enough ambient light to make an interesting photo - but you should try both). See what these guys used.

    http://images.google.com/images?svn...&q="star+trails"+exposure+minutes&btnG=Search
     
  3. Sparky

    Sparky Member

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  4. Ray Heath

    Ray Heath Member

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    basic rule for this, and the similar subjects of lightning and fireworks, camera on tripod, shutter on B, aperture on f8, expose for as long as is required to capture the scene, cover lens between events if necessary, add flash to near ground objects to render detail
     
  5. Lee L

    Lee L Member

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    Sky fog is a problem as mentioned before. You can print through sky fog with negatives to some extent, but not with transparencies. Another problem is color shift (different rates of reciprocity failure in different emulsion layers), but that can mostly be balanced out by a lab with most modern negative films. For slide film, try Ektachrome 200, which has little reciprocity failure and very little color shift, and the color shift tends to a pleasing blue that seems more natural than red or green shifts.

    Sky fog will depend heavily on your observing site, so get away from local lights as much as possible. Bracket exposures widely. If you have time to get results back and try again, you can keep notes and find the longest time that you can run without sky fog.

    Go here: http://cleardarksky.com/csk/prov/Michigan_clocks.html to find a dark sky nearby and look at the column for light pollution. You can get a map of the sites, or go to an observatory on that page. Once on an observatory page, you can click on a link to light pollution and get a light pollution map of the area to look for public places to shoot or find out how good your location is. From the light pollution map you can display a Google map of the area with streets, etc.

    Stars will trail 15 degrees per hour.

    Let me know if you have other questions.

    Lee
     
    Last edited by a moderator: Aug 14, 2006
  6. dschneller

    dschneller Member

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    Tip: if you want the circular star trail look, point your camera towards the north star.
     
  7. Carol

    Carol Member

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    A little hint, if you are getting your film processed at a lab it is a good idea to take a daylight shot first so they know where to cut the negatives. A rough guide for 400 speed film is f3.5 or f4 for exposures up to an hour. If you have plenty of time take several shots for different lengths of time. You will be surprised how many stars show up on film that you couldn't see yourself. Also the colour is pretty cool too. Good luck.
     
  8. wfwhitaker

    wfwhitaker Member

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    As has been suggested, the star trails will be more interesting nearer to one of the poles, in your case north. At your latitude that should be high enough up to avoid including ground objects.. unless you wanted to, which may be interesting, too.
     
  9. PhotoJim

    PhotoJim Member

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    And if a person doesn't know where Polaris is, it's easy: in the northern hemisphere, it's due north, and it is as many degrees above the horizon (assuming a level horizon) as you have degrees of latitude at your location. For me, I'm at 50.5 degrees north, so Polaris is 50.5 degrees above the horizon. Roughly. Curvature of the earth overstates this a bit, but that's being picky.

    In the southern hemisphere there is no obvious "south star" although the Southern Cross, Crux, can point you there. The same rule applies in reverse though. Look south. Look above the horizon the same as your latitude south of the equator.

    At the equator, both celestial poles are at the horizon, one north and one south.
     
  10. Sparky

    Sparky Member

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    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.
     
  11. naturephoto1

    naturephoto1 Subscriber

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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
     
  12. glbeas

    glbeas Member

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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.
     
  13. Lee L

    Lee L Member

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    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
     
  14. Tony Egan

    Tony Egan Subscriber

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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.
     
  15. Lee L

    Lee L Member

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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