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Thread: Film for Star Trails

  1. #1
    mstrozewski's Avatar
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    Mavourneen

    Film for Star Trails

    I've been doing a lot of reading about using film for star trails. The advantage is longer exposures with little noise, than what you'd get with a DSLR. I purchased a used Canon Elan 7N today and going to throw on the 50mm F1.4 and bought a 3200 ISO film to take still shots of the stars, but going to buy the Fuji Velvia 50-200 for star trails.

    any advice on the trails or a particular type of film for astrophotography?

    Thanks!

  2. #2

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    Eugen

    Re: Film for Star Trails

    Hi Mavourneen,

    I am no expert and IMO, you should use your existing digital camera.
    It gives you much more flexibility and by using a stacking software you can get results which wouldn't be possible when using film.
    It is not necessary to have one long exposure because:
    - the noise gets worse the longer the exposure
    - if you have anything else but the sky (any other ground light sources) it will be blown out by long exposures.

    If you combine 20 x 3 minute exposures at 100 ISO that will be the equivalent of a 1 hour exposure, without the noise problems. If you take these shots consecutively without any intreruption (less than 30 seconds between consecutive photos) then you might not be able to see any breaks in the trail.

    I will say it again: I am not an expert and this is my honest opinion.

  3. #3
    mstrozewski's Avatar
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    Re: Film for Star Trails

    Well, when I bought the film, they recommened ISO 100 film. they were out of stock so I bought ISO 200 and I don't plan on stacking, if I want to do that I'll just do it with the 7D. The point of the film is to get the most out of the image without the sensitivity of the digital, so I can reduce the exposure on 200 ISO, instead of 2 hours, just shoot at 1 hour or even 30 minutes. But I also just want to do some still shots of the stars. The ISO should be reduced greatly in the film, rather than the sensor on the digital heating up and creating extra noise.

    Thanks for your thoughts!

  4. #4

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    Re: Film for Star Trails

    If you use film for long exposures, you will run into a problem called Reciprocity Failure. In other words the sensitivity of the film to light changes when you get into long exposures. You do not have that problem when you are using a digital sensor.

  5. #5
    Steaphany's Avatar
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    Re: Film for Star Trails

    Hi Mavourneen,

    Your ISO 200 film will do just fine. The impact of Reciprocity Failure will be minimal on a star trail exposure as the two areas of impact involve an effective reduction in the ISO, but as you are starting out at ISO 200, you will not notice this, and a shift in color balance, which is not all that disastrous as the colors that the film will be recording all fall along the black body curve of the color gamut. Worse adjustment that you'll have to consider is scanning the negative and then picking what star you want to define the equal energy white reference point for the image, the other star colors will simply fall into place.

    Noise is not an issue with film, and with color films, the processed image will be comprised by the dyes activated by the silver grain which is subsequently bleached from the emulsion. This too will not be much of an issue as many ISO 200 films have excellent resolutions.

    The greatest issue that you may be facing is the sweep of the arc from such short exposures. ( Short for star trail images ) Stars will sweep across the sky at a rate of 15 per hour, so you need to consider what length star trails are you after to determine the exposure time. If you do decide to go for a multi-hour exposure one problem I ran into doing this years ago was the evenings humidity and temperatures would cause dew to condense of the lens which would result in an image where the star trails fade out prematurely.

    Do get your images scanned and please post your results.

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