At first glance it would seem this photo was taken at noon, looking good you notice something strange: the trails of light that can be seen at the top of the image are stars, the photo was taken to horse midnight! Full details of the photo are: D40, 18-55, 1771 seconds (29.5 minutes) f22. To balance the warm light of the moon I set the white balance to incandescent (about 3500K). Using Sunlight on the balance is obtained almost gray sky and the foreground with a yellow cast.
I did experiment with long exposures in the past, but none I had ever completely satisfied.
I found a tutorial that explains a bit 'of things about how to photograph star trails, and I decided it was worth trying again.
The intent was to photograph the trails of the stars, making them the longest possible, but I have been very limited choice of equipment and in the evening.
Without thinking, in fact, I decided to do this right in the photo peak of the full moon that illuminated the landscape so that it becomes as it is of the same day. On a moonless night I got the dark blue sky and the foreground black (maybe not completely black, because of various lamps and other lights).
limit that I found rather in the equipment, however, is what distinguishes a digital camera: the sensor. This component, due to the current passing through it, heats up, generating thermal noise, which manifests as purple streaks inside the frame when the sensor reaches a certain temperature. Before the purple halos (in this picture did not come forward) shows a certain amount of digital noise, combined with several "Hot pixels", which degrade the overall image quality. During my tests I noticed that the noise is "cumulative" among other shows, or, as the temperature sensor between the end of exposure and the beginning of the next does not change, each frame will be louder than the previous year. In my case, the purple streaks occurred in the third consecutive exposures, lasting 30 minutes, which means that the D40 at ISO200 and summer temperature at night (say, 22-23 ° C) stands about half an hour before showing the first halos. This problem may partially solve activating the noise reduction on long exposures, which automatically performs the subtraction of dark frame, getting rid of stains, some hot pixels and some noise. On the other side of the coin, however, doubles the exposure time, using the extra time to take the dark frame.
Another big problem is the battery, probably a full charge, in a long exposure, will last about 2 or 3 hours (I did not proof of), limiting the opportunity for long exposures. For fotografarele trails of stars in any significant way (ie the stars that are nearly half a turn) are needed, depending on the season, from 4 to 8 hours. And with the cold, the battery lasts even less, and you might start to finish the charge within the first half hour.
The simplest solution to all these problems lies in the past: the film.
The film does not produce noise in long exposures, does not need energy to be impressed, or at least it uses very little (using the shutter autofocus SLR needs a bit 'of energy to remain open, but my mechanics as FM can operate well without batteries).
It only remains to solve the lack of reciprocity, which creates an underexposure and color shift.
The first problem in reality there is little: the stars, the bright light, giving the film nevertheless, the sky will remain a bit 'darker, highlighting The stars. And the first floor we wanted it black, no?
The second problem is solved using a blue filter, or a film balanced for tungsten light (the classic incandescent bulbs, look '!), Such as Fujifilm Fujichrome 64T, 64T or Kodak Kodachrome. Too bad that these films are rather hard to find, and they cost a lot '.
I think I'll let the sky turns orange, I think it's a color that gives it:)
I decided that I will use the film will be a Kodak Elite Chrome 100, perfect for testing, since the box of 3 rolls of film costs only 5 or 6 €.
soon with some more experiments!
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